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Have a strange one here.. Car, 1995 wagon Lt1, was running fine before this.. A/C compressor went out, installed new compressor and hoses and all related needs, replaced all hoses since I was in there, changed thermostat, and belts. Put everything together, changed spark plugs (NGK) filled it up with water/AF started it, ran fine, no leaks, bled the little air valve on the thermostat housing a few times. Have not plugged in the AC compressor yet. (still need to evacuate it.. etc). Car, has 5.7 with heavy duty cooling, 1 mech fan and 1 elec fan plus various other towing package items. Problem is, as long as you are driving it, all is normal. As soon as you let it idle for a minute or so, the engine kind of stumbles and the elec fan comes on and the check eng light comes on.. If you drive it for a few seconds, the light goes out and the fan turns off, or you can just kill it and start it and all is fine for about a minute and it does it again.. Temp gauge never shows over halfway, as it always has and hoses never shows over 150 or so with a thermal gun.. Smog pump fuse is good. Thermostat seems to be working right also.. Irks me that GM engineers made it near impossible to pull the error codes (paper clip trick does not work on this model) Normal OBD-1 do ot work on it either . Dealer said they would pull the code for $150, and before you say it, Autozone nor O'Reilly's can do it. '94, '95 5.7 are some special sort of bird. Any help will be appreciated...
 

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Get that check engine light read. .. Better still, just take it to your Chevy dealer and let them fix it.
 

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The CEL means that the code was thrown that will probably point you directly to the problem. Get the proper cable to do your own diagnostics, download (free) eehack and go to town - or let the dealer sort it out. This cable is well-known to be the best one, and most reliable one out there.
 

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Thanks.. No dealer ripoffs for me.. I don't mind spending a few bucks to get the proper tools.. I just couldn't find any obd1 stuff to work on my '95 caprice, but it looks like you have one so it must work.. Does your vin have the P for the eighth number? I will check it out and let you know..
 

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Nope
A and B are power and ground
B is field service enable.
You might see a voltage reading, dont know, but it ain't power!

A ground
M data

As other posters have stated, these are the 2 connections needed to communicate with the 94-95 PCM
20200112_103753.jpg
 

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Yes, these cars need an enhanced OBDI software scan (two years only, as it was obsoleted by OBDII in '96). Some scanners can interface with these computers, but most cannot. If you are decent with a computer, then the best bet is the recommendations already made (get your own USB cable and use a laptop).

Albeit if touching a computer scares you, then I can dig through my notes on a few off-the-shelf scanners that should work. Of course there have been previous discussions about this subject on this forum.

Once you scan the code, post it here. There are a few codes that are misleading (ie: knock sensors which sometimes will report as an ignition system fault). So we can help you do the proper diagnostics.

In fact, the symptoms you report sounds like a knock sensor issue I chased for a while on a '94. Replacing the A/C system parts and hoses puts you at risk of disturbing the knock sensor and/or the wiring to it on the passenger side. In my experience, simply unplugging the knock sensor can be enough to cause intermittent connection with these 25 year old connectors. And worse, just bumping the connector with a tool or tugging the wire can cause a crack in the wire or the sensor housing itself. And then this will cause a random knock sensor code...often at idle for some reason. My theory is that once you start driving, the vibration can be enough to make the connection again and turn off the light. Not saying this is your issue, but it happened to me and I figured I'd share my experience.

I'm also wondering if you got a little water in the Opti during your cooling system maintenance if you spilled any. That can cause random CEL problems too.

Get the code and report back. Otherwise we are just guessing.
 
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