Compounded Problem?
Question:
- Hide quoted text — Show quoted text – > 94 GMC > 5.7L TBI > 4 speed automatic electronic shift (sorry if wrong choice of words) > (Sorry for being long winded, but I like to include as many details as > possible for you to evaluate) > Hi all, I’m in need of some help to troubleshoot some weird things that have > been happening with my rig. > This morning (dreery wet rainy morning) I started my truck like any other > morning, let it idle for warmup at least 5 minutes. When I put it in > reverse it started to run rough (no gas peddle applied), gave it a little > gas backed up some, off the gas, brake and then stalled out (dash battery > warning light was on). Started it again, ran rough for a few seconds, put > it in drive still rough (no gas peddle applied), stumbled a little bit more > and then smoothed out when starting to move. After that it ran fine. The > in-dash voltage meter appears to be normal (15V on the guage, about 13.4V > measured with a VOM) same as it’s always been. > Background info: > One morning this winter (similar incidents have occured since) it stalled > out on me while idling (was cleaning the snow off of it after a storm). It > seems to be doing it when the weather is wet and/or cold (first start of the > day). My theories on the problem are that it happens when the computer > switches modes (closed loop, open loop), and/or a sensor or component is > going bad or is bad and the computer cannot compensate for it correctly. > Another theory I have is that the idle is set too low (200-250rpm on the > guage, sorry didnt’ check with a offboard tach), and the computer cannot run > the engine properly at this speed. I’m not sure if this is relevant, but > I’ve noticed stopped at a red light, foot on brake idling (headlights off, > but DRL on), signal light on, the in-dash battery guage would fluctuate in > synch with the sound of the blinker. > HELP! > After that incident the engine ran fine, but while driving I noticed a > longer and louder than usual sound apparently coming from under the hood > (Shoulda stayed home in bed!). Anyhou it was a "shhhhhhhh" sound similar to > brake pads dragging on the rotor. I noticed the sound on other occasions as > well but it quickly dissapeared and was not as noticeable. (sound varies > with engine speed) It seems to go away once the engine gets warmed up to > temperature, but took longer this morning for whatever reason. On the other > hand I’m doubting my previous claim that the sound is coming from under the > hood. The reason for that is the "shhhhhhh" sound was not as noticeable > when the transmission was put in neutral, and became more apparent when put > in drive again. While in neutral, I varied the engine rpm’s with some gas > and the sound seemed to have gone away(neutral). > This is the best I can describe the symptoms. It seems to me that the two > symptoms lead to seperate problems, but I trust that the group will be able > to shed some light on these issues. > Sincerely, > PIC
This may be completely worthless, but you get what you pay for. On my 2000 Silverado, I had the same problem you describe, but my engine would sputter, backfire and die. Once it warmed up a little all was fine. After 2 alternators, 3 code scans, new plugs, and different fuel, it came down to the positive battery cable. It looked OK on the outside, but internally was corroded beyond belief for a truck so new. Might be worth looking into. Derek
Response:
Different truck – similar problem. 1994 S10 – 4 cylinder 5 speed. About 3 – 4 months ago on rainy days, just a few minutes after start-up I’d get a misfire or two, then everything would be fine for the remainder of the day. I changed the plugs, the filter, and the ignition wires and it still happens, but only on rainy mornings. I’ve taken it to a mechanic and they can’t seem to find anything – no codes, no obvious causes. I’m think I’ll try the rotor next, but after that I’m running out of ideas. I recently read that a malfunctioning Catalytic converter can cause misfires, but I’m not sure how to diagnose that one? Any help?
– Hide quoted text — Show quoted text -> I’ve owned the truck for a year and a half now. I haven’t checked for any > codes yet, will do so today. The check engine light has not come on that > I’ve noticed anyways(I assume you mean while the truck is running on a > regular basis and not when the stall actually occured). Recent work only > involved a balljoint replacement. Last summer I replaced the plugs, wires, > distributor and rotor also the engine accesory belt. The tranny was flushed > with new filter installed last summer as well. I also replaced the fuel > sending unit in the tank due to a rusted/leaking metal hose wasting the go > juice, and the fuel filter was also replaced (Last summer). That’s about all > the work I’ve done to it. (Obvious regular maintenance omitted) I’ve been > told before that an engine would not run properly/get lubricated at such a > low rpm, but I’m serious. It’s probably higher than that, but that’s what’s > displayed on the in-dash tach. As far as starting and idling goes, when > first started the in-dash tach displays about 900-1k (morning start). When > really cold (winter) it went up as high as 1500rpm. Regardless of > conditions once up to operating temp, the rpm’s go down to about 250-300 > when in neutral, 200-250 when in drive, foot on the brake. I will test > these nubers for you some time today with an external tach. > "If the engine is running good after you get moving like you > stated…then you can eliminate most all the secondary ignition > system…..as long as it is only an at idle or an at take off/from stop > problem." > The preceeding is correct. The stumbling/stalling only occurs "when it > wants to" and after the first morning start. Subsequent starting during the > course of the day does not show any signs of this. This almost makes me > think that it’s normal (based on my understanding of open/closed loop > operation). Because it runs rougher/richer after initial start up (closed > loop) then runs smoother with lower rpm’s once in open loop. Subsequent > starts during the day…I don’t let it idle as long as first thing in the > morning. So the closed loop-open loop transition would occur while driving, > engine at higher rpm’s than when the transition occurs during first morning > start up (leaving it idle for longer). Is it possible that it’s MY timing > with the "mode" transitions causing this issue? If it is possible then > there is probably nothing wrong with my truck (stumbling/stalling). It does > seem to make sense, IF my understanding of the process is correct. > "Same thing goes for the fuel system… > I would suspect an injector problem, weak fuel pump or restricted fuel > filter….but you stated that the problem started AFTER the engine warms > up….leading me to believe it runs OK before that…which would all 3 > of those." > It does appear to me that there is a "window" when it will occur, if I leave > before or after this "window" then the problem will not arise (Truck > stumble/stall). As for the engine warmed up before doing it’s thing, it’s > subjective. I let it idle for a rough amount of time, the time varies > between 5 and 15 minutes(longer when colder outside temp). I’m not sure if > this qualifies as the engine being warmed up. I can guarantee that the > thermostat has not opened when this occurs (based on my guess to determine > if it has opened goes as follows: temp guage goes up, up, up, up, reaches a > peak, then when thermostat starts to open, temp goes down, down, then stays > put when thermostat is opened). When it stumbles/stalls, the temp guage > didn’t start to register a temperature change yet, and no heat coming out of > the vents if i put the blower on, heat to max. > "If you don’t have a check engine light on and it runs good till warm > up….and it runs good after you get moving….then you can eliminate an > ELECTTRICALLY FAILED sensor as the problem…..and eliminate a fuel > mixture problem…..a code would and will set if the computer detects > any of this." > The preceeding is correct. BUT again, the engine warmed up is subjective as > explained above. > As far as the "shhhhhhhhh" goes, it sounds to me as being mechanical in > nature(sound was heard with windows up, so it may in fact sound different > from the outside caused by cab deadening the pitch/frequency of noise). > I’ll keep an ear out on that one and I’ll let you know if I find anything > new/different. > Thanks alot for the help! > PIC > Compounded Problem? > 94 GMC > 5.7L TBI > 4 speed automatic electronic shift (sorry if wrong choice of words) > (Sorry for being long winded, but I like to include as many details as > possible for you to evaluate) > Hi all, I’m in need of some help to troubleshoot some weird things that > have been happening with my rig. > This morning (dreery wet rainy morning) I started my truck like any > other morning, let it idle for warmup at least 5 minutes. When I put it > in reverse it started to run rough (no gas peddle applied), gave it a > little gas backed up some, off the gas, brake and then stalled