Fuel Pump Stalling

[Brewster]

I finally got the engine running on my SC yesterday. Ran really well for around 10 minutes then it started cutting out. Initially I thought it had run out of fuel as I had only put around 10 litres of fresh fuel in and the pump sounded funky.

Put some more fuel in and struck it up again fine. This time, 5 minutes later it conked out again and the fuel pump was sounding stressed, as if it was dead heading. On investigation it was also warm to the touch. I replaced the (new) fuel pump for another new fuel pump, but it had exactly the same symptoms.

The fuel filter has now been changed but the problem still persists. What else could be causing the blockage? All the fuel lines are new front to back and it ran fine which suggests to me it isn't kinked, but something getting worse over time. Do the fuel accumulators ever clog/seize up?

I'm going to start splitting lines tomorrow, but it's got me stumped.

[butzsi]

Your problem is likely to be rust/dirt flakes being sucked out of the fuel tank and blocking the inlet side of the pump internally - try tapping the inlet end of the pump onto some clean paper on a hard surface and see what comes out.....

Chris

[Brewster]

The tank is a new Dansk one, never had fuel in before yesterday. After changing the pump I can confirm clean fuel flows out of the tank OK.

[Bruce M]

Perhaps disconnect the return hose from the fuel distributer (which is after the pressure regulator) and make sure the excess fuel pressure / flow is being bypassed correctly (pressure regulator isn't seized & return line is clear).
The warm up regulator might disguise a seized pressure reg for a few minutes.

[Brewster]

Cheers Bruce, I'll try that tomorrow. I'm going to start at the return connection at the tank and work backwards to see where the pump will run freely and where it stops.

[Brewster]

Well it's got me absolutely stumped. All flow and return lines are clear. It starts and runs beautifully. Then, after 5 minutes it splutters, cuts out and the fuel pump starts working very hard.

I've proved fuel flow to the accumulator, then through it and the filter to the fuel distributor. Something is preventing a healthy return flow at the engine end, but only after it's been running for a while. I've had the fuel distributor off. The plunger moves fine and the pressure regulator is as clean as a whistle (carefully set back exactly as it was taken out). Fuel flow to and from the regulator is fine.

If I can't fathom it I refuse to spend exorbitant amounts of cash trying to solve a CIS issue buying expensive components that aren't assured to be the issue. I'll just have to park the car up for year or two whilst I save up for PMOs and do away with whole contraption. I'll be so deflated though. It drives great as long as you don't want to go for more than 4 minutes.

[KS]

Where is the pump mounted? If at the rear, then this is the same problem my car had. Now cured by mounting it at the front, so it only has to suck fuel a short distance.

Don't forget, some of the generic fuel pumps (Bosch and Bosch copies) work better at the front – the one on my car was sold as being suitable for use at the rear, but clearly wasn't.

[Brewster]

The fuel pump is mounted just beneath the tank in the standard place. Both pumps I have tried are Pierburg ones, not Bosch, but it'd be strange that it would work fine for 4 minutes before stalling. Not to mention that when I split the outlet of the filter and put it into a bucket it pumps gallons per minute through. I'm almost convinced it's either the fuel distributor or the WUR. Just not enough to spend well over £1k speculatively trying to fix it when I could put that towards PMOs in the future.

[impmad2000]

The tank is breathing isn't it ? Not pulling a vacuum ?

[Brewster]

Yeah. I even took the filler cap for a good time while fiddling just to convince myself. It is almost exactly like you'd expect it act with a vacuum on the tank, but it's a dead head of pressure on the pump somewhere after the filter and before the return hose.

[Brewster]

I'm almost convinced that it's a problem with the fuel distributor or the WUR, but both are expensive to buy on a hunch. Knowing my luck it'll be that Pierburg pumps don't work with my set up or that the Dansk tank I have installed has a funny angle on the return connection and swirls fuel wrong in the tank, etc. CIS; It's fantastic when it works and once it does it's bombproof. When it goes wrong it just sh!tty witchcraft

[impmad2000]

I'm pretty sure I have old WUR and Distributor you can borrow. They are of unknown condition though as they been in the shed for years. I'll take a look at the weekend, if you like and if you don't get a better offer on the Wanted advert

[Bruce M]

So you have opened up the pressure regulator (part of the fuel distributer)? And it's clear / free moving (outer pointy bit with O-ring, shims , springs & inner piston with O-ring)?

My next step would be to remove the pressure regulator internal bits, put the cover bolt back on and run the pump to check you get a unrestricted flow back to the tank. This may also clear any gunk from the distributer, if you're lucky.

[Brewster]

So you have opened up the pressure regulator (part of the fuel distributer)? And it's clear / free moving (outer pointy bit with O-ring, shims , springs & inner piston with O-ring)?

My next step would be to remove the pressure regulator internal bits, put the cover bolt back on and run the pump to check you get a unrestricted flow back to the tank. This may also clear any gunk from the distributer, if you're lucky.

Yeah I've had all the pressure regulator out of the distributor and it looked brand new. Looking through my history the distributor was replaced not that long ago and looks in good nick on the outside too. It all ran perfectly a year ago before I stripped the engine and box and the only things that have changed fuel-wise are the tank, pump, and lines front to back.

I'm pretty sure I have old WUR and Distributor you can borrow. They are of unknown condition though as they been in the shed for years. I'll take a look at the weekend, if you like and if you don't get a better offer on the Wanted advert

That's a fantastic offer and one I'll take you up on. After doing a thorough search on all the 911 forums worldwide it seems this issue has never been discussed before. If I put your spares on and the issue remains exactly the same that would point to something else (bad aftermarket tank design? God knows), but at least I won't have shelled out a four figure sum on parts that may not be the issue. PM on it's way.

[crisc204]

Sorry I haven't read the whole lot just the request for parts.

Are you happy its not a relay or wiring to the fuel pump, or an alarm/immobilizer fault?
The fact its getting warm is why I suggest this.

If they get warm normally I find the wiring's faulty or the pump is faulty,
Also what fuel lines run down the tunnel? std Porsche?
check any new flexi fuel for kink's when sitting in their fitted positions.

If you need a SC wiring diagram for the fuel/eng I can do that