elwesso wrote:
Looking thru the thread again, everything looks good on paper Matt.. My engine at 180k had basically the same compression numbers as yours (and I drive my car hard). What I find interesting is that the 2nd cylinder in on both banks looks to be running the leanest. They all look a little lean though.
Carbon build up is possible, however it's odd that it would happen at such high RPM and no where else.. Most times you see detonation at low speeds under load.. SO normally you'd see it say at 40MPH in 4th gear during lockup, or climbing a hill in 4th gear, or something like that....
What I find interesting is that the same thing happened on 2 different engines in the same car, which means it has to be something specific to the vehicle. Carbon buildup isn't really that big of a problem on the Q engine, especially to the point where it would cause detonation. I've never heard of that, even on cars that are babied. The cats could be another issue, you can always gut them out to see if that does anything, and then replace as necessary. You also have a set of cats in the exhaust manifolds that would probably be worth looking at too. It won't cost anything to gut the cats.
I think the next route would be to inspect the cats. If you ever had a bad injector or continual misfiring, that would destroy the cats. If it were me, I'd probably start with the cats in the exhaust manifolds.
+1 - I recently had an ordeal with my 99 Maxima where I had a series of strange (hard to start from flooding, engine wouldn't idle, engine wouldn't start, you name it across the board issues) on the 2nd engine that the dealer couldn't find that were caused by the following problems. In my case one problem helped cause the next.
1) Broken injector pintle caps on two injectors (Phase II type) resulting in way too much fuel on cylinders 2 and 5 (yep both banks). Since the original injector rails were moved to the newer engine, it inherited the problems from the old engine.
2) Cooked/plugged up cats. After I had the car towed home from the dealer and paying $750 (ouch) for another misdiagnosis, I removed the upstream O2 sensors so the engine it could breath and it started up. Once I got it running with the O2 sensor holes open, the excessive carbon build up started burning off and it would start and run without issue. Again, the newer engine inherited cooked/plugged up cats, bad injectors, and all of problems that plagued the original engine.