out (dash > battery warning light was on). Started it again, ran rough for a few > seconds, put it in drive still rough (no gas peddle applied), stumbled a > little bit more and then smoothed out when starting to move. After that > it ran fine. The in-dash voltage meter appears to be normal (15V on the > guage, about 13.4V measured with a VOM) same as it’s always been. > Background info: > One morning this winter (similar incidents have occured since) it > stalled out on me while idling (was cleaning the snow off of it after a > storm). It seems to be doing it when the weather is wet and/or cold > (first start of the day). My theories on the problem are that it happens > when the computer switches modes (closed loop, open loop), and/or a > sensor or component is going bad or is bad and the computer cannot > compensate for it correctly. Another theory I have is that the idle is > set too low (200-250rpm on the guage, sorry didnt’ check with a offboard > tach), and the computer cannot run the engine properly at this speed. > I’m not sure if this is relevant, but I’ve noticed stopped at a red > light, foot on brake idling (headlights off, but DRL on), signal light > on, the in-dash battery guage would fluctuate in synch with the sound of > the blinker. > HELP! > After that incident the engine ran fine, but while driving I noticed a > longer and louder than usual sound apparently coming from under the hood > (Shoulda stayed home in bed!). Anyhou it was a "shhhhhhhh" sound similar > to brake pads dragging on the rotor. I noticed the sound on other > occasions as well but it quickly dissapeared and was not as noticeable. > (sound varies with engine speed) It seems to go away once the engine > gets warmed up to temperature, but took longer this morning for whatever > reason. On the other hand I’m doubting my previous claim that the sound > is coming from under the hood. The reason for that is the "shhhhhhh" > sound was not as noticeable when the transmission was put in neutral, > and became more apparent when put in drive again. While in neutral, I > varied the engine rpm’s with some gas and the sound seemed to have gone > away(neutral). > This is the best I can describe the symptoms. It seems to me that the > two symptoms lead to seperate problems, but I trust that the group will > be able to shed some light on these issues. > Sincerely, > PIC > PIC, > Waaazzzz…..upppppppp??? > great post …..best I’ve seen yet > …. > sounds like it runs good after you get going down the road? just an idle > problem? > 200-250 rpms is too low…and will cause the altenator to flutuate the > gauge because of low output. > 200 to 250 rpms … > when wet and/or cold makes me think it might be an air density > issue…..check the MAP sensor > combined with a ..shhhhhhhh..noise ….could be a hose off the MAP > sensor > (doubt it though….) > how long you owned the truck? > you got any codes? > check engine light on? > any recent work done? > whats been replaced in the last 12 months? > …… > If the engine is running good after you get moving like you > stated…then you can eliminate most all the secondary ignition > system…..as long as it is only an at idle or an at take off/from stop > problem. > Same thing goes for the fuel system… > I would suspect an injector problem, weak fuel pump or restricted fuel > filter….but you stated that the problem started AFTER the engine warms > up….leading me to believe it runs OK before that…which would all 3 > of those. > If you don’t have a check engine light on and it runs good till warm > up….and it runs good after you get moving….then you can
… read more »
Response:
The weird thing is that it runs fine on initial startup, it’s only after it’s been running for a while that it acts up while still idling and the initial loading of the engine (Put in drive or reverse). It’s done it as well when in the winter when the air is dry (Canadian winters). PIC
– Hide quoted text — Show quoted text -> The THUMP THUMP could be the spark plug wires being bad, I had that happen > to me a couple of times. They get damp from the moisture in the air, you go > to start the truck, it runs like crap untill the plug wires dry out due to > the heat of the engine. Then it runs ok. Check the wires first then get back > to us > Steve > 94 GMC > 5.7L TBI > 4 speed automatic electronic shift (sorry if wrong choice of words) > (Sorry for being long winded, but I like to include as many details as > possible for you to evaluate) > Hi all, I’m in need of some help to troubleshoot some weird things that > have > been happening with my rig. > This morning (dreery wet rainy morning) I started my truck like any other > morning, let it idle for warmup at least 5 minutes. When I put it in > reverse it started to run rough (no gas peddle applied), gave it a little > gas backed up some, off the gas, brake and then stalled out (dash battery > warning light was on). Started it again, ran rough for a few seconds, put > it in drive still rough (no gas peddle applied), stumbled a little bit > more > and then smoothed out