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1989 LeSabre no spark on 4 cylinders


jbengle
04-26-2014, 11:14 PM
I need some help getting my Buick to start. It is a 1989 LeSabre Limited with a series 1 3800 engine. I only have spark on cylinders 3 and 6 (paired on ignition coil). I have run tests to see that I have that I have 12 volts to the ignition module, 12 volts out to the crank sensor, signals coming from the crank sensor. I pulled the coil pack and found that I only have a signal on the blue wire supplying 3 and 6. I don't get a signal on the green and yellow wires supplying the other 4 cylindars. My tests would indicate that the ICM is bad. I replaced the ICM and out of desparation the coil pack and I still have the exact same problem. I cleaned the aluminum surface to make sure I have an excellent ground. Any help would be appreciated.

Blue Bowtie
04-27-2014, 07:46 AM
Welcome Aboard!

I believe it does, but I'm not sure - Does the '89 also have a cam position sensor? If so, verify that the signal from that is a sharp square wave (on/off with no wandering voltage).

Tech II
04-27-2014, 10:58 AM
The cam sensor has nothing to do with spark, only fuel timing....you can disconect the cam sensor and you would still have spark....

Since you have wires in the ICM, this is obviously the Magnavox coil....one coil with 6 terminals......

Basically, you have 3 individual colored control wires......and one wire with three contacts(this is the power to the coils)...with the coil removed, you attach a test light to one of the three contacts in the power line.....attach the other end, to one of the 3 individual lines......crank engine.....test light should flash....then move test light connection to another individual line.....crank engine, and light should flash....then finally the third line.....if it flashes on all three circuits, you have a bad coil.....if it only flashes on one or two legs, bad ICM......if it flashes on none of them, either bad ICM or bad crank sensor.....

You replaced the ICM and Coil? Were they new or used from a junk yard?

Are your ignition wires ok?

jbengle
04-28-2014, 09:13 AM
Thanks Tech II. That was my thoughts as well. I did the exact test as you described it. I got a flash on one individual line, but not the other two. That led me to believe it was a bad ICM. I replaced the ICM with a brand new one and got the exact same results. Then I changed the coil pack with a new one even though I was positive that was not the problem. Of course, my symptoms did not change. Is there anything else in the circuit that would cause this symptom or did I just get really lucky and have a bad ICM with the same problem as my original?

I believe the ignition wires are good. I tested some of them by moving them to the coil towers that are firing and I got spark through them. They are beyond the problem area so I don't think they are relevant in this situation... yet.

Tech II
04-28-2014, 10:59 AM
That is crazy......the only possible thing I can think of, if that new ICM is ok, if somehow the crank sensor is bad or the slots of the harmonic balancer are damaged(ever lose a serp belt?) and it is not generating the proper signal to the ICM?

But usually, with a crank sensor, it's all or nothing.....but strange things do happen....I guess I am inclined to replace the crank sensor....

Also is there a wobble in the harmonic balancer, or was there a noise coming from the engine before you lost your spark?

jbengle
04-29-2014, 01:13 AM
I cannot answer your questions about the history of the vehicle. It belonged to my uncle and has been sitting in a field for 3 years. I guess I will try the crank sensor. I have read that it requires a special alignment tool, then I have heard that you can use a feeler gauge. I have also hear that you can eyeball it. Any tips on changing this will be welcomed.

Tech II
04-29-2014, 09:25 AM
Yes, GM does have a special tool that holds the sensor in place while you do the final tightening.....it has to be spot on so the vanes on the back of the harmonic balancer does not hit the sensor.....have never done the feeler gauge method.....

jbengle
07-02-2014, 08:36 PM
I finally got around to changing the crankshaft position sensor. While putting it back together I noticed a plug harness hanging down. After searching around for a while I found the sensor that it plugged into. It looked like it is the cam position sensor. Anyway, I plugged it in, put everything back together and the car started instantly. Thank you very much for your help.

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