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K-jet pressure test results - help

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I have been chasing a poor start (cold and hot) for some time, and have now been able to run pressure tests (thanks Paul C).

Background:
new fuel pumps and filter
timing checked and ok
wur blasted through with carb cleaner and air, no sign of blocked gauze, voltage and resistance checked and OK
metering head plunger checked and ok
metering head primary pressure regulator checked, new o-rings, looks ok
fuel delivered (quantity) at filter meets spec

When cold will start on fifth injector and then die, repeat about 4 times and then will run, if extra throttle added, can ease off throttle after a couple of minutes, idle is high, but if idle valve adjusted it makes starting harder, as does leaning the mixture.

Fuel pressure results (air temp 15C):
system pressure (fuel pump running, engine off) 4.5bar

cold start with WUR and AAV unplugged 4.75bar - idling about 1500rpm
after 10 minutes, idle has increased to 1650rpm, fuel pressure still 4.75 bar
after 15 minutes fan cuts in at oil temp 54C, idle up to 1900rpm, pressure still 4.75 bar
after 25 minutes oil temp 84C, idle up to 2000rpm, pressure still 4.75 bar

engine off, pressure drops like a stone to 0.7 bar

try to restart, fuel pressure up to 4.5bar as soon as fuel pump on, but engine won't start
close gauge valve to WUR and switch off pump, pressure drops like a stone again.

Then test fuel delivery pressure as per Bentley manual with pressure gauge attached to fuel filter outlet:

fuel pump on, pressure off the scale - so more than 7 bar
pump off, pressure drops to 2.75 bar instantly then holds
after 10 minutes pressure still 2.3 bar

Looking at Haynes, Bentley and online, I get slightly different info on what pressures are acceptable, partly I think because US spec cars are set differently to European.

My take on this is that the WUR is not working, or a line to/from is blocked, as control pressure is not low enough when cold. Is it worth trying a rebuild kit, or should I just get a replacement WUR?

Where am I likely to be losing residual pressure when engine off? The last test suggests that pump non-return valve and accumulator are OK, as pressure is holding. If the pressure loss is on the return to the tank, is that the primary regulator in the metering head, and specifically the allen head plug in the very end (which I haven't looked at yet).

I know many people have asked similar questions before but I can't see the wood for the trees!

cheers

Lee



 

1986 GTI Cabriolet ("dambuster")

2000 Mk4 Cabriolet Avantgarde (bought for the mrs)

2001 Zafira 1.8

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check the link in my signature for 'k-Jetpressuretests.pdf', it has the relevant bentley sections printed out in it. the other kjet one is quite handy also

but in short:
  1. your system pressure is too low, it should be 5bar
  2. your WUR appears to be non-functional, it should range from around 1.2-2.5 bar as it warms, then sit around 3.5bar when fully hot.
  3. you probably have some kind of leak in the metering head if residual pressure drops instantly, and when testing at filter outlet it holds fine

take the fuel pressure relief valve out, perhaps the o'rings have split

just to check, you tested it inline with the pipe from front/top of metering head to wur, and had a pressure gauge with a tap in it yes? closed the tap to measure system pressure, then opened again to check control pressure?

Hello my name is John and I'm a dub addict.



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John,
thanks for replying. The tests were with a k-jet specific test kit, following all the instructions in Haynes and Bentley. The test kit was between the FD and the WUR, with the gauge on the FD side of the tap.

I have recently changed the 2 o-rings on the pressure regulator - having found that it was missing the large o-ring, and the small one on the tip was deformed.

I will try increasing system pressure by adding a shim to the pressure regulator.

One other question - should the main plunger in the FD have any o-rings on it - I have seen conflicting info online, especially some exploded parts diagrams which show an o ring on the lower part of the plunger - does this create a seal when the plunger is at rest? I am not sure where else the FD would lose pressure - unless the pressure regulator isn't closing properly.

I will change the WUR and take it from there.

cheers
Lee

1986 GTI Cabriolet ("dambuster")

2000 Mk4 Cabriolet Avantgarde (bought for the mrs)

2001 Zafira 1.8

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Whats the history of the car?
Is this issue suddenly started or are you trying to get an old system going again?
The high idle sounds like an air leak but if its a problem youve picked up from someone else it could just be badly adjusted trying to overcome other issues that you have already diagnosed.
I've just had an issue with my campaign thats been stood for 25 years. The WUR was stuck like the engine was up to temp. When you tried to rev it from cold it would just die and spit back similar to a carbed engine needing the choke pulling out. However it would tick over fine at a correct rpm when cold
The other issue I had was the plunger was sticking in the MH. When I switched off the system pressure would disappear but it was through the injectors as the plunger wasn't shutting off after switch off. When i reprimed the system the injectors would squirt some fuel and then the plunger would shut causing a double flood situation making it hard to start when hot .
Have you tried pulling one of the injectors and running it on three with the pulled injector into a clear bottle and then seeing what happens during switch off and restart? Could be all sorts of things but this simple test help me nail my hot start issues but as i write i'm thinking that as your dropping straight to 0.4 then its probably not this as the injectors would shut before it got to 0.4

