Fuel Injection help needed
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  1. #1
    Real cars have hydraulics DoubleChevron's Avatar
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    Default Fuel Injection help needed

    Hi Guys,

    Grab a coffee, maybe some choclate and get rested, this is some heavy reading

    why won't my CX run ??

    Background: Over a month ago I degreased and hosed under the bonnet to clean it for a Road worthy, while I was rolling up the hose I heard the motor stop ... It hasn't run since ...

    I wasn't hugely concerned, I cleaned out the spark plugs tubes, checked the fuses ... Nothing.

    I noticed the car would run for a few seconds then stop... Over the next couple of weeks I bought some needle files and contact cleaner and have cleaned lots of spade terminals under the bonnet, I was sure as soon as I found the right dirty connection it'd run again (most of the spade connectors were just about green inside).

    No Joy, it wouldn't run. I found if I held the ignition in the start position the car would continue to run (and grind the sh!t out of the starter motor). I disconnected the starter motor, wedged the ignition into the 'start' position and moved the car into the shed.

    Cleaning as many connectors I could find solved nothing (I had several wires even drop out of there crimps on the spade connectors !!), so I hit the circuit schematics.

    I've now spent hours looking at the schematics and trying to find something wrong somewhere on the car with no luck at all.

    As the car will run with the starter engaged I have checked the circuit schematics, with the starter engaged the following

    happens:

    -the starter soleniod gets power
    -Pin 50 of big blue (the fuel pump relay) get power
    -Pin 4 of the injection ECU gets power
    -cold start timer gets power (unchecked, should run without this)

    So were giving the starter soleniod power to crank the starter, Pin 50 of big blue power so the fuel pump will run, and I'm guessing pin 4 is power for the injection computer so it'll let the car start.

    The fuel pump is running and can be heard turning off after the car stops (I even mechanically wedged the points of Big Blue closed forcing the fuel pump to be powered all the time) --The motor still cut out. This leaves only the power to pin '4' of the ECU being the difference between the 'start' and 'run' on the ignition as pin '4' having power.

    The problem is obviously something not getting power with the ignition in the run position.

    With the igniton wedged in the start position I started measuring voltages. Pin TD of Big Blue had 12volts when it doesn't with the igniton in 'run' position. Pin TD feeds power to Pin 1 of the injection ECU and pin B1 of the ignition ECU. I
    wondered if maybe Big Blue was playing up and if there should always be 12volts at the 'TD' pin of big blue. I ran a 12volt wire to pin TD holding it at 12volts permanantly. The car still stopped as soon as I let the ignition key off of the start position.

    I started checking the 'run' position wiring from the schematics. There should be:

    -12volts at Big Blue pin 15 (yes)
    -12volts to pin N11 of the injection ECU (yes)
    -12volts at the injector relay (yes)

    The injector relays switches on and powers:
    -all the injectors (yes)
    -fuel calcutator (irrelivent, I haven't check this --for the onboard computer)
    -Pins 10 and 29 of the Injection computer (yes)

    Hmm, I seem to have power everywhere it's needed, why will it only run in the start position...

    Lets check everything else that'll stop it running:

    From the injection computer:

    --Pin 13 reads about 1000ohms to earth through the temp sender, this would be about right.
    --The air flow meter connectors at the injection computer (irrelivent, the car should still idle and run poorly without the air flow meter connected).
    --earch points at injection computer pins 16 and 17 look ok

    On to the ignition computer:

    --We have power at the coils
    --about 70 ohms at the computer plugs for the flywheel sensors
    -- the rest of the terminals are for tacho etc...

    I started the car with one HT lead off wedged where it would spark against the rocker cover. I wedged the ignition in the 'start' position and started the car on 3cylinders, I watched the spark as the key was allowed to drop back to the 'run' position, it continued to spark until the motor stopped. --this rules out ignition, the problem is with the fuel injection.

    What else can stop a motor (me clutching at straws):

    -- I removed and cleaned the flywheel sensors, swapped them over and put them back (no change).
    -- Pulled the cover of the injecion computer and checked for power at the circuit board (thinking that maybe there was a problem with the connectors) --all ok.

