GTi DX low control and system fuel pressure

Hi all, hoping someone has some suggestions for things I may have missed.
I have an 86 GTi cabby with a DX engine, it will run for around 5 minutes and then misfire and stall.
I have checked fuel pressure and the control pressure doesn't even register on the gauge. When closing off the supply to the WUR I can get the pressure up to 2.5 bar. Opening the tap back up and the pressure starts to drop.

Things I have checked/replaced
In tank lift pump, fuel pipes, filter and earth wire.
High pressure fuel pump and pipes.
Accumulator
Fuel filter
Spark plugs, HT leads, coil, dizzy cap.
Purged lines into a cup no dirt.
There are no fuel leaks that I can see
Checking pressure at the filter and I chickened out at 6 bar.
Pressure relief valve removed and all o rings are still round and look like new.
WUR opened, no leaks, bimetallic strip bends when 12 volts applied, reassembled and no difference to running or pressure.
Removed metering head feed line and no gauze filter present.
Timing checked with a strobe at 6 degrees BTDC

Might be something I've forgotten but any help will be appreciated.

Thanks
Rich

Is that from cold start then gets better once warmed up? Or does it do it hot or cold?

With mine from cold it would run for a few minutes then revs would drop right down to the point it would keep stalling until it had warmed up a bit, though don't recall it misfiring. Turned out the auxiliary air valve wasn't working properly. Something still isn't right now but it it is better after a good clean out and doesn't cut out

If I don't close the tap on the fuel pressure gauge kit then the engine dies before getting warm. I can keep the engine running by artificially increasing fuel pressure using the pressure test kit.

I think the AAV is working as the engine revs high for a few minutes then calms down to around 1000rpm. A few minutes later the misfire starts.

I think everything points to the WUR but I can't find anything wrong with it. I have ordered another one, no guarantees it will be any better but worth a try.

I'm wondering if there is anything else that can affect control fuel pressure.  

Im no expert when it comes to mechanics, and I've not tested my system pressure  so can't help with that (probably not any help to you at all to be honest)

Can test AAV in situ by squeezing hose to it, when cold revs drop when warm shouldn't make any difference.

Did you order a second hand or refurbished WUR? You can get a rebuild kit for them off ebay for around £34 which I will try at some point as I think my issue is WUR or wiring to AAV, perhaps both. But need want to get ignition timing And mixture checked/set first.

https://www.ebay.co.uk/itm/184451697447?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=VBNcl3M6S-K&sssrc=2349624&ssuid=ywyXn1ORRP-&widget_ver=artemis&media=COP

Yeah same here, I'm no mechanic just been a lot of googling recently.

I was looking at those rebuild kits but then saw a second hand WUR and AAV on eBay for not much cash. If that doesn't work I think I'll try the rebuild kit. I've also seen one for the metering head which might help.

That's on my list as well to send it somewhere for fuel mixture. My only worry is I could be adjusting the mixture to hide another problem.

If you're near sheffield you can always borrow my timing light and pressure test kit but if it's running ok it might be best to leave it.

Me too, drives my Mrs mad!

Ah right, I've seen them on ebay but ones I've seen asking price is usually around £100 each, which I can't afford without knowing that's the issue. I did strip my WUR and clean it out which has definitely helped, hence I want timing etc looking at first, but car doesn't seem to fast idle from cold which makes me think AAV still, I know it works as I've had it off and tested it. Plus now I seem to have a weak spark on cylinder 1 too


Yeah, I know what you mean, don't want to adjust it then the car not work at all, can always adjust it back I suppose. mines daily at the moment too so has to work, ish.

I appreciate the kind offer, but I'm on the Isle of Wight!

Normal for the Gti not to rev high when starting from cold, mines always at 1000rpm since we got it in 1994.

It's carb cars that normally rev higher when cold.

I can't remember the exact figure but I think the injectors need over 3 bar system pressure to open so in theory the car shouldn't even run.
I  don't know how you did it but if you got 6 bar at the filter I would guess the problem is with the pressure regulator in the metering head. I know that adding shims increases the pressure but other than that I don't know much about it, perhaps you've got fuel leaking past the valve.

To test the pressure at the filter I just removed the fuel line to the metering head and screwed the pressure gauge direct into the filter.

It could be the pressure regulator in the metering head. Apparently though a 1mm shim adds 0.5 bar. When I checked the pressure regulator there doesn't seem to be enough space for all the shims I would need plus the spring. Maybe the spring has gone weak for some reason but I haven't been able to find a replacement.

I will buy the reseal kit for it though just to rule it out.

Something I did forget to mention, any pressure I do manage to create, if I turn the engine off that pressure will last for hours.

86sam said

Something I did forget to mention, any pressure I do manage to create, if I turn the engine off that pressure will last for hours.

That residual pressure is a good thing.

Briano1234 said

86sam said

Something I did forget to mention, any pressure I do manage to create, if I turn the engine off that pressure will last for hours.

That residual pressure is a good thing.

I'm thinking this tells me the one way valve in the pump is working and the pressure regulator in the metering head otherwise it would just drain back into the tank.

If you're only getting 2.5 bar system pressure but 6 bar at the filter that would point to the pressure regulator,  if when you open the tap on the gauge the pressure drops away altogether that could be a fault with the WUR, they both could be playing up, only a guess.
I would put new o rings in the regulator first and see if that restores the system pressure.