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:
     

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