Porsche Enthusiasts Club Forum

Hi Chas,

Yes totally with you on the frustration of intermittent faults!

I'm going to get a new fuel filter in before I start sniffing about at recon AFM or retrofitting a MAF, if only to rule it out.

The MAF option looks very wise but not cheap. I agree a recon AFM is no doubt a close second and certainly looks cheaper and at least good enough for the ~300bhp mark.

I could really do with these silly intermittent things going away so I can get chipping etc. Sadly the mantra has got to be "make it work right as standard first" - ...once it does, then I can muck about with fuel pressure, maps, boost control and maybe sniff about at upgrading to a dual port wastegate (as the nice lads at JMG are talking me into!)

I would second the fuel filter.

I would also say it could be the fuel pressure regulator, which has either failed causing high fuel pressure, or the diaphragm has ruptured, causing fuel to get into the vacuum hoses.. Worth doing a fuel pressure check and take off a vacuum hose from the fuel pressure regulator and sniff it for the smell of fuel.

Hi Jon!

Spooky you should say that...

I took my car out today so I can go directly from work to a friend's house this evening. Guess what?! It stinks of fuel and there's petrol all over the pipe into my nasty FSE power boost FPR and also coming out of the hose into the fuel rail.

I've called Steven / Jamie / Mark and asked them to FedEx me a Bosch 3bar, those 24pin Classic chips and a piece of standard fuel pipe they have for me.

Let's hope I can get the bits fitted OK myself on Saturday afternoon.

Going to my mate's house in the Golf now!!!

Jon,

Can an FPR become intermittent? When I pulled the vacuum hose off my regulator, it did not smell of fuel at all. My sympthoms are not quite the same as Phil's or Porker's though, but there do seem to be some similarities. The one consistency I have found with mine is that it tends to do its rough running business as per the quote after I come off the loud pedal, and come to use it again, where it will not rev with any load, to the point of sometimes barely running at idle.

Fuel pressure regulators can be intermittant, one failure mode is the diaphragm rupturing, which usually results in fuel getting into the vacuum lines.

Another failure mode is the valve inside sticking, where the fuel pressure can be too low, too high or just right, depending on the mood of the car.

Another failure mode is for the valve to stick pemanently high, which can seem intermittant, as the high fuel pressure will cause the fuel pump to cut out or overheat, which means it may run for a while, then either cut out, or, due to the fuel pump loosing power rather than cutting out, causing a lower more preferable fuel pressure... In other words, in this case you might get a car which runs, albeit rich for a while before it cuts out, or for a while and then runs much better.

The problem is, sometimes these things fail over time, so the car might have had the airflow meter tweaked on several MOT's over the years to give a better idle mixture/emissions, to compensate for high fuel pressure... Meaning the car passes MOT's but is not very fuel efficient, does not reach full power potential and gives poor fuel economy.. But then.. one day, the fuel pressure gets that high that the fuel pump starts cutting out, which opens a can of worms... Due to garages assuming the fuel pump is failing... and a new one might make it run again, but the real CAUSE is still there, pretty soon after the new fuel pump will begin to fail as well... So the garage next assume it is a warranty failure and replace it again.. Eventually, someone realises the fuel pressure is too high, replaces the regulator, but then the car does not run because of the "tweaked" airflow meter.

One of the worst things of running a specialist garage, we get everyone elses problems which garages have not managed to cure... So when we change a fuel pressure regulator and explain to a customer that now the car does not run at all, but it has good fuel pressure, the customer instantly assume that we have misdiagnosed the problem, or that we have buggered their car up, when indeed, just as we are trying to tell them, we now need to find the next fault, which, in this case above, could be the airflow meter has been meddled with, possibly even years ago...

Symptoms and Causes... Sometimes the symptom can point to one part, but really that part may be failed, but the cause may be another failed part.. Don't ever own a Porsche specialist... its a nightmare!! But I love it!

My 3bar reg is in, it still idles ok but gives a funny shudder if I let the throttle shut quickly. Presumably that's over fueling doing that. I'm just doing my chips now!

let's see if she drives in 30mins or so once the boxes are back in the footwell

Just for the record, I no longer have an intermittent lack of power.

The car runs like a dream with the new JMG/9XX chips and 3bar bosch fuel pressure regulator.

I'm putting my problem down to fuelling issues, not the AFM.