radar502

My 93 ( service Eng. soon ) light comes on as soon as the Motor changes over from ideal to run mode. I have changed the EVAP. solenoid all the trans pressure switches still no change .. Anybody know what happens when it changes over from ideal to run .. Maybe I can narrow it down from there . Thanks ..

JimLentz

Check for codes as shown here.

radar502

Thanks but I am past that point and have changed the stuff the codes show that is wrong and still have the codes witch is 26 .. My question is ,OK the light is off till the motor changes over from ideal to run them the light pops on ,what changes when the motor changes over for ideal the run .. I am trying to narrow the problem down .. Thanks ..

JimLentz

Not sure what you mean from idle to run? Once engine warms up a bit the system goes into closed loop where it uses the O2 sensors to adjust the fuel/air mixture.

radar502

Yes and the idle valve closes Ok . It may take the system that long to run a check then pop the light comes on . After changing EVAP. solenoid. and a few other things the light stopped coming on as soon as the eng, was turned on now it comes on as soon as the idle valve closes and it goes into the run mode witch is a closed loop deal .. I called the Corvette Doc. shop in Houston said it may be the EVAP. system leek and good luck finding it need a smoke machine and it might even be the gas cap sometimes a new cap will do the job.. I'll just have to keep digging .. thanks ..

mixalive

Its easy to make a smoke tool to test for vacuum leaks with a quart can, aquarium pump, tubing and a cigar. Search up on utoob.
https://www.r3vlimited.com/board/sho...9787&p=3669787

radar502

Thanks for the info . I found charcoal bits in the purge ling coming from the canister so I am going to say that the canister has gone bad like the rest 25 years old .. The canister come today so going to blow out all the lines and check the ends for cracks ET. and them make a smoke machine for good measure .. Thanks ..