Lean Misfires at 2700-2800 rpm

[TurboBob]

12v is fine

[badass3000]

regulator213/DoctorDex anything new?
this is driving me crazy

[DoctorDex]

I've got my car running again, however, I'm still waiting on my "new" ecu to arrive. So no news yet. You'll be the first to know once I get it installed.

[DoctorDex]

Bad news. New (good) ECU didn't make a difference. Replacing the ECU wasn't done in vain though, it did fix the CEL I was getting because the old ECU wasn't putting out enough voltage to power the TPS.

Now I'm really starting to wonder what the hell it could be. Its got to be something mechanical, perhaps bad rings or timing belt is off a tooth? When it is missing I can hear an air wooshing/hooting/bumping type sound (its hard to describe) that sounds different from the BOV and like I noted before, when it is missing I see pressure fluctations on my blitz dsbc display. I suppose it could be CAS??

Has anybody done a compression test?

[DoctorDex]

Latest update:

Problem seems to be getting worse as I'm starting to see an increasing incidence of low load knock in the 1800 - 2900 rpm range. This morning it knocked (3-4 sustained counts) every time I'd go through the 1800 - 2900 rpm range. It would even knock if I'd blip the throttle in neutral. After driving for a few minutes, it seemed to settle down.

When I reviewed my logs, it doesn't appear as though I'm too lean as my O2 voltages are 0.89 V with the TPS @ only ~45%. I can't hear any knock/ticking. The only thing I can hear is what sounds like regular valvetrain noise. Just to be sure I wasn't getting the dreaded rod knock I sent my oil away for analysis. Analysis was normal, except for the fact that I had slightly higher levels of iron or aluminum. Apparently this is from my top end, but they said this could be normal if I am racing my car. However, I'm not sure if driving a car like its stolen on a daily basis counts as racing... I was pretty late with my oil change, so maybe this also had something to do with it.

Next weekend I'm going to change my wires (finally) so I'll report back if it helps or if the low load knock gets worse.

[badass3000]

I am installing a new engine right now. I will let ya know if I still have this when I start it up.
I did a compression check before I yanked the old engine and everything was fine.
This still sounds electrical to me tho.
I have tried a different PTU, coils, spark wires, plugs, but not a CAS yet.
I can drive mt car with the turbos unhooked, open throttle body, so mabey that will eliminate a few things

[DoctorDex]

Originally Posted by badass3000

I have tried a different PTU, coils, spark wires, plugs, but not a CAS yet.
I can drive mt car with the turbos unhooked, open throttle body, so mabey that will eliminate a few things

I've tried driving with the turbos unhooked/open throttle body and the problem was still there. I've tried changing plugs, wires, coils and ECU to no avail.

Are you re-using the CAS from your old motor, or is everything going to be new? I'm tempted just to buy a new CAS so that I can cross it off the list. However, I hate throwing money at the car just based on a hunch. If your problem does go away with the new motor with new CAS, would it be too much to ask to have you install your old CAS on the new motor? It'd only take you a couple of minutes... If the problem returns then we'd know for sure it was the CAS. Any help you can offer would be greatly appreciated.

P.S. When do you think you'll have your new motor installed and ready to go?

[badass3000]

Less than 2 weeks till complete. its just a new bottom end
I dont have a new CAS but have no problem finding a known good to use once Im back up.
I am very commited to finding the solution to this.
If I cant find it in a month I will probably pay someone to TS it for me.

[DoctorDex]

Quick update:

I advanced my base timing to 10* and I _think_ the lean spot has moved slightly. However, this is only preliminary information as I'm going to need some more time to test this theory on different days as it could possibly be due to the hot weather we've had lately.

Now with the base timing set to 10* it starts missing @ a little over 2500 rpm and it gets really lean @ 2600 rpm and it stops missing by 2900 rpm. Whereas, with a base timing @ 7.5* the missing would start ~ 2600 rpm, it'd become really lean (14% leaner) @ 2700 rpm and the missing would continue up to ~ 3000 rpm.

Maybe this points more to CAS???

[J-Ville VR-4]

Originally Posted by DoctorDex

Maybe this points more to CAS???

From what I've seen in this thread, that appears to be the one part that nobody has tried replacing yet. Do all the people who are experiencing this problem have the 1st gen cas on the rear cylinder head, passenger side? Is there anyone out there with this problem with the 2nd gen crank and cam angle sensor setup? If so, speak up!