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Hi Yomp,
previous owner had dealt with the rusty fuel filler issue - there are receipts for a complete replacement of the fuel system from a donor car, which was a few years back. When I first had the car the engine ran fine. My problems started when the car died and I discovered that the rubber hoses in the tank for the lift pump had badly degraded and black gunge had killed the lift pump. Since then I have replaced both fuel pumps as the main pump was a bit crusty as well. Since then the car has been mostly off the road as I have tried off and on to resolve this issue - just managed to get it running enough to get to my classic-friendly mot garage - he is an ex-Porsche owner and confirmed I definitely have a fuelling issue. Had previously done the fuel quantity tests, etc. I have checked the injectors with the engine off, but will give your suggestion a try of having one out and see what happens at engine off, and will do the same with the fifth injector, just in case.
I have had the plunger out and it looks OK - I would have thought that with such a massively high control pressure, the plunger would go back down pretty quick, but who knows?
I will keep at it and will probably be back for more advice once I have changed the WUR, and maybe shimmed the regulator.
cheers
Lee

1986 GTI Cabriolet ("dambuster")

2000 Mk4 Cabriolet Avantgarde (bought for the mrs)

2001 Zafira 1.8

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my wur was giving high pressure to the plunger but still not enough to shut it. I've just switched the MH and not yet looked at the original plunger to see whats going on.

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That's useful to know. Having done a bit more research, I am wondering if the new o-ring I fitted on the tip of the primary pressure regulator is the wrong size - slightly too big. I have ordered some of the next size down and will give that a try to resolve the residual pressure loss. The other thing I will try is to blast the small fuel channel on the FD return from WUR , as the hose itself isn't blocked, but it can apparently be a cause of high control pressure.

All good fun (I think) - would love to have her running right for the Summer.

1986 GTI Cabriolet ("dambuster")

2000 Mk4 Cabriolet Avantgarde (bought for the mrs)

2001 Zafira 1.8

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When they're sorted and well maintained they're very reliable.
My other GTI I've owned for 8 years,  once I sorted it out I never have to go near it. The campaign I picked up hadn't been run for 25 years so you can imagine what state the fuel had got into inside all the components. The previous owner had managed to get it running but it wasn't right.
I'll go out this morning and fire it up with the new WUR ive fitted. Hopefully its cured it. The problem with these issues during warm up is you only have a small window to be able to test it before it warms up so it becomes a slow process of elimination!

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Today I ran all the tests again (except the delivery pressure) and results the same. I also did a full set of injector tests and all 5 passed - no sign of leaking, and the FD plunger passed as well - as soon as I let go of the air flap the injectors stopped spraying. Everything points to the WUR.....

1986 GTI Cabriolet ("dambuster")

2000 Mk4 Cabriolet Avantgarde (bought for the mrs)

2001 Zafira 1.8

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You can manipulate the wur by taking it off the block but leave the pipes connected. You have to disconnect the wires as its not long enough. If you then undo the 4 remaining screws the back will come off but be carful not to lose the spring, cup and plunger. If you can then get it started, put the plunger back into the diaphragm and press it with your finger you should hear the engine note change as it goes rich and then weak.
I'm not convinced that the rubber hoses degrading have caused your issue.

When you say;-
"cold start with WUR and AAV unplugged 4.75bar - idling about 1500rpm
after 10 minutes, idle has increased to 1650rpm, fuel pressure still 4.75 bar
after 15 minutes fan cuts in at oil temp 54C, idle up to 1900rpm, pressure still 4.75 bar
after 25 minutes oil temp 84C, idle up to 2000rpm, pressure still 4.75 bar" It does sound like the WUR is gving too high pressure when cold but I would expect the revs to improve with heat not rise higher.
Something must be way out of adjustment. When my Wur was high it ticked over when cold OK but wouldn't rev cleanly until warm.
Does yours sound rich or weak when cold?
 

