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Strange fuel system issue PLEASE HELP!!

Posted: Sun Jul 28, 2019 9:51 pm
by Confusedgtiowner55
Hi All, thanks for taking a look at my post.

I have been trying to get my 6n2 polo gti 2000 1.6 back on the road and I’m having some issues getting the engine going. I’ve narrowed the issue down to a fuel system problem as I’ve changed the battery, ignition coil, ht leads and plugs.

I was starting to troubleshoot the fuel system so started with the fuel filter. To depressurise the fuel system I removed the fuel pump fuse and cranked the engine, the engine then fired and settled to an idle and would rev in response to the throttle (fly by wire). The engine then died as it was only running on the residual fuel in the system as the fuel pump was disabled by the fuse being removed. When the fuse was replaced, the engine wouldn’t start again.

The engine also runs when the fuel pump is disabled and a can of engine starter is sprayed directly into the throttle body when the air filter is removed. I’m considering changing either the fuel pump or relay but not sure on the best way forward given the symptoms.

Many thanks in advance for any advice.


Re: Strange fuel system issue PLEASE HELP!!

Posted: Mon Jul 29, 2019 11:46 am
by 937carrera

Seems strange that the car started when the fuel pump fuse was removed - it's then only residual pressure that can allow fuel to flow and I would not have thought that would be enough to allow it to rev.

For that reason I would start by checking the fuel pressure regulator. If it is holding too much pressure then the quantity of fuel being delivered would be too much for normal conditions.

It is also possible to remove the fuel rail, reassemble and watch the injectors squirting into some containers when cranking (I have a set of 4 j2o bottles for this purpose)

Re: Strange fuel system issue PLEASE HELP!!

Posted: Mon Jul 29, 2019 12:02 pm
by Bazzad88
Hi, does the car start at all now? Or does it just crank?

Re: Strange fuel system issue PLEASE HELP!!

Posted: Tue Jul 30, 2019 6:19 pm
by Confusedgtiowner55
Hi Guys

Many thanks for your replies.

I agree, very strange symptoms so the FPR is a good shout. The fuel pump is clearly pumping fuel as there is fuel going into the injectors. It has been off the road for three years so I was hoping it was a blocked fuel filter but that isn’t consistent with the symptoms, will change anyway as it seems a good idea at this point.

I was thinking it was possibly the fuel pump relay as the pump might not be coming on at the correct time.

I think the FPR makes sense as it got closer to firing when I removed the air filter from the throttle body, introducing more air to mix with the over fueled engine. It also produced some white smoke when it started without the fuel filter fuse in pointing to too much fuel in the mix. Is my logic correct.

It would be very helpful if someone knows what is the bar rating of the FPR, I’ve been looking around the net and 3 bar seems like the consensus.

Many thanks for the input, be great to get it running again, had the gti for about 10 years and was perfect for nipping around london!


Re: Strange fuel system issue PLEASE HELP!!

Posted: Tue Jul 30, 2019 6:48 pm
by 937carrera
The OEM part number is 036 133 035 A

I would have said 3 bar without looking, and that's what I have found too

It will fit many cars

You can test the fuel pump relay by opening the drivers door after it has been parked a while. That whirr is the fuel pump priming to system pressure

Re: Strange fuel system issue PLEASE HELP!!

Posted: Mon Sep 16, 2019 1:52 am
by Confusedgtiowner55
Hi, many thanks for the advice.

I changed the FPR with no change to the symptoms. I recently changed the fuel pump, again with no joy as the engine still fires with the fuel pump fuse removed.

I purchased an OBDII reader to see if this would simply tell me the issue but it gets very close to the end of the scanning process then says it cannot complete the scan. Does this point to an ECU problem?

I’m definitely running out of ideas at this point so any help would be greatly appreciated.


Re: Strange fuel system issue PLEASE HELP!!

Posted: Mon Sep 16, 2019 8:06 am
by 937carrera
I would ignore the OBD reader problem for now, it could be that at fault, unless it works OK on other cars.

This is a wierd one, so you will have to be logical in the diagnosis.

Does the fuel pump relay run when you open the drivers door ?

Disconnect the electrical connector to the pump and check for 12v with ignition off, on and in the start position (fuse in, and out if you like)

Remove the injector rail complete, reconnect the electrical connection to the pump and as mentioned before place each injector into a receptacle and watch for fuel spray when you are cranking the engine