1996 Firebird goes through coil packs

#1

1996 Pontiac Firebird 3800 V6. Car and electrical system have about 180 K on them. Engine is a factory new longblock installed in 2005 because old engine overheated. Its got about 30K. I have changed the plugwires, fuel filter, cleaned injectors, etc in the past 6 months…about every month a coil pack goes bad in the car. Starts intermittently missing ( as it is doing now) and eventually ramps up to misfiring all the time, running on 5 cylinders. It’s not heat related because the weather outside is Oklahoma cold weather and its not always the same coil that goes bad. Since April I have changed them out about 6 times. Code reads multiple misfires and check Cat Converter. i’ve had mechanics tell me its a design flaw. Others tell me its a strsnge case. Had computer checked to see if it was delivering a constant elec. current that might be breaking down the coil but nothing out of ordinary was detecterd. Anyone? Anyone? It is driving me crazy!!!

#2

Always the same cylinder? Has the plug been replaced? What is different about that cylinder? Is that coil for it close to a heat source? Are starting resistors used with those coils to allow full voltage on start and less when running?

#3

Follow these instruction carefully when changing ignition coils. You need the repair manual to check the ignition control module.
The current that the ignition coils carry, or produce, may be too high. If resistance spark plugs are spec, use resistance spark plugs.

#4

The problem might be with the ignition module. The module operates in two modes. The Start and Run modes.

During the start mode, the module allows full battery voltage to the ignition coils. This ensures there’s a hot enough spark to allow a cold engine to start when the fuel mixture is rich. Once the engine starts and ignition switch moves to the run mode, the module switches to the run mode. It’s at this time where the module reduces the voltage to the ignition coils because it doesn’t take as hot of a spark to keep the engine running and it allows the secondary ignition components to last longer. Much like how a ballast resistor/wire used to work on point type ignition systems.

So if the module is failing to switch to the run mode after the engine starts, the voltage supplied to the coils will be too high and will shorten their life.

Tester

#5

Has it been determined for a FACT that the coils are really bad or is this a case of guessing at it, the vehicle runs fine due to coincidence for a while, and then acts up again.
Changing coils out 6 times means wild guessing IMHO.

Multiple misfires could point to a faulty crankshaft sensor or a MAF sensor; not unheard of on these cars.

What about the spark plugs? You did not mention those and misfiring plugs can easily knock out plug wires, coil circuits, and even ignition modules.

When you changed the plugs wires did you reinstall the new ones with the metal heat shields if the original wires were equipped with them?
Hope some of this helps.

#6

Its definitely faulty coils. I replace the faulty coils and it runs like an indy car for a month or two then begins to hesitate…last time wires were changed they were clipped back into original clips…I dont know anything about stock heatshields. ive always had the plugs done professionally…

#7

If the coils are legitimately going bad then the problem is not the coils themselves. There’s an issue causing them to fail; misfiring plugs due to whatever reason (fouled, gapped too wide, etc.).

This era of 3.8 in the Camaros/Firebirds did have some issues with the plug wires. GM even had a campaign going at one time in which they were paying for new wires even on out of warranty vehicles but I’m sure that campaign is over by now.
(A campaign is simply a factory good-will warranty that has been extended.)

The reason for the heat shields is that the plug wires are located so close to the exhaust manifolds (2 rear cylinders on each side) that the heat can cook the wires. The shields help to prevent this.

Without car in hand I have no idea. If the coils are really failing (a test with an ohmmeter could show a problem) then it falls back on the plugs IMHO since the wires were replaced.
Wrong plugs, wrong heat range, plug gap too wide, etc. could damage the coils.
Maybe a random misfire caused by a crank sensor or MAF sensor is killing the coils. A few minutes won’t hurt but operating an engine with a chronic poor running problem could do it.
Hope that helps.

#8

whats the IMHO? and when I go to see my mechanic what specifically should i ask him to look at? is there a way to tell if the ignition module is stuck in the start-up phase …delivering initial start spark at all times? Can it be tested with a scope…voltmerter, etc? And if it can be…what is the normal operating range supposed to be once the car is running? When it is being cranked? Love the car, hate the headaches