Check Engine Light/Transmission not shifting properly

[VinnyVan]

Howdy, folks! Having a little problem with my van and I hear this is the place to ask questions.

I have a 1994 Astro EXT. stock with 4.3 V6 and 4L60E transmission, 130,000 miles. Recently it's been having problems. Five times out of 6 the check engine light comes on and stays on at startup. I pull it into Drive and try to pull away, and it pulls away in a jerky fashion, as if it's rapidly shifting between gears with very little power getting to the ground. Around 10mph, it finally decides it's happy with second gear and I'm off. In that 1 time out of 6 that the light doesn't come on, it runs completely normally. Could it be a faulty sending unit or wiring problem? It's been acting like this since I got it stuck in the snow pack and had it pulled out. Could something have been knocked underneath?

Thanks for any help or suggestions.

-Vincent

[LiftedAWDAstro]

What is the code? How does the tranny fluid look and smell? If you were hammering on it while trying to get unstuck you could have done some damage internally. Get us the code and we can go from there. It may simply be an engine misfire.

[VinnyVan]

I checked the transmission fluid; didn't smell burnt, looks healthy. We didn't hammer on anything to get it out of the snow, just hooked up a truck and pulled it out. Now, as for the code. I'm assuming that's where I go under the dash and ground the diagnostic terminal and count the flashes on the check engine light.

After grounding the terminal, I got a sequence of three flashes (one, a pause, then two in rapid succession) three times, which I've read is a Code 12 which means the diagnostic system is running properly? Then I got 4, 2 three times, then back to 1, 2.

[Kabey's Van]

Code 4-2 is for a malfuctioning ignition modual or EST curcuit is grounding out or has a faulty power source.

[VinnyVan]

I'm new to working on automotive applications, so I'm not quite sure what's going on, then. If it's a fault in the ignition system or EST circuit, then why is the transmission acting funny? Is this fault causing the ECM to default to limp mode?

Well, now we have it narrowed down, what should I look for? I read a page on code 42, and it sounds like I need a multimeter (specifically an ohmmeter) and a test light to see if the ignition module is faulty or if it's just a wiring harness fault?

[Kabey's Van]

A miss fire will cause symptoms that will make it feel like your trannys' not functioning properly.
It's not like the old days, everthing has to work in unison. Gotta love computers.
It's unlikely the problem is in your wiring loom as it is more likely to be a connection somewhere.
Is the code a soft code or a hard code?
Meaning, if you reset the SES light does it come back on as soon as you fire up the engine or does it take a while for it to come back on?
You will need a test light or better yet an ohm/volt meter.
Peter

[ihatemybike]

The ICM can be tricky to test. My '94 would start cold, but once it warmed up the van had fits. The ECM tested fine when removed, but by then it was cold. Apparently old ones can be affected by the heat. I think the jerkiness you feel might be caused by the engine not running correctly.

The ICM costs between $25 and $60 depending on mfg on http://www.rockauto.com. I'd replace that first and go from there.

[Kabey's Van]

I didn't know an ECM was so cheap. I thought they were like $400, and yes computers are effected by heat.
Based on the cost I would swap it out for a new one too, then if it is a wiring problem you will then know.

[VinnyVan]

I reset the SES and started the engine and immediately the light came back on and I got the same code again. I don't have much electrical testing equipment on me right now, but when I can, I'll post back. Thanks very much for the information, everyone.

-Vincent

[LiftedAWDAstro]

How is the cap and rotor condition? Could be moisture under the cap causing this and you may only see it under load. Pull the cap and see what it looks like. If crusty or wet, replace them.

[ihatemybike]

I didn't know an ECM was so cheap.

Oops, edited to ICM aka Ignition Control Module.

Oh and for what it's worth, the '94 ECMs run $72-$235 depending on mfg.

[VinnyVan]

How is the cap and rotor condition?

Nice catch! I pulled the interior cover off, removed the cap and chipped all the crusty crap off the contacts. The contacts still look pretty good, so I put it back on. Connect the battery, start it and bingo! It's running normally again. Took it for a little drive, and no problems. I was thinking way too complicated; didn't think of the easy stuff first.

Thanks very much, everyone! It's good to be cruising again.

[LiftedAWDAstro]

Glad you got her running again. I would suggest picking up a new set at your local GM dealer when you get a chance.

[VinnyVan]

Will do; thanks again!

[WVKayaker]

Ain't this site the ticket!
Way to go Dean!