LT1 won't idle/run right

[JKDGabe]

I did search, I swear! I'm probably doing something wrong I know...

 

It's running really rich. Will sometimes stumble badly from a start, once it loads up it takes off and runs fine from 2500-3500rpm then stumbles again. I replaced the MAF sensor and that made it alot better but it still does it sometimes. When the check engine light comes on it fixes the problem and runs like the proverbial bat. It had the o2 sensors replaced about 3k miles ago. I know the best thing to do would be have the codes read but have tried and it said the car wouldn't respond, don't know where to go to have it done now. It's a 95 Z28 btw. Any idea's on what to do?

[80LS1T]

Well the OPTISPARK unit is always a suspect but yours is a 95' and should be the most up to date vented style(less pron to problems).

 

I think your going to need to take it some where to figure out why you cant communicate with the PCM to read codes. Its kind of like shooting in the dark right now.

 

If you cant communicate with the PCM, something(one of the sensors) might be taking down the BUS(communication line between modules). Start unplugging sensors that are on the 5 Volt reference(MAP, TPS, MAF, etc) and see if communication comes back so you can read codes. Once/if you get communication back you will know which sensor is causing the problem. Just replace it and clear the codes and see how it runs then.

 

 

Guy

[jack46]

Well if you still have a communication error. I would fix all grounds on the PCM. Many of the communication problems are aggravated by poor grounds.

 

Specifically A2, A18 (A = Red), C32 (C = Gray/Clear), and D1 (D = Blue). What I do on mine is splice into harness for these wires, and run the four wires from them to a bolt connected to a solid connection on the chassis.

 

Of the wiring harnesses I have had, none had what I call robust grounds. I also paralleled in a ground at the coil on the front of engine.

 

A stupid question also is are you sure you have an OBDI ECM? Someone sold me an ECM they said was OBDI, but it was OBDII. It ran rich and would not communicate.

 

Good luck

[JKDGabe]

Thanks guys. It may well not be the original computer and a buddy came by yesterday and said he'd had that problem. '95 is supposed to be OBD1 right? The obd1 wouldn't even plug up and the obd2 did but didn't read it. I'll check the grounds and then look for a shop that knows what they're doing.

[jack46]

'95 is supposed to be OBD1 right?

Yes the PCM has OBDI programming.

 

The obd1 wouldn't even plug up and the obd2 did but didn't read it.

Ok I'm not certain what you are saying. A 94/95 PCM is an OBDI program the connector to the PCM is OBDII. I think OBDII programming (PCM) started in 96 (front and rear O2's).

 

Externally the OBDI and OBDII PCM look identical. Internally there is are a few differences the Flash are larger on OBDII and other subtle changes.

 

Even what I said is confusing so it is easy to get it backward. If you never talked to the PCM I would bet it is OBDII. I would simply put an OBDI on and see if it corrects the problem. Then get a PCM programmed for your car.

[Zoldman]

In '95, the Z28 LT1 was OBD1, but GM used an OBD2 connector for the ALDL port......go figure.

 

Check your PCM part number; it should be 16188051 (if it is from a '95 OBD1 Camaro).

 

Bill

[Pop N Wood]

Chevy used OBDII hardware on the 94 and 95 LT1's. That is the beauty of those years. You have all the advantages of OBDII (like reprogramming them via software) without being governed by the OBDII smog laws.

 

Give Tim240 a heads up on this one. He had a 94/95 LT1 that he reprogrammed. I would think an OBDII code reader should work.

 

BTW, sounds like your engine is running bad because it is trying to go into the closed loop mode but is getting a bad input from some sensor. When it throws the check engine light on, it must be giving up on the bad sensor and is running in the open loop mode using canned fuel settings. You really need to get the error code reader working.