Question: constant blinking on check engine light

[PokerJoker]

No check engine light on when I bought the car...bulb had been removed. Replaced bulb and had erratic flickering, so I pulled the computer cleaned all the connections, pulled the chip and reseated it.

Now, just getting a continuous blinking of the Check Engine Light. It never goes off, and doesn't stay on, just constant blink, blink, blink.

Any idea's?

 

[bill81vette]

pull the bulb back out.
now you know why it wasn't there to begin with...

 

[Peer81]

The question is. Does the ECM go into closed loop or not? If the ECM says in open loop then you'll need to take a second look into it. Can you get a normal 12 code from the ECM?

Greetings Peter

 

[Tim81]

I hate to say it but I think your computor is shot. Maybe you can borrow a good used one just to check it and be sure. Mine would do that same thing however when I unplugged the 4 pin distributor connector (like when you set your timing) the light would stay on constantly, ended up being the computor.

Good Luck Tim

 

[Wajulia]

That is not a normal response from a working computer. Try to read the codes. If you do not get the 12 code, the computer is not operating correctly. Check the connections again, then it is probably the computer

It is not to expensive, about $100, you will need to transfer the prom. Without the computer the car will run ok, full rich and no timing advance. Your gas mileage will be horrible, the car will smell very rich. I wouldnt run it long like that, clogs cats, builds up carbon on everything an costs a fortune to run

 

[PokerJoker]

This car had the cats and air pump already removed when I bought it. I'll check the ECM for codes, but the last time I tried that...nothing, just blinking.

The guys at the shop just want to pull the distributor and go with no computer, he says the original carb will work fine, but from everything I've read it won't.

If I'm not running the smog pump or cats, will the computer set off a code? I'm just not sure what to do at this point.

 

[Tim81]

If you decide to run without the computer you will need to change the carb and distributor to pre computor units. Not sure if your TCC will still work or not, but if the computor is bad now its probably not working anyways. Pay the 100 for a replacement computor you'll be further ahead..

 

[Wajulia]

Removing the cats and air pump will have no effect on the computer. The question is what else has been removed. Probably not a full list, but for the ECM to work you need the o2 sensor, throttle position sensor, temperature sensor, map sensor and speedo sensor. I might have missed one but ther is not much more

The 1981 carb does not run well without a computer. It will run full rich, which is very rich, and there is no way to adjust it. To run an 81 without a computer you need to change the distributor and the carb. Many have done so. But that will take about $400 -$600 dollars. Why not fix the computer. Many here have done that also. It is not that hard and works as good as a new carb and distributor.

 

[PokerJoker]

I'll try that first, I just have a bad feeling about pulling all the original stuff at this point. It just seems to me it's so close to being right, it would be a shame to give up now. Basically took it to the shop because of a small "miss" and lack of power. They ran a lot of tests and tried to set timing. They say the timing wont stay set because the computer is changing it. If that is actually the case it seems the computer is trying to do something. Also, don't you need to drive it awhile for the computer to actually calibrate, I've had a dead battery so I'm sure the computer has been reset.

Maybe just driving the car awhile will help it more than anything? I'll try to pull some codes first and post an update.

Thanks for everyone's help, I'm open to all suggestions.

Jeff

 

[PokerJoker]

Removing the cats and air pump will have no effect on the computer. The question is what else has been removed. Probably not a full list, but for the ECM to work you need the o2 sensor, map sensor and speedo sensor. I might have missed one but ther is not much more

The 1981 carb does not run well without a computer. It will run full rich, which is very rich, and there is no way to adjust it. To run an 81 without a computer you need to change the distributor and the carb. Many have done so. But that will take about $400 -$600 dollars. Why not fix the computer. Many here have done that also. It is not that hard and works as good as a new carb and distributor.

Thanks Wajulia, for the comments.

I really believe I'd rather fix whats there than replace it with something else. It's good people who understand these cars confirm what I'm feeling. I did pick up an original 81 computer and prom from a guy yesterday to give it a try and see if it changes anything. If not, I'll just pick up a rebuilt ECM. I'll post an update as soon as I can.

 

[PokerJoker]

You too Tim81

Thanks for your help. I've read ya'lls posts on this same subject and searched and searched for more info on this topic. I've had this car for about 3 years now. Never been able to enjoy driving it, (been working on it) but it's getting close.