when starting to move. After that it ran fine. The > in-dash voltage meter appears to be normal (15V on the guage, about 13.4V > measured with a VOM) same as it’s always been. > Background info: > One morning this winter (similar incidents have occured since) it stalled > out on me while idling (was cleaning the snow off of it after a storm). > It > seems to be doing it when the weather is wet and/or cold (first start of > the > day). My theories on the problem are that it happens when the computer > switches modes (closed loop, open loop), and/or a sensor or component is > going bad or is bad and the computer cannot compensate for it correctly. > Another theory I have is that the idle is set too low (200-250rpm on the > guage, sorry didnt’ check with a offboard tach), and the computer cannot > run > the engine properly at this speed. I’m not sure if this is relevant, but > I’ve noticed stopped at a red light, foot on brake idling (headlights off, > but DRL on), signal light on, the in-dash battery guage would fluctuate in > synch with the sound of the blinker. > HELP! > After that incident the engine ran fine, but while driving I noticed a > longer and louder than usual sound apparently coming from under the hood > (Shoulda stayed home in bed!). Anyhou it was a "shhhhhhhh" sound similar > to > brake pads dragging on the rotor. I noticed the sound on other occasions > as > well but it quickly dissapeared and was not as noticeable. (sound varies > with engine speed) It seems to go away once the engine gets warmed up to > temperature, but took longer this morning for whatever reason. On the > other > hand I’m doubting my previous claim that the sound is coming from under > the > hood. The reason for that is the "shhhhhhh" sound was not as noticeable > when the transmission was put in neutral, and became more apparent when > put > in drive again. While in neutral, I varied the engine rpm’s with some gas > and the sound seemed to have gone away(neutral). > This is the best I can describe the symptoms. It seems to me that the two > symptoms lead to seperate problems, but I trust that the group will be > able > to shed some light on these issues. > Sincerely, > PIC
Response:
I’ve owned the truck for a year and a half now. I haven’t checked for any codes yet, will do so today. The check engine light has not come on that I’ve noticed anyways(I assume you mean while the truck is running on a regular basis and not when the stall actually occured). Recent work only involved a balljoint replacement. Last summer I replaced the plugs, wires, distributor and rotor also the engine accesory belt. The tranny was flushed with new filter installed last summer as well. I also replaced the fuel sending unit in the tank due to a rusted/leaking metal hose wasting the go juice, and the fuel filter was also replaced (Last summer). That’s about all the work I’ve done to it. (Obvious regular maintenance omitted) I’ve been told before that an engine would not run properly/get lubricated at such a low rpm, but I’m serious. It’s probably higher than that, but that’s what’s displayed on the in-dash tach. As far as starting and idling goes, when first started the in-dash tach displays about 900-1k (morning start). When really cold (winter) it went up as high as 1500rpm. Regardless of conditions once up to operating temp, the rpm’s go down to about 250-300 when in neutral, 200-250 when in drive, foot on the brake. I will test these nubers for you some time today with an external tach. "If the engine is running good after you get moving like you stated…then you can eliminate most all the secondary ignition system…..as long as it is only an at idle or an at take off/from stop problem." The preceeding is correct. The stumbling/stalling only occurs "when it wants to" and after the first morning start. Subsequent starting during the course of the day does not show any signs of this. This almost makes me think that it’s normal (based on my understanding of open/closed loop operation). Because it runs rougher/richer after initial start up (closed loop) then runs smoother with lower rpm’s once in open loop. Subsequent starts during the day…I don’t let it idle as long as first thing in the morning. So the closed loop-open loop transition would occur while driving, engine at higher rpm’s than when the transition occurs during first morning start up (leaving it idle for longer). Is it possible that it’s MY timing with the "mode" transitions causing this issue? If it is possible then there is probably nothing wrong with my truck (stumbling/stalling). It does seem to make sense, IF my understanding of the process is correct. "Same thing goes for the fuel system… I would suspect an injector problem, weak fuel pump or restricted fuel filter….but you stated that the problem started AFTER the engine warms up….leading me to believe it runs OK before that…which would all 3 of those." It does appear to me that there is a "window" when it will occur, if I leave before or after this "window" then the problem will not arise (Truck