Idiot light. On the highway. 86 GP, 305

[ilduce]

So I've got a check engine light on the highway after ten miles. I can idle it for half hour, floor it on the entrance ramp, whatever. Once I'm highway driving for awhile the light comes on. If I restart the car it won't be on until I hit the highway again. I don't notice any difference once the light's on, although I've always wondered if the secondaries open properly (real nice pickup but unimpressive top gear response). It's done this since I bought it. It's tuned up except for a carb rebuild and engine timing and it still comes on.

Any idea which of the various sensors could cause the light to come on from exclusive highway action? I know it's a guessing game, but this forum always comes in for me. Could anything other than a sensor, say a grimy carb, cause the light to come on?

 

[carpenter383]

Sounds like the egr valve isn't opening when it should (low load high manifold vaccume) not a big deal really. You could see slightly lower fuel mileage though, because when the egr valve opens it leans out the a/f mixture with exhaust.

 

[RockSS]

Sounds like the egr valve isn't opening when it should (low load high manifold vaccume) not a big deal really. You could see slightly lower fuel mileage though, because when the egr valve opens it leans out the a/f mixture with exhaust.

Yup that be my guess also, I've got an 87 ss same thing pulled the code and it comes up egr... prob. is it was changed so idk.. doesnt matter loosing the computer soon anyway.

 

[Bonnewagon]

Did you pull a code? Even if it's intermittent try pulling a code while it's on. The only thing I can think of in high gear is the lockup converter, but I'm not sure if that would set the light.

 

[ilduce]

Thanks for the ideas. I don't have a code reader, otherwise I'd do the code after a highway operation. Maybe it's the EGR failing, my engine runs on the rich side, but then again the carb could use a rebuild, too. For an EGR function test, do I press in the diaphragm and see if it pops back out? And, is there any way to know whether or not the secondaries open properly?

 

[megaladon6]

you don't need a code reader, you can use a jumper wire to connect 2 pins together and the light will blink out the code.
look it up in the owners manual for the exact procedure.

 

[azmalibuwagon]

you don't need a code reader, you can use a jumper wire to connect 2 pins together and the light will blink out the code.
look it up in the owners manual for the exact procedure.

true. I'm betting it's the EGR or the oxygen snesor.

 

[megaladon6]

yeah, but why bet? it's better to know

 

[ilduce]

you don't need a code reader, you can use a jumper wire to connect 2 pins together and the light will blink out the code.
look it up in the owners manual for the exact procedure.

My owners manual doesn't say how to jump pins to find out the code. It only says to have the car serviced if the engine light comes on. I've got the owners manual for the 86 GP and Bonneville. Can you explain how to do it?

 

[megaladon6]

sorry, not the owners manual, the repair manual
mines buried, but i'll see what i can find.