Digifant fuel pump & relay running when ignition on

Discussion in 'Electrical' started by carver, Jan 6, 2019.

  1. carver Forum Member

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    Hi all,

    I know fuel pumps running constantly with ign on usually points to a blown ECU but figured i would post a video to see if anyone had any ideas.

    The car has had a fair bit of welding done and the person that did it, had the battery disconnected but not the ecu - not sure if this could cause problems, seems daft leaving it on the car in hindsight?

    I've removed the cover from the fuel pump relay to see whats happening, literally sounds like its welding!
    https://www.dropbox.com/s/oslvau5n82oupze/video-1546787382.mp4?dl=0

    I've tried another relay and it does the same thing :(

    This doesn't happen with the ecu relay removed and the pumps work if i manually close the fuel pump relay..

    any help appreciated
     
  2. clarky1961 Forum Member

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    i live in north east england gateshe
    theres a short in there needs found bud if used mig or arc welders you get greef gas ok
     
  3. carver Forum Member

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    mig welder mate

    I've took fuse box out,all plugs look good that go to fuse box. Took fusebox apart can't see any obvious damage but it's hard to see past the top few tracks. Fusebox has got that wiffy electric smell to it not sure if that's normal though as they do get hot.

    I'll try another fusebox sometime and see if any difference

    Cheers
     
  4. rubjonny

    rubjonny Administrator Admin

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    swap 17/18/100 relay to slot 12 does it still do it? if not, then I'd say ecu is bust or wiring from it.

    have a good look at the ecu wiring though, there are 2 earth's for it one to battery and another to the cylinder head. to rule out ecu relay issue you can make a jumper wire like so:
    ecurelaybypass.jpg
     
  5. carver Forum Member

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    cool ill give it ago, i knackered the fusebox putting it back together :(

    hopefully i'll get time to go to scrappers or i'll have to pay ebay prices!

    Thanks
     
  6. rubjonny

    rubjonny Administrator Admin

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    same as mk3 golf so hopefully will be a couple in there you can rob one from. used on later caddy van and early 6n polo too so keep em peeled
     
  7. carver Forum Member

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    yer the one i've broke was from a mk3, been to scrappers this morning but was only mk4s and a few mk5s and all the polos had the newer boxes. There was 1 mk3 gti but it was locked away and i wasn't allowed to get to it when i asked about it.:(

    Regarding testing the wiring what would you recommend? I've had a look at the plugs at the fusebox side and all looks good as does the plug for the ecu.
    If theres a break/short in the wiring somewhere then if i do a continuity test on the ecu wiring, in theory i should be getting continuity on other wires when there shouldn't be?

    I've had the ecu apart and it does look mint, surely the ecu itself couldn't cause such a bad short at the fusebox without there being noticeable damage on the ecu motherboards?

    cheers
     
  8. rubjonny

    rubjonny Administrator Admin

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    1st check once fusebox is replaced is as I say, try a 17/18/100 relay in slot 12 and see if it still does it or not. That'll tell you if there's an issue on main fusebox power/earth or pump wiring. if it runs fine, then it can only be something on the ecu wiring side or ecu itself.

    next thing have a general checkover of all the ecu loom, look for dirty or loose earth connections to head and battery, make sure main battery earth to gearbox is good. unplug the ecu connector and the 5 pin plug next to the ecu, check pins are all straight, tight and clean.

    on the 5 pin plug female side with the original fuel relay fitted and ignition on, put an earthed wire into the red/yellow wire socket then the fuel pump should run. if it does plug the 5 pin connector back in and do the test again at the ecu connector pin 3. if that works fine then you know nothign wrogn with ecu connection to fusebox on the relay trigger.

    other ecu pins to check:
    1 - red/green - cranking live
    13 - brown - earth to battery
    14 - black/yellow - ecu relay power
    19 - brown/white - earth to cylinder head

    so for example with a multimeter between power pin 14 and the earth pins 13 & 19 you should see good battery voltage ignition on
    i21462.gif
     
  9. carver Forum Member

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    Thank you i'll do this once i get a fusebox on it.

    I've had a good look at the earths and they look sound. I'm getting earth continuity everywhere, body, block, cylinder,inlet and all back to neg battery etc

    I tried continuity testing the G1 plug at the fusebox end and found continuity on black wire and red/blk which go to the coil but i guess the coil should have continuity? I've ohm tested the primary circuit on the coil which is saying 1.4 ohms, Haynes manual says it should be 0.4 - 0.8 but not sure if mines high enough to be causing the issue i have. Once it's back together with the fusebox will the fuel pumps prime as they should without the coil connected? if so that's something else i can try.
     
  10. rubjonny

    rubjonny Administrator Admin

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    the fuel relay will still trigger fine with coil unplugged, the ecu power is separate from the coil

    coil is pretty far out from haynes spec yeah, is it a genuine bosch?
     
  11. carver Forum Member

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    ok cool i'll give that a go, the fusebox wasn't blowing any fuses even though it was shorting at the pump relay and the coil has no fuse so i'm hoping it's that but it probably wont be :lol:

    I replaced the coil about 6 years ago and only did a few hundred miles on it and the cars been stored and welded since then. I think i got it from GSF but not too sure, it's black with no label or colors.

