94 Trooper Check Engine Light

My parents bought a 1994 Trooper used a few weeks ago. S model, 86k miles. Supposedly had a new head gasket put on right before they got it - it was smoking a bit after it warmed up on the test drive, but hasn't come back
since - figuring it was burning off something after the change (hadn't been driven between the change and test drive). I'm only mentioning that in case it plays in somewhere here. They drove it over to our house this evening, and dad says the check engine light is coming on. Not when idling, apparently it goes off then - but comes on when either accelerating or at highway speed - can't remember exactly now. This has been the first day of really warm weather they have driven it - possibly related?
A quick search over on groups.google.com says possibly O2 sensor or EGR valve? Thoughts, suggestions?
Thanks in advance!
Wesley
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Well, it could be lot of things, did you pull the code from computer? The proplem depends upon what code is stored in the computer. The plugged EGR valve passage is pretty common one but try to get the code first. You have an pre 96 model which is OBDI computer. It is very easy if you do not already know it already, here is how you do it:
There is 3 pin plastic connector sticking our of the middle console next to drivers right foot, jumper pin 1 and 3 with a paper clip when the Key is "ON" position but truck is NOT running. The "check Engige" light will start flashing, it will flash each code for 3 times. It is a 2 digit code it will flash the first digit then pause and flash the 2nd digit, then lognger pause. e.g flash-flash-flash-flash Pause flash-flash-flash-flash would be "44". Once get the code either look at the Haynes manual or search the web for what it means.
Ignore first code, which is 12 and it will flash for 3 times. All it means it that computer is getting into the diag mode and also give you enough time to get ready to observe the real code.
By the way "44" is the one which means Lean condition which could be contributed to the O2 sensor or EGR Vavle.
Hope it helps Thanks
Wesley wrote:

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Thanks for the info, that's certainly a good place to start. I'll give it a try...
Thanks again!
Wesley

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Wesley wrote:

secure, recheck and check once more: gas cap on tightly ! if necessary, replace the rubber o-ring around the gas cap
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Tom wrote:

Never ever heard of the gas cap issue causing a code on anything before OBD2 vehicles.
I doubt OBD1 is *that* sensitive.
Either way the orig. poster needs to check the codes and if the gas cap is somehow actually the problem, great.
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