stumble/stall). As for the engine warmed up before doing it’s thing, it’s subjective. I let it idle for a rough amount of time, the time varies between 5 and 15 minutes(longer when colder outside temp). I’m not sure if this qualifies as the engine being warmed up. I can guarantee that the thermostat has not opened when this occurs (based on my guess to determine if it has opened goes as follows: temp guage goes up, up, up, up, reaches a peak, then when thermostat starts to open, temp goes down, down, then stays put when thermostat is opened). When it stumbles/stalls, the temp guage didn’t start to register a temperature change yet, and no heat coming out of the vents if i put the blower on, heat to max. "If you don’t have a check engine light on and it runs good till warm up….and it runs good after you get moving….then you can eliminate an ELECTTRICALLY FAILED sensor as the problem…..and eliminate a fuel mixture problem…..a code would and will set if the computer detects any of this." The preceeding is correct. BUT again, the engine warmed up is subjective as explained above. As far as the "shhhhhhhhh" goes, it sounds to me as being mechanical in nature(sound was heard with windows up, so it may in fact sound different from the outside caused by cab deadening the pitch/frequency of noise). I’ll keep an ear out on that one and I’ll let you know if I find anything new/different. Thanks alot for the help! PIC
– Hide quoted text — Show quoted text – > Compounded Problem? > 94 GMC > 5.7L TBI > 4 speed automatic electronic shift (sorry if wrong choice of words) > (Sorry for being long winded, but I like to include as many details as > possible for you to evaluate) > Hi all, I’m in need of some help to troubleshoot some weird things that > have been happening with my rig. > This morning (dreery wet rainy morning) I started my truck like any > other morning, let it idle for warmup at least 5 minutes. When I put it > in reverse it started to run rough (no gas peddle applied), gave it a > little gas backed up some, off the gas, brake and then stalled out (dash > battery warning light was on). Started it again, ran rough for a few > seconds, put it in drive still rough (no gas peddle applied), stumbled a > little bit more and then smoothed out when starting to move. After that > it ran fine. The in-dash voltage meter appears to be normal (15V on the > guage, about 13.4V measured with a VOM) same as it’s always been. > Background info: > One morning this winter (similar incidents have occured since) it > stalled out on me while idling (was cleaning the snow off of it after a > storm). It seems to be doing it when the weather is wet and/or cold > (first start of the day). My theories on the problem are that it happens > when the computer switches modes (closed loop, open loop), and/or a > sensor or component is going bad or is bad and the computer cannot > compensate for it correctly. Another theory I have is that the idle is > set too low (200-250rpm on the guage, sorry didnt’ check with a offboard > tach), and the computer cannot run the engine properly at this speed. > I’m not sure if this is relevant, but I’ve noticed stopped at a red > light, foot on brake idling (headlights off, but DRL on), signal light > on, the in-dash battery guage would fluctuate in synch with the sound of > the blinker. > HELP! > After that incident the engine ran fine, but while driving I noticed a > longer and louder than usual sound apparently coming from under the hood > (Shoulda stayed home in bed!). Anyhou it was a "shhhhhhhh" sound similar > to brake pads dragging on the rotor. I noticed the sound on other > occasions as well but it quickly dissapeared and was not as noticeable. > (sound varies with engine speed) It seems to go away once the engine > gets warmed up to temperature, but took longer this morning for whatever > reason. On the other hand I’m doubting my previous claim that the sound > is coming from under the hood. The reason for that is the "shhhhhhh" > sound was not as noticeable when the transmission was put in neutral, > and became more apparent when put in drive again. While in neutral, I > varied the engine rpm’s with some gas and the sound seemed to have gone > away(neutral). > This is the best I can describe the symptoms. It seems to me that the > two symptoms lead to seperate problems, but I trust that the group will > be able to shed some light on these issues. > Sincerely, > PIC > PIC, > Waaazzzz…..upppppppp??? > great post …..best I’ve seen yet > …. > sounds like it runs good after you get going down the road? just an idle > problem? > 200-250 rpms is too low…and will cause the altenator to flutuate the > gauge because of low output. > 200 to 250 rpms … > when wet and/or cold makes me think it might be an air density > issue…..check the MAP sensor > combined with a ..shhhhhhhh..noise ….could be a hose off the MAP > sensor > (doubt it though….) > how long you owned the truck? > you got any codes? > check engine light on? > any recent work done? > whats been replaced in the last 12 