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Thread: Missing, running rich and genrally crap....

  1. #1
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    Missing, running rich and genrally crap....

    1994 RR 3.9 V8, a few weeks ago started to develop a misfire, at first was only when stopped at lights in drive , it was also idling really low, say 500rpm, then it seemed to do it whenever it felt like, sometimes it would be fine, other it would do it, then it got worse, misses till about 2800rpm and sometimes is undrivable. It also runs really really rich, you can smell it and when you take of hard it blows a bellow of black smoke. I have replaced the spark plugs, the leads, the cap and rotor button, the fuel filter and the air filter is new. It doesnt fire on 6 and 7 (3rd right and back left cylinders from the front) I checked the timing and it was definatly way too advanced, it was about 6deg. (it supposed to be about 2) I havnte been running premium all the time, but now i think of it it seems to be better if i do use it. I am almost 100% sure it is a fueling issue, or becasue of me running lower octane fuel and the the timing so far advanced could i have possibly put a hole in a piston(s), a sticky valve, or it could be a computer or air flow sensor issue.

    Anyone have any ideas, I really need to fix this.

  2. #2
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    fault finding time...

    start out with a vaccume check, if the needles bouncing all over the shop its a sticky inlet valve or an inlet not closing. or an intermittant air leak.

    do a fuel pressure check, make sure that the fuel rails pressure is stable.

    then do a compression test, cold, then hot, then do a wet (one or 2ml of oil into each cylinder before testing) test and see what that reveals..

    one by one with the engine off disconect sensors and go for start, if its still hiccuping and farting around that aint the one, shut down, put it back together and go the next sensor


    nada?

    remove your injectors fit them on longer hoses and check their spray pattern.

    they all look ok?

    adjust the bleed air bypass screw and see whats what....

    something in that lot will make a difference and throw some light on the subject.
    Dave

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  3. #3
    mcrover Guest
    Vac leak, more than likely intake manifold, vac guage will tell you or try a bit of break clean while it's running may pin point where it's leaking.

    It will be running rich as the computer will be trying to compensate.

    Im not a rangie V8 owner and rarely work on them but I would have thought that 6 deg advance would be on the low side of normal unless you run huge compression but I dont know.

    I would try a vac test first and then do what Blk Knight said, the vac guage should tell you the most, whether it be gasket, valve or drop in comp.

  4. #4
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    My money is on the airflow meter.

    Next time it runs like that, try wiggling the Airflow meter plug and see if there is a change. I have fitted new plugs to them in the past to aleviate similar symptoms. The main reason for the failure of the pins in the plug is that the loom to the AF meter hangs unsupported and pulls at the plug, wearing or bending the pins in the plug.

    6 deg isn't enough, I would go to 9 BTDC as these are all 8.13:1 comp engines.
    JC

  5. #5
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    All good advice ^ ^ ^ & some may be prove to be necessary, but to possibly save you aggro & won't cost anything, try this........................
    Switch off. Remove Air Flow Meter multiplug & with some electronic cleaner spray, do the male & female terminals.

    Then, with pointy nose pliers, carefully give the male terminals on the AFM a slight twist so they are tighter when you replace the plug.

    Then, see how you go. You may be surprised.


    Ed. OOPS, Justinc. You posted while I was typing. Two great minds & all that shyte........................

  6. #6
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    Did you replace the rotor & cap with genuine lucas ones as i and other people have have trouble with them in the past. I put my old one back in till i got a new genuine rotor button.


    All the best Mark

  7. #7
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    Quote Originally Posted by 4bee View Post
    All good advice ^ ^ ^ & some may be prove to be necessary, but to possibly save you aggro & won't cost anything, try this........................
    Switch off. Remove Air Flow Meter multiplug & with some electronic cleaner spray, do the male & female terminals.

    Then, with pointy nose pliers, carefully give the male terminals on the AFM a slight twist so they are tighter when you replace the plug.

    Then, see how you go. You may be surprised.


    Ed. OOPS, Justinc. You posted while I was typing. Two freat minds & all that shyte........................

    ...And YOU editted while I was adding a quote! This means we are onto something....surely.

    JC

  8. #8
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    Did not word that post right ment to say i had trouble with non-genuine rotor buttons and dist caps. Put my old genuine lucas one back in and all was good again.

    Mark

  9. #9
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    bugger that means i'm totally wrong then ??

    Mark

  10. #10
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    My first thought is the ECU water temp sensor. If the computer senses the engine is cold it turns on the "choke", by enrichening the fuel vs air.
    This could quickly wet a plug or two.
    The injection diagnostic was published on this site aweek or so ago so perhaps search for the thread.
    Sometimes it can be just a bad connection on the sensor. Not sure on a 94 but on a 92 itis situated at the RH(drivers side) top front of the inlet manifold. It has two wires into an injector type plug.
    It should read about 200-700 Ohms at operating temp. If more that is the problem.
    Regards Philip A

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