Stalling after full boost with bigger turbo.

[Jimmaey]

Hey guys, ive had some great help here on the forum so im going on to my next issue. My engine stalls after spooling up my turbo on full boost. I have no boost leaks , my G4 sensor is ok, and my maf is also good. My isv looks ok aswell. Diverter valve is a forge so no leaks. when the engine is warm and i dont go full throttle everything is ok. As soon as my KKK 27 turbo spools up and the system gets over 1.7 Bar the stalling starts. When the engine is cold again everything is ok again.

any tips where to look next?

[quattro-nick]

fuel problem? how is your fuelpressure?what ecu are you using?

[Jimmaey]

fuel pump seems okay since starting is great and no hickups. its running on a custom mapped ecu and fuel pressure is a manual fpr that was recently swapped because my last one was broken. the previous owner ran about 4 bar but i think she performs better at 3.6 bar.

[Error404]

The fuel pump can easily be under-performing under maximum load and still operate fine under normal conditions.
If the car is mapped for a 4bar FPR and you have changed it to 3.6 then you are going to be running lean so be very careful what you're doing.

[UrS4boy]

Why do you think a K27 turbo is appropriate? What do you mean by stalling? Stalling to me is when you come to a stop and the ISV and ECU can't get the idle speed set and the RPMs drop too low. I think you are trying to describe something else, not stalling.

How do you know that your diverter valve piston isn't stuck? A stuck valve might "stall" the turbo between WOT shifts.

[Jimmaey]

the k27 was on it by the previous owner. the car was a mess when i bought it. i reduced fuel pressure because she hiccups and then came on boost with some moderate black smoke. the fuel pump dont think it can be that because its a 034 motorsport drop in capable of 500 + hp. and stalling is indeed engine cant maintain idle. it doesnt even try to correct the rpm just boost and then engine shuts off untill i turn.over the key again and she starts again like nothing happened.

[Jimmaey]

how do i test the correct function of the fuel pump under load? i just tested the fuel pump by hooking it up to 12 volts and it worked. now that you mention it the car has been sitting idle for 5 years. many things can happen including that dreaded fuel pump

[RichLV]

You need a fuel pressure gauge to check fuel pressure both on idle and on boost. After that VCDS would help to read the error codes if you have them. Also, reducing the fuel pressure was not a good idea I think.

[jogi730]

I seem to be having a similar problem with mine at the moment. When it starts to boost, the engine just cuts out. They are having a mare trying to solve it at the garage

[vti2]

Ignitioncoil malfunction.

[newsh]

Hiccup and black smoke on a 3B can be bad dizzy timing.

[newsh]

Do a proper boost leak test

[RichLV]

Do a proper boost leak test

If it's leaking then usually there's not enough boost. Can be seen on the gauge. Unless it's leaking like the whole boost hose comes off. Misfires are most likely ignition or fueling related.

[newsh]

Stalling after full boost with bigger turbo.

If it's leaking then usually there's not enough boost. Can be seen on the gauge. Unless it's leaking like the whole boost hose comes off. Misfires are most likely ignition or fueling related.

Rich it has a huge turbo, even with a leak it will not be short of boost.


I'm not reading this as a misfire, OP says when engine is hot and having been above 1.7bar it stalls (but I think he means it dies) and won't run until re-started.
If there's a boost leak the motor will run rich on boost and lean on idle. He's reduced fuel pressure to make the car run better on boost but off the throttle it's now very lean and ECU can't react quickly enough to keep it running.
Fault codes would probably show adaptation errors.

Could be wrong though.

And if it a 3B I'd be checking dizzy timing.

[RichLV]

Rich it has a huge turbo, even with a leak it will not be short of boost.


I'm not reading this as a misfire, OP says when engine is hot and having been above 1.7bar it stalls (but I think he means it dies) and won't run until re-started.
If there's a boost leak the motor will run rich on boost and lean on idle. He's reduced fuel pressure to make the car run better on boost but off the throttle it's now very lean and ECU can't react quickly enough to keep it running.
Fault codes would probably show adaptation errors.

Could be wrong though.

And if it a 3B I'd be checking dizzy timing.

I was referring to jogi730, rather than OP.