cparke

I have two very weird things going on with my readings in this block (camshaft position & adjustment).

First, while my normal positions are 0 on both banks, they do intermittently jump to -3 or +3 (I never get a reading of -2 or -1 or 1 or 2 what this happens) and then fall back to 0. While those values are still within spec., that is really weird, isn't it? What could I have checked to figure that one out?

Second, camshaft adjustment is never activated, even when driving in 2nd gear at 4000+ RPM. It just never changes to ON. While the car seems to be running fine, that doesn't seem right, does it? What could I have checked to figure that one out?

As always, thanks for your thoughts...

4Rings::G2 boosted::

the camshaft advance only gets activated at full throttle

cparke

What about my numbers jumping up and down by 3, what does that mean?

4Rings::G2 boosted::

and only between 2500 and 4500 RPM (IIRC).

On newer engines, like the 3.0, it's an infinately adjustable advance that I belive is also utilized at partial throttle.

I don't know the answer to your second question, I never tried to log these. I'm guessing the cam position sensor has a 3 deg resolution, and it's likely that the timing belt flex causes it to show a bit off at times. If it was always off in one direction I'd worry, but since it goes up and down I'd say it's probably normal behavior. The only problem it could be is a failing cam chain tensioner, but that's somewhat unlikely.

cparke

It is 1 degree resolution from -3 to +6 (and +16 to +25 when cam adjustment is activated). I have seen -2 to +1 as well as 0 to +3 and 0 to -3.

4Rings::G2 boosted::

Good to know, as I said it was just a guess

cparke

Cyl 1. & cyl. 6, which are paired on the coil segment. I've change the ignition coil twice, once originally in April, then when cyl. 1 & 6 misfired together a month ago, I had it changed under warranty and the problem went away until now (one month later). Maybe this is related to these other problems: fuel trim seems richer than it should be, cam. positions jumping forward and back by 3 degrees, and knock sensors occassionally going to 12 during normal driving.

Lean misfire from a timing problem (exhaust valve not fully closed) is my best theory, but why on both cyl. 1 & cyl. 6, and why not consistently? Could your idea about timing belt flex and/or failing tensioner support this configuration of problems? But then you said that's unlikely, why?

4Rings::G2 boosted::

one: problem with the spark on that coil would cause incomplete burn, which can definately affect your trim levels. In that case the trim levels going rich would be a result and not the cause of the misfires.

two: if the mixture is too lean due to a problem with one of the sensors (MAF?) or due to a leak, then the coil with the lowest voltage will be the first to misfire, which I guess in your car is coil for #1 an #6.

either way I'd check the ignition electronics in front of the coil to see if there's a problem there.

The reason why a failing tensioner is unlikely is because you didn't report any noise, usually a loose chain will hit the valve cover and make noise.

cparke

Intermittent incomplete burn causes a too rich condition, which causes the ECU to cutback fuel using the averages. That means the engine is actually running lean most of the time. According to you, this means if a lean misfire occurs in one cylinder, it could cause the coil's paired cylinder to also misfire even though the coil itself is good?

I'm not sure I follow why a lean misfire on one cylinder would cause the paired cylinder to also misfire. The plug sparks as usual in the misfiring cylinder, it just doesn't ignite the mixture. So why would that stop the paired spark plug from igniting its mixture as usual? To me, the electronics are the same regardless of whether fuel ignites or not.

I guess I'll have to find a way to determine if/how an incomplete burn can happen to figure out what to do next for this car.