a 'Boys own' story!

[LYT4X]

Originally Posted by lefthooker

What's on at Oulton Park this weekend?

quattro Owners Club AGM.

[LYT4X]

Followed by some of this:

[Isimmo]

Originally Posted by LYT4X

Followed by some of this:

Good lad, ten points...

[lefthooker]

Looks like 1982 all over again. Great stuff.

[LYT4X]

OK, first proper competitive forest outing now booked.

Saturday 3rd August 2013 - Speyside Stages Rally.

www.speyside-stages.co.uk

I'm going to use this event as a competitive shakedown, so no heroics are planned. That said, who knows what can happen after the clock starts ticking.

[john johnson]

Knowing you !

[LYT4X]

What a crap weekend.

There had been an issue all week with the car dropping fuel pressure above 3k revs. We thought we had it sorted, but after 10 miles from cold it appeared again. Managed to get to scrutineering on the Friday evening, but that was the end of our rally. We were working on the car until 2am but to no avail. Totally gutted.

Still, car is in one piece which is more than can be said for a few who did start the event.....





We've checked the tank breather, swirl-pot breather, removed the upstream fuel filters before the Bosch 044 pumps in case they were restricting flow, changed the fuel pressure regulator, checked for kinks in lines etc. There's nothing restricting flow into the pumps and there's lots of flow out when we pull the lines from the base of the tank.

Before lots of wild suggestions, bear in mind the car has been faultless over 1500 miles so there's nothing intrinsic about this problem. Before the problem started, a new fuel gauge was installed and the tank was drained and re-filled several times to calibrate it. Now the car will run all day long at 3bar fuel pressure and will go as it's meant to when it's cold. However, after it's warmed-up we just cant press the loud pedal without dropping fuel pressure and resulting detonation etc. The fuel pumps are getting very hot and I suspect they are trying to push vapour due to the heat. I've been thinking this through all weekend and I'm now wondering if it could be something as simple as a bad earth to the pumps.

[20vcqdriver]

Have you checked the return line pressure regulator and its small bore vacuum pipe?
The 044 pumps do run hot, How hot is hot exactly?!!

[LYT4X]

Originally Posted by 20vcqdriver

Have you checked the return line pressure regulator and its small bore vacuum pipe?

Yes - it'sl ok, and the in-line filter to the manifold is clear now too.

Originally Posted by 20vcqdriver

The 044 pumps do run hot, How hot is hot exactly?!!

Not too hot to touch, but too hot to grasp for any length of time!

I think we have a voltage drop at the pumps - possibly a bad earth. We are seeing 12+volts about 2" from the pumps but only 10v across the pumps. My guess is the heat comes from too much current draw at the lower voltage. A pump is drawing about 16amps!

[Tim C]

Bad luck John, unfortunately there always seems to be disappointments when trying to compete with a quattro.

Ever since curing my friends under fueling problem, I've been an advocate of a local relay for the fuel pump with a direct (fused) feed from the battery switched by the normal fuel pump supply.
There is a graph in the Bentley manual showing fuel flow against pump voltage, it drops off quite dramatically, so full battery voltage at the pump/s is essential.

If you have a small volt drop problem it will get worse with a bit of heat, it is then a downward spiral of heat/volt drop/heat......
I've just cured (touch wood) a similar hot starter motor issue by eliminating any resistance in the circuit.