: Misfire and bad cat - cause or effect?



m3driver
11-13-07, 02:13 AM
So the V throws a check engine light as I'm midspan of the San Mateo bridge, it's running fine so after crossing the bridge I head home and park it. Call the dealer and take it in the next day which is a Friday. Got an DTS loaner (which after 3 weeks I'm actually beginning to like).

So on Friday afternoon I call to see what's up. Service writer says " we just got to it but the codes say misfire cyl #7. Keep the loaner and call back Monday".

Tuesday morning I call and they say they replaced the coil, but it still shows the code.

Call Thursday - new spark plugs, new injectors. Still throwing the same code.

Hmm - ok....

Call the next Tuesday "don't know but we have our best guy on it. We're going to do a compression and leakdown test."

Friday morning I call and tell them I need to get some stuff out of the car. I go over and as I'm walking into the repair bay I see the front wheels are off. As is all of the front suspension. And the crankcase. WTF! I look in the engine bay and see both heads are off and #7 piston is out of the block.

So I introduce myself to the mech and basically ask wtf in a nice way. He says they haven't been able to figure it out but no matter what they did cyl 7 was still misfiring. So after one thing led to another and some weird indications on the compression check (psi would build but then miss a few strokes of compression) and they also found metal filings on the oil drain plug they decided to pull the head.

Cylinder 7 was fouled with carbon, the rest looked fine. Exhaust valve also looked burnt.

So I asked to see the spark plug. They didn't know where it was. Asked if they bench tested the original injectors. Can't find them either.

The mech said they were sending out the heads for rework and putting in new rings on cyl 7.

Fast forward to Friday #3. I stop by because I need more stuff out of the car. Engine is reassembled, and they think it's fixed but don't want to run it since the drivers side cat is fouled. And the cat just so happens to be on national back order. Unkown when they will get one. He thinks the bad cat caused the problems in cyl 7.

So all in all I'm not real thrilled about this. Car is an early build 04 with all of 27K miles on it. From my take it was a bad injector dumping too much fuel into the cylinder which caused the carbon build up and that unburnt fuel is what killed the cat. I'd have thought that a bad cat would have thrown an emissions code before burning up a cyl so I think their theory is BS.

So now I'm looking at a car with 7 old sets of rings, and a shitty service history. Luckily its still under warranty, but I think the value is all shot to hell now.

Any opinions on what you guys think the real problem was/is?

Anyone else have this problem?

How about my chances of having GM buy me a new motor or at least give me an extended warranty for free?

Marco

Naf
11-13-07, 05:21 AM
HMMM...

This is an interesin one...

I have seen cats fail and headers melt at the seems. But thats due to lack of fuel and too hot of a burn. It could have been your ignition system wasnt up to par and cylinder # 7 just lucked out...Plus your emissions codes wont be thrown because you have 3 other cylinders workin their ass off keepin it clean. You are lucky you didnt have too lean of a mixture that would have costed you the whole engine. As for the metal shavins i am baffled.

I think you can negotiate with gm and probably pay for half the cost of a new engine. They will try and throw some driver induced stresses, which we all dont need. 50/50. It will cost less on warrantee work and labor tie ups.

best of luck to ya

m3driver
11-13-07, 08:22 PM
HMMM...

This is an interesin one...

I have seen cats fail and headers melt at the seems. But thats due to lack of fuel and too hot of a burn. It could have been your ignition system wasnt up to par and cylinder # 7 just lucked out...Plus your emissions codes wont be thrown because you have 3 other cylinders workin their ass off keepin it clean. You are lucky you didnt have too lean of a mixture that would have costed you the whole engine. As for the metal shavins i am baffled.

I think you can negotiate with gm and probably pay for half the cost of a new engine. They will try and throw some driver induced stresses, which we all dont need. 50/50. It will cost less on warrantee work and labor tie ups.

best of luck to ya

Thanks for that. Since it's still under warranty I'm not paying a dime for anything ;-). I'd be happy getting an extended warranty out of them for cost.

