service engine soon light

vegavairbob · Post by **vegavairbob** » Thu Jun 28, 2007 9:33 am

'89 GT 2.8/auto.
service eng. soon light comes on sometimes, then goes out.
grounded terminal with ignition on..
got the diagonostic code- 1 flash
followed by 2 flahes (3 times)
then no stored trouble codes come up???
note-when i ground terminal, rad fan comes on (with engine hot)
also rough idle-
(fuel filter/pcv last changed-unknown)
thanks, bob

quad4gtz · Post by **quad4gtz** » Thu Jun 28, 2007 6:13 pm

This has not set as a hard code. The problem is probably intermittent, and just on the borderline of faulting ECM specifications. You need to check for the code when the issue is most apparent and/or the engine light is on. Otherwise just start looking for anything that may pose a problem... misfire, vacuum leak, EGR sticking. If your not sure about the last time the fuel filter was done... it is due.

vegavairbob · Post by **vegavairbob** » Fri Jun 29, 2007 9:52 am

thanks for reply...
i checked egr by haynes manual rec.- by pushing it in...it moves freely.
could a shifting gaskit in fuel cap cause light to come on and go out?
is dirty fuel fiter most likley causing slightly rough idle?
also-how important is replacing ignition wires (120k miles) for smooth idle. not sure if they were changed.
bob

rweatherford · Post by **rweatherford** » Fri Jun 29, 2007 7:44 pm

I would probably clean the IAC and the TB. If the car is not missing under load then I would not suspect the ignition system. If it misses at idle then I would suspect a bad injector.

You need to check all of the spark plugs and see what condition they are in. They will tell you more about each cylinder than I can.

The gas cap will not cause any problems on an 89. Only on the OBD2 95-96 models.

You will just have to try a few things at a time to try to decide what it is.

Doing the code trick when the engine is running (field service mode) may tell you a few things. I can't remember which way it is, but when the SES light is on in that mode it shows rich and lean by flashing. If you rev the motor up and then let off the motor should go lean. I think the light will go off. If it does then off is lean and on is rich. The light should go on and off at a regular interval if the sensors are working correctly.

If the car has an old O2 sensor then you might try replacing it. They are not that expensive now.

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