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  1. #1
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    Default Back-firing when starting

    I get an occasional bang when cranking the car over and it's sometimes hard to start...iirc, the crank sensor was suggested last time I mentioned this.

    Any other ideas?

    wrinx
    My Q4 in the Garage

    www.alfaromeo155.co.uk ............................ □□□-V-□□□ .................................. www.ilmostro.co.uk

  2. #2
    mpampis_'s Avatar
    mpampis_ is offline Running smoothly
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    If the crankshaft's sensor doesn't work the car won't start. Most possible the camshaft sensor. Is it reving nice?

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    %100
    defective cam shaft sensor
    (cam shaft socket / cable)

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    Interesting, mine does the same. Sometimes it pops a bit and starts a second after you have stopped cranking it.

    Will clean up the plug and cable tomorrow and see if that makes a difference.
    Drivers:
    - Red 155 Q4 Winny
    - Red 33 16v
    - Green 33 16v SW
    - Mrs Wombat Freelander

    Projects:
    - Various Alfa 33s

    Awaiting a grand re-awakening:
    - Red 75 3.0 Cloverleaf
    - The Wombat winter Freelander

  5. #5
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    Quote Originally Posted by the wombat View Post
    Interesting, mine does the same. Sometimes it pops a bit and starts a second after you have stopped cranking it.

    Will clean up the plug and cable tomorrow and see if that makes a difference.
    Mine used to do that but not now...in fact it seems to have got a bit harder to start when hot.

    ...so it might just be that the wiring needs cleaning up???

    wrinx
    My Q4 in the Garage

    www.alfaromeo155.co.uk ............................ □□□-V-□□□ .................................. www.ilmostro.co.uk

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    The phase sensor on mine was replaced when I got it back on the road 8 years ago. It gave very similar symptoms!

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    Did it stop back firing...?

    Phase sensor being the Hall sensor on the right of the head?

    wrinx
    My Q4 in the Garage

    www.alfaromeo155.co.uk ............................ □□□-V-□□□ .................................. www.ilmostro.co.uk

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    Yes, and yes, that's the one.
    Could have been other issues too though. It was all a bit new to me then!

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    Typically...you can't get this from Alfa anymore

    p/n is 7689407 (previous 60809511).

    wrinx
    Last edited by wrinx; 02-06-12 at 18:58.
    My Q4 in the Garage

    www.alfaromeo155.co.uk ............................ □□□-V-□□□ .................................. www.ilmostro.co.uk

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    £400!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    http://www.ebay.co.uk/itm/Phasensens...-/350420677001

    wrinx
    My Q4 in the Garage

    www.alfaromeo155.co.uk ............................ □□□-V-□□□ .................................. www.ilmostro.co.uk

  11. #11
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    Thats got to be available elsewhere!!

    Unbelievable price.
    1994 Alfa Romeo 155 Q4: Dozeing in the garage.
    2009 Audi A4 tdi: Everyday drive.
    1994 Alfa Romeo 155 , 1995cc Std Standard Black

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    Agreed...although it's worrying that someone has bought one, perhaps they are really that hard to find

    wrinx
    My Q4 in the Garage

    www.alfaromeo155.co.uk ............................ □□□-V-□□□ .................................. www.ilmostro.co.uk

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    A fool and his money are easily parted!

    Do you have any idea who makes them?
    1994 Alfa Romeo 155 Q4: Dozeing in the garage.
    2009 Audi A4 tdi: Everyday drive.
    1994 Alfa Romeo 155 , 1995cc Std Standard Black

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    Fiat Coupe in a breakers yard would be my choice. It should fit I think.

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    Mine too...I have a friend who breaks Coupes

    wrinx
    My Q4 in the Garage

    www.alfaromeo155.co.uk ............................ □□□-V-□□□ .................................. www.ilmostro.co.uk

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    My car also back fire's when turning the starter. I have changed the cam's to more race spec. Do ecu need new parameter or Will this be correct when timing is adjusted

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    Maybe of interest - not sure about it working on a 16vT though.
    http://www.fccuk.org/forum/ubbthread...Number=1348499

  18. #18
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    Checked the connector on mine today. 2 pins of the 3 quite badly corroded. Cleaned everything up and on a couple of fire ups, seems to have instantly improved it, but will keep an eye over the next week.

    I was talking to my brother in law about the 155 24v V6 conversion I am just started on at present, as the 2.5 12v does not have a cam sensor, but the 3.0 24v does. I wanted to ensure that was not going to cause problems. Examination of the 2 different engine wiring diagrams reveals all

    Apologies if you already know this...

    The 156 V6 ECU (where my 3.0 engine originally was transplanted) has a pulse signal for each coil pack, and a signal for each injector. The 2.5 155 has a combined coil pack where spark plugs are paired up, and the same with the injectors. This means that the injection/ignition system only needs to know where TDC is because it injects and sparks every turn of the engine. On the more sophisticated later ECUs, the fuel and spark is only on the appropriate engine stroke (induction for injection and compression for spark), so the ECU needs to know when the inlet valve are open for injection, and when all valves are closed (for ignition), hence the cam sensor signal is needed as well as the crank position sensor.

    The cam sensor does very little (apparently it can help fine tune injection and ignition timing) when the engine is running. To prove the point, I disconnected mine when the engine was running and it continues to run fine. But, cam position is needed for starting to get injection and ignition in the right place (curse those 4 strokes!!).

    On the 12v V6, you get an injection pulse and a wasted spark every engine rotation for a given cylinder.

    So if the cam sensor is starting to mis-read, you will get the popping and banging when trying to start. Again, to prove the point I tried to start the Q4 without the cam sensor connected - exactly the same symptoms as in this thread, but with no eventual start.

