B18FT wont accelerate on boost

**Phil B** · Saturday 5th November 2011, 15:00

Bit of an update, i did a voltage test on the lambda sensor today, it should be reading a regular fluctuation between 0.2v-0.8v, and im getting a constant reading of 0.2v with no fluctuation which would indicate a dead sensor, ordering a new one next week so should hopefully sort it out.

**T4Rick** · Saturday 5th November 2011, 16:04

Originally Posted by Phil B

Bit of an update, i did a voltage test on the lambda sensor today, it should be reading a regular fluctuation between 0.2v-0.8v, and im getting a constant reading of 0.2v with no fluctuation which would indicate a dead sensor, ordering a new one next week so should hopefully sort it out.

Sounds good mate keep us updated

**Phil B** · Tuesday 8th November 2011, 20:23

Ok, lambda sensor replaced, getting a good voltage reading from the signal wire, ecu reset by disconnecting the battery for a while and...

Its still running the same.

Oh well looks like a complete engine wiring check at the weekend, fun...

**T4Rick** · Tuesday 8th November 2011, 22:11

Im sure you will sort it lol,i had wiring problems when i did mine mate and the answer was staring me in the face but i couldnt see it with me looking at the car for so long lol

**Phil B** · Wednesday 9th November 2011, 18:04

Ok next thing to try tonight, as i found out the other day the diaphragm valve on the icv is prone to breaking quite easily causing a dodgy idle speed and a boost leak under load which sounds about right from my symptoms. Going to block off the icv all together and take that stupid valve out of the equation, reset the ecu again and go for another run

**T4Rick** · Wednesday 9th November 2011, 18:28

you could do but im sure the car would run like the choke is on.do you have a picture of your icv

**Phil B** · Wednesday 9th November 2011, 21:31

You can set the idle speed on the throttle stop screw, not technically the right way to go about it but ok for the sake of testing.

Blanked of the icv and vac pipe to the diaphragm valve, that combined with the lambda sensor it does seem to be running smoother and picking up better, but its still not running right at full boost.

Seems to only happen at full throttle, full boost, after 3.5krpm. Im convinced theres a boost leak somewhere. The recirc noise from the turbo changed dramatically shortly after i started having the problem too, originally it was one smooth "hiss" but now its very prominent "flutter", which im led to believe may be a fault with the recirc valve, so blanking that off is going to be the next test i think.

**T4Rick** · Wednesday 9th November 2011, 21:42

Originally Posted by Phil B

You can set the idle speed on the throttle stop screw, not technically the right way to go about it but ok for the sake of testing.

Blanked of the icv and vac pipe to the diaphragm valve, that combined with the lambda sensor it does seem to be running smoother and picking up better, but its still not running right at full boost.

Seems to only happen at full throttle, full boost, after 3.5krpm. Im convinced theres a boost leak somewhere. The recirc noise from the turbo changed dramatically shortly after i started having the problem too, originally it was one smooth "hiss" but now its very prominent "flutter", which im led to believe may be a fault with the recirc valve, so blanking that off is going to be the next test i think.

Your making good progress now Phil

**Shadow** · Wednesday 9th November 2011, 22:25

if the recirc valve is fluttering it means the diaphragm in the recirc valve has failed. it will make the idle rough and it will be leaking under boost. a good upgrade for this valve is to get one from an audi tt it looks exactly the same as the standard one but it has much stronger internals.

where about's are you based?

**Phil B** · Wednesday 9th November 2011, 22:59

Thanks, i thought that might be causing the problem too

Ive read about that mod on the 480 club forums, its the "710N" recirc valve i believe.

Orignally it never made the fluttering noise it was one smooth darth vader-esque exhale. i was hoping to try and bypass that aswell tonight but i couldnt find anything to plug the pipe with.

I will be fitting the VW valve at some point but if i can get it running by blanking it off for now that would be great, ill try that tomorow.

Thanks for all the help so far, much appreciated

Based in north wales

**Shadow** · Thursday 10th November 2011, 01:05

believe it or not but C size battery's can be used to block the two pipes when the recirc valve is removed

**Phil B** · Thursday 10th November 2011, 08:27

Haha, thanks for the tip ill do that

**Phil B** · Thursday 10th November 2011, 21:44

Well the batteries fit perfectly but still not sorted the problem by removing the recirc valve unfortunately. Turbo still fluttering too so obviously not that that was causing it as id hoped.

Ah well, going to spend a day on it at the weekend testing and checking everything over til i find the fault.

**Shadow** · Friday 11th November 2011, 02:34

if the turbo is still fluttering it could be compressor surge your getting. not sure what it is exactly what causes it but have you checked the waste gate to see if it is sticking closed and that it moves freely and make sure you have the boost control valve plumed in correctly.

**Phil B** · Saturday 12th November 2011, 16:34

Ok another update, just done a fuel volume test as i dont have a pressure tester. The fuel pump should be running at 2.5bar at tickover which is enough to supply 1litre of fuel every 30 seconds. After 30 seconds of running i barely had a mug full of fuel, so theres something wrong with the fuel pump wiring somewhere, going to hotwire it tomorow and see if it runs at full pressure.

**T4Rick** · Saturday 12th November 2011, 16:48

Originally Posted by Phil B

Ok another update, just done a fuel volume test as i dont have a pressure tester. The fuel pump should be running at 2.5bar at tickover which is enough to supply 1litre of fuel every 30 seconds. After 30 seconds of running i barely had a mug full of fuel, so theres something wrong with the fuel pump wiring somewhere, going to hotwire it tomorow and see if it runs at full pressure.

That isnt good Phil you should fill a glass really quickly lol.Do you have a blockage?

**Phil B** · Saturday 12th November 2011, 18:31

I suspect its a wiring problem, theres 4 wires to the pump so i suspect its not getting a signal from one of the relays, tomorow im going to find out which the main feed wire is and hotwire it to get it running at full pressure, then just fit a hidden switch

**Phil B** · Sunday 20th November 2011, 00:27

Problem now sorted

Not a wiring problem at all, turned out to be something much more stupid.

When i changed the fuel pump i also put a new filter on, and the pipe unions for the fuel filter were seized on the pipes, which meant when you turn the union the whole pipe would twist with it. Anyway, knowing this at the time i fitted one pipe then twisted it so that when i tightened the other side up it would twist back the other way and theyd both be ok. But it turned out i hadnt twisted it enough and when i checked it today i found a big kink in the feed pipe from the pump to the filter which is what was causing the poor fuel pressure. Beacause of the foam shield around the pipe i never noticed this initially and have had a problem ever since.

Feel a bit of a prat really but hey, live and learn

Thanks very much for all the help and advice, appreciate it

Phil

**Shadow** · Sunday 20th November 2011, 00:39

at least you found the problem. don't why i didn't think of that it's quite a common problem that one.

**Phil B** · Sunday 20th November 2011, 02:02

Ah right didnt know it was a common thing. I should have checked it when i first did it.

The reason i found it was i took the feed pipe off the fuel rail and put 12volts to the pump and it was just a slow dribble of fuel well under what it should have been, so it either had to be some sort of blockage or the pump was knackered, which seemed unlikely as it worked fine before