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got dem no spark blues

697 views 7 replies 3 participants last post by  sea dog 
#1 · (Edited by Moderator)
After installing a new trans dip stick tube in my 90 f-body 3.1 v-6, the car had no spark. It cranks just fine just no spark. Fuel pump primes. Had known good coil, icm, & pick up coil for dist, so I swapped them in. Still no spark. Added a ground to dist, made sure icm screws were clean, as well as dist body where icm sits. No spark still.

Car ran fine before dip stick R & R. The system uses the small dist with 8 pin icm and external coil.

Checked all wires going to ecm for continuity and short to ground. All was well. Swapped in 2 known good ecm's just in case. All engine and ecm grounds are good. All ecm and engine power wires are good.

When ign sw turned to run or start, coil gets battery power. Output to icm from coil gets battery power. C line from icm back to coil gets battery power. When cranking, voltage drops a little because of starter draw, but not enough to mess with ignition function.

Here's the problem. When car is cranked, dist shaft is turning, C control line from icm to coil does not go from power to no power. It stays lit. So icm is not turning on & off. And 3 other known good icm's are not turning oon & off either.

I'm not real familiar with the est aspect of the ign sys, but from what I've read in factory service manual, and online, this is a bypass system and icm should fire the coil without the est system working. Code 42 is proof. Dtc 42 is a problem with est. Code 42 troubleshooting starts with engine running, so est failure doesn't keep ign from creating spark.

I've swapped in an old 4 pin coil in cap dist, it sparks like up a storm, Turned it by hand and it worked. My icm will not turn on & off so coil will not spark.

Any ideas will be good. Anyone know what voltage or ohms readings the 4 est lines from icm to ecm should test as?
 
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#2 ·
Made a little progress today. No spark yet. Decided to try reversing the pick up leads to see what happens. When I spun distributor by hand, I now had fuel pump runing while dist turned & injectors opening & closing.

Just to see what would happen, I switched pick up coil wires back to original places and fp & injectors still ran when I rotated dist shaft, So 1 step forward here. I at least know now that reference line between icm and ecm is functioning. As no fuel pump or injector activity without it.

Tried disconnecting the tan/black bypass line with no improvement.
 
#3 ·
When it rains it pours. Today I broke out my scope. I wanted to see if est wires from icm to ecm would have any distinctive wave forms. Turned on scope and main power fuse blew. Changed fuse just to make sure and blew that one too. Now I have to fix my scope, as well as having a non running daily driver.

I believe my next step will be to find a witch doctor to drive away the evil spirits hanging around me. Still, anyone have any ideas. Haven't heard from Fred on this. He always has some good ideas.
 
#4 ·
I really don't know much about the EST setup.
 
#8 ·
I will title this post "Attack of the dumb A monster.

Fixed the no spark problem with the help of Brian on gearhead efi. He had same problem and noticed he had hooked up coil connector that had B+ and tach signal backwards. Normally this connector can't be plugged in wrong, but his had broken plastic parts that allowed incorrect connection.

I looked at my connector, sure enough it was partially broken, allowing me to connect it backwards. Turned it the correct way, I now have spark.

Took away from this experience to never assume that connectors that are designed to connect only one way, still do after many years of use. Also this gave me a chance to put new electrical tape and convoluted tubing around wire harness. This is something I've wanted to do for a while.
 
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