hab dazu was bei den Volvo-Kollegen gefunden:
Quelle:
http://www.volvoclub.org.uk/faq/EngineFIComputer.html#ECUFuelPumpControlCircuitRepair
"ECU Fuel Pump Control Circuit Repair.
[Tips from Michael Craig] My 940GL with B230F and LH2.4 suffered from a secondary fuel pump relay supply failure, caused by faulty ECU. This problem apparently required a new ECU - VERY expensive. As I am an electronic engineer by profession, I do not believe there is such a thing as 'beyond repair' -atleast for electronics! After a lot of web searching, I managed to gather a small amount of information about the Bosch ECU. Armed with this and an oscilloscope, I was able to diagnose that the circuit within the ECU that controls the fuel pump relay had failed. Further research led me to believe this was a fairly 'standard' fault, as there are a couple of companies here in the UK who specialise in this particular fault, however the prices quoted for repair are still very high - in the order of £200. This motivated me to re-design the relay control circuit, the details of which I will share with you!
The pump relay control circuit functions as follows:
When the ignition is initially switched on, the pump runs for about 1 - 2 seconds, in order to 'prime' the fuel rail. If the engine is not started within that time, the pump must stop. You should be able to hear the pump running, so you can test this function by listening! If the engine is not started and the ignition left on, the pump will not run again (see next).
When the engine is started, the EZK ignition unit sends a series of pulses to the ECU, the rate of which is proportional to the engine speed. When these pulses start, so must the pump. This is how the pump control logic knows if the engine is either starting, running or stopped.
When the engine is stopped, the pulses from the EZK cease and the pump also stops. If the engine stops for any other reason, it must be assumed that the EZK will also stop, therefore so will the pump.
The 555 timer IC is operated as a slightly modified 'missing pulse' detector. Pulses from the EZK are used to hold the timing capacitor (22uF) in a discharged state. Should these pulses cease, the timing capacitor will charge through 390k and the timer output will change state, turning off the relay drive transistor BC140. The LED and 2k2 are a visual indication of the output state for testing purposes, and could be omitted. The 1uF capacitor ensures that the timer runs on power up, which gives the initial ignition on pump run. The transistor BC107 is really just a switch, and the zener 6v8 limits any spikes from the EZK.
It is possible to construct the circuit using stripboard about the size of a matchbox, which will fit inside the ECU, making a really neat repair. None of the components are particularly critical - most any transistors could be used, however the pump relay draws about 20mA. (This pump relay is actually part of a double relay - two relays in one case - often referred to as the 'LH Jetronic' relay). MOST IMPORTANT - Always disconnect the car battery before removing any ECU connectors. These ECU's are not well protected, and spikes will kill them.
ECU Missing Pulse Detector Workaround [Ed Pennings]
I have been able to test the self-built replacement fuel-pump-relay control unit in my Volvo 940 from November 1990. My car has the OEM Bosch LH Jetronic 2.4 part no. 0 280 000 595. The loss of fuel pump relay control is a well known problem of the Jetronic 2.4 with part numbers 0 280 000 59x. This replacement control unit is the size of a match box and can easily be built inside the ECU housing. I found out that I had to change a few components in order for the unit to function properly: pump on after contact on - then fall off after one second - then on again when starting and motor running (= obtaining pulses from the ignition unit) - and fall off when engine stops running while contact on (for example after a car crash). It is basically according to what Michael Craig wrote above but with a few adjustments. The unit is basically a missing pulse detector. My Volvo is running OK now with the fix installed inside the original Jetronic."