Caprice mystery engine skip

[kevm14]

This problem has not come back. Almost 303k now.

New issue. Probably electrical/sensor. At 304,xxx 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.

[kevm14]

Eventually this all stopped and I drove home normally. I did have to reset the EPROM in the ZIF socket...

A little frustrating but like most problems, won't cost me much money, just some time and frustration to diagnose and repair.

The more I think about it the more I think I need to reflow the solder on my ZIF socket pins. I put pressure in one direction (sliding sideways) and the SES light would blink rapidly indicating PROM error. Pressure the other way fixes it. Since I did that, no issue. This might be my issue...and probably has been intermittent for a while now.

[kevm14]

I reflowed the solder on the ZIF socket. Then I did it a second time and added solder. Still seemed to lose connection when I put pressure on the socket. It seems a lot better than before but honestly, it's not worth the hassle. So I just found my junkyard ECM (92 Roadmaster L03) that I never used and swapped my chip into the stock carrier. I think I am done now. If anything weird happens again, it shouldn't be the ECM itself.

Some pics.

This was my OEM ECM but I had installed the 24 pin ZIF socket. That must have been a good 11 years ago.

The junkyard ECM:

I forgot to snap a pic of the stock carrier. This is what it looks like:

$_35.jpg (8.68 KiB) Viewed 1028 times

Much more positive connection, but way more inconvenient when tuning. Except I haven't tuned it recently except for emissions a few years back.

I even put the cover back and also put the kick panel back the proper way.

While I was in there, I pulled my HVAC fan out. A mouse has gotten into my interior but I did my best to clean out the fan and area where the fan goes. The vent air smells nasty still. Goddamnit.

[Adam]

You need more cats.

[kevm14]

I need to do the elaborate mouse trap setup like Bill has. I just don't feel like it right now. Pulling the HVAC fan is annoying though. I may have to pull the cowl cover and vacuum in there, too.

On topic: I wanted to see if the ECM was good still so I started the Caprice on the stock 92 Roadmaster L03 chip. That was hilarious. It barely started. It took a good 5-8 seconds to stop bouncing from like 300-500 rpm and then slowly came up. It was really rich but eventually settled into an idle that was stable. The L03 uses smaller injectors so the ECM basically was dumping too much fuel in.

The one downside to using this ECM is if there is ever an EPROM problem. The way these old C3 ECMs work is there is a backup resistor network chip that gives you fixed ignition timing (or possibly two advance values, depending on RPM) and a very rough fuel calibration. When I was having chip problems a few weeks back (the story about the torque converter not locking), this had happened. Driving normally, the engine didn't feel totally broken which is why I didn't notice at first. That's because that backup chip was designed for my L05. With the Roadmaster ECM, the backup chip would probably be all wrong, similarly to how bad it ran on the EPROM. But the whole point of switching to that ECM was to avoid EPROM problems so I think I will just take that chance.

[bill25]

Pulling the HVAC fan is annoying though.

That's why I ended up putting traps under the car. No elaborate setup. I just drive the front of the car over a couple traps on the ground, and added a bag of moth balls under the hood. Hopefully that works.

[Adam]

Mothballs work, but smell like your grandmother's closet.

[kevm14]

I think I see where they are getting around the cowl. This morning they moved a roll of TP I had in the door pocket and dragged some of it up behind the hood latch release area. This is much worse that it has ever been and I mean so far this year, and ever.

[Adam]

Put the cat in the truck for a while.

[Adam]

Or drive it every day for a week. Although, that might make them just move to the Caprice...