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Thread: 98 D1 V8 bad fuel economy - 43.2L per 100km - vacuum advance?

  1. #31
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    Worth checking/replacing coolant temp sensor for the efi. Usually very low on power and black smoke when they fail. But if it’s not getting up to operating temp, will chew some fuel. I have half radiator covered in winter to get temps up, even after replacing thermostat. Also worth checking that tdc on balancer is true, mine is out.
    '93 D1 V8 auto
    '93 D1 200Tdi 2-door, ARB's, MD transfer, sill tanks, winch, 2"lift.......
    '95 D1 V8 auto......gone
    '86 V8 RRC.....gone

  2. #32
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    Hi guys,
    the fuel consumption figures that have been mentioned seem rather high to me. We have owned our '95 D1 V8 since 2012 and have averaged 18.9l/100km over the time we have owned it. Best figure was 13.8l/100 and worse was 31.5l/100. Does the OP have Rovergauge, its a useful bit of software for the D1. Also our car does have oxy sensors and did have cats as well. Cats are long gone. Unfortunately I've just been told to hurry up (we are going out) but google search and you may find some intering info from Mark (cant remember his last name) he's written a fairly good guide. Plus the good info here should sort it. I also think you should check the mechanical soundness as well.

    Cheers, James NZ

  3. #33
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    I got 52L/100km when the coil packs died on the D2 V8 so I'd say an ignition issue as others have said.

    Edit: Since changing the packs and leads it now varies between 13L/100km on long distance trips to 19L/100km towing a 2 ton trailer.
    Last edited by LRT; 15th February 2018 at 04:08 PM. Reason: more info
    REMLR Registrant No. 436
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    1976 RRC Suffix D
    1979 Series III GS FFR
    1980 Series III GS FFR with a Perentie RFSV tub
    1991 Discovery 1 3.5 V8 3 door
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  4. #34
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    Suck on it

    Remove the line from the manifold to the vac advance. Suck on it and hold the vacuum with your tongue. If it the suction holds it's fine and time a timing light tune.
    if not it's buggered and most the fuel in your tank will pour out the exhaust. Low power and rubbish sounding engine.
    careful of cheap eBay jobs when buying the new unit. I had 2 fail instantly.
    check all other vacuum leaks and ensure the manifold is connected perfectly to the MAF.
    clean the MAF with cleaner as suggested.
    economy should be down around the 16-18 litres per 100km.

    then ****fart around with all the other bits and bobs. (O2 sensors temp sense etc.)

  5. #35
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    Quote Originally Posted by Redfoxie View Post
    Remove the line from the manifold to the vac advance. Suck on it and hold the vacuum with your tongue. If it the suction holds it's fine and time a timing light tune.
    if not it's buggered and most the fuel in your tank will pour out the exhaust. Low power and rubbish sounding engine.
    careful of cheap eBay jobs when buying the new unit. I had 2 fail instantly.
    check all other vacuum leaks and ensure the manifold is connected perfectly to the MAF.
    clean the MAF with cleaner as suggested.
    economy should be down around the 16-18 litres per 100km.

    then ****fart around with all the other bits and bobs. (O2 sensors temp sense etc.)

    How is P I S S a swear word but not fart?

  6. #36
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    Quote Originally Posted by Rick1970 View Post
    Also worth checking that tdc on balancer is true, mine is out.
    What's the method for this?

  7. #37
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    Quote Originally Posted by twr7cx View Post
    What's the method for this?
    Dial indicator with extension to reach piston crown is the nice way.....

    I made up a dummy spark plug with a rod welded into it, just long enough to reach piston crown before TDC. Remove all plugs (just to make it easier to turn over), dummy plug in No1, gentlyeturn over with socket and extension bar, mark balancer when you feel piston touch, rotate opposite direction and mark again. Mid point between marks is TDC.
    '93 D1 V8 auto
    '93 D1 200Tdi 2-door, ARB's, MD transfer, sill tanks, winch, 2"lift.......
    '95 D1 V8 auto......gone
    '86 V8 RRC.....gone

  8. #38
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    Replaced the thermostat and gasket this afternoon. The temperature gauge now gets up to the half way mark.

    As a bonus I found the disconnected vacuum hose for the vacuum operated cruise control, reconnected it and the cruise control works.

    Next up when I get some time is to replace the vacuum advance unit on the side of the distributor < 98 D1 V8 - distributor vacuum advance replacement > and check/set the timing, idle and MAF.

  9. #39
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    Quote Originally Posted by twr7cx View Post
    My father recently purchased a stock standard 98 D1 SE V8 with 115,000km on it. He has a work car for Monday to Friday so it doesn’t get used much but we’ve found the fuel economy to be ridiculously high and testing confirmed it at around 43.2L for 100km. This is an issue both expense wise but also as the tanks range is so limited.

    So far I have changed all fluids (engine oil and filter, automatic transmission filter and fluid, transfer box, front and rear diff oils), changed the spark plugs (NGK standards gapped according to Rave), the air filter and replaced two ignition leads which had damaged plug boots.

    While there I found the vacuum line to the distributors vacuum advance to have perished at the boots and the suck test indicated that the diaphragm had an issue.

    A new vacuum advance unit is on its way, would this be the sole cause for such poor fuel economy? Or is there other areas that I should check? We are aiming to get it to a more reasonable 20L per 100km range which I think is reasonable...
    I'm running a bog standard Disco Two V8 4L automatic, cruise control, standard tyres. I run it on 98 RON, and get between 600 and 700 km's to the tank, this is driving at speed limits (including 110 zones) with a half roof rack, bullbar, load etc. 20l per 100kms seems a lot of fuel, I get around 15l/100km, and better if I'm just crawling around at lower speeds (say 80 km/h). I don't stand on the load pedal too much, unless I put it in sport to overtake a road train or something.
    It sounds like I have the same spark plugs etc, but I replaced all the leads a while back (pain in the ...., but you can do it by loosening a few bolts, having a diagram, and leaning over the motor - don't need to take everything apart).
    Good luck.

    I

  10. #40
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    Quote Originally Posted by twr7cx View Post
    Replaced the thermostat and gasket this afternoon. The temperature gauge now gets up to the half way mark.

    As a bonus I found the disconnected vacuum hose for the vacuum operated cruise control, reconnected it and the cruise control works.

    Next up when I get some time is to replace the vacuum advance unit on the side of the distributor < 98 D1 V8 - distributor vacuum advance replacement > and check/set the timing, idle and MAF.
    Just out of curiosity is the cruise control the same on the Disco 1 & 2 V8 auto? Mines a pain in the ... to set, have to hold it a while, at the speed, to get it to take at that speed. If I just click it on it sets itself about 7km/h lower ... any idea?

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