K-Jet Experts - please help (latest update Pg 6!!)

I've had all 4 injectors out and directed into containers.  When I run the fuel pump manually and lift the air flap, I'm getting good flow.  When I leave the injectors out but refit the fuel pump relay and try to start the car normally, I'm not getting any flow from the injectors.

This is the bit that's really confusing me.  The metering head appears to be working as expected manually, but when I try to start the thing, I'm either not getting enough vacuum to lift the airflap and open the injector flow, or possibly the fuel pump is not maintaining pressure off the ignition switch.

Certainly an odd one and I can imagine how frustrating it must be!
How do you do know you aren't getting fuel when it's all back together? Just curious so it can be confirmed or ruled out.
You could pull the air filter out and try it, would be less restricted and possibly easier for the flap to lift if you had a dental mirror you might even be able to see it move.
Are you able to check vacuum as I suggested? Kind of a reverse compression test. Your compression would have to be really low to not move the air plate I would think.
How freely does the plate move manually?
Could the throttle be sticking and not opening? No, can't be that as on normal idle it would be shut anyway and only pulling air through the idle screw route.
I don't know enough about the fuel pump relay circuit to suggest anything there, but I thought it was a dead cut off so if all the safety paths aren't good then it (the pump) wouldn't run at all.
Not sure I'm helping really!

Cheers for continuing to try and help. I know the injectors aren't flowing during cranking because I've left all of them out and directing into glass jars and when I turn engine on starter, there's no fuel. I hear the system priming every time I turn on ignition.

I reverted back to the 16v WUR and adjusted the cold control pressure to 1 bar (according to Bentley manual at 10 deg it should be between 0.9 to 1.3).

There is absolutely no stiction or stiffness in the airflow flap or the metering head plunger, everything feels light & smooth.

I can't see any source of a vac leak, surely it would need to be a hell of a leak to prevent starting completely.

I've actually tried manually lifting the air flap while my wife turned over the engine on the starter but still couldn't get it to fire up.

This is one of those faults that's going to be something simple.
 You could try leaving the fuel gauge connected  with the tap open so you're reading system pressure and see what you get  when you try to start it with the relay in place. If you get system pressure doing that then surely the trouble must either be an air leak or the valve timing miles out and I'm not sure if that's possible.
When you crank it do you get anything at all?

Did a compression test, all plugs removed and cranked over with throttle fully depressed.

A bit low on the first round, but I put that down to the fact the engine hasn't run yet.
Cyl 1 = 130psi
Cyl 2 = 120
Cyl 3 = 140
Cyl 4 = 115

Put a teaspoon of oil into the plug holes and repeated:-
Cyl 1 = 160
Cyl 2 = 160
Cyl 3 = 165
Cyl 4 = 150

I ran the fuel system again with the relay bypassed, cold control pressure 1 bar. Then connected the plug, switched on ignition and control pressure rose to 3.4 bar. This appears to indicate the WUR is good.

I removed CSV, refitted fuel pump relay and cranked engine with the thermo timer switch terminals jumpered as per Haynes, no fuel from CSV at all.

I'm wondering if the fuel pump relay itself could be faulty, or a bad earth somewhere, which allows pump to prime on ignition switch, but as soon as starter is engaged it isn't actually pumping fuel? I guess I can try starting again but with the relay bypassed and pump running continuously, even for a brief test?

Sorry I was wrong in the last post, with the tap open you'll read control pressure not system, I suppose you could have it open and then briefly close it while cranking to see if system pressure is there.
 

Been doing loads of reading up on these problems. One thing I had read was that if the fuel pump relay doesn't see the Rev counter signal from the coil, the fuel pump will not run.

Just checked and when the engine is cranking over there is no sign of the Rev counter moving. I have the earth connection to the rocker cover, and there are 2 black wires to the coil 3-blade connector. What should I do next?

If it's any help on the coil I have a red/black and a green on terminal 1 and two blacks on terminal 15.
I've had a quick look at the wiring diagram in Haynes and the red/black does go to the fuel pump relay, the gear shift indicator control unit and then to the rev counter.
The green and one of the blacks go to the ignition module.
That's the limit of my understanding of it.

I've got continuity in the red/black wire from coil to the 31b relay connection at the fusebox.

I can't seem to get a stable resistance reading on the multimeter across the HT circuit. Could my coil be faulty but still giving a spark on engine cranking?

I've just read this through briefly. Have you tried cranking with the 5th injector into a jar to see if you get fuel out of it? It should start no problem on the 5th injector even if no fuel at the 4 main injectors. It'll only run for a few seconds mind.

Hi Graham, I have tried this with no success. I'm getting no fuel to any injector during cranking including 5th injector.

When I manually run the fuel pump and lift the air flap, I'm getting fuel. The system pressure & control pressure are good.

I'm thinking now I could have a dodgy ignition coil as the Rev counter isn't working so the fuel pump relay will not allow pump to run during cranking.

Doesn't the hall effect sender on the side of the dizzy provide the signal for the rev counter?

paceman said

Doesn't the hall effect sender on the side of the dizzy provide the signal for the rev counter?

I'm assuming cos I have spark at the plugs that the hall sender is ok, but the coil signal out to the fuel pump relay and Rev counter is not working. I could be barking up the wrong tree completely.

You could try this, at least it will prove where the trouble is.

for testing and/or to get the car working while you find one you can pop a 17/18 relay to the fuel pump socket. it will bring the pump on all the time with the ignition, if this happens and car runs fine you know the pump and wiring is all ok.  The only problem with this is the pump wont cut out if you crash the car, you'll want to get a proper relay asap

Electrical would kind of make sense given what you've seen with your guages.
Found this regarding rev counter signal:
Looking at the haynes wiring diagrams it does look like it gets its feed from the coil via the fusebox. A red wire from the fusebox connects to the rev counter terminal on the printed circuit board. It also looks like there is another feed from the printed circuit board and it certainly gets its earth from the circuit board also.

Not sure how you can easily test it though….

Following might be useful,

https://clubgti.com/forums/index.php?threads/fusebox-faq.219775/

I'd be checking coil -ve (black/red) to the FB - would guess the FP Relay takes this feed, and then it goes out to the rev counter.

J

I've got continuity on the red/black wire back to the fuse box to the small pin 31b connection on the fuel pump relay. So I'm thinking either the coil is sending out the signal or the relay is not staying energised.

I presume I would have to check for voltage at this relay connection during cranking to confirm what's actually happening 

ok so what you see at the main injectors is correct, no fuel should be injected unless the flap is lifted. make 100% sure there are no air leaks, check all the folds of the metering head boots, vac lines, idle screw o'ring etc.

if your fuel pump is running while cranking then you know the fuel relay is happy. if not, check the red/black wiring to the coil and make sure you have spark. if its a ce1 fusebox you can swap the 17/18 relay into slot 2 then the pump will be on all the time with ignition which will help while troubeshooting.

you need 5bar system pressure, to check that you run your gauge inline with the WUR line and have the tap closed.

your compression is a little low on the first test but the oil test is good. hopefully its as you say just need to get the car running and figures will improve.

if your 5th injector isnt working then this wont be helping at all, so next thing to do is get this fixed. you should have cranking live on the red/black wire, this is fed by the red/black wire in the 2 pin male spade plug near the fusebox, you should have a wire from the headlight loom C plug plugged in here. The green/white wire on this plug is left empty on UK spec.

the green/white wire on the 5th injector goes to the thermoswitch in the front flange and should be earthed while the engine is cold. to bypass the thermoswitch you can disconnect it and poke an earthed wire into the pin

rubjonny said

ok so what you see at the main injectors is correct, no fuel should be injected unless the flap is lifted. make 100% sure there are no air leaks, check all the folds of the metering head boots, vac lines, idle screw o'ring etc.

if your fuel pump is running while cranking then you know the fuel relay is happy. if not, check the red/black wiring to the coil and make sure you have spark. if its a ce1 fusebox you can swap the 17/18 relay into slot 2 then the pump will be on all the time with ignition which will help while troubeshooting.

you need 5bar system pressure, to check that you run your gauge inline with the WUR line and have the tap closed.

your compression is a little low on the first test but the oil test is good. hopefully its as you say just need to get the car running and figures will improve.

if your 5th injector isnt working then this wont be helping at all, so next thing to do is get this fixed. you should have cranking live on the red/black wire, this is fed by the red/black wire in the 2 pin male spade plug near the fusebox, you should have a wire from the headlight loom C plug plugged in here. The green/white wire on this plug is left empty on UK spec.

the green/white wire on the 5th injector goes to the thermoswitch in the front flange and should be earthed while the engine is cold. to bypass the thermoswitch you can disconnect it and poke an earthed wire into the pin

Have checked all the air and vac system and cannot see any splits or cracks anywhere, all new hose clips/clamps have been used and everything is secure.  The only bit I haven't checked is the idle screw o-ring.

I'm getting 4.9bar system pressure, swapped relay 17 into the FPR slot and the pump runs ok.  I still am not convinced the pump is running while cranking, hence my query over the coil signal, although I do have spark ok on all 4 plugs.

I've just checked the 5th injector again.  I'm getting cranking live of 10.6V with the thermo switch connector earthed as you describe (battery terminal voltage measured at 12.7V).  But when I reconnect the plug and leave the thermoswitch bypassed, on cranking the engine I'm getting no fuel at all from the 5th injector.  I guess I need to replace this before I can continue much further.  I guess the engine needs this initial jet of fuel to fire, which in turn allow the airflow meter to lift and engage the main injectors to keep the engine running.  So I'm missing the first stage in the whole process??  Is this logic correct?

Pistol - Do you mean you've tried to start it with the No 17 relay in place and it still won't go?