Mk1 Golf GTI Fueling Problem/Misfire/Lumpy

Discussion in 'K-Jetronic OEM injection' started by redwolf01, Jul 31, 2019.

  1. redwolf01 New Member

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    Hi Guys.

    I have been assisting a friend with his MK1 Golf GTI Restoration. Having owned it since he was 21 its been off the road in the garage for the last 20 years. We are now very close to completion after battling a number of electrical issues (ceramic fusebox related – PIN8 etc).

    Our problem now is getting it running ‘properly’, which we believe is a fuelling issue.

    The car is an unmodified 1981 1.6 8v GTI.

    As part of the rebuild we have installed the following new fuelling parts.

    · New Tank and Filler Neck

    · New Fuel Pump

    · New Accumulator

    · New Fuel Lines (Braided from the Quiff)

    · New Fuel Filter

    · New Injectors

    · New Fuel Pump Relay

    The remaining old/original kit:

    · Metering head, we have cleaned the best we can, and the plunger is clean and unmarked

    · Air Flow Sensor looks OK and moves freely

    · WUR – Cleaned the gauze filter

    · 5th Injector

    · All injector braided lines.

    I have tested fuel pressure as per Haynes and all looks good. With fuel pump running and an injector in a jar and lifting the sensor plate the fuel that comes out is ‘tizer’ (or iron bru) in colour. We assume that is old fuel/contaminant in the metering head and maybe other components not changed. We are running some Sea Foam cleaner through to see if that can help clear.

    So back to the problem!

    The car will start and idle though sounds like it has a slight misfire/lumpy and is hesitant when you blip the throttle. But it wont rev past about 2,000 RPM. We took it for a spin to try to get some fuel blasted through it, but it just baulks and misfires when you put your foot down and wont pull. We have tinkered with mixture but I don’t think it is too bad and looks ok with the old-school Gunsons Colourtune .

    This is where I will probably get my terminology wrong, but here goes. So, with head under the bonnet and car running I operate the throttle by hand and it has what I would describe as a two stage operation. Stage 1 just opens the first butterfly valve in the throttle body and it revs reasonably well here, but when I pull further and engage Stage 2 which opens the second butterfly valve for more air/fuel then the revs don’t really increase, it baulks a bit and I hear a strange sound from the air box which I assume is it trying to suck more air. It appears that when this is happening, for some reason the Air Flow Sensor Plate is not rising any further and therefore not pushing in the plunger and giving more fuel.

    To test the theory, I unclipped the air box and stuck my hand in… sure enough when I open the throttle the plate/arm does not raise any further. If I give it a hand and push it up the revs do raise… still misfiring but it will rev in stage 2 with my intervention. There does not appear to be any restriction/obstruction when I gently push it up, and the noise from the airbox would suggest sufficient vacuum.

    So in summary, it revs OK ish during Stage 1 of throttle opening, but when you go further its as if the sensor plate won’t move past the initial raising in stage 1.

    Anyone got any ideas/suggestions?

    Once we get it to run a little better, we will take it for a proper tune.

    While I am on, we also have an interesting conundrum with the ignition timing that might be related to the rough running. It is all statically timed, but I can move the distributer what I consider a significant amount without it appearing to change the engine tone/running. If I go too far then it struggles to turn over as it is firing on the compression upstroke. Is it normal to have such distributer movement with little perceived change in performance?

    Thanks for any help provided. Kev
     
  2. rubjonny

    rubjonny Administrator Admin

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    does sound like the fuel metering head is at fault, dirty fuel coming out of it isn't a good sign.

    if you remove the fuel metering head from the top of the air flap assembly does the flap move nice and free thru the full range of movement?
     
  3. redwolf01 New Member

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    Yes, with metering head off flap seems to move very freely. Even with it on it seems quite free until fuel is pressurised, I guess your pushing against the plunger which now has some fuel pressure. I will take it off and check again though, just to be sure.

    I am reluctant to split the metering head to clean as the rebuild success rate without leaking seems low!
     
  4. rubjonny

    rubjonny Administrator Admin

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    yeah thats correct, once the pump is running the fuel head is pressurised so will offer a bit more resistance when you try to lift flap. should still be smooth and not notchy

    agreed splitting the metering head isnt always successful, plus have to shop around till you find a seal kit for it. no guarantees it'll be salvageable either if its had grit thru it they're usually trashed
     
  5. redwolf01 New Member

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    This might be a stupid suggestion, but is there any value in blowing through the fuel head with compressed air gun, or is that likely to cause damage?

    Any thing we can soak it in to remove old 'jellied' fuel/sludge if there is anything in there?
     
  6. rubjonny

    rubjonny Administrator Admin

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    I cant see that doing a great deal, its already got fuel blowing thru it at 5 bar. maybe reverse the feed and return hoses and jump the fuel relay you might get lucky and have it blast out something inside causing a blockage that way. To do that loop a wire between in relay socket where the relay terminals 30 and 87 go. With it being an 81 the relay may still be on the fusebox, or it might have the VW recall done where the relay is relocated above the fusebox to prevent the pin on the fusebox burning out

    if you remove the plunger in the bottom then drop it upside down in a bucket of clean fuel or similar fuel safe cleaner you might get some results that way, main thing is make sure the outside is spotless first so as little dirt as possible comes off the outside
     
  7. redwolf01 New Member

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    Thanks for that. Relay was on the fusebox but Pin 8 was badly burned, so we moved the relay above fusebox and I made a 'VW Recall' Cable which works great.

    Will try soaking it. Cheers :thumbup:
     
  8. redwolf01 New Member

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    OK, I have taken the fuel metering head off the car to give another inspect and clean. Removed the plunger and all looks OK. I am now wondering if I can (or should) remove the plunger housing for further cleaning? It shows as a hex as if it screws in, but does it? Or should I leave well alone?

    I do not intend to split the head!
    Metering Head.jpg
     
  9. rubjonny

    rubjonny Administrator Admin

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    undoing that nut wont get you anywhere, the housing will only come out once the 2 halves are split unfortunately.

    have a read of this guide, its not too scary really the main thing is getting hold of a rebuild kit with all the o'rings etc inside. If you got that its just a case of split, clean, rebuild with proper sealant taking extreme care to get every last bit of grit out of it.

    might be worth having a look at the pressure control valve in the side if you can find a seal kit, 035198691 which includes new o'rings plus a new copper washer to seal the valve into the metering head. I've had a good look but cant find anything, but the kit includes 7.5mmx2mm viton seal, 3.9x1.8mm viton seal and A12x15.5mm copper washer

    if the valve has gone normally you would just get warm start issues, but its another thing you can remove and clean at the very least and another hole you can fill with carb cleaner or similar ;)

    another thing I just thought of, on the main banjo hose from the fuel pump some have a filter inside the bolt, which was apparently supposed to be removed at one of the service schedules. If this is still there it may be completely clogged by now, see if you can find a plain bolt. Or do what I did to get out of a bind and destroy the filter then pick the remains out. obj make sure you get all of the chunks of plastic out the bolt ;)
     

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  10. dubztubz Forum Member

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  11. dubztubz Forum Member

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  12. redwolf01 New Member

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    Thanks guys.

    I am delighted to tell you she is now running and pulling 1000% (if there is such a thing) better.

    We spent the weekend with the metering head soaking in paraffin and numerous treatments of carb cleaner and blast out with air. Reassembled and installed a pressure gauge and did a number of tests.

    System Pressure with Fuel Pump running was 5.2 BAR, with fuel pump switched off it dropped to 2.5 BAR and held for 15mins. So my view is that pressure is fine and no leaks.

    We then made up an injector test rig to check all delivered same amount of fuel, which they did. Injector Rig.jpg

    Put everything back together and did a bit of timing/distributer fiddling and it fired up and ran well. Took it out for a run and it is great, accelerated well and only the slightest of hesitations. So its now booked in for some fine tuning with CO2 and timing kit.

    Thanks for all your help. Thankfully we didn't have to split the head, just intensive cleaning, patience and some luck!

    Cheers Kevin
     
  13. rubjonny

    rubjonny Administrator Admin

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    Great news, I'll point someone else to this thread who is having similar issues :)
     
  14. jimmy2gti New Member

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    I get a permission error when im trying to download the pdf, if its easy i could get a drive link or so
     
  15. rubjonny

    rubjonny Administrator Admin

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