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Thread: Huge Disco misfire problem

  1. 6th April 2007, 07:07 PM #1
    muddy69 Guest

    Huge Disco misfire problem

    When the engine is cold, it runs reasonably well, but as the engine warms to running temperature, it develops a chronic misfire. Have been unable to rev beyond 2800 rpm which thought only occurred when moving, but I have since discovered happens all the time. If I rev it with the clutch in, it will reach about 3000rpm and then cough, splutter and drop the revs back. Last night noticed that it had a split small air hose coming off the plenum and repaired that thinking I'd solved my problem, but I didn't. The Disco can bearly get up to 100km/h on freeway before it wants to die.
    I have had MAF replaced two years ago, new plugs 12 mths ago, new stepper motor 12 mths ago and new fuel pump also. I run premium fuel and my filter will need to be replaced (170k kms on clock and possibly the original one still fitted).
    Can anyone assist with the correct location of the fuel pump relay which RAVE tells me is inside the drivers kick panel, trouble is I don't have the same coloured wiring to identify it on my 94 Disco. Has anyone had similar problems and any possible suggestions to remedy a chronic misfire..?
    TA
    Muddy.
    94 V8i Disco Series One.
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  2. 6th April 2007, 07:24 PM #2
    4bee's Avatar
    4bee
    4bee is offline Cynical Moi?
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    My immediate reaction was a restricted fuel filter, or possibly a restriction in the lines, causing it to starve when you get the speed up & it needs more fuel.
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  3. 6th April 2007, 08:41 PM #3
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    Blknight.aus
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    hows the leads, coil/coil packs, dizzy cap look?

    it might be breaking down at higher rpms, with so little difference between max loaded rpm and unloaded rpm Id be less inclined to blame the fuel system and more so the electrics.

    what pick up system does the engine have?
    Crank angle or Cam angle sensor?
    Hall Effect?
    Optical?
    Magnetic?

    Dirty or damaged parts in any of these can give funny running at higher RPMs but still be ok enough lower down in the rev range.
    Dave

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  4. 6th April 2007, 10:28 PM #4
    muddy69 Guest
    Not sure about the pick up system. Will jump and have a look tomorrow. Has me stumped, but I'm inclined to think electrics too.

    Will pull the plugs, leads, dizzy tomorrow and have a gander...will post a reply asap as I need to tow soon and this is driving me mad...
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  5. 7th April 2007, 11:36 AM #5
    byron
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    Quote Originally Posted by muddy69 View Post
    my filter will need to be replaced (170k kms on clock and possibly the original one still fitted).
    .
    First off change that Fuel Filter........ then come back if there's still a problem.

    Fuel filters on the Disco 1 EFI V8's have to be changed at least every 4 years OR 80,000 klms whichever comes first.........so you should be on your 4th fuel filter by now! - not still the original!
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  6. 7th April 2007, 12:23 PM #6
    muddy69 Guest
    Thanks Byron..I'm in the middle of it right now. will then post any problems after wards
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  7. 7th April 2007, 01:24 PM #7
    muddy69 Guest

    Misfire problem resolved/Coil & Ignition Amplifier values

    Well thanks for the assistance with this one Byron. The problem was that the fuel filter was almost completely blocked..

    New filter in and she's running like new again....

    Just out of curiosity, I tested the Ignition Amplifier module (test number 4 in RAVE) and I got a reading of 17000 ohms. This is well above the manual specs of b/n 2000 & 5000ohms.

    I tested the resistance of the side terminals on the coil and got no resistance. Tested the resistance of the HT terminal to the side terminals an registered 7400 ohms...is the coil / ignition amplifier on the way out or am i within specs.

    I have no problems starting.
    Mudd
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  8. 7th April 2007, 01:28 PM #8
    muddy69 Guest
    Sorry, but I should thank everyone who said it could be the filter...
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  9. 7th April 2007, 02:17 PM #9
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    4bee
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    orry, but I should thank everyone who said it could be the filter...

    Fank oo.


    I found this out the hard way on my S2A. RAA Mech. said it was the Carb. Had transported to carb bloke. Carb bloke found the tank pickup was blocked with a coating. No, not POR 15. Some red stuff like jerrican liner.

    Gave identical symptons as yours.

    Good that it's fixed though.
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