BAD COIL-No engine light? 02 bird

J

Jackie’s ride

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Jan 9, 2017
Thunderbird Year
2005
My friends 02 Thunderbird has a real bad mis fire and he just dumped some kind of engine cleaner in the gas tank. While the mis fire is a bit better it is still far from right. I think it is the coil pack or spark plugs but there is no engine check light on. He thinks it will get better the more he drives it. What do you all think? The car only has about 45,000 miles on it.
 

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I would have a trusted mechanic look at it. I just had the #7 coil replaced on my 04 with 46k on the clock. While we were at it, new spark plugs (they worked but they were 14 years old), cleaned the throttle body and put in new fuel filter. I had tried 3 tanks with Seafoam first. It doesn’t get better. He’s probably wasting a lot of fuel as well.

The difference in how the engine runs is amazing.
 
Jackie’s ride said:
My friends 02 Thunderbird has a real bad mis fire and he just dumped some kind of engine cleaner in the gas tank. While the mis fire is a bit better it is still far from right. I think it is the coil pack or spark plugs but there is no engine check light on. He thinks it will get better the more he drives it. What do you all think? The car only has about 45,000 miles on it.
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I have an 02 with 54000 miles. Started getting a miss. No check engine light. Thought maybe bad gas. Took to dealer and found out #4 coil was bad. I had a set of coils and dealer installed one with a new spark plug. No more miss. Dealer charged about $275 for new spark plug and to install my coil. Got my coils on Amazon for about $50
 
I forgot, I also had no engine light and no trouble codes on the OBD. I asked my mechanic and he said that the misfires have to exceed a certain threshold before the problem will code. I’m somewhat skeptical about that explanation.
 
Jackie’s ride said:
My friends 02 Thunderbird has a real bad mis fire and he just dumped some kind of engine cleaner in the gas tank. While the mis fire is a bit better it is still far from right. I think it is the coil pack or spark plugs but there is no engine check light on. He thinks it will get better the more he drives it. What do you all think? The car only has about 45,000 miles on it.
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Many 02-04 T-birds a have misfire problem. I discovered this about 7 0r 8 years ago when my 02 started misfiring. Dealer changed plugs and one coil and it was Ok for a while, but started again. I investigated and found that 03 and 04 T-birds had a recall to re-install valve covers that were not installed correctly at the factory. For some unknown reason, 02's were not recalled. Anyway, oil leaks out of incorrectly installed valve covers and coats the coils. If you haven't looked, the coil-over-plugs and plugs are in tubes in the valve covers. Oil leaks into the tube and coats the COP, eventually causing all the COPs to short out. So, after seeing how much the dealer wanted to re-install the covers ($2500 about 7 years ago, including 8 new coils, valve cover gasket sets and spark plugs) I did it myself over a weekend for about $800 in fomoco parts. No misfires since!
 
TXBluebird said:
I forgot, I also had no engine light and no trouble codes on the OBD. I asked my mechanic and he said that the misfires have to exceed a certain threshold before the problem will code. I’m somewhat skeptical about that explanation.
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I agree with your skepticism as my friends bird is missing about as bad as possible and still running with no engine light triggered.
 
I'd like to add a little insight to this since I've turned quite a few wrenches to date.

These engines are extremely similar to a BMW M62 4.4 liter V8 - which is an amazing powerplant in its own right, but also suffers from similar issues that I've been reading here. So what we've got is a coil-over-plug setup, where the "boot" feeds down through a tube that's O-ringed in the M62. By the sound of things, the 3.9 Liter we have works the same way - 4 O-rings and a valve cover gasket. If the O-rings fail, oil gets in, pools up around the plug, boils, cooks the boot, ruins the coil.

The BMW coils are generally Bremi's or Bosch's with a giant heat-sink surrounding it - the T-birds are much smaller - and I suspect prone to failing due to heat-soak. Generally when a coil like this starts to fail, it'll sometimes arc right against the tube the boot feeds down in to, which generally can cause a misfire. This is pretty easy to spot because you'll see a visible discoloration or burn mark on the coil near where the boot attaches. If the coil is failing internally within all the resin insulation, well... that's a different story.

Each coil is supposed to act like an "In-Cylinder Sensor" so when a misfire starts to develop, you're supposed to get a CEL on the dash with a corresponding "Misfire Cylinder X" code. Sometimes the misfires come and go, so the ECU will continually get battered with a fault code that comes and goes constantly.

In any event, the best thing to do in this case is stop as soon as you notice the misfire. Pull the coils and plugs and inspect them (I know, file this under 'duh' but you never know, this might help someone less mechanically familiar). If you have a fouled plug, you'll notice it even if you're not familiar with engines (one of these things will not look like the other... one will be sooty, pretty black, maybe even have a carbon chunk on it). Replace the coil and the plug immediately.

The pinned thread in the subforum has a great link for a set of 8 coils on Amazon for less than 50 bucks - just do that. I have only owned my Bird for 6 days and I've got a set on order "just in case" because 50 dollars for 8 is an absolute blessing compared to the 90-140 dollars EACH the BMW ones I used to go through cost.

If you have 1 fouled one, go ahead and replace all 8 with that set so they're all new, replace all 8 plugs, and keep the remaining old coils as "rainy-day spares" in case you ever get stranded somewhere with a misfire. It's just cheap insurance.
 
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