Jeff

 

[Wajulia]

Let us know what happens with the new computer. There is a lot of help here to sort it out once it starts acting as expected

Another note, it is a misconception that the 1981 computer "learns". It does not. Once the temperature reaches 180 it should go into closed loop. Driving the car will not change it any

 

[Wajulia]

Something came to me while I was riding my motorcycle (strange stuff can come to you on a bike)

Your mechanic should have been setting the timing with the connector to the Distributor disconnected. This puts the HEI into a bypass mode and eliminates any computer inputs. The timing should be set to 6deg as per factory specs (many threads on this say that 12 deg works better, but I have never been able to prove it). So the mechanic should not have seen any fluctuations caused by the computer.

That in no way eliminates the computer. It seems to be unconscious. But you may want to check to see that the mechanic is setting the timing correctly.

 

[PokerJoker]

Well, I told him I didn't want to change the distributor yesterday morning and settled up with him and drove her home...it was a rough ride home.

I did ask him if they had disconnected the 4 pin wire from the distributor before they set the timing and he said they had. I'm not sure about that. On the way home it threw the power steering belt...I think they had the belts off while in the shop and put it on the wrong pully (smog pump is gone, so I suppose that could be an easy mistake)...don't think it damaged anything. I put a new belt on this afternoon.

Going to check and set the timing myself now. Another thing while it was in the shop...he rebuilt the electric choke, now I know for a fact the green wire was routed around the front side of the engine and down the left side of the engine bay area. It is now routed around the back side, so I thought "that's strange", he had cut the wire and spliced it into a large orange wire going into the distributor. I'm guessing the choke light wouldn't go off even after the rebuild, so took it out of the equation.

Do any of you guys know where that choke should be wired into, maybe I can fix it.

Checked for codes...pulled the fuse first to reset and see if I could just get a 12. When I jump the terminals with a paperclip, check engine light just blinks so fast you can't even count...then a pause, but not even a pause its so quick and then blinks so fast the light basically is on solid...it just does that over and over. I'll try to swap the computer with the used one I picked up Saturday and see if I get any changes. Will update soon.

 

[Wajulia]

I will check the choke wire when I get home tomorrow You are right it should be routed from the drivers side across the front of the Carb and then onto the choke. Did he say why he was working on the choke? If you are worried that the choke is not working we can check it easy enough. Until then, i would Try to put it back and work through one issue at a time

You need to change the ECM, no normal operation causes what you are seeing. If the new one is good, you will instantly start getting some data that helps you to sort it all out. Don't get frustrated, this can all be sorted out

 

[Peer81]

Connecting something to the distributor is a way to get a good 12v source. Could be your original choke wire didn't have a good 12v so they changed it. I also connected the heating element from the O2 sensor to the distributor.

Greetings Peter

 

[Wajulia]

The original choke wire is green, goes across the front of the carb and connects to the t-fitting on the fender wall shown in the picutures below. I have my wires wrapped to try to make the engine look a little tidier. Normally, the green wire should be quite visible. (the schematic says it is light blue, but it looks green to me)

Looking at the schematic, taking the 12 volt source from another place bypasses the choke heater relay. This relay basically just allows the chock to have its own 20A fuzed circuit. It is now sharing a circuit with the distributor? And of course -- the choke light will be on. I am not sure why you want to do this instead of fixing the original circuit.

The arrow points to the wire

Let us know what happens with the computer

 

[geekinavette]

I don't know about '81 specifically...but a lot of the earlier GM ECMs flash the CEL rapidly like that when there is a problem reading the EPROM. Bad EPROM, bad socket connection...etc.

 

[PokerJoker]

Okay, swapped the computer this morning and a couple of things happened...

1. Blinking check engine light is now just a solid check engine light!
2. The constant "clicking" I hear from the carb just before starting (normal) I think its the MC solenoid...now no clicking, but it still starts.
3. Tried to pull codes by jumping the last two terminals on the right side of the connector under the ashtray. No codes, light just stays on solid...I do hear a single "click" from something out in the engine area, but it just happens when I make initial contact with the paper clip.
4. I drove it, and it seems to run slightly better, but I still have some hesitation when I give it the gas, and it just doesn't seem to be running smooth.

A couple more things...I set base timing and changed the O2 sensor (with the correct two wire sensor) thanks. When I checked the timing after the shop set it, the timing line was way above the scale, maybe 16 or 18? As I rotated the distributor it brought the line down into the scale, but it seemed like the engine idle was slowing way down (almost to a stall), finally just settled on about 12.

So that's it for now, I'm not sure how to get the codes if the light won't blink and get the MC solenoid clicking again. Any ideas?

Thanks for all you help.

 

[Peer81]

Phwo this is a difficult one.

First the clicking mc solenoid sound is only hear-able when you want to read the codes NOT when you want to start the engine!
Are you sure the other ECM is a good one as the light stays on and you can not pull any codes?

With the ECM light on the ECM will stay in open loop so there should be no to little difference with a broken ECM I think.

Greetings Peter