00 P.A. Low spark on #6 coil

[MN_Max]

Greetings!
Girlfriends car, 2000 Park Avenue with 170,000 miles. Ran great up until this week.
Runs fine cold. When the engine warms spark gets very weak on #6 coil. Will idle OK and start fine...But when the engine warms and you step on the gas, a definite misfire.

What I have done;
Had the codes run, they showed 1. bad coolant temp sensor OR low coolant OR bad thermostat. I replaced the coolant sensor, thermostat.
Misfire on #6 cylinder.

No change.

Installed new spark plugs because the old ones were cooked (probably never changed). New Bosch Platinum plugs.

No change

Gently pulled the plug wires off the coil packs one at a time to observe spark. 1 thru 5 good blue spark 1-1.5" long. #6 hardly any spark at all, very weak yellow spark.
Swapped the coil packs around, put the #3 and #6 coil pack in another location, put a known good coil in the #3 and #6 location.

No change, still very weak spark from #6 coil terminal.

Tried a new ICM (Ignition Control Module).

No change...



Any suggestions??

[discnik]

Have you tried using a different plug wire ?

Just a thought

[MN_Max]

Originally Posted by discnik

Have you tried using a different plug wire ?

Just a thought

Thank you for responding!
Yes I have, tried a known good wire on #6, no joy.

Not the plug
Not the wire
Not the coil
Not the module

If it was the crank sensor it would not be the same cyl. all the time, correct?

[HotZ28]

What is the resistance of the #6 wire? Have you pulled the #6 plug to inspect it since you installed new ones? You could have the beginnings of coolant injestion from the UIM. Do a coolant pressure test! Remember, #6 is closest to the TB and would be affected first. BTW, it’s not a good idea to remove the wires from the coil terminals for testing spark! This procedure can damage the ICM on an DIS ignition. It’s better to remove the wire from the plug and use a spark tester, or an old plug gapped to .250 & grounded to the engine block!

[MN_Max]

Problem solved!

Plug wires, one bad coil.

Talked to a tech, he asked me if one of the spark plug terminals (on the coils) was rusty or discolored.

"Yes, but not the one that's misfiring"

That's your bad coil.

Replaced that coil and new wires, runs as new!

Thanks to the two that responded (HotZ28 and discnik) that responded.

[MN_Max]

You were both right
I couldn't see the forest for the trees.

[HotZ28]

Congratulations & thanks for the feedback. I hate to be the one to tell you this, but Bosch Platinum plugs will not last very long with the DIS ignition. If you detect misfire after about 5K miles, you might as well change the plugs to ACDelco, NKG, or Autolite that are recommended for your engine.

[MN_Max]

Thanks for the heads up HotZ, I'll keep that in mind.

I wish you could have seen the plugs that came out of that engine, I'm sure they were installed at the factory. 170+K miles. I don't see how they were firing at all.
I checked the gap on a couple, over .085"