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Thread: intermittent problem 92 3.9

  1. #1
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    intermittent problem 92 3.9

    Hi. I have just about gotten to the bottom of all of the crappy electrical issues as a result of the head gasget replacement job.

    I have cleared all of the fault code, 21 initially (this car has oxygen sensors) and followed by 19 (TPS/airflow conflict), an 02 followed by a blank screen. Dashboard lights are now gone (oil pressure cable had been attached to the distributor) She now runs just as beautifully as when I bought her a couple of years ago, apart from 3 times in the past 3 weeks when I have lost power ( at sometimes awkward moments) and the car has stalled after a real struggle with idling. Strangely on all three occasions she has started up again fine after a minute or two.
    I am suspecting coil/amp unless anyone has another idea?
    Where should I start?
    Cheers in advance.

  2. #2
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    Bigdog how are you?

    It sounds like you had a real amateur working on Max.

    You should know that the car has a special amplifier (Hitachi?) which was specified by Unichip. If you need a new one contact Graeme Cooper. It is located under the air cleaner at the back of the LH flat section of the mudguard.
    The coil is a 717 solid state and you have a spare in the bits I gave you.
    however I doubt that this is the problem.
    The TPS conflict may be an old code as for some time the TPS wires were disconnected as the join in the wires had separated. This may have happened again with the mechanic. They had to be lengthened to fit the position on the Thor manifold.
    The test is whether the injection cut off works over 1500RPM. As you know by a previous question it is quite noticeable. If the TPS is reading correctly the injection cutoff will work so give that a check.
    Maybe there is a fuel pump problem or simply that the fuel is old and has absorbed some water.
    Regards Philip A

  3. #3
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    It might be the fuel pump wiring, I've seen quite a few failed connectors over the years. One connector is on the pump housing and one is above the rear muffler. Carefully inspect each for blackened nylon around the pins and repair/replace as appropriate. Also worth checking the MAF connector plug and maybe borrowing a good known MAF.

  4. #4
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    Quote Originally Posted by PhilipA View Post
    The test is whether the injection cut off works over 1500RPM. As you know by a previous question it is quite noticeable. If the TPS is reading correctly the injection cutoff will work so give that a check.
    Maybe there is a fuel pump problem or simply that the fuel is old and has absorbed some water.
    Regards Philip A
    Thanks Philip. Injection cutoff is now very noticeable now that I have cleared the other errors so this would suggest the TPS is good. Contaminated fuel, maybe? Each event has been during or immediately after an incline so maybe heavy water moving towards the fuel pickup point in the tank?
    I will recheck the TPS wires as I did see a hint of bare copper on that connection. I also found that the wiring for the Fuel Temp sender had dropped onto the exhaust manifold and melted the outer sheath. Does extreme heat play tricks with electrical signals? I didn't see any copper to metal contact but it could be hidden by the charred plastic?
    Thanks again.

  5. #5
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    A little bit of a pattern is forming here. The problem has happened for a fourth time now, and in exactly the same location as the first event, and after a similar trip duration. I have refueled 3 times now from different servo's so since the first incident so I will rule out fuel. I checked the wires to the pump and all looks ok.

    The scenario is: take the car for a good run, 30+ kms so it is at full operating temperature. Stop and take a break i.e. sit and wait for the kids coming out of school. Start again, travel for another 10-15 kms at reasonable speed (80kms hr) so again the car is at full operating temp, and then coming to a junction on a trailing throttle, and once revs drop to below 1500rpm, the engine starts to splutter and misfire badly. This just happens to be on a slight incline but I am ruling this out. The engine then dies.

    Pull over to the side of the road, wait for the car to rest a little (I was going to say cool down but at this point the temp gauge is still rising from the heat soak) for 2,3,4 minutes. Start the car again and ....Bingo.....back to normal running for another week!

    I am not sure if I saw a whisp of smoke this time? I have a slight coolant drip into the valley and when I pull up at lights in the dark with the headlights on I get some steam moving forward from the engine bay and into the light beams so it could have been this. There was no electrical or burning smell but I do have a flickering Washer Bottle fill warning light that flickers on/off at its own free will (hit a bump and it goes off) so I do have a wiring issue somewhere.

    Any suggestions before I start dismantling the inlet manifold looking for wiring faults? I am currently traveling approx 350 kms a week and I have done 1400-1500kms since the first event so this is not a frequent event.

    Cheers.

  6. #6
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    Similar to mine early on in the piece.

    Hi. Bigdog,
    Your Disco's issues are similar to what I experienced initially, then it got progressively worse, took me 18 months and a lot of trial & error to pin down.
    In my case it was the coolant temperature sender unit that communicates with the ECU, it is the one that has an electrical clip the same as your fuel injectors.
    Be sure that you purchase the Britpart replacement where your socket goes onto the metal housing as the Lucas replacement goes onto a plastic part of the sensor which created challenges (the Lucas ones had an issue where the plastic would just spin when you torqued it up).
    Good luck.
    Lee

  7. #7
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    Thanks Lee. That would make sense as it was the coolant cable that was left sitting on the exhaust manifold after the head gasket job. I have a spare sensor but i now suspect the cable.

    The pattern was broken yesterday as the car stalled whilst idling in a traffic jam on the way home from work yesterday. I will check the cable today.

    Cheers

  8. #8
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    As a check I ran the car with the fault code reader attached until the next incident and came up with a Code 19 again:

    Code 19 - Throttle potentiometer input low/airflow meter high. Usually indicates a problem with one of the two mentioned parts. Refer to tests 17, 18, and 19 of the continuity test procedure.

    Can anyone let me know what the Continuity tests 17, 18 and 19 are please? I have a spare MAF (3 actually) but not a spare TPS so will now try and get one as a spare - any suggestions on the best source for one of these?

    Cheers.

  9. #9
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    Code 19 - Throttle potentiometer input low/airflow meter high. Usually indicates a problem with one of the two mentioned parts. Refer to tests 17, 18, and 19 of the continuity test procedure.

    Have a check on the TPS wires ,as I had to lengthen them to fit the Thor. I crimped and shrink wrapped the joins but a ham fisted mechanic could have disconnected one.
    BUT this is not the cause of your problem as I ran the car unknowingly for about 6 months with no TPS and it ran fine except that I had no injector shutoff at 1500RPM. In any case just take notice of whether you still have injector shut off.
    It could be the MAF but once warm the MAF is really secondary to the 02 sensors.
    I would be carefully checking the wiring loom that goes across the back of the engine to the washer bottle and to the coil/MAF and ignition module as you have had a problem ( with the washer level light), with emphasis on the connection of the wire that goes to the coil/igniter that tells the ECU the engine is running. It comes off the MAF sub loom.
    The "mechanic" I think has a lot to answer for.
    Regards Philip A

  10. #10
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    Seems mechanics have to double as electrical engineers these days Philip,
    with a dose of electronic engineering to boot.

    cheers, DL

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