Yes I have see two cases where the cam blot has backed off even with the prescribed level of torque applied. Weird. A little loctite on the bolt takes care of this. loctite that you can remove of course.

Thanks for the confirmation!

Quick follow up question ... if the cam gear slipped (as indicated by several folks), wouldn't that problem result in getting a fault code thrown? The only code we see is P0492 (Secondary Air Injection System Insufficient Flow), which seems unrelated to the timing / low compression situation.

Thanks much in advance.

It should definetly throw a timing related code, such as p0011,0021,0012,0022


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I'll double check, but there definitely was no such code after the rough idle condition started, no CEL either ... only P0492. Wondering what might be the reason ... ?

For problems like this I think it is be to start with-- there are no coincidences when working on a vehicle.

I agree with both of your conclusions.

Secondary air injection system adds air for about a minute or less for cold starts. Purpose is to heat the cats faster so engine goes to closed loop faster. Malfunction would not impact compression.

Haven't been exposed to one cam off timing but I would be shocked if there were no bank and/or individual cylinder codes and check engine light.

A failing/failed vanos makes noise that you haven't mentioned.

Seems to me if timing gear is loose enough to jump timing there would be chain slop noise. Assuming that is incorrect, if bolt has come loose it could get looser as the engine runs. I wouldn't run the engine or only for brief troubleshooting necessity. Reference is to catastrophic engine damage caused by breaking a timing chain.

How much difference in bank to bank compression?
After you got different reading from one bank did you go back to the other bank to see if it might be a problem with tester?
Have you check vanos solenoid connection?
What were individual cylinder compression readings?

Thanks. Couldn't hear any specific timing chain noises, just very rough idle and sometimes some knocking-like sounds. If a VANOS is failing, could that produce the "low compression in one bank" condition? The bank (driver side) with low compression shows between 45-60psi in all 4 cylinders. The other side was around 160 I think.

Yes, failing/failed vanos can cause loss of compression and spark knock.

Do you know what actually fails on a vanos? Is it mostly the solenoid or is there any mechanical failure in the vanos unit?

^All of that would have been touched by the shop who did your guides. Just curious why you are diagnosing it instead of just dropping it off with them?