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Also with the WUR unplugged I would expect the pressure to stay the same regardless of what it is for quite a while because just ticking over the block doesn't heat it up that quick to affect the bi metalic strip which is why it has a bit of assistance from its own little heater. Unplugging that will delay the change of state wouldn't it?

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I think my mixture is out. Before I had the gauges to do proper tests I had to richen the mixture to get it to start - which makes sense if the WUR isn't working, so it is too rich all the time as there is no variation in control pressure. When I ran the tests today, once it was warm it was idling way too high, so I leaned it by about 1 and 1/2 turns of the mixture screw and the rpm dropped to about 1000-1100, but it seemed a bit lumpy.

Thanks for the tip about manipulating the WUR, but I reckon I would be bound to lose the spring!

If I get hold of a replacement WUR I will probably strip the current one down and see what's what.

You might be right, the black gunge could just be a coincidence. Everytime I have cracked a joint in the system or run a test the fuel has been nice and clean, with no signs of contamination.

cheers

1986 GTI Cabriolet ("dambuster")

2000 Mk4 Cabriolet Avantgarde (bought for the mrs)

2001 Zafira 1.8

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Make sure you get a WUR that you know is functioning correctly otherwise it'll make the situation a lot more confusing! :lol:

The spring is not that small to lose in the back of the WUR and I still think it might be worth trying to manipulate the diaphragm manually to see if it makes any difference to the engine note. Taking the back off and removing the spring should instantly lower the output pressure of the WUR and you would be able to weaken back the co screw but you only have a limited time before the engine becomes too rich through warming up. Once it goes rich press in the diaphram with the plunger and the engine should lean out.
You've got nothing to lose as you think the WUR is defunct anyway.

Rather than adjusting the CO screw to drop the revs I would go for the throttle screw on the back of the throttle body.

Is your aav working correctly? ie shutting off the air as it warms.

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Thanks Yomp - today I took your advice - if my WUR is faulty, where is the harm. So I removed and opened it up. Inside it was very clean indeed, came apart very easily. But what I found was a completely blocked inlet filter gauze. Nearly lost it when it came pinging out, and managed to lose 1 of the 5 screens but cleaned up and all back together. Onto the car, and lo and behold fuel pump on, guage tap open and a cold control pressure of 1.2 bar - hooray :)  Fired up and stayed running second time, running ok, and then died unexpectedly about 30 seconds in, with the control pressure up to1.4 bar (WUR plugged in). Figured that as I had previously adjusted it to run with a non-working WUR it would be set much too rich, so leaned the mixture a bit at a time, and tried restarting, but no-go, even the fifth injector. Decided to go back to basics and check for a spark - no spark at no 1 or no 2. Distributor looked ok, so checked the resistances on my recently fitted new Bosch coil - both primary and secondary were much higher than they should be. Luckily I still had the old (I suspect original) coil, connected that up and did the spark check on no1 and it started on 3 cylinders! Fitted the old coil properly and started again. This time it ran fine, if a bit fast. System pressure is still a bit low at 4.5 bar, but control pressure started at 1.2 and rose to a steady 3.4-3.5 bar in less than 5 minutes, at the lower end of the acceptable pressure range. Ran it for 30 minutes and once warm fiddled with mixture and throttle air valve to get it idling about 1000 rpm without sounding too lumpy. Then checked the residual pressure and hot starting - I suspected this would still be a problem. Engine off and pressure dropped instantly like before. But if I fired her up straightaway, after 30 seconds wait and after 2 minutes wait, she fired and ran ok. But when I left it 10 minutes, she wouldn't start, as I expected. Hopefully the new o-ring (on its way in the post) for the tip of the primary regulator will fix the residual pressure issue, and possibly also increase the system and control pressures a bit. At least this is a step forward!

Yomp - thanks for the advice and encouragement.

Lee

1986 GTI Cabriolet ("dambuster")

2000 Mk4 Cabriolet Avantgarde (bought for the mrs)

2001 Zafira 1.8

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A step in the right direction at last. :thumbs:  
Weird how the sparks started giving problems though. Is it possessed by something? :lol:

I'm no expert in K-jet but have learnt how it works over the years from badgering around with it. Once understood its simples!  :ninja:
I think the WUR I took off mine maybe suffering the same blocked gauzes. Its ages since I took them out of one. Is it done by removing the 4 screws holding the diaphram in place or do you flick them out the pipe hole you can see them from?

Regards your hot start issue, I know you have diagnosed it already but a test worth trying if required……
Does your pump prime when you switch on the ignition? Some replacement aftermarket fuel relays will only start feeding power to the pump when they see a signal form the dizzy. (The oem ones prime as soon as ignition goes live) So on the aftermarket one you have to be cranking to get the pump building pressure but at the same time your injectors are trying to fire fuel in so your loosing pressure which badgers up the mixture leading to poor starting. If it doesn't prime on ignition on then just flick the engine to start but don't hold. Just enough to make a signal at the dizzy so the relay kicks and the pump runs for a few seconds. Do this three or four times and then crank it to start it. You might find it starts a lot easier as you would have rebuilt pressure without losing it back out the injectors and get a cleaner start with a better mixture.

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Another hot start issue I've seen is when pressure falls too quick and the hot engine bay boils the fuel in the lines which causes difficulty starting when hot.

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Thanks.
My normal relay is an aftermarket that doesn't prime, but at the moment I have done rubjonny's relay swap with the relay right underneath it so the pump runs with the ignition.

I had removed the diaphragm in the WUR before I suspected a blocked gauze - it was the only thing left as everyhting else was so clean - even the diaphragm wasn' stuck to either of the plates. So i pushed mine out from behind with a pin, took a fair bit of pressure, and then it went flying about 2 feet! I suppose is might be possible to pick it out from the outside to save opening it all up. Splitting the gauzes was fiddly - I used the pin (pinched from the missus sewing box  :lol: ). Luckily I had read online that they are multiple layers or I might not have tried. There was a layer of debris between each gauze, but a spray of carb cleaner did the trick. I have left the gauge in place awaiting my o-rings. Plus I think I might have found a source of suitable shims if I need them - we shall see.

cheers

1986 GTI Cabriolet ("dambuster")

2000 Mk4 Cabriolet Avantgarde (bought for the mrs)

2001 Zafira 1.8

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One hot start issue I've seen is that during cranking, the voltage can fall too low meaning that the pump can't raise the pressure enough. It doesn't occur with cold starting because it fires the 5th injector to put some fuel into the manifold, and the 5th only needs just above 1bar to fire some fuel - the other injectors need the higher pressure.

Of course, as soon as the car is started the starter motor isn't spinning so the voltage recovers quickly.

So, have a look at the wiring to-from the fuel pump and also its relay, anything dodgy here can be the issue. And also look at the battery voltage during starting, starter wires, etc etc any weakness here won't help.

A good test would be to temporarily rig a wire to "fire" the 5th injector on a button, or something like that.

                                

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wow…. i've been having similar problems (try & have a look at my thread for all what's been going on)
i've replaced a lot of new parts, Coolant Flange, TTS, sensors, 5th Injector, Bosch Lead, dist cap, Rotor Arm, G13 water flush, Hoses, air filter out running while getting the air hoses 'flushed' with injection/air cleaner & cleaned out the meter box while running the engine… So one of the last things was to check the WUR my mate came to mine yesterday, so disconnected the WUR lead, on the WUR PINS this was tested at 22ohms - good, Wired the coil lead to earth, connected the reader to the connectors, then turned it over got 9.4volts which is good according to Haynes/Bentley, so this means the WUR is working. Prior to this I did a 5th injector test, which went well, similar connecting the coil lead to earth & turning it over… after the test i started it, my mate did say that it smelt 'rich'… so i've done pretty much all i can with renewing, servicing, gaskets, cleaning & it is running a whole lot better off start up - so it needs a tune! so after this i'm hoping it will be cold start sorted, it is a whole lot better!! running better too… I use super unleaded always & put Millers fuel cleaner in it quite often… had the tank/floater checked before… it's been a long process






 

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good progress! couple things to add:
the o-ring you mention between the fuel head and air flap assembly is just an air seal to ensure no air can get between the 2 assemblies. strictly speaking it wont affect the running as any air that gets thru here will still be metered as it'll come in before the metering head cone, but its unfiltered air which you dont want. The VW part number is 049133485A, its NLA but heritage ave stock:
https://www.vwheritage.com/shop/049133485A/o-ring-fuel-valve-air-flow-meter-mk1-2-golf-jetta/

with the fuel prime or non-prime, it makes no difference either way. when the system is fully functional the fuel pressure will build so fast when its cranking over you will notice no difference either way. the non-return valve and fuel accumulator is there to ensure you have fuel in your main feed lines up to the meterign head so the pump doesnt have to fill these up again on a cold start (as well as preventing fuel evaporation in the injector lines etc)

main issue you are left with now is the low system pressure, get that sorted and fingers crossed everything else will fall into place.

you also have the residual pressure problem but thats probably related to the metering head issues you have, since testing at the fuel filter outlet direct showed good residual pressure was retained.

Hello my name is John and I'm a dub addict.



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