Still dealing with igntion miss on '87 Buick V-6

[Touring5]

Well, I'm still having ignition issues with my '87 Buick Century 3.8L.

To recap, the motor was running rough and smell of unburnt gasoline was evident at the exhaust pipe. Through a bit of trial and error I found that when either or both of two of the plug wires were removed, the motor didn't run any differently. Those two wires are both fed by the same coil on the ignition coil pack. Thinking that I probably had a bad coil I removed the pack (contains 3 coils, each coil serving two cylinders). Testing with a multimeter revealed that the primaries and secondaries all tested within spec. Since the suspect coil was one of the end positions, I found that the coil can be installed rotated 180 degrees. Doing so, the same two cylinders were not getting spark - meaning the problem didn't follow the coil. As an educated guess I bought a new ignition module (this car has had ICM/coil issues multiple times over it's life) and installed it today. Problem is the same.

Now I'm stumped. I'm curious if anyone knows if the ECM sends signals to the ICM for each cylinder or pair? Or more broadly, what else might cause this condition.

One bit of info: the car was being driven and running smoothly when I had to make an abrupt stop on a bumpy railroad crossing - when I accelerated away the engine was running like garbage (as one would expect with two missing cylinders). Also, this is the Motorola/type 1 ignition system. Any sensor or wire that could have busted?

I'm out of ideas and welcome any thoughts....

 

[71Chevyguy]

Just trying to go over this in my head since I owned a car with this same powertrain in it before and had some issues.Worked on many of these as well. Have you tried moving that coil to a different set of cylinders on the ign module to make sure THAT coil functions properly? I know those engines have really bad issues when the crank position sensor is not aligned properly which uses a special alignment tool IIRC. Seen that many times on those engines.Also check for cleanliness below the crank pulley, if your front seal is seeping it may be leaving a huge oily mess on the crank sensor and that can affect performance as well. Another thing that goes wrong on those 3.8 engines is the harmonic balancer goes bad and wobbles, I wonder if that could possibly trigger a misfire because of the teeth wobbling on the pulley the crank sensor is trying to pickup. I believe that is a waste spark ignition system where those cylinders are paired up because it does not matter if the spark goes through the other cylinder at that time since it is on the exhaust stroke. If one plug or wire is bad the other cylinder will not work either. It has to be a closed circuit. Have you checked the plugs for fouling? Tried "rotating" the plugs to different cylinders as I call it? Try to rule out the basic stuff completely before going nuts with the more complicated stuff. Fuel injector is another one I would look at. Make sure the wires are pushed on the injectors and have a good connection. I will keep thinking about it today and if I come up with anything else I will post back later. Good luck with it, don't give up on it though, those are good engines. Only other thing I can think of is if the timing chain was really loose it may have jumped time, I kinda doubt that though.

 

[Touring5]

The area of the pulley does have quite a bit of oil residue, as it's right near the oil filter mount. One of the two sensors does appear to have oily/greasy residue on connector - hmmmm.

The coil pack is a single unit with all three coils together. Through my reading I found that if the coil pack is installed turned 180 degrees it still works fine - just the cylinder number marking on the towers will be wrong. After checking the resistances of the coils I installed it rotated and the same two cyls weren't firing - indicating the problem didn't follow the coil (if the two bad ones were fed from the middle coil, this test wouldn't have been viable). After installing the new ICM, I did install it correctly BTW.

From my reading it sounds like the ICM uses crank sensor pulses to trigger the coil firing sequence, but after the car starts (above 400 RPM), the ECM then controls the ICM (?)

It was odd that the problem occurred immediately after making a hard stop on railroad tracks. It didn't seem violent when it happened, but one of my first thoughts was that I bottomed out and broke the catalytic converter - that was before I diagnosed the two cylinder miss...

 

[Hokiefyd]

The coil packs aren't removable separately?

The way I read your post, you turned the entire coil pack around? So if the coils read 1-2-3 and 4-5-6 left to right, the cylinders that were fired by 1 and 4 were now fired by 6 and 3? And the problem was the same?

Have you ruled out ECM problems? The reason I ask is because my mother used to have a 1985 Olds Ciera wagon with the Buick 3.8L and it ate through ECMs like they were going out of style. As I recall, it was a TBI version of the engine, possibly with a large round air cleaner on top. Is that how yours is set up?

 

[MichiganMadMan]

Simple first: Check for backed out, relaxed or corroded pins on the connector at the ICM.

If those look good, find a pinout for the ECM and verify that the wiring harness doesn't have any trouble. You will have to remove the ECM and probe the corresponding pins. Don't just check that it goes where it is supposed to, check that it doesn't have a "bonus ground". My experience is that a sudden issue, tied to a vehicle event is usually a harness getting pinched by something that moved and "bit" it.

If you are 100% sure the wiring is good, then look into an ECM. I have only seen a couple ECM's that took a dump over the years, most were explainable (welding, etc). I condemn the ECU last, not first.

A sensor issue would cause all cylinders to have an issue, not just one coil.
The ECM has three outputs for the ignition system, it fires the spark plugs every time the cylinder is at TDC regardless of if it is on compression or exhaust (waste spark).

 

[Touring5]

Yeah, I think it's called the "type 1" system made by Magnavox - I happened to be doing some work at a Delco Remy plant durning the 1988 period when they were making the "type 2" that uses separate coils. Also, the magnavox coil housing is squared and the towers are opposite each other, rather than side by side. The primary terminals along one side are wired in common and the other side has individual terminals for each coil - thus it's symmetrical. A website that had primary and secondary resistance values for it mentioned that if it were installed rotated it would still function (as long as the wires were in in the same positions not terminals).

Anyway here is a picture of the coil pack:

[img:center]

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As far as the ECM, that's an issue I have avoided thinking about

but am now somewhat suspicious of. It's an old Buick and used as a backup vehicle and have been hoping to fix it without spending big bucks. Funny about your mom's ECM issues. This car was my mom's car and it has had (as I recall) the ICM/coil system replaced 3 or 4 times since new, the first was only about a year after she bought it new.

 

[Touring5]

The connector at the ICM didn't look derranged, but I wanted to give it a good squirt of Deoxit but my little can was empty.

So you're saying "ring out" the harness point to point AND for shorts? I haven't delved into the ECM on this car ever - if it's like the ICM and mounting bracket I may need to pull the engine to find it - (chuckling sarcastically)

 

[SteveSRT8]

Just spent half a day figuring out that my employee's 88 Buick Park Avenue had a bad PCM.

It can be very tricky to be sure. We went to the junkyard and got lucky for a hundred bucks!

Note that I have spent hours on many cars looking at COMPONENTS when the real problem was WIRING/CONNECTIONS.