crank sensor help
 

Hey,

new to the forum. glad i found you all. anyway, here's my deal:

1990 Bonneville, 139,000 miles. Won't start when the engine is warmed up. starts great cold. took it to a local repair shop. they estimated around $700 to fix it. Said crank sensor was bad, and that made the ignition module bad. I replaced the ignition module myself a month or two ago. Went to the same auto parts store to get the crank sensor. They said that they couldn't come up with a way how the crank sensor could make the ignition module bad. So I have two questions:

1. Could the ignition module be bad as a result of the crank sensor?
2. Can I change the crank sensor myself, and, if so, any tips or tricks to make it as painless as possible?

Like to tackle this tonight, if I can. Any response is greatly appreciated.

Mike

I think the wiring for the ICM may go through the crank sensor. So the ICM may appear bad, but not really be. Your crank sensor is behind the crank pulley. You'll need a 24mm (I think) 6 point socket and something to hold the flywheel to get the crank pulley bolt off. Pre-92 crank pulleys don't require a pulley puller, IIRC, so once you get that bolt off, it should be pretty easy. Make sure to carefully measure the location of the old sensor before you remove it. The new sensor will likly be adjustable and not in the correct position on the bracket if it comes with one.

Thanks for the quick response. I'll give it a run.

crank
 

You can ensure the sensor is set properly by using a .030 feeler gage to set the gap with the balancer blades. This will ensure it is centered. Most aftermarket sensors come with instructions for doing this.
Let us know how it goes and welcome to the club.

I also can't think of any way that the ICM could make the crank sensor go bad, or the other way around. I've heard of both failing often, but never one taking the other one out with it. This is why I just avoid mechanics whenever possible...

The wiring for the crank sensor does originate from the ICM, or at least pass through it. Maybe that's how they got confused.

Hopefully they at least got the part about the crank sensor being bad right! :lol:

It does make me wonder though... I had a bad ground from my ICM to it's bracket, and it really acted like a bad crank sensor. The problem was that the ICM (without good ground) wasn't even supplying the crank sensor with it's ground, so it couldn't function. Cleaning up that mounting surface fixed it. Probably not your issue, but worth a thought.

crank
 

The garage would have to test for a loss of signal from the sensor to tell if its bad. Few do this. They just throw parts at it at your expense until its fixed.
I agree its highly unlikely that one would take the other out, crank vs module.

Thanks for all of the feedback.

Ran into some issues with getting the crank shaft pulley off. Any thoughts on how to hold that thing tight while I crack the bolt?

Under the other end of the engine is a plastic cover hiding the flywheel. Use something like a large screwdriver in the teeth or a hole to jam the flywheel. Then you can get that bolt off there.

The crank pulley bolt is best removed with an impact wrench. That way you don't need to hold it.

A follow-up
 

First, thanks for all of the help so far on this. I feel pretty incompetent sometime when it comes to this stuff.

But, I have another problem. Got the new crank sensor in (after much blood, sweat, and tears). Car turns over and fires (good sign) but you really gotta crank on it to get it to actually start, and it won't for long. If you give the engine a good revving (say 30-60 seconds) it'll idle, but very rough. try to give it gas again and it'll kill. Some things that came to mind were:

1. timing is off
2. those jerks at the repair shop were right and ICM is shot (although I would rather hope not)
3. there's more wrong with bonnie than i wanna tackle

What are your thoughts?