ignition problem with 90 camaro

[cocobolo95]

Even though this is not directly a fuel injection problem it is related to the whole ecm, injection, est system.

Long story short, I did some completely unrelated work in engine compartment of my 90 camaro 3.1 v-6. When done I had no spark and no injector opening. Security light comes on and goes off as normal. Fp primes when key turned on. No spark unless I do the old trick of attaching wire to tach terminal and touching it to ground. Coil fires then.

System uses small cap, separate coil, 8 pin icm.

When I put a test light on control wire, white wire, light comes on with key on. Does not blink when cranking engine or turning dist by hand.

1)I have tested wiring to ecm for continuity and shorts to ground. All is good
2)I have pulled the entire engine harness, unwrapped it and inspected each wire.
3)Have substituted known good coils, icms, dist pick up coils, and ecm's, with no spark still.
4)Only little bit of progress I made was when I reversed the pick up coil leads. All of a sudden I now have injector pulse & fp runs with dist shaft turning.
5)When I put pick up coil leads back to original position, injectors and fp still run when dist shaft turns.
6) Made sure all ground wires were hooked up and good ground. As well as all power wires.
7) With key on there is B+ to coil, out from coil to icm, and out from icm on white control wire.
8) problem is icm is not switching on & off.

From what I've read, this system is a bypass type that should give spark without any est control from ecm. Yet, no spark.

Any suggestions or ideas would be a great help as I'm ready to find a witch doctor to drive away the evil spirits. I have one more test I will try tomorrow. I have made a replacement 4 wire est circuit to run from dist to ecm. I will try that.

[Six_Shooter]

What was the "unrelated work" that was performed?

[cocobolo95]

Would you believe I had changed the transmission dip stick tube seal to start this mess. I've been trying to figure this out for over 2 weeks now.

[Six_Shooter]

In the process of replacing that dipstick tube, is it possible that you removed/disconnected/disturbed the grounds that are attached to the rear of the right side head? ;)

[cocobolo95]

Both grounds from ecm are there, as well as, ground strap to firewall. All grounds are clean. When doing continuity check have 0 ohms resistance. 2 grounds on left cylinder head are also good.

Battery negative cable runs to front of engine as it should. Smaller ground from battery negative goes to left inner fender. One last 10 gauge ground wire goes to lower passenger side of engine, near where air pump is.

If my new 4 wire connector between distributor and ecm doesn't work, I believe I will put 5 volts on the tan/black bypass wire, simulating ecm signal and see it that induces icm to fire coil.

[Six_Shooter]

The the 5V signal does not cause the ICM to fire the coil, it turns timing control over to the ECM. You can have the ECM completely removed from the car and you will still get spark.

[cocobolo95]

My understanding was what you said, that dist should have spark with no hook up to ecm. I'm grasping at straws now. I've tested the B+ wire going from ignition switch to coil. There's no voltage drop when I turn dist shaft by hand. When using the starter, voltage drop is within acceptable levels at low 11's. B+ wire from coil to icm is good. And control wire has B+ voltage.

It's problem is, there is no switching on & off of voltage like there should be. I've tested the pick up coils I have, all have proper resistance, and all produce the proper range of ac voltage required to switch icm. I've had all my icm's tested multiple times to get them good and hot. No failures. As stated in first post, all components I used were tested by me and are known good.

Would grounding the white control wire from ecm to dist cause a spark, like when I ground the white tach wire? Or would it fry the ecm?

I'm ready to start pulling my hair out. There's no way that all my known good ignition components could have failed at once. Also, when I changed pick up coils I merely switched to another known good dist. No air gap problems to contend with.

[brian617]

Had one give me a lesson the other day very similar problems and diagnostics. Turned out the B+/tach signal plug was plugged in backwards. The locating pins on the connector had been broken off.

[cocobolo95]

My connector plug is in the same shape as yours. So I will give reversing the plug a try. Will report the results later. Thanks for the tip.

Bingo, that was the problem. Bad condition of tabs on connector allowed me to plug it in backwards. I am used to it fitting only one way, so I overlooked this as the problem. Now I feel like such a dumb A, but poop happens and I will move on from here.

Special thanks to brian617 for showing me the error of my ways, and once again proving, the simplest of details can leave you stranded.

[brian617]

Made me feel super stupid too lol.

[Six_Shooter]

What plug is this that can be plugged in backwards?

[brian617]

Should have taken a picture. Technically when the plug isn't broken it can't be plugged in backwards, but years after many hammer fists the skirt around the plug that has the alignment tabs was completely broken off.

B+/Tach signal plug on coil, grey connector.