    The motor runs more smoothly than it ever has before with the key wedged in the start position (no doubt due to me fixing all the dodgy connectors and contacts). This rules out any vaccum leaks on the intake side screwing the mixtures up --it simply wouldn't run at any time otherwise. I've already checked the airflow meter to turbo pipes when i removed the aircleaner to check the wiring behind it.

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    Where to now ?? Buggered if I know, anyone else have any ideas ??

    seeya,
    Shane L.
    'Cit' homepage:
    Citroen Workshop
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    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

  2. #2
    Moderator Alan S's Avatar
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    If the car was the old coil & distributor type, it would be a blown ballast resister on the coil; that is exactly the symtoms they display.
    Find out what takes the place of that & you're home.
    Give Brad an e-mail and if/when he ever gets around to reading it, he should be able to tell you where to look straight up.

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  3. #3
    Budding Architect ???? pugrambo's Avatar
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    Quote Originally Posted by Alan S
    If the car was the old coil & distributor type, it would be a blown ballast resister on the coil; that is exactly the symtoms they display.
    Find out what takes the place of that & you're home.
    Give Brad an e-mail and if/when he ever gets around to reading it, he should be able to tell you where to look straight up.

    Alan S

    i'd have to agree here
    the car on starting gets the full 12v to the ignition and once started the resistor knocks it back to 9v, if the resistor i dead then you don't get anything or maybe just a small spark which is not enough for the car to run on

    just one thing you need only hold the key to make contact just before engaging the starter to achieve the full 12v to the ignition system unless the switch is like a pug and once released you can't re-engage the starter without turning the car all the way off first

    we did this once in a toyota with similar symptoms and drove it home this way as it wasn't too far to go and not having any tools was the simplest thing

    once the resistor was replaced all was fine
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  4. #4
    1000+ Posts Haakon's Avatar
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    might be a silly question, but is the ignition barrel OK? (also, did you hose off the engine with it running thats asking for trouble...)

    My ignition barrel on my R25 is starting to show its age - it makes the stereo go CRACK when i turn the car off, and whilst driving one night, the acc. circut cut out (leaving me with no stereo, indictaors etc). It simply has worn contacts and will need replacing.
    The barrel sounds like it has simply lost its contact for the ign circut in the run position, but still makes it in the start position (if I read all that right) I would try hotwiring the car at the 4 big wires that come off the barrel to test.
    I tried to drown my sorrows in alcohol, but the bastards learnt how to swim

  5. #5
    Real cars have hydraulics DoubleChevron's Avatar
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    Hi Guys,

    my grandfather already said immediatly "check the ballast resistor", it doesn't have one, the coils and powered and earthed through the ignition computer. There is still a nice strong spark at the plugs as the motor dies.

    I've ruled out the ignition as I have 12volts everywhere I should have 12volts with it on

    Anders has come up with some really good suggestions over on the QA board as well, time for me to work out what he's saying

    thanks,
    Shane L.
    'Cit' homepage:
    Citroen Workshop
    Proper cars--
    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/showthread.php?t=90325
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

  6. #6
    Real cars have hydraulics DoubleChevron's Avatar
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    IT'S FIXED !!!!!!!

    I was working my way through the earth points (again --thinking possibly I could have some earth loops happening) when I noticed the ABS relays under the wiring harness. While I was cleaning the extremely poor connectors on these I noticed a plug that wasn't plugged together properly. After fixing the broken spade connectors on one of the plugs under the spare wheel holder the plug hadn't plugged back together properly ...

    I plugged this together properly and the car was away again !!!!

    Now to work backwards and find out why the hell my best efforts didn't find this, after all I had all the right signals and connections at the computers and big blue :? I'll let you know what this connection was that prevented the car running that wouldn't show up with any testing

    thanks for all your help guys !!! I doubt I'd have ever got this fixed without your help

    seeya,
    Shane L.
    'Cit' homepage:
    Citroen Workshop
    Proper cars--
    '85 Series II CX2500 GTi Turbo I
    '63 ID19 http://www.aussiefrogs.com/forum/showthread.php?t=90325
    '72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
    '78 GS1220 pallas
    '92 Range Rover Classic ... 5spd manual.

    Yay ... No Slugomatics


    Modern Junk:
    '07 Poogoe 407 HDi 6spd manual

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