    Interestingly, there can be similar symptoms if the earth for the engine is bad.

    Sorry if everyone already knew the above. I found it fascinating, and it was coincidentally part of the discussion on how to wire up the 24v V6 to the 155 V6 ECU.
    Drivers:
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    - Red 33 16v
    - Green 33 16v SW
    - Mrs Wombat Freelander

    Projects:
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    Awaiting a grand re-awakening:
    - Red 75 3.0 Cloverleaf
    - The Wombat winter Freelander

  19. #19
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    Thanks for that

    I'll check mine over as it's definitely getting harder to start, although a duff battery and dodgy alarm/immobiliser aren't helping

    wrinx
    My Q4 in the Garage

    www.alfaromeo155.co.uk ............................ □□□-V-□□□ .................................. www.ilmostro.co.uk

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    This is a timing problem and the phase sensor (hall sensor) controls it. It has a very simple architecture and very hard to break its internals. It usually suffers from overheated connectors and after some time passed they get crispy and very easy to get cracked, so the connectors usually don't work and we can see the engine backfiring especially on starting. Just check the cabling and go on.
    The Fiat Coupe 16V Turbos use the same sensor and can be found easily but usually price is very high. I have a spare of them and will change the whole injection system and replace the ecu if both fails... Some old versions of this engine (Other Fiats and Lancias) has distributor directly attached to there instead of this phase sensor for timing.
    Only Lancia Delta Evo II 16v, Fiat Coupé Turbo 16v and 155 Q4 is using this sensor on this planet. Maybe someone can find an alternative for the sensor inside of this part. Just open the 2 screws and you will see a cylinder cut horizontally about 1cm or less and a sensor creating a signal when this section comes in front of it. If we can find a replacement sensor for it it would be praiseworthy...
    1991 75 1.8 ie (Alfa Rosso) EX
    1996 155 Q4 (Alfa Rosso) EX
    1994 155 Q4 (Alfa Rosso) EX
    1990 75 Turbo America (Alfa Nero) EX
    1990 75 3.0 QV (Alfa Rosso) Rising from its ashes.

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    Check the earths as well. The tech discussion from my BiL seemed to go along the lines of:
    - Bad earth robs the ignition system of energy so weak or no spark
    - Once cranking stops, might get a good pulse that creates a good spark
    - If there is fuel, might be lucky and the good spark ignites it and spins the engine which runs, or might be unlucky and get a backfire
    Drivers:
    - Red 155 Q4 Winny
    - Red 33 16v
    - Green 33 16v SW
    - Mrs Wombat Freelander

    Projects:
    - Various Alfa 33s

    Awaiting a grand re-awakening:
    - Red 75 3.0 Cloverleaf
    - The Wombat winter Freelander

  22. #22
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    The earth cables don't make the ignition system suffer only starting engine. You can feel something going wrong at anytime you are driving your car and your car's electrical controls can act meaninglessly like the windows won't open etc...
    My car started to squirt water to screen without any effort while cruising and wipers didn't work
    1991 75 1.8 ie (Alfa Rosso) EX
    1996 155 Q4 (Alfa Rosso) EX
    1994 155 Q4 (Alfa Rosso) EX
    1990 75 Turbo America (Alfa Nero) EX
    1990 75 3.0 QV (Alfa Rosso) Rising from its ashes.

  23. #23
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    Quote Originally Posted by rumbler View Post
    The earth cables don't make the ignition system suffer only starting engine. You can feel something going wrong at anytime you are driving your car and your car's electrical controls can act meaninglessly like the windows won't open etc...
    My car started to squirt water to screen without any effort while cruising and wipers didn't work
    Very off topic but...

    Wiper earths etc are normally different earthing points to the chassis than the main engine block earth, which in most 90s Alfas was battery negative strap to gearbox. ECU was also earthed to the cam cover or plenum on quite a few cars.

    I reckon washers and wipers are likely to be a separate issue with a chassis earth.

    If the engine block earth is badly corroded/not making a good contact, it can be detrimental to a good spark when power is going through the starter motor. Worst case, if the ECU is earthed through the block and the main earth is faulty, might get some random ECU behaviour (never experienced that though). Correct that it is on startup, but the issue being described will be ignition related because of this.

    It can be replicated, loosen off the ECU and gearbox earths. If you suspect its happening, easiest test is a jump lead from battery negative straight to a clean part of the head to bypass the suspect faulty block earth.
    Drivers:
    - Red 155 Q4 Winny
    - Red 33 16v
    - Green 33 16v SW
    - Mrs Wombat Freelander

    Projects:
    - Various Alfa 33s

    Awaiting a grand re-awakening:
    - Red 75 3.0 Cloverleaf
    - The Wombat winter Freelander

  24. #24
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    If you take a look at the electrical pdf http://www.berlinasportivo.com/Techn...Electrical.pdf you can see just how many different earth points the 155/Q4 has. Some of these are in dodgy places susceptible to rust, so its always good practice to make sure you've got a good earth and connections before checking anything else.
    1994 Alfa Romeo 155 Q4: Dozeing in the garage.
    2009 Audi A4 tdi: Everyday drive.
    1994 Alfa Romeo 155 , 1995cc Std Standard Black

  25. #25
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    Bit more extensive testing today. No backfire when starting, but still takes a little bit of cranking to start when warm.
    Drivers:
    - Red 155 Q4 Winny
    - Red 33 16v
    - Green 33 16v SW
    - Mrs Wombat Freelander

    Projects:
    - Various Alfa 33s

    Awaiting a grand re-awakening:
    - Red 75 3.0 Cloverleaf
    - The Wombat winter Freelander

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