Misfire 4.2 BFM

[mcs]

Yeah these have a twin pump setup.

The second pump is on at start up and on high load.

I have just not heard of these having a fuel pump fail before. Plenty of these cars do much higher mileage than mine (134,000 miles)

When the car misbehaves, I turn it off and on again and it comes good for about 20 seconds.

Mike

[Mechcanico Lee]

Seeing what the fuel pressure does when it faults will tell the story .

[mcs]

Originally Posted by Mechcanico Lee

Seeing what the fuel pressure does when it faults will tell the story .

Hi Lee,

More to this story, I pulled the intake off to clean/check it while i was replacing a bonnet cable that had snapped, and I found there to be an intake resonator tube that comes off and sits behind the PCV. It turns out that my mechanic had zip tied this rubber tube too close to the PCV and it was slowly being carved into.

I suspect when it was very hot, air was allowed into the crack and therefore through the TB, though the hose looked still sealed when I took it off the car to check.

I taped it up for ****s and giggled and had to drive 2 hours to brisbane during this 42 degree C heatwave. If the pumps were going to overheat, they really would have done then. The car made it there and back no problems apart from a little lack of power due to the heat I suspect.

Nevertheless, it is going into Audi on the 4th for a fuel pressure, vacuum, MAF check and it will let me know what is going on I suppose. If the car shows no symptoms and the vacuum and MAF check out, then it must be the pumps and they get replaced.

Mike

[Mechcanico Lee]

Yes something like that is possible , very often with diagnosis it's a case of rule out the things the symptoms show that it could be .

Like you say it can go along time , if with fuel gauges fitted it faulted and fuel pressure was not affected you can tick that off the possibles list .

Thing is with taking it in to the dealers for test will they have the time to go drive it for hours and hours till it does the fault or will they just test it ,and at time of test all was well at that time ??

[mcs]

Ok, the report from Audi,

Vacuum system tested perfectly.

Fuel pressure has been tested at the rail and the pump and it's perfect.
The maf has tested fine at all speeds.

It was definitely the intake hose.

The car is now getting new tyres again as the last of the original batch got tread separation.

The bonnet cable and boot latch motor have also been replaced

[Mechcanico Lee]

So this pcv valve that the resonator had carved into you need to replace that ?

could you post some pictures of it if you get time .

[mcs]

That is the pipe with the tape covering the split caused by the pipe being zip tied to the small valve motor.

[mcs]

Originally Posted by Mechcanico Lee

So this pcv valve that the resonator had carved into you need to replace that ?

could you post some pictures of it if you get time .

I still had some sluggish performance and a slightly confused gearbox;

So I took that round pcv off and cleaned it out.

The engine became as new. Seemingly found 30 hp and the everything seemed to smooth out. The PCV then became noisy.

So I opened the PCV to check the rubber diaphragm and it was torn.

It must have become stuck and then torn itself. A new one has been ordered and will completely mend the engine.

CHECK YOUR PCV people. It is very important with these motors.

[mcs]

Lee,

You were right. The main fuel pump failed on the way home from the Sunshine Coast last weekend. Leaving me 350klms from home.

I left the car there and hired a car to proceed home.

I went back last weekend and rewired the secondary pump to remain on to drive the car home.

Sorry for the doubt.

[mcs]

If anyone gets stuck on the side of the road, you can jump the secondary fuel pump at the relay in the boot above the battery.





I installed a manual switch in place of the relay switch, which will enable the car to run normally on one pump provided the fuel level is above 1/4 of a tank.

I switch it off when I park the car as it will flatten the battery running all night.