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VS MISS-FIRE UNDER LOAD, POWER LOSS AT OPERATING TEMP.

Discussion in 'VR - VS Holden Commodore (1993 - 1997)' started by family fix it man, Nov 3, 2018.

  1. family fix it man

    family fix it man Member

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    Hi I'm a bit stuck with this problem.
    I have a bad miss-fire at about 2000 to 2600 RPM. Worse when hot. Probably needs a top end job, (slight oil in coolant, oil clean) but I can't afford that at the moment.
    Worse under load, seems to go away over 3000 RPM, but I don't want to have to rev that much.;)
    Manual V6, new fuel pump, new injectors, throttle body cleaned. (Fuel return line in tank has no clamp, as I couldn't get the fitting off to replace that one)
    Coils seem OK.
    I am thinking plugs or fuel, or CAS, or temp sensor, air sensor, but it runs fine at idle (bit of high idle though, then settles).
    Also starts missing after cornering, which I think points to fuel?
    Fuel filter done a few 100k ago, but I suspect it might have picked up some dirt from the pump change.
    No error codes. (was thinking of getting ALDL cable, but no codes with old paper clip)
     
  2. _R_J_K_

    _R_J_K_ Well-Known Member

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    Done any other basics like plugs? I've had a similar issue on one of my other cars fixed with new leads.

    CAS generally works or it doesn't, no in between. Temps sensor makes it drink petrol. Other common ones are coils and DFI module.
     
  3. family fix it man

    family fix it man Member

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    Yeah done the DFI and coils not too long ago.
    I am going to check and replace the plugs, leads are new (ish).
    I've done CSA before, and agree it shouldn't be that.
    Had thought in would miss all the time if it was the plugs, but they might be breaking down under heat/load?
     
  4. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    Pull the plugs and check the gaps. If over 1.5mm either close up the gaps (if the electrode and earth straps aren't to badly worn) or replace.
     
  5. family fix it man

    family fix it man Member

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    Yeah, I will do. I hope It's that simple.
    Also have a strange symptom, when I remove the fuel pump fuse, (to depressurise) the starter won't turn over. I remove the fuel relay and it will.
    Figure that one out?
     
  6. family fix it man

    family fix it man Member

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    Fuel consumption is normal, just the annoying miss when hot under load.
     
  7. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    You should always pull the relay for the fuel pump as it's a 2 way relay and it will power the fuel pump once the engine gets oil pressure.
     
  8. family fix it man

    family fix it man Member

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    OK. I'm sure the manual said pull the fuse.
    I'll use the relay from now on, but the starter should still work with the fuel pump fuse out, right?
     
  9. HSVBMW

    HSVBMW Member

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    Sounds like swirl pot,return line has def popped off if no clamp. If car has 1/4 of a tank of fuel or less fill above half say 3/4 and see if runs fine. If it does thats what it is. Not only under acceleration and cornering will the car starve for fuel but the pump will over heat and cut out and eventually die young. Swirl pot must be full at all times no matter amount of fuel in tank to keep supply and pump cool.
     
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  10. family fix it man

    family fix it man Member

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    OK, pulled the plugs and checked the resistance of the leads, (and the new injectors just in case.)
    Leads checked out fine.
    The old bosh plugs were sparking yellow, with gaps of about 1.7mm
    Cleaned (and set to 1.1 mm the plugs) the MAFS and it went like a dream for the test drive.
    However after we stopped for a swim (about 1/2 an hour) it was missing continuously on the way home.
    New plugs go in tomorrow.
    Dose anyone out there know if the MAFS will work better after a clean if it is on the way out? Or do they just give up like the CAS.
    I hit some bumps on the test, so not discounting the idea that the return line might be off, but it ran sweet on the test.
    Thanks for all the help.
     
  11. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    MAF certainly does work better when clean. Easiest way to check the MAF is to look at the little wires between the posts, they should be clean and shiny. If dirty/black definitely clean.

    The 1.1mm gap is really to small for an n/a ecotec, New plugs will definitely help.
     
  12. family fix it man

    family fix it man Member

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    OK thanks mate. The old plugs are going in the bin tomorrow. and I'll gap the new ones at 1.5mm as spec.
    I'll give the MAFS another spray too just for good measure.
     
  13. family fix it man

    family fix it man Member

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    No, it's not that as still missing with the tank full. Thanks for the info though .
     
  14. _R_J_K_

    _R_J_K_ Well-Known Member

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    If you've still go the old ones laying around I'd swap them on (provided they weren't causing issues before) as an elimination. Doubt it's your leads from what you describe but can't hurt.
     
  15. VS_Pete

    VS_Pete Donating Member

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    I run AC Delco Platinum plugs 1.1mm
    Part Number 19238475
    Cheap too.
     
  16. immortality

    immortality Home of the smoky breakfast Bacon! Staff Member

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    On an ecotec?
     
  17. jeepster

    jeepster Member

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    I had an Ecotec doing that (misfire under load) and it turned out to be a loose spark plug - i.e. no compression on one cylinder.
    However that also caused rough idle.
     
  18. VS_Pete

    VS_Pete Donating Member

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    Yes on the VS.
    From memory a VT supercharger ran the plug.
    So I got one to check length all was good so got 5 more.
     
    Last edited: Nov 5, 2018
  19. family fix it man

    family fix it man Member

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    OK, put the new plugs in, 1.5mm gap NGK was all SCA had .
    Definitely did help (new fuel filter too), more power.
    And cleaned the MAFS again.
    It ran smoothly, almost perfect for half an hour.
    The engine is missing constantly now. So frustrating, checked the leads in the dark, no visible leak.
    Relay CLICK sound near the rear of the engine? About 3 or 4 clicks after the engine is turned off.
    Any help ideas would be great.
    Vacuum lines maybe?? ?
     
    Last edited: Nov 8, 2018
  20. family fix it man

    family fix it man Member

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    Sorry yes. Ecotec.
     

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