Fuel pump relay, perhaps an interesting alternative at EUR 2.65?

  • The fuel pump relay is always an exciting topic and although mine is still doing its job well, I'm always interested in reading here and trying to think of alternatives. After a lot of research, a combination of this circuit (around EUR 2.65) and a standard relay might be a replacement (with a bonus effect for anyone without an intank pump or general warm start problems):

    1. as I understand the original relay correctly, it needs the intermittent signal from terminal 1 of the ZSP (or from the distributor) through the induction sensor. If the engine stops (in the event of an accident) and the ignition is switched on, the CP should be switched off.

    2. the circuit above switches on a consumer (in the diagram a small lamp, in our case the control winding of a standard relay) as soon as it is supplied with power and switches it off again after an (individually adjustable) time (0-60 sec) (regardless of whether the circuit is supplied with power or not (I think this depends on the capacitor mentioned).

    pff.de/wcf/attachment/1011651/

    3. since the signal from terminal 1 is a continuous ON-OFF-A.... the circuit is "restarted" again and again and the load is constantly supplied with current (as long as the "countdown" time is longer than the switching cycle of the distributor signal).

    4. if the motor stops (or is switched off), the "countdown" timer switches off the KP relay and thus the KP. Just as it should be.


    (Presumed) bonus effect:

    Since I've been without the intank pump for about 1 year and thus had no problems with cold starts, I had to realize that the warm start occasionally took place with initial hiccups: does not run immediately on all cylinders (after a few accelerator pedal strokes everything is smooth again). I think the intank pump is missing here in order to build up the required pressure immediately. The circuit could solve this problem in that the CP would run according to the set "countdown" time when the ignition is switched on and then switch off. This would build up pressure in the K-Jet in advance.

    Note: My Benz with D-Jet has such a function built into the analog electronic control unit: When the ignition is switched on, the KP runs for 1-2 sec.


    The relay integrated in the circuit can handle a maximum switching current of 10 A, presumably the current consumption of the KP is higher, in which case a standard relay must be connected downstream and take over this part. Whether there is a 4-pole standard relay that fits into the relay plate and whether the wiring can be modified accordingly, as well as the location of the circuit, remains to be seen...

    I'm curious what you think of this... if it's nonsense, please let me know carefully, I'm not an electronics engineer...

    LG

    Sven

    This post has been automatically translated.

    Mercedes Benz 250CE AUTOMATIK /8 :pfeil: "STRICH(8)ER", 1970 das Pensionsauto meiner Großeltern, Lenkradautomatik, Schiebedach, elfenbeinfarbenes Lenkrad ...
    Porsche 924 2.0 Liter, Sauger, Transaxle :pfeil: "TRANSE", 1982 hat sich Muttern den Traum vom Porsche erfüllt ...
    Mitsubishi Pajero 2,5 Liter TD, V24, Pajero :pfeil: "WIXXXER" (auf Spanisch, dort wird der Wagen als Montero angeboten), 1991, Nachfolger meines Sahara-Pajero Serie 1
    Dieser Sammlung fehlt nur noch: Citroen "SM" ]:-)

  • Hi Sven, I see you have replied to my thread. In principle this could work, I just don't know whether the timer is restarted by the intermittent signal, because that depends on the assignment. If this only causes the relay to oscillate, we have gained nothing. So you would have to try it out. It is also possible that this control unit does nothing with a relatively high-frequency signal.

    Greetings Louis

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  • What I also just saw: How do you want to supply the relay with the terminal 1 signal? You can only energize the circuit, from this point on a timer runs. If you now connect the ignition positive, the pump will run after a set time. So again, nothing gained. If you connect terminal 1, it will never switch through, as the timer is always de-energized and thus reset. And the through-connection of battery plus is missing. The current for the pump must not run via the ignition switch, that is too much for it.


    PS: your attachment does not work

    This post has been automatically translated.

  • your attachment does not work

    here is the drawing of how the timer should be connected according to the supplier:

    and here how I thought about it in the circuit diagram of our 924

    Note: As the maximum switching current of the relay on the timer relay module is specified as 10 A and the original KP relay is designed for 30 A and the fuse protection is also 16 A, it is necessary to supplement the timer relay module with a downstream standard relay. In the drawing, I have converted the original KP relay into a standard relay (with 4 connections). Terminal 1 on the relay socket on the central electrics does not have a Visavis pin on the standard relay, but only serves as a connecting terminal for the green control line to the timer relay module. The supply line from the ignition positive to the standard relay is routed via the timer relay module.

    provided I understand the TSZ correctly:

    1. The ZS is supplied with ignition plus via terminal 15.
    2. The primary winding conducts the current from terminal 1 to TSZ terminal 6
    3. There, the connection to earth (terminal 5 on the TSZ) is interrupted internally by the signals from the induction sensor on the distributor in order to induce the ignition voltage in the secondary winding of the ZS.
    4. Originally, the fuel pump relay (terminal 1 there) is also switched through to earth via the connection to the ZS (also terminal 1). The circuit in the original KP relay is designed so that if this intermittent signal is absent, the relay is switched off.
    5. If the original relay were to be replaced by a standard relay, it would look something like the drawing from which I have deleted the symbol for the electronics and the coil in the relay would be connected directly to ground terminal 31 (brown connecting line)
    6. The standard relay would be controlled via the timer relay module, which would be inserted in the supply line before terminal 15 on the KP relay.
    7. Ignition positive via terminal C15 on the central electrics also supplies the circuit on the timer relay module, the "negative" side of which is connected to terminal 1 on the KP relay and ZS or terminal 6 on the TSZ via the green "control line".

