VW ABF trying to fire up with 22ms+ injector times SOMETIMES

Discussion in '16-valve' started by specr3, Sep 19, 2020.

  1. specr3 New Member

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    Hello all,
    first time posting here and English is not my first language so sorry in advance if anything is hard to understand..

    The car: 1995 G3 ABF (immo digifant 3.2) with stock Climatronic, that is fitted with a LPG injection system - other than that 100% stock from what I know.
    This is skipable
    February of this year, the car developed a rather interesting condition - it would idle smooth but first getting it to the idle (900-100rpm) and then going from there till 2000, would require me to jab the throttle very fast (as stupid as it is, the same that Jeremy Clarkson was doing to that RV in The Grand Tour). Above 2000 till 4000 ish it did run and I managed to drive the last 100kms of my trip like that.

    I couldnt get it fixed myself (plugs, cables, fuel filter, checking the vacuums, coil, temp sensor, relays, throttle position sensor), so during the Covid lockdown it was at my mechanics shop and they got it running with new crack position sensor (Valeo brand), fuel pressure regulator and a used ECU which had the immo disabled.
    Main problem
    Few months later (when travel was possible), I get my car and notice the current problem - sometimes, no matter hot or cold engine, it would require a solid 30-60s of cranking the engine for it to fire up with the result of strong petrol smell from the exhaust.

    Through the ODB and the LPG ECU diagnostics, I saw that whenever this happens, the injectors would slowly go from 22, 19 etc ms till 10 ish when the car goes to 500-600 rpm and requires me to press the gas pedal to go to normal idle speed (1000 ish for cold engine).

    Now, to exclude the LPG system out of this. Yes, the petrol injector signal wires are chopped and wired though the LPG controller, which enabled me to see their ms times in real time since the OBD is rather slow. Firstly the LPG controller to see these high injector times, would mean that the petrol ECU is sending them and secondly, I have tried with the LPG controller unplugged and the wires bridged - no difference, still refusing to start.

    At this point basically everything is checked/replaced except the wiring of the car.It has been scanned multiple times for erros and watched real time that the temp sensors read correctly. It does run sort of decent, but this long cranking would just burn my starter sooner or later.
    We tried new Hella crank position sensor since while cranking the RPM needle would either sit on 0, or swing between 0-200 or stay at 200 (different everytime) - no difference.
    The engine harness is hardened but the wires still look intact. The only known wiring problem is that once, while trying to get the fuse box back in its place, something behind it sparked.

    That's the problem, explained as detailed as I can.
    Any tips for where to look now are highly appreciated since I'm close to selling it and getting something D/TD (have enough of this electrical BS already).
     
  2. SwervinMervin New Member

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    Have you tried unplugging / removing the LPG system to eliminate that as a potential cause of your problems ? Checked the idle switch ? Seems that the problem is electrical or wiring related if you've swapped out all the other parts you mention.
     
  3. specr3 New Member

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    Yes, I made an adapter to unplug the LPG and run the car without messing with the wires. As I already said above - no change.
    About the idle switch, can I check it from the OBD diagnostics?
    Pretty much everything has been replaced or verified through the diagnostics that it works - TPS, ISV, IAT, coolant temp.. Have my doubts that the lambda sensor gets stuck sometimes but that shouldn't matter for trying to start it cold...
     
  4. rubjonny

    rubjonny Administrator Staff Member Admin

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    using the obd diagnostics, check engine speed while its cranking. if it doesnt go up, then crank sensor signal isnt making it to the ecu. on mine I had intermittent cut out and non-start, I found crank sensor pins were not fully seated in the ecu plug. pushed fully home and that sorted the problem.

    check the idle switch is working also, I had another issue where randomly the power would cut out and found my idle switch behaving very strangely. sometimes stuck closed, sometimes it would only show closed if it moved the throttle a mm or so off the stop.

    check the wiring to both the idle switch and throttle position sensors round the back of the inlet also, its almost always baked rock hard by exhaust heat and cracked all the way along
     
  5. specr3 New Member

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    I dont know if the OBD is just that slow or the signal is really missing - during cranking, the VCDS showed 3XX for about 5s cranking and when it first tried to fire up moved to 450. That's when the tach arrow moved above 0 for the first time too.

    The Idle switch appears to work since the value block XXXXXXXX, the forth digit was 0 when the throttle was closed and changed to 1 when opened it - that being said again it took a good few seconds to update in the program. Will check it with a multimeter later too.

    They are indeed baked but dont seem to be cracked or falling apart - will be on the look for a new engine loom or atleast a sacrificial one to get all the connectors and redo all the wiring myself..
     
  6. rubjonny

    rubjonny Administrator Staff Member Admin

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    ok so you can see that the engine isnt firing up till it sees a crank signal, if you have a new and good make sensor check the wiring from the sensor back to the ecu. also I was diagnosing a non-starting abf which had a new crank sensor but no signal. after removing it I found a chunk of old crank sensor stuck in the hole the previous mechanic hadnt noticed. pulled all of that out and replaced, problem solved
     
  7. specr3 New Member

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    I can rule out that option since I have the 2 previous sensors - the OG one (which the isolation is cracked/baked), the Valeo one and now in the car is a again brand new Hella.

    I'm waiting on a friend who also owns a ABF to come back in town. Then on his I will be able to configure my oscilloscope and test both his sensor and mine while cranking (have sort of extension made from a sensor wires and connectors that I got from a junkyard). If they behave similarly then for sure its either my ECU or the wires.

    What I truly don't understand is why its still pumping fuel when it doesn't see the crank signal? According to the repair manuals, it should turn off the fuel pump 1 second after it looses/doesn't see that signal. Could it be that it still opens the injectors while there is left over pressure in the fuel rail which would explain actually why it can never start on the first try of long cranking.
     
  8. specr3 New Member

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    So after 8 months of long cranks, a lot of money spent for parts ad labor, the car is fixed!
    What ended up being the fault for all this nonsense (hard start with petrol (rpm needle jumping up and down during cranking) and LPG system not working properly) was the brand new, Topran brand vacuum fuel pressure regulator. It was filling the vacuum line with petrol which then went into the intake there for the raw petrol smell. Ofc the engine will never start with low fuel pressure, and then the LPG system determines engine loads by the vacuum so that being messed up caused it to misbehave.

    Moral of the story is don't trust a part only because its brand new - cheap sh*t (the Topran was 12 euro) is cheap for a reason.
     
  9. rubjonny

    rubjonny Administrator Staff Member Admin

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    thats a fun littlew issue to track down, glad you eventually got to the bottom of it :)
     

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