Overall need help

[Trstrugar]

I am in need of some experienced advice here. I bought a 1994 gmc 1500 with a 5.7l from a 1995 Tahoe, and a 700r4 transmission from I don't know where. The truck runs and drives, but runs extremely rich, and runs codes for a variety of different sensors including the maf sensor, mat sensor, 02 sensor, and IAC. The IAC is wired incorrectly because the after market harness was all black, and the wires were not put in their correct places. The truck has a custom 2.5 inch exhaust with no cats. It runs like **** on start up, and wants to bog down. If anyone can give me some advice I would appreciate it

 

[Justin S]

If i'm not mistaken, 94 engines were OBD1 and 95 switched to OBD2, so it kind of sounds like they tried to splice in some stuff and make it work, but obviously didn't quite work out. With the little info given, it might be a good idea to get a whole used engine harness and rewire it to your computer and start there. Worst case, swap the TBI for a carb and get rid of all sensors.

 

[jkeaton]

My 95 is still obd1. The ******* year. Only 95 stuff will work in a 95 truck. 96 was full obd2.

 

[Trstrugar]

to be completely honest I don't even know that the engine that's in it is from a 95 Tahoe. That's just what he told me. The body was in such good shape and it ran so smooth when it was driving I went for it. It seems like if the engine that's in it was not obd1, it wouldn't run, or would throw a hell of a lot more codes. It's just throwing codes for pretty normal wear and tear sensors. What exactly would switching to a carburetor involve? I've done a lot of Trouble shooting, but I'm not really sure where to start with this it feels a little overwhelming with the engine and transmission not being orginal, and no way of knowing what is going on with the wiring

 

[Justin S]

Pretty much just a new intake meant for a carb, and a carb, then you can delete all of the sensors and wiring. Just need to put in an in line pressure regulator

 

[jkeaton]

You are answering your own question if you are getting codes for all those sensors. You need to correct the codes first. Probably that 95 engine is not compatible with the 94 PCM.

 

[Trstrugar]

I know you are right jkeaton. Sorry to talk across 2 forums with you about this, I'm thinking that the o2 and the IAC are the main culprits. I just don't know what I can do to make the o2 sensor behave. And I don't know which one I would need to buy anyway because the engine and tranny are not stock. I'm not sure what the 700r4 transmissions come out of

 

[jkeaton]

I would say the first thing you need to do is positively identify the transmission. There has to be some tag or data plate on it somewhere which would have a model/serial number or something so you can truly find out what year it is. But, the codes for the sensors are not related to the transmission, more towards the PCM if the engine is indeed a 95 and the truck is a 94.

 

[sntrym]

The 94 and 95 engines are the same. There is no MAF on a 94 or 95, only 96 and up. Your first step would be find out why it's running rich. One common issue is the coolant temp sensor located on the top of the intake manifold. Get a multimeter and measure the resistance. Here is a link that contains the values at certain temps: http://67-72chevytrucks.com/vboard/showthread.php?t=425788

I would fix the IAC wiring, clear the codes, test the CTS, and go from there. Also, check the PCM to make sure it's the right one for that engine. It's behind the glove box.

Also verify the engine is what you were told. Is the intake manifold plastic or aluminum?

 

[michael hurd]

Yes, you need to identify the transmission, also check the engine casting at the back to see if it says 5.0 or 5.7.

As far as the engine itself goes, there is literally no difference in a TBI engine from year to year.

If someone swapped in a 5.0L where a 5.7L lived or vise versa, you will have incorrect tables for the injectors.