1987 Chevrolet Flatbed one ton

[Ford 335]

Background:
1987 Chevrolet C/R30
350 Throttle Body
Manual transmission
After driving a long period 50-75 miles the "Service Engine Soon" light appears. I can stop, turn it off, immediately restart and the light is gone. Drive another 50 or 75 miles and the light reappears. Oil level is good, no discoloration. Water level is good - no oddities there. Engine sounds good and is running smooth. Road conditions, good, nice even two lane state highway running 55 - 60 miles per hour.

Any ideas about what could cause the light to appear? Or, ideas about how to test and identify the problem?

Thanks for the help!

 

[Dennis Benson]

Could be a vacuum leak, that would throw the sensors off.

 

[Anonymous-0]

My 94 gmc 2500 had the same symtoms, a few weeks later the fuel pump stopped working.Had the code checked after I fixed it,memory in computer said low fuel pressure.This may be some help

 

[Kris Golden]

My '89 Suburban's "service engine soon" light comes on at about the sixth mile every time. It is so consistant I can point it the second it comes on between here and town. Been doin' it for years.

 

[WA-Hal]

I would suggest checking what codes have been stored in the computer--I bet there is something there if the check engine light has come on multiple times.

Doing the diagnostic work first makes sense. You may save yourself some money by not replacing parts that really don't need to be replaced.

Just off hand, I would suspect the Oxygen sensor unless it has been replaced. But it would be stupid to just replace that sensor unless the codes in the computer suggest that as being the problem. Good luck!

 

[ericlb]

i dont know if '87 had a computer or was still ecm, but one thing that absolutly will turn that lite on [ there are numerous things] is a bad oxygen sensor in the exhaust how many miles does the truck have on it? check that first

 

[Ford 335]

Thank you everyone. Your suggestions are very helpful. I have 72,300 miles on it right now. I have the original paperwork and the original set of extra GM keys the dealer taped to the paperwork when it was sold.

That paperwork does not solve the problem but your suggestions can get me moving in the right direction of finding a solution.

Thanks!!

 

[Anonymous-0]

Most likely low fuel pressure or a vacuum leak, will cause a slight spark knock that will be very occasional. the ECM will count those things and when the count gets high enough will set the light.

On a TBI you can jumper the diagnostic terminal under the dash to make it give you the codes. Use the factory (not Haynes Chilton etc) manual ($30 or les on evilpay) to run the trouble tree.

 

[AllanC]

A vacuum leak would have to be bad to mess the sensors, the computer would just compensate. Does the truck run ok, or is it faltering when the light comes on?. EGR system on TBI unit can cause lights, still runs fine. If there is a round cap on the egr controller, there is a filter under there. I plugged will cause a light.

 

[jaydee]

I had a plymouth minivan,the check engine would come on for no aparent reason. Did this for years, finally fixed it. I placed a business card over the top of it. The car never left me stranded, and finally sold it after 14 years old.

 

[Ford 335]

Thank you, the truck is running fine. Mechanically it shows no sign of trouble except for the light. That is what is very perplexing.

 

[Ford 335]

I will do some more diagnostics. Your comments help me narrow the search. Thanks!

 

[circus]

A trouble code has been entered. Access the code by using a jumper wire at the diagnostic terminal and turning the key to on. The check engine light will flash the code. Look up the code in a manual. It"s a start but it"s not as useful as it sounds.