    Cheers
     
  12. rubjonny

    rubjonny Administrator Admin

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    ok put the coil on the list of 'possible things to replace in future' but it wont be what's causing the fuel relay to buzz anyway
     
  13. carver Forum Member

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    Thanks RJ, i'll update once fusebox is back on and i've tried what you have suggested
    :thumbup:
     
  14. carver Forum Member

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    Update,

    Fusebox back on but still shorting/buzzing relay (coil disconnected)

    Tried putting relay 18 in slot 12 and no buzzing, earthing the 5 pin female at the ecu makes the relay turn on without buzzing.

    I've ended up taking the wiring out :lol:
    50257621_591104741317292_3026601270954688512_n.jpg

    I've tried another ecu and it does exactly the same thing.

    tbh it didn't take long to get the looms out and now i can have a better look
     
    Last edited: Jan 19, 2019
  15. carver Forum Member

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    Does anyone know what the voltage should be for the red/yellow wire on the G1 plug?
    With mine unplugged from the fusebox with the ignition on, test probe on the terminal for red/yell and other probe on the +battery it's showing 0.1 volt.
    With the fuel relay unplugged and G1 plugged in, the only voltage i can see present where the relay goes is 10.4volts.

    Battery is new and showing 12.7v, i get battery voltage at the main fusebox power connections.

    I'm at a loss on this now, i've tested all the wiring continuity wise as well as testing to see if the wires have any voltage drop and none do. The pins and plugs look ok on the ECU side also.

    What i don't get is why the relay is buzzing constantly with the ignition on when the ecu is only meant to be priming?

    I'm on a second ECU/amp now as well as fusebox so it must be the wiring but so far it all looks ok. I've been hoping to find a broken ground, weld splatter between two wires etc but nothing. Need to move the car soon and currently it's not looking promising for it [:v:]
     
  16. rubjonny

    rubjonny Administrator Admin

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    did you split the whole lot down to check for damage end to end, both the main fusebox bit and the ecu loom? its all covered in tape so thats not original for a start, though not in of itself a warning sign as if its a later car the looms would have been wrapped in cloth tape which will have rotted off by now so it may have just been taped up to repair

    if the fuel relay runs properly if you earth ecu pin 3 that pretty much tells you the wire from ecu to g1/3 is fine, though its possible theres a short between this wire and another in the loom which is tricky to track down unless you split the tape off and physically check the wiring end to end
     
  17. carver Forum Member

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    Pretty much, I've taken all the tape off the loom except for the loom that has the battery connections and main feed wires to the fusebox, I'm going to strip that too but i get battery voltage at the fusebox feeds and when the loom was in the car the lights worked fine. I've checked for shorts on the headlight plugs and removed the resistor thing.

    Essentially there's 3 looms isn't there, i haven't found any bad looking wires at all other than the earth for the ECU looks to have some rust going on so i tried running another earth from the ecu plug to the neg battery post but it didn't make any difference.

    I've also tried "turning" the ignition on at the red plug (H1) just incase there's a problem with the wiring that goes to the ignition switch and but same thing.

    The only thing i haven't tried is a different battery, battery is new from GSF and shows good voltage and as i say it ran the lights fine so i highly doubt its anything to do with the battery but it's something i'll try when i next connect the looms up on the floor again :lol:

    These looms are hard to get now aren't they, all on ebay currently look shite and expensive for what they are. Probably easier to just do a 1.8t conversion than rebuild the looms but i need to concentrate on bodywork this summer so i need to find the problem.

    cheers
     
  18. rubjonny

    rubjonny Administrator Admin

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    Yeah 3 looms, headlight, main engine sensor/wiper and ecu loom. Earth wise theres main battery to fusebox, one in main bay section to head for the cluster and 3 more in ecu loom one to the head and 2 wires in the same ring terminal from ecu and spark module to battery negative.

    Its possible the battery is duff, when they go sometimes you see nice voltage without load but it drops right down once you put any kind of load on it. though saying that fact the 18 relay runs the pump fine kinda rules that one out...

    does the relay stop buzzing if you unplug the ISV?
     
  19. carver Forum Member

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    When i first realised the relay was buzzing everything was connected in the engine bay and although hadn't been ran for over 5 years it all looked pretty much as i left it. However the ECU relay wasn't where it should be, it was upside down in slot 5 iirc which also probably rules out it being the new battery as i think the relay was moved so that there was no buzzing when the ignition was turned on...There was no reason the fusebox area should have been touched really. (Car has been away from me for over 5 years)

    Now the wiring is out the car i don't have anything plugged into the looms other than the bare minimum:
    Battery
    ECU/Amp
    Fusebox (Live & Earth,G1,H1)
    ECU relay
    Fuel pump relay
    Earths connected straight to neg battery

    The most annoying thing for me is out of the 4 cars I've had that ran Digifant 2 I've never had this problem, in fact the priming of the fuel system was something that always worked even when i did a GT conversion in my mk3 polo and the wiring was a proper mess for a short while.

    Honestly I can't wait to hear the fuel pump relay click on for a second or 2 and then go off as it should, defo isn't a problem i expected to have and has kind of messed up my progress on the car so far.:cry:
     

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