Flickering Check Engine

[Bow-Tie Guy]

Hello, all.

I've got an '81 with a flickering Check Engine light. Did a lot of searching on the subject and everything leads to checking the flashing codes. Here's the problem I'm having. The check engine light just randomly flickers while running. When I try to check the codes, I don't even get the initial 1-2 diagnostic flash code. In fact, I get nothing at all! But once I start the car, the flickering starts up again.

I just had the carb rebuilt and the car is running pretty smooth. I wouldn't care about the darn light if it weren't for the fact the I need to smog the car. (Gotta love California...:W)

Anyway, I'm suspecting that the flickering is the result of a short in the ground wire from the ECM to the Check Engine light, but what would prevent the 1-2 code from flashing in the first place? Bad ECM, too? Should I start with the wire first and work back to the ECM? (Man, I hate electrical "issues"...;help)

 

[TimAT]

If the CE light on with the key engine not running? Maybe go by an Autozone or something and have them plug it in to their code reader. No codes, and without looking at an 81 factory service manual, I'd guess that if the light is NOT on with the key on and not running the check engine light driver in the ECM is gone. IIRC, there is a section in the manual for CE light problems.

 

[Bow-Tie Guy]

Thanks, TimAT.

Yep - no CE light when the car is "on", but not running. Flickering only starts up when the car is running.

Gonna mess with the wire itself tonight after work. Track it down in the center console assembly, inspect the wire and giggle it around. Maybe even check the bulb itself. If I get no new results or an unchanged situation, I guess I'll be looking at a new ECM. ad

 

[TimAT]

I wouldn't just jump out and buy an ECM- exhaust all the troubleshooting first. Get the factory service manual and FOLLOW the trouble code tree- save yourself lots of hassle and $$.

It's very possible that a replacement ECM will have problems you don't really have now- get it checked for codes, fix them in lowest number to highest in order, and then if the CE light is still not correct, think about an ECM.

 

[Peer81]

Its a very tricky system that only uses one bulb. If the bulb has a bad connection or the wires on the print (on the back of the dash) has a bad connecting you already have the problem you discribe.
Good luck!

Greetings Peter

 

[Bow-Tie Guy]

TimAT - Thanks a-million for the responses and suggestions! I was a bit busy with Easter and all so, to be honest, I didn't get the chance to do much over the last few days. I'm going to try and poke around in the next couple evenings after work. I ordered a factory service manual (as that seems to be the one manual I DON'T have!), and am waiting for its delivery.

Peer81 - Yep, I was suspecting the possibility of a bad bulb and/or wire myself. Kinda hoping that it's a simple (and inexpensive solution) rather than a "worse case scenario".

I promise to give an update on what I find, as I know it can be a bit disappointing for others who have similar problems to see these types of threads die with no resolution.

 

[Bow-Tie Guy]

Hi, all. Just wanted to provide an update and resolution to this topic.

Well, it looks like a new ECM is in order. Connected the battery (it was disconnected for about 4 days), and turned "on" the car without starting it last night. Lo and behold, I get a nice steady 1-2 flash on the Check Engine light. (This was something I never got w/o jumpering the ALDL before!) I let it flash for about 4 or 5 times just to see if there were any other codes flashing - none. From there, I start the car and the steady flashes are replaced by the flickering CE light again. The only thing different this time over the past is that I notice a definite pause between flickering. (Ex. flicker-flicker-flicker-off, repeat.)

I turn off the engine/car and turn it "on" again to see if I can repeat the 1-2 flash. Nothing. Start the car and I get the flickering CE light again.

I cleaned off the two ALDL terminals under the ash try and tried jumpering them - no 1-2 flash. Checked all the wiring harnesses for good contact - nothing new. Checked the bulb - seems fine.

I'm back-probing the white ECM connector pins with a test light as per the '81 Service Manual, but everything is leading straight to a bad ECM. The very fact that I'm not able to repeat anything consistently aside from the flickering confirms my suspicions that it's the ECM. The back-probing only adds to the suspicions. Well, that's where it stands. I just wanted to let others know. Thanks to CAC for the advice and suggestions.

 

[Vette D.R.S.]

Any update ?? got a 81 that I will be putting ECM and emissions back on, so interested with all the quirks of the system.


Dave

 

[Bow-Tie Guy]

Yep, it turned out to be the ECM unit. Had one on order with Eckler's but after several weeks, I still didn't get a notice about when it was shipping. So I had to cancel the order and bought one within a couple hours from O'Reilly Auto parts (of all places!)

Now, no more flickering check engine light!

 

[Vette D.R.S.]

Well Bow Tie, congrats on the repair, glad to know what it was, not real glad to hear about Ecklers, as I've got parts on order and nothing is moving.

Thanks for the reply

Dave