94 chevy truck EGR Woes

Mudacon1

94 chevy truck EGR Woes

Unread post by Mudacon1 » Mon Nov 01, 2010 6:25 pm

I have a 1994 Chevy truck. When I bought it, there was a vacuum line disconnected on the engine. I looked at it and found it be the line between the EGR Valve and the EGR Control Module. (Note: Like this, it ran fine but, the check engine light would come on.) I hooked up the vacuum line and the truck started chugging. It would surge all the way down to 200 rpm and back up. Upon further inspection found the EGR to be wide open.
I took it to the mechanic. He looked at it, tested it, hooked the computer to it etc. He could see that the computer was asking for the valve to be opened 99% and the control module was happy to oblige. He put a new MAP sensor on it and did some more test. Same thing. His Computer was telling him that everything was in "normal" parameters. As far as he can tell there is nothing "telling" the computer to request the EGR valve to 99%.
First of all does it always ask for 99% (when it does ask correctly)?
Second and Mainly, Does this mean the computer needs replaced?

I am hoping there is a simpler solution, and less costly!

lappy

Re: 94 chevy truck EGR Woes

Unread post by lappy » Mon Nov 01, 2010 8:03 pm

With you just buying this truck and finding that EGR was disconnected, it sounds like the previous owner was trying to fix this problem. He left it off so the truck would run better. There is no one thing that tells the PCM to turn on the EGR valve. There are several parameters that must be met before the computer will control the valve. It is possible that the computer had been replaced but the chip inside was not swapped over to the new computer. This chip has to do with EGR and knock sensor systems.

Mudacon1

Re: 94 chevy truck EGR Woes

Unread post by Mudacon1 » Mon Nov 01, 2010 8:11 pm

Ok, So how do I find out if the chip in the ECM is wrong?

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