Causes of lean conditions

[ike84]

Ike -

Ahhh, misfires, I knew I was forgetting something!

I think of misfires very differently in these engines. If you break down the causes of misfires (not preignition or detonation, that is a huge pet peeve when people use those 3 terms interchangably, which you do not, and for that I thank you ) you are either going to have one of two situations - the person tinkered with something and didn't put it back together OR a catastrophic event has happened and your engine is now likely toast.

Here's what I mean by that.

Bonehead changes spark plugs, doesn't reconnect coil harnesses properly, and now there are misfires. Or removed injectors to "clean them" and damages them in the process or didn't hook them back up properly. I had a mentor who used to say "whenever a problem arises, always looks to where the hands of man have been". I think that is true for a lot of issues that get brought up on the forum and is one of the hardest things for us to help with for obvious reasons.

If it's not that, it's a catastrophic event. The timing chains on these motors don't stretch, so we don't gradually lose timing the way high mileage engines of the days of ol would. However, one systematic issue I'm aware of with timing is the chain tensioners. When those pads wear down, the dme is able to monitor the deviation and throws a code if it gets out of spec (which I think is 9deg). When the pads completely go, the chains jump the rails. Now the whole valve train is free floating and with this being an interference engine, you're now in the market for a new one.

The one exception I can think of was the guy recently who had a bad lifter spring after filling up with ****************ty gas. That was incredible luck that his engine survived unscathed there and he is the only person that I can rember seeing post something along those lines. Otherwise, I can't think of anyone else who has had valve train issues over the past few years.

The other notable exception here is what Stl is experiencing, which looks for all the world to me like a short in his wiring harness. Damn rodents. Again though, probably 1 in a million luck.

My point of all this is that I think of misfires in its own category, usually heralded by other leading events, active symptoms, and (usually) additional codes.

For your testing scheme, I think you are spot on. There ain't nothin wrong with feeling and smelling your engine. It's amazing how much information you get from your senses if you let them work!

I think your testing for a vac leak is brilliant. Reason and method must always accompany the madness. I would only point out though that the car must be in closed loop operations for it to be valid. A lot of us understand that principle, but there are some that definitely wouldn't. Not their fault, it's a complicated system, but its another factor that makes it difficult to help sometimes.

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