Misfires 3B - running on RS2+spec

[filip.krticka]

I'm looking for an advice what to do.
I've done few search, but wasn't successful with posts.

Car was running fine and it was really nice to drive. But something went wrong.

The car misfires only when the throttle is fully applied, possibly only when the car get full boost 1,8-2.0bar It misfires mostly between 3000-4000.

I have another strange observation. When I start the engine The revs goes to 1500rpm than drops almost to 1200rpm again to 1500rpm than back to 1200rpm after this it's fine and it's steady at 1000rpm. This is happening no matter if the engine is cold or hot.

Can somebody clarify what the root cause is?

Under my suspicion:
-Fuel regulator valve (still original)
-Fuel filter – changed 3years ago
-Power supply to the fuel pump
-fuel pump position in the fuel tank
...

-Idle stabilisation valve??? Can it cause misfires?




Spec:
My engine was rebuild 2700km ago. Running sweet.
RS2+ spec something like 360bhp I guess. 2bar of boost.
Brand new turbo, wagner IC, etc...
Bosch green RS2 injectors,
034 bosch fuel pump
Sensorason the engine are brand new.

What was changed or is brand new.
MAF-RS2, Air filter is RS2,
Silicon hoses all-round, no boost leaks
N75 changed after the rebuild
Bypass Valve, OEM 710N
MTF, rotor arm, rotor cap, leads, spark plugs.
dizzy drive brand new
Coil was changed for another one

[filip.krticka]

forgot to add, that car doesn't go to the limp mode.

[bertman]

How old are your coil packs ?They can suddenly start playing up with higher boost

[filip.krticka]

I don't have coil packs, just single coil as default for 3b engine.
Original coil can be tired ... born in 1991 with 290k km on odo. The second one is the same age but with 80k km on odo only.

I'm aware of that 3B isn't great at all. But the car was running fine. I'm running this setup for almost 3 years without any big issues. Last time I was struggling with missfires it was resolved with new brend new coil leads.

[DeS]

I don't think OE 710N dump valve can hold more than 1,6 bar of boost. But it still doesnt solve missfire issue.

[220bhp]

who mapped your car.

[Tonks4x4]

Try replacing the fuses that run along side the main fusebox. Even if they are not blown, I had a similar problem on my 3B that took a long while for me to find.
It was the power to N75/ idle valve etc.
There was a slight discolouration to the fuse pins but it was not blown, it would test for continuity but would not pass 12v????

[filip.krticka]

who mapped your car.

Car is running on MTM chips.

[filip.krticka]

Try replacing the fuses that run along side the main fusebox. Even if they are not blown, I had a similar problem on my 3B that took a long while for me to find.
It was the power to N75/ idle valve etc.
There was a slight discolouration to the fuse pins but it was not blown, it would test for continuity but would not pass 12v????

Thanks it make sense. I'm going to have a look on the fuses.

[filip.krticka]

Just for the clarification. I had a call with friend on mine, who know these old Audis.
He asked me if the car is doing big bang after the hesitation, which is what the car does.

I'm going to revise the pipelines which goes into the control unit. If there is an leakage, moisture etc.

[filip.krticka]

The root cause has been found. New RS2 MAF sensor doesn't work properly. Change it for the spare one which I have at home and car runs fine.
MAF looks ok, like brand new one. Wire is in one piece. Don't know what is causing that.

[220bhp]

Result: thumbs: