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328 fuel injection

Discussion in '308/328' started by rizzo308, Jun 16, 2011.

  1. rizzo308

    rizzo308 Formula 3
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    #1 rizzo308, Jun 16, 2011
    Last edited by a moderator: Sep 7, 2017
    So i removed the air cleaner box today and found the plug into the fuel dist was unpluged car was running ok what is this plug for, any help much app.
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  3. Iain

    Iain F1 Rookie

    Jan 21, 2005
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    Not sure what exactly its called (fuel pump safety switch maybe?) but the effect of having it unplugged is that the fuel pump runs as soon as you switch the ignition on.

    Normally it will only run when the engine is cranking or running.

    Question is I suppose whether its been unplugged on purpose (because maybe the switch in the circuit is broken & so this is the only way to make the fuel pump run) or whether its just worked its way loose. You'll soon know if you plug it back in & try & start the thing. If the car won't run then the switch has gone (no idea where it is though!).

    If everything works OK with it connected then I'd just plug it in & leave it. It should have a little wire clip to hold it in place though (as do all the other similar connectors).
     
  4. mwr4440

    mwr4440 Four Time F1 World Champ
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    #3 mwr4440, Jun 16, 2011
    Last edited: Jun 16, 2011
    Someone pulled it. FOR SOME REASON.

    At least on my car there is NO WAY that terminal can come apart by itself unless it was completely broken into many little pieces.



    You pull it to make the fuel pump run, "charging/pressurizing" the fuel system w/o the engine running.

    I bet they were looking for fuel leaks and neglected to put it back together.

    I have used that technique when I changed out all my plastic injection lines.



    I am sure there are other reasons to "pull it" and am just not there in my education of all things Ferrari/Bosch yet.
     
  5. DGS

    DGS Four Time F1 World Champ
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    That connects to the "fuel pump safety switch" and is grounded when the airflow is zero.

    It's part of the fuel pump starting circuit.

    When you turn the key to "on", the power runs to the fuel pump starting relay (relay "s") coil, and is grounded through that AFM switch, causing the SPDT relay to activate.

    When you turn the key to "start", power from the start position is fed through fuse 9 to the activated position of the starting relay, which activates the regular fuel pump relay (relay "r").

    Once airflow moves the plate from its rest position, the ground lifts, and the fuel pump starting relay is deactivated, which feeds ignition power to the fuel pump relay.

    If the car stalls, the safety switch grounds, causing the fuel pump to stop, until you activate the starter again.

    Because this is a CIS system ("Continuous" injection), the fuel injection is squirting fuel into the manifold whenever the fuel pump is running (whether the engine is running or not).

    Having the injection squirting fuel into the manifold when the engine isn't running will very quickly build up a "mix" so rich that the car won't run (flooded). Not to mention a fire hazard -- especially in an accident.
    So you only want the fuel pump running when the car is running.

    Removing that connector is common to fault isolation on the fuel pump electrical circuits, but leaving it off isn't a fix -- just an iffy patch. Has the car flooded on you?

    And, as said, someone may have unplugged it for testing (e.g. CIS system pressure checks) and forgotten to plug it back in.

    If the car will only operate with that off, then either the safety switch is shorted to ground or misaligned, or F9 is burned out, or there's an issue with the fuel pump starting relay ("s").

    The underlying issue (if any) should be fixed, and the connector should be left plugged in.
     
  6. Iain

    Iain F1 Rookie

    Jan 21, 2005
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    Good explanation (as usual!) but my understanding was that you only get fuel to the injectors when the big brass coloured plate on the CIS is depressed (which it is by airflow when the engine is running & sucking air).

    Is that not the case & it is as you described? (i.e. fuel pump running = fuel all the way to the injectors regardless?
     
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  8. mike996

    mike996 F1 Veteran

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    #6 mike996, Jun 16, 2011
    Last edited: Jun 16, 2011
    THe fuel pump supplies fuel to the K-jet fuel distributer. The distributer supplies the fuel to the injectors as needed. THe distributer does not send any fuel to the injectors unless the engine is cranking to start or running.
     
  9. Iain

    Iain F1 Rookie

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    #7 Iain, Jun 16, 2011
    Last edited: Jun 16, 2011
    Under normal circumstances yes - because the fuel pump won't be running.

    But if you pull the safety switch connector on top of the CIS head (as above) then that will start the pump (with the ignition on).

    That pumps fuel round the circuit from the LH tank through the CIS & back to the RH tank.

    Question is: Does it also send fuel to the injectors? Or do you also need to depress the big plate on the CIS head to do that? (my understanding was the latter).
     
