1995 Lesabre - Ignition Control Module

A couple of weeks ago the engine was misfiring and randomly shaking badly. After a search on this forum I found the solution in a post by HotZ28: http://www.automotiveforums.com/vbulletin/showthread.php?t=769587&highlight=ignition+control+module+lesabre

It turns out that one of the coil packs was bad (on visual inspection, only one of the two terminals had a spark). I replaced it and everything was fine until today. On my way home the engine started misfiring and randomly shaking. When the car didn't start up again, I assumed that it might be more than just another coil pack going bad.

I took the ICM out and had it checked at two separate stores and it failed both tests. Obviously, I will replace it.

My questions however are: 1) Did replacing only one coil pack, instead of all three, have any dire consequences with regards to the ICM, 2) How do you check the coil(s) primary & secondary resistance to see if they are all within spec.

Thank you.

My questions however are:
1) Did replacing only one coil pack, instead of all three, have any dire consequences with regards to the ICM,Not likely, but when testing DIS ignition coils with the engine running, you must be aware that once the magnetic field collapses, the high voltage surge has to go somewhere! If it cannot go through the wires to the plug, it will find another path to ground, which might send the voltage back through the ignition module, PCM driver circuit, or through the insulation inside the coil itself. This can be very damaging to these parts. BTW, when was the last time you change the ignition wires & plugs?


2) How do you check the coil(s) primary & secondary resistance to see if they are all within spec.Thank you.
I usually use a spark tester connected to the spark plug end of the ignition wire & grounded. While cranking the engine, observe the spark. If you see a crisp blue spark, the ignition coil is working properly. If you only see a pale yellow spark, more than likely, you have a weak coil.

For testing the coils primary resistance while removed from engine, use a paper clip to insert into the primary side terminals. (Female - Bottom side of coil) and place the two leads of your DMM on these to check resistance.

On the secondary side, place the leads across the two coil output terminals and set your meter for reading K-ohm. The specs for resistance on the Delco DIS ignition should be -- Primary (ohms) = 0.5-0.9 (ohms) Secondary = (k-ohm) 5.0-8.0

Thank you for the wealth of information. Unfortunately, I didn't think about the consequences of "the high voltage surge" and may have inadvertantly screwed up the ICM while trying to determine which coil pack was malfunctioning :loser:. I will keep my fingers crossed that I didn't do more damage to other electrical components.

With regards to the plugs it has been about 30,000 miles and a little while longer for ingnition wires. Funny you should ask though, because about two weeks ago I posted to get some feedback and received some excellent recommendations: http://www.automotiveforums.com/vbulletin/showthread.php?t=1059182

I took the ICM off and had it tested. It failed, so I replaced it; however, when you accelerate pass 53mph, it has a very noticeable shake. With regards to the coil packs, they were all within specs (Primary (ohms) = 0.5-0.9 (ohms) Secondary = (k-ohm) 5.0-8.0), even the one that I thought was bad and replaced.

The parts guys at the parts store mentioned that it might be the crank and/or cam sensors. Both were replaced about 18 months ago when the engine light came on and showed a code for the crank position sensor.

Any suggestions? :banghead:

Thank you.

You mentioned that the plugs have about 30K miles, Do you recall the brand used? Even though the coil resistance is within range, that does not necessarily mean that the coils are firing with full voltage. You need to invest in a "spark tester" to really determine if the coils have enough fire power. Under normal acceleration and at 53 mph, the trans should be in 4th gear & the TC in lock-up; therefore, the engine is placed under a load with light acceleration, which brings out otherwise unnoticeable misfire. I still think you have secondary ignition misfire. i.e. wires, coils, plugs.

Already purchased a "spark tester". Here is the one I purchased:
41860

What do you think? It is the Lisle Inline Spark Tester #20610.

I am going to replace the plugs and wires with AC Delco Rapidfire (No. 14) plugs and either Napa Belden or AC Delco or Autolite Pro wires.

BTW, I saw this at O'Reilly's when I purchased the tester:
41861

It is was about $50+ and is described as a Lisle coil tester.

You mention, "...the TC in lock-up". Sorry for my lack of knowledge, but what is this?

Already purchased a "spark tester". Here is the one I purchased:
41860

What do you think? It is the Lisle Inline Spark Tester #20610.

I am going to replace the plugs and wires with AC Delco Rapidfire (No. 14) plugs and either Napa Belden or AC Delco or Autolite Pro wires.

BTW, I saw this at O'Reilly's when I purchased the tester:
41861

It is was about $50+ and is described as a Lisle coil tester.

You mention, "...the TC in lock-up". Sorry for my lack of knowledge, but what is this?
The 20610 will work; however, I like to SEE the spark, so I much prefer;

KD Tools (KD 2757)

http://www.tooltopia.com/_img/KDT/KDT2757.jpg

This tester will verify that the energy is sufficient for the spark plug to fire. Attach the spark plug wire to tester end. Clamp tester to engine as ground. Open gap to .150 & crank engine and check for spark. Look for a bright blue spark, which would indicate a good coil, or a yellow spark (if it can throw the gap) which would indicate a weak coil. This particular tester will eliminate the need for the Lisle coil tester.

BTW, the "TC" is the 'Torque Converter', which goes into lock-up @ about 45 mph with normal/light acceleration.
http://www.nextag.com/norob/PtitleSeller.jsp?nxtg=29030a500516-A162203F5A1A38B0&chnl=main&ptitle=541390409&tag=580141297&ctx=oTSkKwx6vtc%2F1rbOu7Kn78%2BpcFnlSfccYS%2FKGSJ2 u8lvw%2BAPWwMWruP0%2Fi3NBLRDI0Zd2QKAUVbQmvtM7AEeTr XEFSlOcNwufry5USEJq%2FcRaJfOLYMaJ2ST69TB%2BXF2Ad2V l%2BnDNsqUfYsSi7RPFcduZfZ4OR7Cg2d7b19APnKS%2B93jTS 37NC9oSECQ15%2BJ122JOO9drj09KMxFrgfYZ0TKgkGr8zl7Cg HDZg7SFR38xIkTzO%2BnJpfsBr6gwVdfNf1yov2Ll18cjfF2ER ZWIQ%3D%3D

I will go and buy one tomorrow. I must be getting old but can you instruct me on the best way to open/remove the black piece (red outline with blue stripes) that holds the front three wires.

41865

Pull straight up, while rocking from end to end.