months? > …… > If the engine is running good after you get moving like you > stated…then you can eliminate most all the secondary ignition > system…..as long as it is only an at idle or an at take off/from stop > problem. > Same thing goes for the fuel system… > I would suspect an injector problem, weak fuel pump or restricted fuel > filter….but you stated that the problem started AFTER the engine warms > up….leading me to believe it runs OK before that…which would all 3 > of those. > If you don’t have a check engine light on and it runs good till warm > up….and it runs good after you get moving….then you can eliminate an > ELECTTRICALLY FAILED sensor as the problem…..and eliminate a fuel > mixture problem…..a code would and will set if the computer detects > any of this. > so…..unless you repost with some added info…and things change…. > then we have a truck that …. > idles good till the engine gets warm > and the computer turns on > and wet and/or cold weather is present > with a ssshhhhhhh noise when in drive only > with a computer not detecting ANY > fuel ratio problems (rich/lean) > sensor electrical faults > low idle faults > and seeing the changes it is commanding. > so….. > check for a stuck Idle Air Controll motor > check the MAP sensor > and then get the tranny checked for a > for a sticking valve causing a convertor release problem. > (has the tranny been rebuilt?) > little DIY tip > most tranny shops will hook a scanner to the truck for you at no > charge…… > good luck….and again…great post > .. > hope we helped > .. > NubbsMcFarkle > good input=good output > if
… read more »
Response:
Compounded Problem? 94 GMC 5.7L TBI 4 speed automatic electronic shift (sorry if wrong choice of words) (Sorry for being long winded, but I like to include as many details as possible for you to evaluate) Hi all, I’m in need of some help to troubleshoot some weird things that have been happening with my rig. This morning (dreery wet rainy morning) I started my truck like any other morning, let it idle for warmup at least 5 minutes. When I put it in reverse it started to run rough (no gas peddle applied), gave it a little gas backed up some, off the gas, brake and then stalled out (dash battery warning light was on). Started it again, ran rough for a few seconds, put it in drive still rough (no gas peddle applied), stumbled a little bit more and then smoothed out when starting to move. After that it ran fine. The in-dash voltage meter appears to be normal (15V on the guage, about 13.4V measured with a VOM) same as it’s always been. Background info: One morning this winter (similar incidents have occured since) it stalled out on me while idling (was cleaning the snow off of it after a storm). It seems to be doing it when the weather is wet and/or cold (first start of the day). My theories on the problem are that it happens when the computer switches modes (closed loop, open loop), and/or a sensor or component is going bad or is bad and the computer cannot compensate for it correctly. Another theory I have is that the idle is set too low (200-250rpm on the guage, sorry didnt’ check with a offboard tach), and the computer cannot run the engine properly at this speed. I’m not sure if this is relevant, but I’ve noticed stopped at a red light, foot on brake idling (headlights off, but DRL on), signal light on, the in-dash battery guage would fluctuate in synch with the sound of the blinker. HELP! After that incident the engine ran fine, but while driving I noticed a longer and louder than usual sound apparently coming from under the hood (Shoulda stayed home in bed!). Anyhou it was a "shhhhhhhh" sound similar to brake pads dragging on the rotor. I noticed the sound on other occasions as well but it quickly dissapeared and was not as noticeable. (sound varies with engine speed) It seems to go away once the engine gets warmed up to temperature, but took longer this morning for whatever reason. On the other hand I’m doubting my previous claim that the sound is coming from under the hood. The reason for that is the "shhhhhhh" sound was not as noticeable when the transmission was put in neutral, and became more apparent when put in drive again. While in neutral, I varied the engine rpm’s with some gas and the sound seemed to have gone away(neutral). This is the best I can describe the symptoms. It seems to me that the two symptoms lead to seperate problems, but I trust that the group will be able to shed some light on these issues. Sincerely, PIC PIC, Waaazzzz…..upppppppp??? great post …..best I’ve seen yet …. sounds like it runs good after you get going down the road? just an idle problem? 200-250 rpms is too low…and will cause the altenator to flutuate the gauge because of low output. 