Odd erratic boost problems

[gmann]

OK, I'll be the first to admit that I'm a moron when it comes to turbo cars...

My 01.5 S4 6MT is chipped (by the PO, I don't know what software) and that is the only mod that's done to the car. Just recently I replaced both pre-cat O2's. After that I was getting problems with boosting issues, normally the car would hit about 18 lbs of boost. A little while after the o2 change I was hitting 18ish lbs and the car would buck, a lot (even at half throttle) then it would just drop straight down to 5 lbs and would only boost up to 5 lbs until I shut the car off. After that it would repeat the same thing. (I shut the car off going down the highway with the car in neutral, started it back up and it would hit 18 again, then buck, and then hold at 5 until I shut off again.

I did some logs tonight when it was only hitting 5, but cant access them ATM because they're on my laptop.

But I did write down the codes...
17965 CHarge Pressure Control: Positive deviation
16684 Random cyl misfire
16688 Cyl 4 misfire detected
16689 Cyl 6 misfire detected

The 4 and 6 misfires are only at idle, and not when the car is under load. BUT when the car is sitting at idle (760 RPM) the load is showing ~18% that seems high to me...

I'm going to swap the coil packs from 3 >4 and 5 >6 and see if the misfire follows the coils. If it doesn't then I'll go plugs. But I REALLY want the boost issue resolved, I've been reading and doing a bunch of searching tonight in archives and didn't find anything that was like mine... N75, DV's? Something I'm unaware ok? I've got boost leak ruled out because that wouldn't change after the car's been shut off.

Thanks in advance.

[mholme]

A boost leak would put you in limp mode and cause misfires. I doubt it would be a coil or plug issue. I'd pressure test, including wastegate lines first before ruling out a boost leak. Short of that, test the N75 if you can, maybe borrow a known good one from someone.

[4RingsCircus]

The new O2s have discovered that you are running lean?

The differences between the front and (older) rear O2 readings is just wrong?

try logging actual versus requested boost.

[gmann]

The new O2s have discovered that you are running lean?

The differences between the front and (older) rear O2 readings is just wrong?

try logging actual versus requested boost.

I did fail readiness on the cat and o2s... I'll do the logging and put up results tomorrow.

[1997gtx]

Do you have stock TBB and DV's?
--Adam

[gmann]

I've got stock everything.

And the computer with VAG COM is currently getting a gig of pictures uploaded to it via CF card thanks to GF.

[gmann]

I failed at logging... I replaced the N75 today with another one, but IDK if the "new" one was good or bad as it was out of a wrecked car... The car will hit ~7 PSI then drop to 5 PSI and won't go any higher than 5 until I restart the car...

I had a problem this summer where all of the sudden out of the blue the car blew a bit of smoke after I turned off the ignition and let the turbo timer run. But I haven't had any of that since then, is one of my turbo's completely shot? I don't hear any weird noises at all under load.

I'm going to try to get my hands on a boost leak tester, otherwise I'll have to order the parts and make one myself.

[gmann]

Nevermind, found out problem thanks to 10secS4, he had it e-diagnosed in less than 5 mins...

[CONTROL ONE]

Well, what was it? And how was it solved?

[gmann]

[gointoscott]

I would also upgrade your dv's if you have the stock dv's. Your asking for turbo failure if those arn't working right.

Glad you found the problem.

[1997gtx]

LoL. I asked about your TBB and DVs a month ago

Glad you got your problem fixed, though!
--Adam

[gmann]

LoL. I asked about your TBB and DVs a month ago

Glad you got your problem fixed, though!
--Adam

You shut your mouth when you're talking to me


I'm glad I fixed the problem too... Now I just need to get new DV's.

And brakes on all 4 corners
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And timing belt service