  10. mwr4440

    mwr4440 Four Time F1 World Champ
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    [if my memory has not faded]

    YES, you have to press down on the metering plate to get the fuel to flow from the FD to the injectors with the plug unplugged and the Key turned to POS 1.
     
  11. mike996

    mike996 F1 Veteran

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    "Question is: Does it also send fuel to the injectors? Or do you also need to depress the big plate on the CIS head to do that? (my understanding was the latter)."

    If the airlow sensor is in the zero position, which it is unless the engine is running or cranking, no fuel flows to the injectors. Now in this case - switch bypassed, ignition on - if you manually press the sensor plate down it will not (unless there is a malfunction) inject any fuel because the the kjet is being told by the microplex computer that the engine is not running - this is exactly the same function that occurs when the Kjet is told by the computer to cut off the fuel at X RPM to avoid engine damage or when the car is coasting down with the throttle closed. In all cases the computer tells the Kjet to put the sensor plate in the zero position so that no fuel flows to the injectors. In coastdown, with the throttle closed, once the engine drops to a predetermined RPM, the flow sensor moves back to the correct position so the car will idle

    I just learned some of this a few days ago after hitting the heretofore unknown-to-me rev limiter.

    Good info on Kjet here: http://www.dmcnews.com/Techsection/Bosch%20K-Jetronic%20Fuel%20Injection%20Manual%20-%20boschtech-12d.pdf

    Also the Bosch FI book by Probst is an excellent source of info.
     
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  13. Iain

    Iain F1 Rookie

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    Great stuff - and very useful. So, as you say, it seems that the Microplex over-rules everything if the engine is not cranking/running (except the fuel pump which can be started by just pulling the connector on the CIS head)
     
  14. mwr4440

    mwr4440 Four Time F1 World Champ
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    Mike,

    I am confused. So did I have it right or wrong?

    REALLY HATE giving out BAD info [if I got it wrong]. :(
     
  15. mike996

    mike996 F1 Veteran

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    #12 mike996, Jun 16, 2011
    Last edited: Jun 16, 2011
    Yes, it's a combination of the way the Kjet is designed AND the interface with the computer. How the Kjet interfaces with a computer is based on the particular car/system. The Kjet can function totally on its own and in a system with essentially no computer interface, the Kjet WILL inject fuel if the ignition is on, the pump switch bypassed, and the sensor plate pushed open by hand. But on the 328 it will not. Earlier FI 3x8's with digiplex ignitions may or may not function the same way - I don't know.

    "I am confused. So did I have it right or wrong?" If it's earlier than a 328 you may have it exactly right! ;)
     
  16. Iain

    Iain F1 Rookie

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    Hmm also slightly confused (or maybe not! :p) It occurs that the CIS head has only the one electrical connection - which is the one you pull to start the pump. So is it the case that this does "double duty" & also allows some kind of valve to open to allow fuel through to the injectors when the engine is running & the plate is depressed? But that this doesn't/ can't operate if the connector is pulled?

    Otherwise I am wondering how the Microplex can tell the CIS NOT to pass fuel through....?
     
  17. mwr4440

    mwr4440 Four Time F1 World Champ
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    #14 mwr4440, Jun 16, 2011
    Last edited: Jun 16, 2011
    :) '81 308 GTSi


    I feel a bit better ..... Should have read closer as he is talking about a 328. :eek:
     
  18. mike996

    mike996 F1 Veteran

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    Here you go, from the Bosch book:

    "The engine-speed information is provided by the ignition system. Inter- vention is via an air bypass around the sensor plate. A solenoid valve controlled by an electronic speed switch opens the bypass at a specific engine speed. The sensor plate then reverts to zero position and interrupts fuel metering."

    If there is "no" engine speed at all, the same thing happens - sensor plate goes to zero - no fuel at injectors.
     
  19. DGS

    DGS Four Time F1 World Champ
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    The fuel pump will keep the CIS system pressurized any time the pump is on.

    The safety switch shuts off the fuel pump when the plate is at "zero".

    Without that, the presumption that no fuel will be injected with the plate at zero is based on the cutoff pressure of the individual injectors -- that the injection pressure *out* of the fuel distributor will be below the injector cutoff.

    Presuming your old injectors cut off at the right pressure. ;)

    Note that the plate doesn't move very far between "zero" and idle ... and you're injecting fuel to the engine at idle.
     
