Porsche fuel pressure problem
I’d really like to be working on my poor old Davrian fitting the seat but that job is currently on the back burner. Why? Well, that’s because of the Porsche 944 and its intermittent fault. However, some progress on the 944 has been made though. A good friend of mine, Nick Cleak, is an ace spanner man and an electrical whizz too and he’s been helping sort out a cutting out and non-starting problem on the 944 that we initially thought was down to fuelling. However, after some lengthy investigations it looks as if this isn’t the case. That said, we discovered there was another problem with the fuelling.
Although the Porsche is a very quick car, I feel the performance should be delivered in a far more progressive and linear manner. At low revs, the acceleration isn’t as rapid as it should be and because of this I’ve long- suspected the fuel pump isn’t man enough for the job. And possibly the pressure regulator could be at fault as well.
To check these items we hooked up a gauge to the fuel rail and then cranked the engine. If the regulator is doing its job correctly, the reading should be two bar of pressure plus or minus - 0.2 bar. Good news, the gauge showed 2.2 bar and doing the leak down test showed exactly the same reading. So far, so good, so I clamped the fuel return line and cranked the engine again. The needle rose to 2.5 bar and stopped, which is not so good. This reading should be much higher. My suspicion about the pump was borne out and the low reading highlighted how the pump was under performing when put under load.
The next morning I ordered a new Bosch pump from FrazerPart, which arrived two days later. I already had a fuel filter and planned to replace
this at the same time and also felt it would be a good idea to replace the fuel tank filter as well. This is only available as a Porsche item and the price is horrendous.
I don’t mind paying for a quality part and I appreciate that Porsche is a premium brand, but I really feel that what I had to pay for such a small, simple, service item was unacceptable. The price for a fuel pressure regulator was even more of a shock and cost over £300 from Porsche. I shopped around and eventually tracked one down. It cost me just £97 ( including international postage), which was far better value. However, I didn’t need the regulator in the end but it’s good to have a spare – moan over (for now!).
The fuel pump (very reasonably priced) is located behind a steel cover plate on the 944 and nestles between this plate and the tank. The in-line fuel filter is higher up, tucked in a recess and the tank filter, as its name suggests, is located in the tank. It’s easily accessible though. Nonetheless, to change it the fuel system needs to be drained. So before tackling any of this work, don’t forget to disconnect the battery first.
When the cover was removed, I was surprised to see that the pump was minus its protective plastic cover. This cover is seemingly fitted for insulation/ vibration purposes and, guess what, it’s only available as a Porsche part. With post and package added, the price would be nudging £100, so my solution was to wrap the replacement pump in self-adhesive sound proofing material and then tuck the pump neatly between the shield and the tank. Cost? Just a few pence!
I also discovered the in- line filter was only semi- supported and the wiring was hanging in free space. So the new filter was attached properly and the wires tie- wrapped securely and routed out of harm’s way. The tank filter simply screws in but although the old one was really clean, I swapped it anyway. We then tested the fuel pressure and found it was 2.2 bar, which is spot on. But when the return line was clamped, the pressure rose to over 5 bar. This means it was the old pump that was at fault and a new one was definitely needed.
Having serviced the 944’s fuel system, attention will now be focused on why the ECU isn’t getting power from the Ignition switch and DME relay. Finally, a quick update on the Jeep. The recently fitted Falken tyres, which are proving to be excellent in normal driving conditions and have improved the vehicle’s fuel economy, have also excelled in the recent snowy weather we’ve had in this part of the world.
Having serviced the fuel system, attention is now going to be focused on why the ECU isn’t getting power from the Ignition switch