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V6 Engine miss

12-05-2014, 11:01 AM
1987 LeSabre v6 engine misses under load. It is a "hard" jolt, miss that happens under slight load weather warm or not. Engine also idles very fast on first start. Wondering if the problem is electrical or vacuum related (or both?). Do not think it is fuel related as pump and filter were replaced a while back. Vehicle has also stalled with difficult restart once in the past few days. Not showing any codes.

12-10-2014, 05:33 PM
So, I guess it is "thanks for nothing". Looks like this Forum is missing something.
Sure, I could (and will), find an answer or general direction elsewhere, but I thought that this was here to quickly find solutions. I am disappointed.

12-10-2014, 08:27 PM
Know nothing about a87 lesabre, but if it actually feels like a miss. I would be checking plugs, wires, etc. You could have a spark arcing to ground.

Tech II
12-11-2014, 11:00 PM
Wow, an '87?

With car idling, take the Palm of your hand and hit the MAF sensor....if it stumbles, you found your problem....

I remember back in the day, the 86-87's had a recall to check the coils and MAF, but that recall is long gone by now....

Do you have 3 individual coils or one large coil(Magnavox)?

Basically, it sounds like a secondary ignition problem....

Like Kat said, could be a plug, wire, or ignition coil......best thing to do is check coil out put at the end of each ignition wire with a ST-125 tester....

12-13-2014, 08:51 AM
Thanks for the replys! Got a couple days off coming so I plan to work on this now. Problem is intermittent but becoming more consistant. Could not find any obvious vacuum lines or electric connections loose.
Car has started stalling at stops unless given just a small amount of throttle at the same time. Miss is definetly "load" related, far more frequent pulling a grade (even slight).
Coil pack is 3 in a row (I think all one unit but will have to check to confirm).
Yes, 1987. 123k miles. Needs headliner and dash (sun/water damage from sitting) & has some transmission gasket leaks I need to fix but otherwise pretty good for a $500 investment.

Blue Bowtie
12-13-2014, 11:39 AM
As previously suggested, it might be good to thoroughly check out the ignition system. Begin with the spark plugs. The condition of the plugs is important, and the gap of the plugs is even more critical since this is a wasted spark system (two plugs per coil).

Inspect the plug wires as well. Measure continuity and expect to read about 500-900Ω per foot of length. Any signs of damage, no continuity, or ozone hazing around the boots or along the wires would indicate problems.

Verify that the coils are clean, not arcing to ground, and not damaged or cracked. Make sure the connection screws are clean and tight, since the coil ground depends on them. Inspect the coil connections and plugs on the top of the ICM mounting plate. Also make sure the ICM mounting plate is clean and not corroded, since this is also critical for coil grounding.

12-13-2014, 05:30 PM
Thanks, working on Jeep problem at the same time and focused on that today. Did find the air filter case had big cracks and air leaks on the intake side after the filter. Partially sealed (duct tape) and had some improvement (no stalling, still some load misfire). Wondering if that is creating vacuum issues and may be root of the problem?

Tech II
12-13-2014, 10:56 PM
If you think you have a vac problem, spray parts of the engine with carb cleaner ans see if there is a change in idle...

Cracks before the MAF will have no effect, just allowing dirty air into engine....

Check for spark with a spark tester...

12-14-2014, 05:11 PM
OK, problem solved (after 15 mile test drive with no miss). Two of three coil packs were missing nuts on one side of the mounting studs and the other side was loose. I am guessing that the packs need to ground through the mounts. Simply tightened the nuts (need to replace the missing ones still). As usual, simple problem that could well have been $$$.
***Need to add, three coil packs together but each is individual.

Blue Bowtie
12-15-2014, 03:52 AM
... I am guessing that the packs need to ground through the mounts.

That's what it says in Post #6.

Did you pull the coil packs to inspect the ICM mounting surface? Since the packs were loose, there may be corrosion there. It's easily solved with a ScotchBrite.

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