Continuing fuel problems

[Quattrodave]

Afternoon all.

Firstly a big thanks to all that helped me identify where the fuel pump control module was located - the garage I had it at were properly perplexed!

So, they fitted it and all was well again, for about three weeks when the day following a successful 350 mile round trip to Plymouth the car cut out again in exactly the same way as before. I managed to get it recovered to the same garage who have had it a week now and have achieved nothing. Their diagnostics is telling them there is no problem at all, everything is running fine, they left it running for an hour, all good, then when reversing out of the garage it cut out on them!!

Beaten they've just sidelined my car and have been working on everyone elses so today I jumped back in my car (they left it on the road in a trading estate!) and drove home, no problems.

Does anyone have any ideas what could be causing this very intermittent problem whereby the engine will cut out and will turn over but won't start due to no fuel delivery for about an hour but will then start up and drive fine again?

It's had a brand new, audi sourced fuel pump control module less than a month ago which was showing as faulty when it did it before. The only other thing that has happened to the car is the front plenum chamber drain holes clogged up leading to a small leak into passenger footwell but as part of getting the fuel pump module replaced this was cleaned out thoroughly and nothing has leaked since.

Any clues or ideas most welcome. Kinda at the point where if this isn't sorted and put to bed soon I'm just going to get it fixed and sell the car :(

[Quattrodave]

Does anyone know roughly how much new fuel pumps would be for a 4.2 fsi? I see there's two in the tank and am just wondering if they're not hugely expensive whether it's worth just getting them both replaced (along with the fuel filter).

Is the fuel filter accessed from the top of the tank per the pumps or is it under the car where they usually are?

[Quattrodave]

Scrub that, just seen, £210 each x 2!!

Maybe worth fully diagnosing rather than just replacing both in that case!

Damn, back to square 1!

[Quattrodave]

So, checking on Audiworld they're suggesting that the left pump is used to prime the right pump, transfer fuel from left to right holds in the tank and to increase fuel supply at higher loads (above 3k)

So as a quick check tonight I started the car (first time) and it quickly sat down to a nice idle, but then when revving it sputtered above 3k and stopped dead at 4k.

[PsYcHe]

How much fuel is in the tank? If it's the transfer pump then it doesn't usually show a problem above 1/4 tank or so.

[Quattrodave]

How much fuel is in the tank? If it's the transfer pump then it doesn't usually show a problem above 1/4 tank or so.

Just over half a tank. So you're not thinking that's the problem then?

[Delboy]

There's a detailed process to test the pumps on these in the tech dump Dave.

Have a look through the D3 common fault section for the tech dump

[Quattrodave]

There's a detailed process to test the pumps on these in the tech dump Dave.

Have a look through the D3 common fault section for the tech dump

Thanks Delboy, I'll take a nosey after work tonight.

CHeers

Dave

[Quattrodave]

Foudn the tech section and the pdf docs thanks.

There's a lotta specialist tools listed, of which I have none! Have printed the necessary pages and may well end up taking the car back to the garage with diagrams in hand!

Was hoping it was something I could check!

May still have a look tonight and see if there's something I can do to make myself feel a little more useful (hate relying on garages - especially when they're busy & slow & can't find out what's wrong!)

[Quattrodave]

So, got close enough to each fuel pump to hear them both running whilst the engine was idling but the rough running still persists.

However, out of curiousity I took a video of the car starting up (from warm), blipping it and then on WOT where again the engine revved only to 4k. Video is linked below - is it me or is that an awful lot of steam and water coming from the exhausts?

This problem started around the time that I got a leak in the passenger (left side) footwell owing to clogged drain plugs in the plenum chamber (now cleared) - could they be related?

http://vid688.photobucket.com/albums/vv243/Daveymaclad/MOV_0321_zpsmmyiobli.mp4

[Mechcanico Lee]

Some thoughts ...

Before the fuel pump module was replaced would the car do the fault regularly or could it behave itself for along time ?
If it was playing up regularly it seems to much of a coincidence to behave for 3 weeks without faulting

You say after the fuel pump module was replaced all seemed well and you have had a good few miles done to confirm that it was good ?

What if either of the In tank pumps are pulling to much current and over loading the pump control module and when the pumps cool back down this allows the module to work correctly again .

I would be scoping the heavy wires to the In tank pumps and see what they are pulling out and the current ripple may show a bad armature .

Some of the bigger mercs albeit diesels that have stirrup type fuel tanks had an issue where one side of the tank would empty itself ..... this would cause the submerged pump to over heat and burn the relay contacts .

This fault was caused ultimately because the high pressure diesel pump was at fault and not returning enough fuel to one side of the tank .

As with any module failure you have to ask why has it failed ....,is there an underlying fault ??

Does the fuel control module vary the voltage to the in tank pumps as engine demand increases ?

From a diagnostic point of view I would be looking at fuel pressure .... compare to spec then when car faulted see what's happening to the pressure at that point .

[Quattrodave]

Was intermittent seemingly random cutting out which would stop car starting for an hour or so but then would start up again fine.

Did two 170 mile runs in the car with little obvious issues save fire it doing 29 mpg on the way there and just 24 on the way back despite driving it the same on the same roads. The morning after the lower mpg run it cut out.

When driving slow and steady at say 1300rpm the revs would oscillate by 1/200rpm even under constant load.

Sily point but will mention it seems to have cut out almost exclusively when turning hard right!

[Architex_mA8tey]

Silly point but will mention it seems to have cut out almost exclusively when turning hard right!

Wouldnt that point to the fuel not being properly transferred from one side of the tank to the other so that the empty tank is then supplying the engine with not enough fuel? :Confused:

[Quattrodave]

Wouldnt that point to the fuel not being properly transferred from one side of the tank to the other so that the empty tank is then supplying the engine with not enough fuel? :Confused:

Yup but I mentioned that to the garage and they glossed over that point so I was cautious to mention it.

Now that I think of it, when I was listening to the pumps individually the left side had both the sound of the pump (the low buzzing hum) and the sound of fuel trickling like a small waterfall. Right side had only the pump sound.

[Mechcanico Lee]

Turning hard right thing .......water in a module ?
Is comfort module on floor under pass side carpets ?

[Quattrodave]

Turning hard right thing .......water in a module ?
Is comfort module on floor under pass side carpets ?

Well passenger footwell did get water ingress so possible the stuff under the carpet is wet, but would the comfort module relate to the engine cutting out?

[Architex_mA8tey]

Well passenger footwell did get water ingress so possible the stuff under the carpet is wet, but would the comfort module relate to the engine cutting out?

Most of us feel uncomfortable when the engine cuts out! :p :rolleyes:

[Quattrodave]

Most of us feel uncomfortable when the engine cuts out! :p :rolleyes:

Haha! :)

[Mechcanico Lee]

When you say plenum chamber flooded with water you are on about the rear bulkhead ? is the engine ecm in there ??

[Quattrodave]

When you say plenum chamber flooded with water you are on about the rear bulkhead ? is the engine ecm in there ??

Under windscreen area I was told had a lot of water in it and blocked drain holes

[Mechcanico Lee]

Yes , think engine ecm is in the bulkhead area , you need to have a look a see if its got any water damage

[Quattrodave]

Left fuel pump identified as faulty, replacement ordered and will be with the garage Tuesday. Hopefully that'll be the end of things:yippee: