Re: Caprice mystery engine skip
Posted: Fri Jul 29, 2016 7:35 am
New issue. Probably electrical/sensor. At 304,xxx now...kevm14 wrote:This problem has not come back. Almost 303k now.
Started it up to go home from work yesterday. It started and then died. Wouldn't restart. Gave it some throttle. It started and was coughing and missing until I revved it to like 3,000, then it was fine. When I let off, it died again. Restarted with throttle and went through the same routine again. There were some exhaust emissions which I think was indicating rich mixture. I ended up with two codes as this was all happening, which I checked. One was TPS low. The other was PROM error. The PROM error is just poor contact between my EPROM chip and the ZIF socket I installed on the board 10+ years ago. Or maybe a bad solder joint between the ZIF socket and the board...hmm.
The TPS issue is weird. When I was revving it, I noticed two things:
1) The TPS % throttle was very low or barely registering, so the ECM assumed a mostly closed throttle
2) The IAC counts were low, consistent with a closed throttle
This could be why it dies when I let off but doesn't explain the rich/misfire crap unless the voltage is just jumping around and it's doing a bunch of pump shot pulses and flooding the engine.
Eventually this all stopped and I drove home normally. I did have to reset the EPROM in the ZIF socket...
I actually had an issue with the TPS signal wire and fixed it a year ago or so. I wonder if the sensor itself is going.
Next time this happens, I will unplug the TPS and monitor voltage and % throttle. If it does anything at all, I guess I still have a wiring issue. If it does nothing (as it should), then I will replace the TPS sensor.
On the way in this morning, it skipped once, unlocked the torque converter, and relocked. This either indicates a very transient computer type issue (EPROM issue) or the TPS issue. A momentarily dropped TPS signal would indicate a closed throttle and unlock the TCC.
A little frustrating but like most problems, won't cost me much money, just some time and frustration to diagnose and repair.