I have been experiencing a sputter like occurance in my 930. This only occurs under full boost at and beyond 5k RPM. The car will continue to push forward but it is almost as though the engine is hesitating. It actually almost feels a bit like little back fires similar to the burble or popping that a lot of us hear when you let off the gas.

I just had my modified fuel head installed and the fuel pumps checked so I am at a bit of a loss. ANY suggestions would be very appreciated.

Thanks in advance everyone.

 

Lots of looksies but no thoughts?

 

So, are you saying that you can get to 5000 rpm under WOT and boost, then it happens? Can you measure the fuel pressures? This will confirm or eliminate the WUR.

 

Don -

Exactly, The car runs great up to 5k (even beyond if I am not at full boost), but when I am at 1Bar and reach 5k RPM I start to experience the stutter. Don't really have a good way of measuring fuel pressure, would have to rig something up I suppose.

Thanks

 

Could be a pressure leak somewhere, explains why it relates more to boost than rpm.
I had this type of problem many times, don't know the details of the 930 even if it's very close to my car (964 turbo). I would check at high pressure places, between turbo and IC, IC and BOV, IC and throttle house etc.

 

I had something similar with mine a few months back. Hesitation above 3000RPM. Turned out to be a dodgy fuel pump. A fuel pressure check will let you know.

 

Thanks guys... what is the best way to check the fuel pressure?

 

Simply hook up a set of CIS gauges. I would go to JC Whitney for a cheap set. You simply need about a 9 bar gauge and the fittings. Any CIS tester fro BMW, Audi, VW etc will be ok.

 

The WUR does control pressure through the range, but I think it's more prone to adversly affect the cold pressure. I would guess a bad pump, fuel filter, or ignition.

 

Both times I've had a bad WUR it only manifested itself on startup and low RPM's.

 

The WUR also has a boost circuit that dumps pressure under boost.

 

I had a similar problem last year. thought it was a fuel problem. ...ended up being plugs!! totally amazed me. now I change my plugs after every race weekend.

 

You learn something new everyday. Does it dump pressure so the fuel head piston can open more and flow more fuel?

 

Yes, depending on the head it will drop 2 bar to enrich the circuit. This is why you see the big AFR dump at first on the dyno then it leans towards the top.