This is something that doesn't happen all the time and that is why it is confusing me. Every so often when I'm driving my check engine light goes on. But if I hit the dash the light will turn off and the car runs fine again. Any suggestions?

 

Read the FAQ on the main page and check the code.

 

that happened to me before

but in my case my ECM had some faulty connection which would cause the car to go into Limp Mode

 

86,

Scan for codes. The ECM will retain error codes for the last 50 engine starts. If you had a code within that period, it will still be there unless the battery power to the ECM was interrupted.

 

Ok, this is my problem. I'll try and detail it a little better this time. This only happens every couple months. I'll be driving and the check engine light will go on. When that happens the car still runs but seriously lacks power. When I let go of the accelerator the voltage goes way down and the oil pressure goes down and it idles low. If I hit the dashboard the light flickers a little bit and goes off. When it goes off the car runs fine for the most part until I stop at a light and it runs a little rough. I'm getting no trouble codes. And after it sits for a while it runs fine. I'm assuming that there is a wire loose either in the dash or on the ecm itself. Does anyone know where to start looking? thanks

 

I'd suggest cleaning the edge connectors on the ECM.

Disconnect the battery ground cable at the battery. Remove the lower panel trim in the RH footwell, then lower the ECM from its mountings. Unlock and remove the edge connectors from the ECM and remove the ECM from the vehicle. Be careful to disconnect the connectors on the buffer module (yellow box) on the back of the ECM before removing it. Inspect the connections at the ECM itself. If they are dull and oxidized, you can use a standard pencil eraser and stiff brush (1" paint/chip brush with bristles cut shorter) to clean them lightly.

Before reinstalling the ECM, inspect the plugs and all their connections visually. If there are signs of burning or overheating, you have a major chore ahead of you. Cleaning and bending the connectors in place is a PITA. If the connectors are not heated and damaged, brush and blow out the contacts and reinstall the connectors, then remove them again. Plug and unplug each connector fully, several times, to use the wiping action of the contacts to clean themselves. Brush and/or blow the connections out to clean away debris, and fully seat and lock the connectors. Reinstall the ECM and try it again.

Often, this alone will fix some of those rogue problems that are usually mistakenly blamed on a "faulty" ECM. While you're in the vicinity, it would be a good idea to trace the ground connectiosn from the ECM and make certain they are clean and tight, too.