Cylinder Misfires on 2001 DeVille with 146K Miles

When the plenum failed on our Buick, we got the same codes. So, you are right.. it could be something other than plugs, wires, ignition modules, etc

When I see "random misfire" codes I think of fuel or fuel delivery, although any part of the ignition that is common to many or all cylinders can be to blame. Doesn't the '01 Caddy have individual coils for each cylinder? If so, rule out ignition almost altogether.

The cheap and easy approach is to start with a bottle of injector cleaner and a bottle of Dri-Gas in the tank. It will take a hundred miles or more of driving for the injector cleaner to do its thing, but that code is fairly heavily "damped" anyway; it takes a while to decide to come in and takes a while to clear on its own.

As 'hls' says, it could be vacuum leaks, too. I just like to start with the easiest when it is non-emergency.

Mike

Very possibly the fuel injection wiring harness, happened to a friend of mine. Was an expensive harness as I remember.

Brian

The problem has to be diagnosed correctly, not stabbed at with a bunch of WAG's. The OBDII system has a ton of information in it to diagnose the problem. Were there any other codes besides the random misfires? Any other codes could be the cause of the misfires. Take it to the dealer and pay him to diagnose the problem. Cars today are computers and cannot be fixed by randomly throwing parts at them like the old days...

And that is sage advice... It could be anything, practically, and throwing parts at it is expensive.

Good advice, but typically "random misfire" codes show up all on their lonesome. All the system knows is that the engine is running unevenly as determined by fluctuating time between equivalent angle sensor intervals. It's kind of the automotive equivalent of "my tummy hurts." Could be anything from bad gas to fouled injectors to neglected PCV. I pride myself on my troubleshooting skills (on the electronic side I do that for a living), but the best that can be done for this is to make everything right and then see what affects the engine after that.

Mike

No, most non-Cadillac techs want nothing to do with the Northstar engine. Can't say that I blame them....it's certainly not hard to work on once you know your way around them and you have the proper tools, but they can be quite daunting if you've never worked on one.

It's quite rare that the rear main seal leaks....and I'd like to know how the dealership can pinpoint the leak to the rear main seal without pulling transmission out. It's far more likely that you have a case half seal leaking, or the oil pan gasket is leaking. Either way, it's a very expensive and labour intensive job.

Did the dealership diagnose the "random misfire" problem and then tell you to replace the plugs and wires, or did you just take the "very little" amount of information you got from Autozone and ask the dealership how much to replace the wires and plugs? If you did the second, I would reconsider and have the dealership perform some proper diagnostics. I can tell you what we do a lot of on these engines. We put a lot of crank position sensors in them (there are two in these engines).

That might be a good idea.

Ian

FIVE HUNDRED BUCKS for plugs and wires ???

Does this dealer operate with a gun and a mask ?

Plugs and wires ( materials ) used to be a $50 job. WhaHappen ?

This is the year 2006, not 1965. This is a Northstar, not a K-car. The dealership routinely makes 100% markup on many, many items. You figure it out.

By the way, to the original poster....I don't believe that you have spark plug wires on this year of Northstar anyway. This year should have the coil pack cartridge with spark plug boots, but that's about it.

Ian

Times have changed. Plugs run from $2 to $10. Wires can be $10 each. Given the age and miles on the car, it would be about time to replace them if they have not been already. I did my 01 LeSabre just a couple of months ago because of mis-fires. It was a lot less than $500 though, more like $120, IIRC at a local shop.

A while back I compiled (in another forum) a list of some of the things that have changed since carburetors roamed the roads. I forget most - many were contributed by others - but some are:

*the radiator could be topped off with a garden hose *to tell if the alternator was working, unfasten one battery terminal to see if the engine dies *the radiator overflow just spilled on the road *the points should be filed or replaced at least once a year *the alternator could be run at full rated output all day *spark plug gap could be set with a gap tool ...

Thanks to all of you for your information and especially

*for the time you all spent* to have such a spirited and interesting discussion. This vehicle will probably go back to the dealer. I got the suggestion of bad plugs and/or wires from the Autozone gal when I told her that I had never had the plugs/wires changed in about 120K miles (I bought the car with 26K on it and I assume the plugs/wires were not changed in that interval. Note also that *nothing* has been done to this car since I have owned it, short of normal tire and brake maintenance and oil changes.) I hoped to find something that could be done locally since the dealer is about 45 minutes drive. The dealer had recently diagnosed the rear main seal problem, but the misfire problem is new. The $500 ballpark estimate for plugs/wires was based on a "what if" question. We did not explore other possibilities when I talked to the service manager. Every local guy I spoke with refused to work on the plugs due to their inaccessibility. I cannot evaluate why they have said this, except to take note of your comments here. Anyway I will go back to Autozone and write down the details of the diagnosis and post them here to see if that helps point in the right direction before I do anything else. I'll be back soon with this info. The engine was stumbling so badly I would have to guess that more than one cylinder was involved. Once again "thank you!" Frank

BTW as for crank position sensors, these were changed twice. When they were bad, the problem was sudden stalls, and slightly slow starting of the Northstar, nothing like this. Also, the second time the dealer told me they were redesigned. If it appears I am contradicting myself about *nothing* ever being done, I meant no regular maintenance on things like plugs or other "tuneup"-type items.

That's funny....the dealership should have known these engines don't have wires.

Hmmmm.....they aren't that hard to change on these engines. The front four are a snap, the rear ones are more difficult only because of the air injection plumbing that has to be removed before the rear coil pack cartridge can be removed. But still well within the realm of possibility for even the intelligent DIY'er.

By the way, the proper response to any suggestion made by someone like the staff at a store like Autozone when it comes to driveability issues would be a polite nod of the head, and then quickly forget anything they might suggest and have it diagnosed properly.

Ian

Ballpark? Which frig'n ballpark are they playing in? BTW I feel 120k miles on platinum plugs was way to long. 80k miles is the most I recommend ever putting on platinums.

If you are at 146k miles on the original plugs and wires then it is surely time to change them and they are the most likely cause of misfires. Sure there are other possibilities, but that is the place to start.

John