Another 91 siverado, many problems, 1 at a time.
Question:
> Allright, somebody shoot me. Took a look at the book, which I should have > done in the first place. Book shows a vent where I thought I was missing a > vacum line, on the egr solnoid. Egr is in place and plugged in correctly. > Map sensor is in place and plugged in correctly. I found the knock sensor in > a box, it appears the machine shop put a plug in place of the knock sensor > during the process of rebuilding, that would explain why it isn’t leaking. > Should I pull the plug and replace the sensor? Would this be causingthe idle > to be high?
BINGO. You need to rip that plug out and put the knock sensor (KS) back in ASAP. That is why you’re getting code 43’s, and that is why your idling high as well. The ECM uses the KS to regulate spark advance. The KS allows the ECM to dial in as much advance as possible without inducing sprak knock. The ECM runs a test on the ESC (electronic spark control system) to ensure that the system is working. If the system is found to be shot (like when the system discovers there is no knock sensor hooked up!), you get a code 43 and open-loop operation with a static, highly retarded spark curve. will save you the hassle of R&R’ing it later on down the line if it decides to crap out on ya.. Regards, Doc
Response:
– Hide quoted text — Show quoted text -> Let me begin with the fact that i rebuilt the motor with considerable help > from a friend. While doing this rebuild i got extremly carried away. Somehow > I ended up with a motor which actually runs (much to my amazment!) I have > little experience with engines and such, however, i am learning quickly. My > truck has just recently begun to use lights on the dash which i do not enjoy > looking at. The check engine soon light came on, ran the code, found error > 43. I understand with this vehicle that could be caused by the knock sensor. > fun part is, with all my retooling, we chose not to put that sensor back in > the truck. At the same time, my motor began idling very high, I don’t have a > tack, but I know it must be idling at or above 1500 rpms. are these issues > related? Should i put the sensor back in the truck? my buddy thought it > wasn’t a good idea with the mods we were performing to the rest of the > motor. Also, the place where the knock sensor plugs into the vacum system is > not plugged. Maybe the problem? i appreciate any info on the subject, and to > all the enthusiasts out there, remember this is only the begining of > correspondence with me.
WOW. What a mess. First off, the knock sensor isn’t even hooked up to the vacuum system. It sits in the water jacket on the bottom of the passenger side cylinder head, just aft of the starter. It has a single wire squeeze-pin connector running to it. Being as it sits in the water jacket, it also serves as a block drain, so if it really were the knock sensor you didn’t re-install you’d have coolant all over your garage floor. So first things first, figure out what that sensor you didn’t re-install actually is and then post back here. The only ECM-monitored components that actually have a vacuum connection are the MAP sensor and the EGR system. So, it’s got to be one of those. Second, an open vacuum line will cause a high idle like you are experiencing. Any unused vacuum ports on the throttle body need to be capped using rubber vacuum caps. You need to have ALL SENSORS INSTALLED for the EFI system to operate correctly. If you don’t, poor performance is the least of your worries. Your engine will eventually grenade if all sensors aren’t hooked up properly. Second, code 43 can be set by many things. The knock sensor is one, the ESC module and incorrect spark timing are others. So, until you figure out what that "extra" sensor you have lying around actually is, and until you climb under the truck and look for the knock sensor as I’ve described above, we’ can’t go any further. Also, it would help to know what type of engine we’re dealing with. I assume either a 305 or a 350? BTW, any other "extra parts" lying around? — Take er’ easy, "Doc" Wrenchin’ since 1992 1988 GMC Sierra SLX aka "Chelsea" 1998 GMC Sonoma SLS aka "Ruby"
Response:
Patrick, Oh yea. The ECM is capable of running in closed-loop mode (monitors input from sensors and actively controls timing, fuel mixture, idle, etc.) and open-loop (runs a default program that causes high idle, no advance, incredibly high F/A mixture). Unless and until you get all the sensors and controls back in place and working, your performance and gas mileage will suck. You also risk destroying the catalytic converter. A quick test is to stand near the exhaust and see how bad your eyes burn. Dean – Hide quoted text — Show quoted text – > Allright, somebody shoot me. Took a look at the book, which I should have > done in the first place. Book shows a vent where I thought I was missing a > vacum line, on the egr solnoid. Egr is in place and plugged in correctly. > Map sensor is in place and plugged in correctly. I found the knock sensor in > a box, it appears the machine shop put a plug in place of the knock sensor > during the process of rebuilding, that would explain why it isn’t leaking. > Should I pull the plug and replace the sensor? Would this be causingthe idle > to be high?
Response:
Allright, somebody shoot me. Took a look at the book, which I should have done in the first place. Book shows a vent where I thought I was missing a vacum line, on the egr solnoid. Egr is in place and plugged in correctly. Map sensor is in place and plugged in correctly. I found the knock sensor in a box, it appears the machine shop put a plug in place of the knock sensor during the process of rebuilding, that would explain why it isn’t leaking. Should I pull the plug and replace the sensor? Would this be causingthe idle to be high?
Response:
Let me begin with the fact that i rebuilt the motor with considerable help from a friend. While doing this rebuild i got extremly carried away. Somehow I ended up with a motor which actually runs (much to my amazment!) I have little experience with engines and such, however, i am learning quickly. My truck has just recently begun to use lights on the dash which i do not enjoy looking at. The check engine soon light came on, ran the code, found error 43. I understand with this vehicle that could be caused by the knock sensor. fun part is, with all my retooling, we chose not to put that sensor back in the truck. At the same time, my motor began idling very high, I don’t have a tack, but I know it must be idling at or above 1500 rpms. are these issues related? Should i put the sensor back in the truck? my buddy thought it wasn’t a good idea with the mods we were performing to the rest of the motor. Also, the place where the knock sensor plugs into the vacum system is not plugged. Maybe the problem? i appreciate any info on the subject, and to all the enthusiasts out there, remember this is only the begining of correspondence with me.
