cutting out...

[marmite]

Recently my car has developed a slight problem. If i have had my foot down in say 3rd gear, and i let off the gas and put in neutral, occasionally the engine will drop to real low revs and cut out. any ideas ? thanks for looking

[TheRedBaron]

Originally Posted by marmite

Recently my car has developed a slight problem. If i have had my foot down in say 3rd gear, and i let off the gas and put in neutral, occasionally the engine will drop to real low revs and cut out. any ideas ? thanks for looking

Does it only happen when you let off the gas after being above 2300-2500 or so rpm, and not when you are lower? If so I might suspect the BPV...

[marmite]

only when falling from high revs.. what is the bpv... ?

[TheRedBaron]

Originally Posted by marmite

only when falling from high revs.. what is the bpv... ?

Turbo Bypass Valve - it releases air pressure from before the throttle plate when it closes (ie when you let off the gas) after being in a boost situation. It's located at the front of the engine on the left (if your looking from the front) side of the flywheel cover, attached to the rubber joint on the intake inlet on the turbo. It is kind of a pain to get to, because you have to spend a few minutes taking off all the turbo piping to get to it. It has a tube that goes over to the throttle body, and a vacuum line to the intake manifold. If you suck on the vacuum line connected to it and find it is not able to hold vacuum, it isn't operating properly - it is both leaking vacuum and not doing its job. About 60 bucks for a new oem one from eeuroparts.

[marmite]

Ah, there could be a problem here. I have an atmospheric dump valve on the car and the pipe running to the inlet manifold is blocked off and also at the turbo end where the standard BOV should be situated. My atmospheric valve is situated on the new front mount intercooler piping...

[TheRedBaron]

Originally Posted by marmite

Ah, there could be a problem here. I have an atmospheric dump valve on the car and the pipe running to the inlet manifold is blocked off and also at the turbo end where the standard BOV should be situated. My atmospheric valve is situated on the new front mount intercooler piping...

That should be fine (it should be close to the throttle body, though) position-wise, if it has an adjustable spring I might make it a little looser and see if that helps (while still staying shut under solid boost of course).

[marmite]

i will try the yellow sping in it tomorrow then and see if that helps. They are fairly easy to change as the valve just screws in. It is situated about the same distance away as the standard one. It's on the upward pipe from the FMIC. Thanks for your help

[TheRedBaron]

Yeah I don't have one of those adjustable ones, but the almost stalling (and sometimes stalling if your aic is weak) is definitely symptomatic of the valve not opening (when I disconnect mine this is what happens).

[marmite]

Sounds very possible. I will let you know how i get on when i change it tomorrow. Many thanks

[Orca]

Originally Posted by marmite

i will try the yellow sping in it tomorrow then and see if that helps.

Is that instead of the green spring, or the blue spring?
If you're using the green spring, then definately change it - it's waaay too soft. I use the blue spring on my T8, with standard APC and 0.35 bar basic boost. I found the yellow one too soft.

Essentially, the valve is not closing quickly enough and the car is over-fuelling.

[marmite]

I am currently using the blue spring and running just over 1 bar of boost.

[Orca]

Nah ... that's the right spring, IMO. Perhaps try the yellow spring with a couple of washers? Maybe just moderate how you drive and don't drop the clutch for long from top boost