There are two cats, one on each bank just after the exhaust manifolds, so i don't see how one could feed heat to the other? There must be spark to ignite some fuel on that bank, otherwise it wouldn't get hot at all.

So there are four logical possibilities (based on everyones input);

1. The cat has clogged & then melted, blocking up the pipe, this would cause misfires on a whole bank. But it's more of a symptom than a cause to me. Why did the cat block up / melt?

2. Injectors are running full-time which sends unburnt fuel down the exhaust. misfires = yes, cat to burn = yes.

3. All coils on one bank are firing at the wrong time, if that's even possible. misfires = yes, cat to burn = yes.

4. The valve timing is out & you have exhaust valves open when firing, that will overheat the catalyst. misfires = yes, cat to burn = yes.

...it's just a matter of proving or disproving each scenario...

 

Josh have you found anything out yet?

 

Yes, of course, I was wrong thinking there is one catalyst. Silly me ! However, how are we getting excessive heat into the exhaust ?

 

It would seem to me that contaminated fuel is unlikely. It also doesn't sound as though the fuel pressure is the cause, but a quick check by depressing the schrader valve is not a bad idea. If it gives of a decent squirt of fuel, the pressure is probably ok.

I'd put my money on a camshaft problem, and I certainly wouldn't start the engine again without checking that out first. Valves & pistons work great in harmony, but don't socialise well at parties!! There is a good chance that the problem is a cam position sensor playing up, which would send the computer into fits of madness. Another possibility is that the forward O2 sensor is unhappy, and that too would send the computer into fits. But I think that is less likely to be the problem, because of the ignition firing problem. If the entire bank is out, then something is telling the computer lies or mechanical failure has occurred. That would indicate either a sensor or a timing chain/valve problem.

My money would be sensor, but I wouldn't start the car again until I was certain that it was not mechanical.

Cheers,

Languid

 

Assuming the cat was at operating temperature when whatever happened did happen it would do what it's supposed to do - 'burn' the excess hydrocarbon it saw. It wouldn't need a spark or external heat source and the reaction would be self-sustaining and particularly aggressive because it was probably seeing a stoichiometric air/petrol mix.

 

I know that everyone thinks the secondary tensioners in the X350 are bulletproof, but they are not, they still have plastic shoes on them that can break off and jam the chain. They key to this diagnosis for me is the description of "clatter". There just isn't anything besides cams/ chains that would produce clatter. A low oil pressure to the tensioners can also result in clatter. If this were my car, the valve cover would be off right now with a guage sitting on the cam flat. By the way, a supercharger can create a clatter if the coupler fails or a bearing fauils and lets the rotors touch. It just occurred to me that an overheat could be caused by a failed bypass valve with overboost in the supercharger although this would affect both exhausts.

 

ooops your right, just goes to show you I dont remember everything without looking. Useally I seem very intellegent because I try not to open my mouth without knowing or verifying first I just looked it up in the wiring diag instead of alldata which is actually incorrect, imagine that. I just couldnt find our wiring diag in the shop so I looked at Alldata, go figure

 

There is something else that could cause clattering at the top end; the variable inlet valve timing device, if its not getting any oil.

 

Fraser, I thought S/C engine didn't have that part.

 

Spot on, it doesnt, it is only on NA engines.

Well, I reckon its time for the techies to examine the engine closely, rather than us speculating.

 

Agreed!

 

Any logged codes? Possible shorted coil or failed tensioner.

 

These engines will rattle with any misfire.

 

I think that VVT was introduced on the S/C cars from the 06 MY.

 

sorry for no reply on my post in a few days I'm working like a mad man out of town. i was able to pull some gas out of the fuel line. 4 mason jars full. there is a odd color to the fuel. i brought them with me to work to have the lab run a test on the quality and impurities (i work in the oil and gas industry.) after i get my results It can determine if bad gas had a hand in my problem or its something else. i did start the car yesterday morning. with it being cold it wasn't too bad, it still missed and I'm certain my cat converter is trashed with the loud exhaust note. no clatter just a rough idle and loud exhaust. I'm going to have to have the car worked on, i just don't have the time to mess with it, or trouble shoot.

 

Waiting on the side line!

 

Sudden failure like that would indicate a single component affecting one bank, not multiple items all failing at the same time. I'd suspect something like an O2 sensor failure on the affected bank. It would act like a fuel problem.

Chjeers

Languid

 

Ill have it this week sometime

 

?????

 

@Jag XJ8 Red. Brutal is near Josh. It sounds like Josh will be dropping the car off for Brutal to look at. That was suggested at one point in an earlier post.