service light just flashes.

[84CUCV]

Being told that my truck is having a mechanical problem. starting to wonder if the computer has something to do with it. any idea? 88 5.7. i am all out of ideas. runs like crap.

any help would be great.

 

[dyeager535]

Not the computer is my answer.

Flashes how? The code "12" over and over, or others?

 

[84CUCV]

no idea. just flashes very fast. whats code 12? thanks

 

[bigblock72]

If the engine light flashes fast then either the PROM is bad or missing or the computer is bad. If that happens the engine will run poorly.

 

[dyeager535]

Very fast huh...I assume this is just "normal operation", not trying to pull codes with a paperclip?

I don't have my manuals here to scan in for procedure, but I would first simply disconnect the ECM, and reconnect. See if problem is resolved.

If that doesn't solve it, I would look at removing the PROM and reinserting it. Should be instructions pretty easily found on the net.

Need to be very careful assuming the ECM is bad, because as with anything electrical, multiple possible reasons for failure can leave you chasing your tail. Connections, wiring, previous owner monkeying around with,etc.

Quick flashing light constantly is a good sign of a bad ECM or PROM, but it IS quite rare for them to fail. Now if you can get your hands on a spare one for testing for free, that you know works, you can always go that route to see if the problem disappears. Its about the fastest option you can have. But in my experience, always check the connections. Swapping ECM's could fix a bad connection, so I'd use that option after simply reconnecting the one you have.

 

[84CUCV]

ok think i got it. dont know anything about these computers. i will look around see what i can find. whats a prom? thanks

 

[bigblock72]

To make sure I understand what you're saying; the check engine light is flashing 2-3 times a second with no stops or breaks whenever the key is on. Or is it fashing once a second a few times taking a break for a couple of seconds and resuming in a slow consistent manner?

whats a prom?

That's the "chip". It's under the small cover that comes off of the top of the computer.

I'm going to assume that it is flashing 2-3 times a second when the key's on. If not disregard the next paragraph. A fast flashing engine light can ONLY be caused by an internal computer or PROM failure. Wiring will not cause it!!

Remove the cover and verify that the chip is pushed all of the way down into the socket. If it's tight then remove the chip inspect for dirt, corossion or contamination then reinstall. Check to see if problem has gone away, if it continues then you'll need to run to the salvage yard and grab a computer and PROM out of a truck/burb or blaze with the same motor and trans as what you have. Connect and see if problem is taken care of.