Any ECM/PCM Experts in here?
Question:
It seems like on at least some engines, that particular diagnostic is only enabled when the coolant temperature reaches the regular thermostat opening temperature (194 degrees F). If you had a 160 degree thermostat, it might never be enabled. I would be tempted to try a few more degrees of spark advance to see if that keeps it happy. If that isn’t practical, I’d maybe look into a custom PCM program with that particular diagnostic disabled.. — Robert Hancock Saskatoon, SK, Canada Home Page: http://www.roberthancock.com/
– Hide quoted text — Show quoted text -> BINGO! > That’s exactly what’s happening Robert. In lieu of a KS signal, the PCM > defaults to full retard, and the truck’s a pig until the code is cleared. > The question is why is it doing this? Why isn’t my engine knocking? Did I > just build it too well or should I be running 87/89 to induce some knock? I > wouldn’t think the 4 deg. BTDC would be enough to screw with it enough to > set a code. Maybe I should (can’t believe I’m saying this) induce some > knocking by advancing the timing a few degrees at a time to see if the > problem goes away. > I thought of something when I first woke up this morning. I never had > problems with ESC (code 43) while running a 160F thermostat. The problems > arose after I switched back to the 195F t-stat. Funny thing is though, > you’d think a hotter engine would induce MORE detonation, not less! > Doc > When you go to full throttle, the PCM expects to detect some knock with > the > standard spark advance settings it uses. If it doesn’t, it assumes the > knock > sensor is not functioning, sets code 43, and probably goes to full-retard > spark advance settings, which probably explains the massive power loss you > saw afterwards.. > — > Robert Hancock Saskatoon, SK, Canada > Home Page: http://www.roberthancock.com/ > > Hi guys, > > I’m a regular over at alt.trucks.chevy but figured I’d post my stumping > > situation here as well! Hopefully someone in one of these groups has > > experienced a similar problem at some point in time with an OBD-I > system. > > So, here goes! > > Well, the code 43 (electronic spark control system malfunction) > persists. > I > > <thought> I had it pinned down to an aftermarket A/C high-pressure > cutoff > > switch causing a PCM brain fart under full throttle, as the code would > only > > set when I mashed it with the A/C on. The code was set today (actually, > > about 15 mins ago on my way home) without the A/C on when I mashed the > pedal > > to race my wife’s Sonoma in the other lane! > > Vehicle specifics: > > 1988 GMC Sierra SLX w/305 TBI and TH400. > > 128,000 miles, 28,000 since engine rebuild. > > Entire ignition system (including PCM) is about 6 months old > > Electronic spark control module is brand new > > Knock sensor is brand new > > So, I replaced the entire electronic spark control system and STILL am > > getting the code 43. Here’s how it happens. When I mash the go pedal, > I > > get an amazing surge of power (the most power I’ve EVER felt from ANY > > doggish 305!) that lasts about 3 seconds, then the engine bogs down, I > have > > NO power and the SES light comes on with a code 43 being set. The code > > disappears after a few minutes and engine operation returns to normal. > > All of the wiring connections are clean and the KS wire is new, as I > found > > the old one had been singed by the exhaust manifold, which I originally > > thought was the source of my code 43 woes. > > I’m going to check if my new PCM is still under warranty as maybe it’s a > PCM > > malfunction? Would my timing being slighty off spec cause this error? > I > > have it set 4 deg. BTDC (spec is 0 deg. BTDC) to compensate for the 60 > over > > bore and high compression pistons/rings (9.5:1). I’ve had it set at 4 > deg. > > BTDC since I replaced the ignition system (about 6 months) and haven’t > had > > any problems thus far. > > Any thoughts? Any at all? Now that I know what this motor is capable > of > > (my 3 second surge of immense power!) I want to find a way to fix the > ESC > > problem and find out where the extra horsies are coming from. > > TIA! > > Doc
Response:
It seems to differ depending on the engine/VIN code as to whether or not it works this way. However, some of them certainly do. For example, the code description for 86-89 5.0L FI, VIN F for code 43 is "The ECM did not detect a knock signal during near wide open throttle operation with coolant temperature above 194
