1992 Buick LeSabre - Intermittment No Start/Stall

[drwilson]

Hi. Ive come across forementioned car with these isssues. ignition control module replaced by another shop/mobile repair guy, part appears to be new but might be faulty. crankshaft position sensor has been replaced and adjusted (by me). no spark when vehicle dies. When the car first came in the condition took two hours to reproduce. All the wires from the module were tested for shorts/opens, all came back good. at a loss...

[ricmorin]

The only way to find these is with a scope that records. Or get lucky. So far you're not lucky.

Since there is no spark, monitor the crank signals and powers /grounds to the module. Review the recorded data when it dies. You can spot the point of stall with voltage as it will drop slightly when the alternator spins down.

I just found an intermittent stall like this, except spark, injector pulse and fuel pressure were all good. The crank sensor was the culprit, except instead fo flat-lining, it threw an erroneous sync pulse whicj confused the module timing, resulting in a stall. Went through a tank of gas before I caught it on 'camera'.

[Tim Martin]

Yea, I agree with ric regarding using a live scope with camera option. Usually gets the problem. Having said that, I have also seen an ecm do the same thing. Beins it is a 92 model the possibility of a faulty ecm is pretty good although i like to identify the wrong part. I do not like to be known as a parts replacer till the problem is fixed. Also, check the ground wire under the ignition module. These were known for corrosion and intermittant connections.

[drwilson]

Im gonna have to try something, seeing as i dont have a scope. The car does have a lot of corrosion. And i dont like throwing parts either. If it was the ecm would there be other conditions too?

[Tim Martin]

Sometimes there is and times there is not. That is one of the uncertainties of gm ecms in that era of time.

[brianp87]

Could be ecm possibly. i would hit it, wiggle connectors etc see what happens. A lab scope is best but you can try

[steven kiser]

i saw a few mentions of anti theft issues. see if there is any sign of coolant contamination on the crank sensor. i'm probably confusing applications here but wasn't there an issue with the harness routing for the cam and crank sensors. check the main plug for the engine harness near the right valve cover. if it were put to me as a shot in the dark i would replace the crank sensor.

[drwilson]

To start thanks for all the input. The car wont start at all, crankshaft pos. sens replaced 3 days ago, checked the wires for any short or open, or overly high resistance, all ok, even on cam pos sens harness. before we replaced the crank pos sens it would start if i pulled the ecm fuse for a bit. it worked fine, cust picked it up, then called two days later, telling us it died completely. Now no matter what cant get it to start.. ecm??

[steven kiser]

i'd go along with that. pulling the fuse in and out may have somehow rebooted the pcm. however i would strongly recommend not do that on a regular basis. it will have adverse effects.

just a quickie here, are you getting any readings through the scanner????

[drwilson]

yea im gonna try not to. on the scanner everything read normal when it was running. Before the crank pos sen was changed rpm reading would read normal, until right before it would die. At that time it pulled code 17. If it sat for an hour or neg batt cable removed, or the fuse it would start back up. now there are no current codes, just a history code 58 for anti theft. key is the same one, nothing else changed that i know of.

[brianp87]

If the vehicle is completey dead an not an intermitent problem then it shouldnt be to hard to find

[drwilson]

yea i think i found it now. Scanner showed no cranking rpm whatsoever. took the harmonic balancer back off and see that something tore up the position sensor.... DOH!

[ricmorin]

There is a special tool to align those sensors. I have one. Because the balancer is an interference fit, you can't really tell if you have it aligned correctly. I've seen some people get away without the tool, but I don't like tempting fate. Also check your interupter on the pulley. The tool also acts as a checker for bent interupters.

[steven kiser]

totally agree with interrupter on pulley. i've seen the balancer loosen on the pulley causing a vibration so even if it's set perfectly the vibration will cause an issue. see if the rubber sleeve between pulley and balancing sleeve is damaged.