  20. mike996

    mike996 F1 Veteran

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    "Without that, the presumption that no fuel will be injected with the plate at zero is based on the cutoff pressure of the individual injectors -- that the injection pressure *out* of the fuel distributor will be below the injector cutoff.
    Presuming your old injectors cut off at the right pressure"

    True, of course. The description of the system function is based on everything working as it is designed to. As noted, if the injectors are "leaking" at lower than spec pressures, then you would have fuel being dumped in the manifold when none is supposed to be.
     
  21. wolftalk

    wolftalk Formula Junior

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    #18 wolftalk, Jun 16, 2011
    Last edited: Jun 16, 2011
    can you elaborate on that?

    afaik, the injection ecu can only control the frequency valve. That can modify the pressures internal to the fuel distributor head - which in turn adjusts the amount of fuel an injector will squirt - but it can't do anything about the position of the air flow sensor plate.

    the sensor plate position is entirely dependent on the amount of air flow past it...or someone pushing it down manually. If ignition on but engine not running and you push down the plate, fuel will squirt out the injectors anyway...just more or less than normal since the frequency valve is not adjusting pressure.

    on the 328, there is a connection between the injection ecu and the microplex (ignition ecu). I don't recall ever seeing what it's for.

    my understanding is the purpose of the air flow safety switch is to shut off the fuel pump in the case of system failure. If a rupture of the fuel system causes the engine to stall, airflow will cease, the sensor plate will raise to it's stop, and the switch will cause the fuel pump to shut down so it doesn't pump the gas out of the tank through the rupture.

    disconnecting the safety switch is relatively harmless...assuming you don't burst a fuel line someplace.
     
  22. mike996

    mike996 F1 Veteran

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    "can you elaborate on that?"

    I don't think I can do any better...;) I'm just basically paraphrasing/quoting what the Bosch info states re the operation of the Kjet. I did phrase it incorrectly when I said no fuel goes to the injector (I knew what I MEANT but I wrote it wrong). As DGS pointed out, fuel is at the injector but it doesn't get injected into the manifold until the fuel distributer pressure is above the minimum opening pressure of the injector. That doesn't happen with the plate in the zero position and the plate won't move out of the zero position unless the engine is cranking/running - regardless of whether the fuel pressure switch is bypassed or not.
     
  23. Brian Harper

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    What is the mechanism for the computer to move the sensor plate? Hydraulic/fuel pressure or some kind of electronic actuator?
     
  24. DGS

    DGS Four Time F1 World Champ
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    On a CIS, the computer doesn't move the plate. The airflow sucked into the engine past the plate pushes the plate away from the rest position.

    CIS doesn't use electrical signals to control injection. It uses fuel pressure as a hydraulic control system.
    CIS with lambda uses a frequency valve to modify the pressure in the fuel distributor that gets metered to the injectors.

    The system is pretty bulletproof. But if it does go off, you have to check each component one by one by one. (Great MTBF, lousy MTTR. ;))
    And that big pie plate in the intake does tend to dampen the "revability".
     
  25. andyww

    andyww F1 Rookie

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    Thats correct, there is no way anything can move the plate except airflow. If the plate is moved and the pump is running, fuel will be injected. Any connection between the ignition ECU and injection ECU (USA cars only, others dont have an injection ECU) must be an additional controlling input for the injection ECU to supplement the lambda sensor. This connection would not be capable of shutting off the fuel as the injection has no electrically-controlled mechanism to do that, apart from turning off the pump.
     
  26. Bandit

    Bandit Formula Junior

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    Disabling the fuel pump safety switch can also help with the common fuel pressure accumulator failure. When the accumulator fails and the engine is hot the fuel can be forced back out of the system. This leads to vapor lock and difficult/impossible hot start issues.

    By pulling the plug you can force the fuel pump to run long enough to fill the accumulator back up and get fuel to the fuel distributor without having to crank the engine over for an excessive period of time.

    Unless your injectors are leaking or the sensor plate is misadjusted you shouldn't get fuel into the manifold unless engine is turning over and generating vacuum at the sensor plate. Otherwise the fuel pressure accumulator woudn't work; all the fuel would be pushed into the manifold once the engine was shut off.
     
  27. Brian Harper

    Brian Harper F1 Rookie
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    So this is not true? I've dealt with a few CIS cars, but I don't know all systems for sure. This is different than what I've experienced, I don't remember it from reading the K-Jet books I have, but I have limited experience.
     
  28. fletch62

    fletch62 Formula Junior

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    This is right, When the sensor plate is in the rest position the metering slits that feed the injectors are closed. If fuel is flowing with the plate in the rest position then there internal leaks in the fuel distributor. If you manually push the sensor plate down with the fuel pump running, the injectors will spray with the motor running or dead.

    Larry Fletcher
    CIS Flow Tech
    www.cisflowtech.com
     

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