Paul H. (near Annapolis, MD)

I was going to post this in the A4 forum, then thought maybe I should post it here since I am chipped. I plan to get myself some Rhino ramps tomorrow so I can check things out underneath, but sometimes there's nothing like a good armchair diagnosis on Audiworld...

Basically it was as the subject says. My car details are in the sig. I was driving home from work on the highway, put it in 4th and gave it about 1/2 throttle. It pulled for a little bit but then as I opened the throttle all the way the car suddered once and sort of acted like it was running out of gas. Major loss of power that sort of came back as I let the gas pedal up. Except it never came back all the way. Now it seems peppy and normal up until the boost gets to about 3 PSI, but that's it. No additional power after that point. The boost never goes above 3 PSI and even this gradually falls off as RPMs go up. Torque falls off correspondingly, and the falloff of both is very smooth and linear. Haven't seen any clouds of black smoke behind the car (or smoke of any color for that matter). The Check Engine light never came on, and there are no DTCs stored in the ECU.

Other than the new power "plateau" it drives ok, maybe runs a slight bit rougher but for the most part very smooth. Idle is very good and sounds normal. And it is still quite peppy up to 3 PSI. I wouldn't call it lethargic at all. Under boost there is only a very slight whooshing sound like air escaping, and I can hear the turbo spool up sounding like it normally does if I'm only calling for about 3 PSI of boost.

If I drive hooked up to VWTool, when I call for power I see a LOT of spurious timing correction in Field 3 of Data Block 012, both positive and negative. But I don't watch this block often enough to know if this is normal. If I look at timing correction for individual cylinders in Block 20 there is almost no timing correction at all (I think Cyl. #3 may have peaked at a whopping 2.3 once or twice, most of the time zero; the rest were solid zero), which is normal even at 17 PSI (I have spent time in the past watching this one).

I figure it could be:

- a boost leak (hose failure)

- total BPV failure (as I was driving earlier today I saw the needle of my boost gauge bouncing every time it went above 15 PSI whereas I have only ever seen this happen once or twice before)

- turbo failure (not inclined to think this since I'm still getting a little bit of boost. Is it possible for it to fail and still work somewhat?)

- clogged fuel line or filter

Anyone care to narrow down the odds or add to the possibilities..?

Paul

monkey2

try an output diagnostic test, and check the electrical and mechanical functions of the wastegate solenoid valve, and check the hose from it to the wastegate for leaks(this creates an overboost condition, causing the ecu to shut it down).

vacuum test the bpv, just because they're prone to failure, but they usually just cause noise and dtc's, not loss of power,

a 98.5, so it has a throttle cable, and no pressure sensor on the intercooler

email me directly if you want, MatJReid@aol.com

Paul H. (near Annapolis, MD)

Thanks!! (You have mail)

Paul H. (near Annapolis, MD)

Turned out to be a loose hose. When I installed my boost gauge I tapped into the cloth covered vacuum line on the front of my intake manifold that goes to the BPV. I used a T-fitting, and the hose to the BPV had come off the nipple. So major air leak and my BPV wasn't opening at all. I am surprised the engine didn't shudder more when I let off the gas, or throw a DTC from running too lean under vacuum. I believe the system goes open-loop under boost -- does anyone know for sure? Nevertheless, I reset the ECU (still no DTCs, but cleared DTC memory then performed throttle adaptation) once I had confirmed the problem was fixed.

My BPV control hose is dried out and somewhat brittle, and probably just did not grip well enough under the nylon zip-ties that came with the boost gauge kit. There is a lot of heat here and that could be breaking down the nylon in the zip-ties. I'll have to get some proper clamps I guess for peace of mind. I also heard the hose crack as I was repairing it, so the hose will need to be replaced as well. Some of you early A4 1.8T owners may want to check yours. Supposedly Pep-Boys carries some hi-temp silicone vacuum hose that is more suitable.

BUT, my car runs great once again!! And it was only a 15 minute fix. This was actually the first thing I checked (couldn't do it until today). I got lucky. Thank God!! I was already thinking about looking for K04 owners who might have a spare K03 they would be willing to let go of cheap to help out a fellow enthusiast. I think Tip cars are harder on turbos because they wind the engine out more. I wonder if I should keep a spare turbo on hand? I could probably replace it myself. So I could keep it in the trunk!! Hah, what a conversation piece that would be...

Paul