200 to 250 rpms … when wet and/or cold makes me think it might be an air density issue…..check the MAP sensor combined with a ..shhhhhhhh..noise ….could be a hose off the MAP sensor (doubt it though….) how long you owned the truck? you got any codes? check engine light on? any recent work done? whats been replaced in the last 12 months? …… If the engine is running good after you get moving like you stated…then you can eliminate most all the secondary ignition system…..as long as it is only an at idle or an at take off/from stop problem. Same thing goes for the fuel system… I would suspect an injector problem, weak fuel pump or restricted fuel filter….but you stated that the problem started AFTER the engine warms up….leading me to believe it runs OK before that…which would all 3 of those. If you don’t have a check engine light on and it runs good till warm up….and it runs good after you get moving….then you can eliminate an ELECTTRICALLY FAILED sensor as the problem…..and eliminate a fuel mixture problem…..a code would and will set if the computer detects any of this. so…..unless you repost with some added info…and things change…. then we have a truck that …. idles good till the engine gets warm and the computer turns on and wet and/or cold weather is present with a ssshhhhhhh noise when in drive only with a computer not detecting ANY fuel ratio problems (rich/lean) sensor electrical faults low idle faults and seeing the changes it is commanding. so….. check for a stuck Idle Air Controll motor check the MAP sensor and then get the tranny checked for a for a sticking valve causing a convertor release problem. (has the tranny been rebuilt?) little DIY tip most tranny shops will hook a scanner to the truck for you at no charge…… good luck….and again…great post .. hope we helped .. NubbsMcFarkle good input=good output if this creates any other info you can add post it…and we’ll dig a little deeper
Response:
The THUMP THUMP could be the spark plug wires being bad, I had that happen to me a couple of times. They get damp from the moisture in the air, you go to start the truck, it runs like crap untill the plug wires dry out due to the heat of the engine. Then it runs ok. Check the wires first then get back to us Steve
– Hide quoted text — Show quoted text -> 94 GMC > 5.7L TBI > 4 speed automatic electronic shift (sorry if wrong choice of words) > (Sorry for being long winded, but I like to include as many details as > possible for you to evaluate) > Hi all, I’m in need of some help to troubleshoot some weird things that have > been happening with my rig. > This morning (dreery wet rainy morning) I started my truck like any other > morning, let it idle for warmup at least 5 minutes. When I put it in > reverse it started to run rough (no gas peddle applied), gave it a little > gas backed up some, off the gas, brake and then stalled out (dash battery > warning light was on). Started it again, ran rough for a few seconds, put > it in drive still rough (no gas peddle applied), stumbled a little bit more > and then smoothed out when starting to move. After that it ran fine. The > in-dash voltage meter appears to be normal (15V on the guage, about 13.4V > measured with a VOM) same as it’s always been. > Background info: > One morning this winter (similar incidents have occured since) it stalled > out on me while idling (was cleaning the snow off of it after a storm). It > seems to be doing it when the weather is wet and/or cold (first start of the > day). My theories on the problem are that it happens when the computer > switches modes (closed loop, open loop), and/or a sensor or component is > going bad or is bad and the computer cannot compensate for it correctly. > Another theory I have is that the idle is set too low (200-250rpm on the > guage, sorry didnt’ check with a offboard tach), and the computer cannot run > the engine properly at this speed. I’m not sure if this is relevant, but > I’ve noticed stopped at a red light, foot on brake idling (headlights off, > but DRL on), signal light on, the in-dash battery guage would fluctuate in > synch with the sound of the blinker. > HELP! > After that incident the engine ran fine, but while driving I noticed a > longer and louder than usual sound apparently coming from under the hood > (Shoulda stayed home in bed!). Anyhou it was a "shhhhhhhh" sound similar to > brake pads dragging on the rotor. I noticed the sound on other occasions as > well but it quickly dissapeared and was not as noticeable. (sound varies > with engine speed) It seems to go away once the engine gets warmed up to > temperature, but took longer this morning for whatever reason. On the other > hand I’m doubting my previous claim that the sound is coming from under the > hood. The reason for that is the "shhhhhhh" sound was not as noticeable > when the transmission was put in neutral, and became more apparent when put > in drive again. While in neutral, I varied the engine rpm’s with some gas > and the sound seemed to have gone away(neutral). > This is the best I can describe the symptoms. It seems to me that the two > symptoms lead to seperate problems, but I trust that the group will be able > to shed some light on these issues. > Sincerely, > PIC
Response:
Look for a vacuum leak somewhere. The shhhhhhh…… will be louder at lower RPM as that is where the engine draws more vacuum.