    I just don't know whether the timer is restarted by the intermittent signal.

    I think so, because otherwise the thing would make no sense. I understand the text in the drawing to mean that every time the circuit is supplied with power, the relay is switched to continuity until the set time has elapsed, regardless of whether current is still applied to the circuit side or not. The process is restarted with every current pulse.

    If this only causes the relay to oscillate


    Of course, this would be pointless and would soon lead to wear. Therefore, the "holding time" of 1-2 seconds should be sufficient, as the frequency would be between 20 and 300 Hz

    It is also possible that this control unit does nothing with a relatively high-frequency signal.


    that would be conceivable, but it should be possible to find out...

    What I'm also just seeing is how you want to supply the relay with the terminal 1 signal. You can


    I hope I was able to explain this above and with the drawing and hope I didn't make a mistake in my thinking

    LG

    S

    This post has been automatically translated.

    Mercedes Benz 250CE AUTOMATIK /8 :pfeil: "STRICH(8)ER", 1970 das Pensionsauto meiner Großeltern, Lenkradautomatik, Schiebedach, elfenbeinfarbenes Lenkrad ...
    Porsche 924 2.0 Liter, Sauger, Transaxle :pfeil: "TRANSE", 1982 hat sich Muttern den Traum vom Porsche erfüllt ...
    Mitsubishi Pajero 2,5 Liter TD, V24, Pajero :pfeil: "WIXXXER" (auf Spanisch, dort wird der Wagen als Montero angeboten), 1991, Nachfolger meines Sahara-Pajero Serie 1
    Dieser Sammlung fehlt nur noch: Citroen "SM" ]:-)

  • Hi Sven,

    Maybe I'm misunderstanding you, but I think you're making a mistake. You cannot supply the timer with ground at terminal 1. The 555 (timer module) only works if it has continuous current. It therefore counts down from the time at which +12V and ground are applied to the connections. During this period, it switches the internal relay through. If you now supply the timer with +12V and power via terminal 1 (incidentally, a control line that should not be used for loads such as here), this will cause the relay to swing open. (because KL1 interrupts the power supply periodically.
    If I am wrong, please let me know.

    Regards

    Louis

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  • Hi Louis,

    but I think you have a mistake in your thinking

    that is quite possible.

    However, I conclude from the English text in the drawing and the information in the German description (above)"If you need to delay more than 60 seconds, the capacitors on the circuit board must be re-soldered." that when the circuit is switched on, the relay switches on immediately and the capacitors are charged according to the set time. The capacitors then keep the relay switched on for up to 60 seconds - even if the circuit is no longer supplied with power. In this case, only a touch pulse could trigger the timer. Perhaps one of the capacitors supplies the 555 for up to 60 seconds? And if you want the relay to stay on for longer, you need stronger capacitors.

    But maybe I'm misinterpreting the specifications... I'll ask the supplier... also because of the current consumption of the circuit with regard to the control line, whereby I assume that considerably more is dissipated from the primary coil through the TSZ

    This post has been automatically translated.

    Mercedes Benz 250CE AUTOMATIK /8 :pfeil: "STRICH(8)ER", 1970 das Pensionsauto meiner Großeltern, Lenkradautomatik, Schiebedach, elfenbeinfarbenes Lenkrad ...
    Porsche 924 2.0 Liter, Sauger, Transaxle :pfeil: "TRANSE", 1982 hat sich Muttern den Traum vom Porsche erfüllt ...
    Mitsubishi Pajero 2,5 Liter TD, V24, Pajero :pfeil: "WIXXXER" (auf Spanisch, dort wird der Wagen als Montero angeboten), 1991, Nachfolger meines Sahara-Pajero Serie 1
    Dieser Sammlung fehlt nur noch: Citroen "SM" ]:-)

  • Hi Sven,

    In conjunction with the potentiometer, the capacitors set the duration of the timer https://de.wikipedia.org/wiki/NE555

    Such small capacitors are never suitable for holding the relay and thus the control coil, they are only a few uF of capacitance. If the current at the input drops, the relay opens immediately.

    I have also read up extensively on the subject. Unfortunately, it's not quite that simple. I am currently designing a special circuit board.

    Greetings Louis

    This post has been automatically translated.

  • Such small capacitors are never suitable for holding the relay and thus the control coil; they only have a few uF of capacitance. If the current at the input drops, the relay opens immediately.

    If this is the case, then of course it makes no sense and I could have saved the letter I just sent to the supplier, but maybe they will suggest something else....

    The prospect of something ready-made and at the price was tempting...

    LG

    S

    This post has been automatically translated.

    Mercedes Benz 250CE AUTOMATIK /8 :pfeil: "STRICH(8)ER", 1970 das Pensionsauto meiner Großeltern, Lenkradautomatik, Schiebedach, elfenbeinfarbenes Lenkrad ...
    Porsche 924 2.0 Liter, Sauger, Transaxle :pfeil: "TRANSE", 1982 hat sich Muttern den Traum vom Porsche erfüllt ...
    Mitsubishi Pajero 2,5 Liter TD, V24, Pajero :pfeil: "WIXXXER" (auf Spanisch, dort wird der Wagen als Montero angeboten), 1991, Nachfolger meines Sahara-Pajero Serie 1
    Dieser Sammlung fehlt nur noch: Citroen "SM" ]:-)