My check engine light on my 1989 5.7 TPI equipped car is on and it's running weirdly but when I jump the pins to read the codes, it won't blink consistently. The length of the blinks and time between them is inconsistent, it won't spit out the 12 code at the start or any time. I can't seem to find anything on this happening anywhere, I'm worried it's a computer issue, but I'm not sure how to proceed on diagnosing it.

 

It is not supposed to be consistent.

If 12 is the only number currently set, the indicator light behavior will be:
-Blink
-Short pause
-Blink, Blink
-Long pause

-Blink
-Short pause
-Blink, Blink
-Long pause

-Blink
-Short pause
-Blink, Blink
-Long pause

Essentially:
-1
-pause
-2
-End

This behavior is displaying Number 12.
Repeated two more times (making it three times in a row).

Each DTC Number currently set, will be flashed Three times before flashing the next DTC Number.

Here is a video of someone displaying DTC Number 12:

 

I appreciate the response, but I understand how the OBD I is supposed to function, I've had the car 11 years and used it before. When I say it's being inconsistent, it's that the length of time the light is illuminated and extinguished follows no discernable pattern, certainly nothing that follows any code. There seems to be 3 or 4 different lengths of time of the blinks and just as many different gaps between the blinks. When the pins aren't jumped, the light remains solid, as it's supposed to.

 

Is the battery fully charged?

 

The battery is fully charged, the engine cranks quickly and fires right up. The idle surges from 700rpm to 1500rpm before leveling off to 800-1000rpm after warming up a minute or so. I can guess a few things about that aspect of it, but the CEL behaving so oddly is baffling. I'll check the grounds, but beyond that, the ECM is the only thing that comes to mind. I don't like throwing parts at a problem.

 

Please Post a video of the behavior.

 

At the ecm ground a9 white/blk wire . If the mil doesn’t flash I’d say it’s bad.
the lack of communication from the ecm is a sign of a bad ecm. Can take a screw driver handle and tap on ecm case while running and see if running changes this flexes the circuit board another test to see if ecm is bad.

 

It isn't doing the 12 code nor does it repeat any other code. It makes what looks like might be codes but it's not functioning at all like normal.

 

Check code koeo, your in field service mode

 

Yep, what tuned said, , , ya gotta have the key on with the engine NOT running for it to properly blink out the codes

 

Ah, yes, as usual, the answer seems to be I'm an idiot who forgot an obvious thing I'd previously done right for years. I'll check on it tomorrow and see what secrets the ECM has to share.

 

Please.

I am truely interested to see the abnormal behavior that is occurring.
I have seen incorrect flashing years ago... and would like to compare what you have going on.

 

Hey no biggie, it's an easy mistake to make, and it sure beats having replaced the ECM only to find out later that the engine running was the cause of the odd CEL activity


Hi Vorteciroc, Jack posted a link to the video in post #8, in that video the odd behavior is seen (and that's how Tuned and I saw that he had the engine running during the code reading attempt)

 

https://www.motortrend.com/how-to/14...ally-speaking/