– Hide quoted text — Show quoted text -> 94 GMC > 5.7L TBI > 4 speed automatic electronic shift (sorry if wrong choice of words) > (Sorry for being long winded, but I like to include as many details as > possible for you to evaluate) > Hi all, I’m in need of some help to troubleshoot some weird things that have > been happening with my rig. > This morning (dreery wet rainy morning) I started my truck like any other > morning, let it idle for warmup at least 5 minutes. When I put it in > reverse it started to run rough (no gas peddle applied), gave it a little > gas backed up some, off the gas, brake and then stalled out (dash battery > warning light was on). Started it again, ran rough for a few seconds, put > it in drive still rough (no gas peddle applied), stumbled a little bit more > and then smoothed out when starting to move. After that it ran fine. The > in-dash voltage meter appears to be normal (15V on the guage, about 13.4V > measured with a VOM) same as it’s always been. > Background info: > One morning this winter (similar incidents have occured since) it stalled > out on me while idling (was cleaning the snow off of it after a storm). It > seems to be doing it when the weather is wet and/or cold (first start of the > day). My theories on the problem are that it happens when the computer > switches modes (closed loop, open loop), and/or a sensor or component is > going bad or is bad and the computer cannot compensate for it correctly. > Another theory I have is that the idle is set too low (200-250rpm on the > guage, sorry didnt’ check with a offboard tach), and the computer cannot run > the engine properly at this speed. I’m not sure if this is relevant, but > I’ve noticed stopped at a red light, foot on brake idling (headlights off, > but DRL on), signal light on, the in-dash battery guage would fluctuate in > synch with the sound of the blinker. > HELP! > After that incident the engine ran fine, but while driving I noticed a > longer and louder than usual sound apparently coming from under the hood > (Shoulda stayed home in bed!). Anyhou it was a "shhhhhhhh" sound similar to > brake pads dragging on the rotor. I noticed the sound on other occasions as > well but it quickly dissapeared and was not as noticeable. (sound varies > with engine speed) It seems to go away once the engine gets warmed up to > temperature, but took longer this morning for whatever reason. On the other > hand I’m doubting my previous claim that the sound is coming from under the > hood. The reason for that is the "shhhhhhh" sound was not as noticeable > when the transmission was put in neutral, and became more apparent when put > in drive again. While in neutral, I varied the engine rpm’s with some gas > and the sound seemed to have gone away(neutral). > This is the best I can describe the symptoms. It seems to me that the two > symptoms lead to seperate problems, but I trust that the group will be able > to shed some light on these issues. > Sincerely, > PIC
Response:
94 GMC 5.7L TBI 4 speed automatic electronic shift (sorry if wrong choice of words) (Sorry for being long winded, but I like to include as many details as possible for you to evaluate) Hi all, I’m in need of some help to troubleshoot some weird things that have been happening with my rig. This morning (dreery wet rainy morning) I started my truck like any other morning, let it idle for warmup at least 5 minutes. When I put it in reverse it started to run rough (no gas peddle applied), gave it a little gas backed up some, off the gas, brake and then stalled out (dash battery warning light was on). Started it again, ran rough for a few seconds, put it in drive still rough (no gas peddle applied), stumbled a little bit more and then smoothed out when starting to move. After that it ran fine. The in-dash voltage meter appears to be normal (15V on the guage, about 13.4V measured with a VOM) same as it’s always been. Background info: One morning this winter (similar incidents have occured since) it stalled out on me while idling (was cleaning the snow off of it after a storm). It seems to be doing it when the weather is wet and/or cold (first start of the day). My theories on the problem are that it happens when the computer switches modes (closed loop, open loop), and/or a sensor or component is going bad or is bad and the computer cannot compensate for it correctly. Another theory I have is that the idle is set too low (200-250rpm on the guage, sorry didnt’ check with a offboard tach), and the computer cannot run the engine properly at this speed. I’m not sure if this is relevant, but I’ve noticed stopped at a red light, foot on brake idling (headlights off, but DRL on), signal light on, the in-dash battery guage would fluctuate in synch with the sound of the blinker. HELP! After that incident the engine ran fine, but while driving I noticed a longer and louder than usual sound apparently coming from under the hood (Shoulda stayed home in bed!). Anyhou it was a "shhhhhhhh" sound similar to brake pads dragging on the rotor. I noticed the sound on other occasions as well but it quickly dissapeared and was not as noticeable. (sound varies with engine speed) It seems to go away once the engine gets warmed up to temperature, but took longer this morning for whatever reason. On the other hand I’m doubting my previous claim that the sound is coming from under the hood. The reason for that is the "shhhhhhh" sound was not as noticeable when the transmission was put in neutral, and became more apparent when put in drive again. While in neutral, I varied the engine rpm’s with some gas and the sound seemed to have gone away(neutral). This is the best I can describe the symptoms. It seems to me that the two symptoms lead to seperate problems, but I trust that the group will be able to shed some light on these issues. Sincerely, PIC
