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87 LeSabre intermitten spark

08-28-2015, 10:24 PM
Hi guys, have a lot of info to go over so here goes.
Car is an 87 Lesabre, 3.8 with around 167,000 miles. Timing chain and gears was replaced at 100,000, so around 67,000 on the timing set.
Fuel pressure is 35 psi at the rail. I checked the injector pulses by noid light, they are working.
The car started running rough and then got to the point it wouldn't start. If it sits for about 24 hours, it will spark and the engine will try to start, but after the first revolution of cranking the engine, spark is gone and wont come back. I have checked the ignition with an HEI spark tester.
I changed the mass air flow sensor, crankshaft sensor, cam sensor, coil pack and computer. I had the new ignition control module tested twice at the FLAPS, passed both times. Installed it, no spark.
I checked the black/pink wire at the ICM, have power when the ignition switch is on. All fuses in the fuse box check good.
I don't believe it jumped time, even if it did I think I would still have spark, maybe Im wrong. I have not put a compression gauge on any cylinders but the valve train is actuating as seen thru the oil filler hole in the valve cover and the engine sounds normal when cranking.
I'm was wondering what triggers the camshaft position sensor? is it just the timing gear itself or is there a trigger that goes on the timing gear? Also, can the PROM chip go bad and be causing this? I replaced the computer with a reman but had to put in the old PROM and the chip next to it (smaller chip) into the reman computer. The computer shows no codes, just flashes code 12. Next wondering if the ignition switch could be the culprit. Also have to replace the harmonic balancer, the rubber has broken down and its clanging, so wondering if the trigger may have slipped. I don't have a wiring schematic to chase down the wiring or relays so may get a Chiltons or Haynes manual. Any help would be greatly appreciated and if I find the problem, I'll be sure to share the fix!

Blue Bowtie
08-29-2015, 10:29 AM
It seems the most of the ignition components have been replaced.

The cam position sensor is triggered by a magnet in the cam sprocket. They can work loose. Even so, the engine should run on the crank sensor alone. However, if the cam sensor input is intermittent, that may be affecting the ICM and confusing the spark timing enough so that the result is spark so poorly triggered that it seems like a misfire.

Verify that the CMP and CKP signals at the ICM are consistent. This thread may have some helpful tips:


09-02-2015, 10:03 PM
The harmonic balancer is bad, again. I replaced it around 60,000 miles ago. I noticed that one of the triggers on the balancer had been rubbing the crankshaft sensor and discolored it (looks like it got hot). I purchased a new balancer and will install it when time allows. Hope this gets the system back to producing spark. I'll keep posting as time allows.

Tech II
09-02-2015, 10:26 PM
If the blades of the balancer were hitting the crank sensor, I would replace that too....

You don't need a cam signal for spark....

09-10-2015, 07:40 PM
Found the problem today. I removed the harmonic balancer since it was bad. When I pulled it from the crankshaft, I noticed the sleeve was cracked and split at the keyway. The balancer had spun on the crankshaft to the point that the trigger was out of time. Inspected the crankshaft and the key, no damage noted. Installed the new balancer, re adjusted the crank sensor and hit the key. Fired up immediately. I have not seem a balancer do this before. Hope this helps someone else. Thanks for the advice and tips!

Blue Bowtie
09-10-2015, 08:54 PM
After 25 years I suppose it was due. Glad you resolved it.

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