About a month ago, I noticed that my Evo would fall flat on its face when going into boost starting at about 4500 rpm. It would tend to happen as intake manifold pressure would cross from vacuum into boost. It was very reminiscent of an intercooler pipe blowing off or fuel cut. I would also get a small backfire in the exhaust - kind of a dull pop. AFRs would go full lean, so I thought it was a fuelling issue. When I logged fuel rail pressure, it was doing exactly what it should, i.e., rail pressure was base fuel pressure + boost. I thought it might be injectors, so I swapped them out, and that had no effect.

Now I'm beginning to think its a spark issue. This would explain the full lean AFR when it happens. Is it possible that a failing camshaft position sensor would allow the car to run fine off-boost but then cause ignition problems at higher rpm?

 

I can't answer the question specifically, but it seems that you would get some faults for signal implausible or below limit value if it were the culprit. If you drive your car for a prolonged period at the trouble area (4500rpm just on boost) you may get the engine CU to give you a clue with a DTC. Are your spark plugs relatively fresh? How's the gap? I ask because misfires allow the air that was to be used for combustion to get into the exhaust, causing what appears to be a fuel cut-off (lean reading). I think you're already looking away from that possibility, anyway.
Maybe somebody who's had a cam position sensor issue previously can better answer this question.

 

It was indeed the exhaust cam position sensor.

 

running good now?

 

How were you able to verify the faulty sensor? Did it set a DTC?

Were you able to use a scan tool under operating conditions to check the waveform and compare it to a good waveform like the CPS? If you did use a scan tool, which one?

Just curious. Should any of us be unfortunate enough to run into something similar. Thanks!

 

Yep. Seems so.

Never got a CEL. It was process of elimination. Popped in a new sensor, and it was back to normal.

 

Glad you got it sorted.

 

Right on! Sometimes you have to just pull the trigger. Thanks again.

 

Me too. Didn't want to miss the Hood River drive this coming weekend.

 

Mychailo, I have seen a ton of them fail. Their proximity to the biggest source of heat on the car makes them very susceptible. Glad you figured it out.

 

Vegas heat I bet.

 

Tubular manifolds don't generally help the cause either.

 

i think... general rule is = If everything else checks out... and you have an issue like this, replace the cam sensor.

It fixed my issue also.

 

Hey Mychailo... I believe mine is pooping the bed right now! thanks for the thread! super helpful. Same thing happened to me.

 

Took me a few days to figure this out on my car as well a few years back... it pissed me off that it didn't just die completely... it once cut off on me in traffic out of nowhere as well prior to the 4500 RPM brick wall...