Your sig says Sandbox, Kuwait. You still over there? I was in Qatar for a while this summer. Not a bad place if you like sand.

Marco

ewill3rd
11-13-07, 09:05 PM
Not sure what is going on there, sounds like a combination of a lot of things.
One of them is a tech having a bad day.

Not sure which is the chicken or the egg here, if a cat plugged and caused a symptom like that it would be for the whole bank, not one cylinder.
The cat can fail in a couple of ways and still pass the diagnostic for the catalyst efficiency codes, although it is rare. Also a cat that does turn the light on isn't necessarily melted or anything it just won't pass the test anymore.

It sounds like maybe something has happened, how long has this misfire been happening?
I don't much like the San Mateo bridge, then again I don't like many bridges at all.
I used to cross Carquinez every day up in the North Bay when I lived out there for 6 years. (before they built the new one)
My wife had a friend that lived down in San Mateo, we went to his house a few times.

You might talk to Cadillac about your concerns, they might offer you a "component letter".
If they do that would be good. It will only cover a few items related to your repair but it might give you some peace of mind.

Don't hold your breath to get the car back soon, I foresee the engine acting up when they get it back together.
Call me a sceptic. I hope I am wrong.
Keep us posted.

JonCR96Z
11-13-07, 09:40 PM
Wow, good luck with that one.

NormV
11-13-07, 11:50 PM
Sounds like more than one problem. An in operative injector would mean 7.5 injectors or less and very rough engine.

For insurance you could do a compression test. Considering the mileage your just passed double the full break in. Depending on how you run the car full break in could be close to 10K miles with the LS based engines and snythetic oil.

Norm

Naf
11-14-07, 01:36 AM
Thanks for that. Since it's still under warranty I'm not paying a dime for anything ;-). I'd be happy getting an extended warranty out of them for cost.

Your sig says Sandbox, Kuwait. You still over there? I was in Qatar for a while this summer. Not a bad place if you like sand.

Marco

Ya, still here...Nuttin much happenin else where to move away to...

m3driver
11-18-07, 11:14 PM
Not sure what is going on there, sounds like a combination of a lot of things.
One of them is a tech having a bad day.

Not sure which is the chicken or the egg here, if a cat plugged and caused a symptom like that it would be for the whole bank, not one cylinder.
The cat can fail in a couple of ways and still pass the diagnostic for the catalyst efficiency codes, although it is rare. Also a cat that does turn the light on isn't necessarily melted or anything it just won't pass the test anymore.

It sounds like maybe something has happened, how long has this misfire been happening?
I don't much like the San Mateo bridge, then again I don't like many bridges at all.
I used to cross Carquinez every day up in the North Bay when I lived out there for 6 years. (before they built the new one)
My wife had a friend that lived down in San Mateo, we went to his house a few times.

You might talk to Cadillac about your concerns, they might offer you a "component letter".
If they do that would be good. It will only cover a few items related to your repair but it might give you some peace of mind.

Don't hold your breath to get the car back soon, I foresee the engine acting up when they get it back together.
Call me a sceptic. I hope I am wrong.
Keep us posted.

thanks. Misfire was never noticeable and motor never felt down on power. I have seen similar things in BMWs were a intermittently bad injector screwed up the computer circuitry and caused some really weird things to happen. Had I been the tech after the easy stuff didn't fix it I would have swapped out ECUs before tearing down the motor. and the metal shavings to me aren't that big of a deal unless there was a lot of them. Every mag drain plug I pull out of a car has some metal stuck to the end of it. I really wish the techs had kept more of the "evidence".

Marco

rand49er
11-19-07, 07:39 AM
Pretty serious effort! Hope you get this one fixed.

As far as having seven cylinders with "old" rings, personally I wouldn't be worried. Those seven will probably go 150-250k before needing to be replaced, and with 27k on them now, they've got a ways to go. Just my $0.02.

ewill3rd
11-19-07, 07:58 AM
What is the status on this car? Did they get it all back together?
Is the MIL out? (check engine light or "malfunction indicator lamp")