Jetronic Not Priming Consistently
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Thread: Jetronic Not Priming Consistently

  1. #1
    Member flock's Avatar
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    Default Jetronic Not Priming Consistently

    G'day,

    In my series 2 205 when I turn the ignition key it doesn't prime first time, even if it has been sitting for a few days.

    My other car used to prime almost every time but this one takes a couple of on-off's with the ignition before you hear the pump prime.

    I've replaced the fuel pump with the one from the working car and tried different tachy relays.

    What determines whether the pump should prime or not? And would this be the reason the engine takes a few more cranks before it starts then my other 205?

    Cheers,
    Lach

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  2. #2
    Fellow Frogger! TassieExec's Avatar
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    Could be the fuel pressure accumulator which is next to the fuel pump as it's job is to retain fuel pressure in the system, taking a couple of turns of the ignition switch is not an uncommon problem in 505's, also check for fuel leaks, they would only have to be small to bleed of pressure.
    Regards
    Neil

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    Ok, I'm pretty sure power isn't applied to the pump unless either the engine is running; ie: pulses from distributor, or ignition switch is in 'crank' position... this is the purpose of the Tachymetric relay. So no 'priming' of the EFI in IGN position before startup.

    I would expect the issue may be the one-way valving in the pump or the fuel pressure regulator is defective and allowing the fuel in the fuel rail to bleed back into the tank when the vehicle is not in use or perhaps a leaking injector (not seating properly).
    Last edited by ng850; 8th September 2017 at 02:19 PM. Reason: added leaking injector... and I'm shit at proofreading!

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    My '87 GTi works like ng sez, no pumping unless the engine is turning, and it mostly fires up instantly.
    But my '92 Si always runs the pump for a second followed by a click under the dash when the ignition is turned on,
    but it doesn't start as quickly as the GTi...
    Makes no sense but that's how it is!

    *Get yourself a fuel pressure gauge and and start checking pressures all over the place.

    **My brain tells me the GTi fires up quicker because the intake charge only has to travel an inch or two to the intake valve whereas the Si charge has to travel about twelve inches to get to the valve. Go brain!
    Last edited by EvilElmo; 8th September 2017 at 02:32 PM.

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    The fuel pressure gauge is a good idea although it won't pinpoint where the leak is occurring if the pressure is dropping at rest.

    It might be time to get the injectors checked and cleaned since you have tried different pumps.

    Quote Originally Posted by EvilElmo View Post
    My '87 GTi works like ng sez, no pumping unless the engine is turning, and it mostly fires up instantly.
    But my '92 Si always runs the pump for a second followed by a click under the dash when the ignition is turned on,
    but it doesn't start as quickly as the GTi...
    Makes no sense but that's how it is!

    *Get yourself a fuel pressure gauge and and start checking pressures all over the place.

    **My brain tells me the GTi fires up quicker because the intake charge only has to travel an inch or two to the intake valve whereas the Si charge has to travel about twelve inches to get to the valve. Go brain!

  6. #6
    1000+ Posts PeterT's Avatar
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    S1-S2 Jetronic, S3 Motronic and the Si are all different, thus behave in different ways. Certainly the Motronic won't prime until the crank angle sensor sends a pulse, ie the engine is turning over. I suspect the Jetronic won't prime until the tachymetric relay gets a pulse from the coil. No idea about an Si.

    That prime function has nothing to do whether the fuel system is holding pressure. The car will just become harder to start if it's loosing pressure somewhere.

    '92 205 Mi16
    '90 Mi16x4

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    Quote Originally Posted by ng850 View Post
    The fuel pressure gauge is a good idea although it won't pinpoint where the leak is occurring if the pressure is dropping at rest.
    It will if you put it all over the place...

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    Quote Originally Posted by EvilElmo View Post
    It will if you put it all over the place...
    How does that work with Pascal's law?
    jaahn likes this.

    '92 205 Mi16
    '90 Mi16x4

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    Fellow Frogger! EvilElmo's Avatar
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    Just trying to help peter, I figure a fuel pressure gauge might help diagnose fuel pressure issues.

    *My bosch jetronic manual sez Jetronic pump is triggered by tachymetric relay which is triggered by the start position on the key.
    Motronic pump is triggered by the ecu via pump relay...
    Last edited by EvilElmo; 8th September 2017 at 08:38 PM.

  10. #10
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    Out of interest early Si has fuel pump relay under dash near ECU and in cars it is under the bonnet near to coolant bottle.

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    Member flock's Avatar
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    Wow this thread got a lot better response than I was expecting.

    I have already replaced fuel rail, injectors and regulator from the old "working car".

    Although now that you mention your GTIs don't often prime I suspect there was just leaks in my old car as it always reaked of petrol whenever I stepped into the garage.

    I guess the next question is why the old car engine started up almost instantly while this one needs to crank for a bit. It's not an issue but I am curious.

    Sent from my E6653 using aussiefrogs mobile app

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    Too many unknowns. State of the electrics/ignition/engine...

    Quote Originally Posted by flock View Post
    Wow this thread got a lot better response than I was expecting.

    I have already replaced fuel rail, injectors and regulator from the old "working car".

    Although now that you mention your GTIs don't often prime I suspect there was just leaks in my old car as it always reaked of petrol whenever I stepped into the garage.

    I guess the next question is why the old car engine started up almost instantly while this one needs to crank for a bit. It's not an issue but I am curious.

    Sent from my E6653 using aussiefrogs mobile app

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