have aproblem with a 769 fuel pump not working.I have run a bypass direct from the the battery and the pump then works. what are t5he most likely items that are at fault.Fuel pump relay./ The airflow meter is the hot wire type
I think you guessed correctly. The most likely item is the FPR.
cheers for that.Where does the fpr lurk on the 760, a 1990 model?
On our (LHD) cars the relay is on top of the tunnel behind the kick panel that is located over the passenger's feet and covers part of the side of the center console. It's the green one.
Cheers mike Iam wondering whether the fpr is at fault.The airflow meter is the hot wire system.Recalling messing with an alfa romeo which used a flap to detect airflow. This had set of contacts attached which during cranking were closed operating the pump(safety crash reasons) Things must be slightly different on the hot wire system. The distributor cap and rotor are knackered, which fits in with the owner saying it developed a misfire and then stopped. There is a sensor attached to no 1 plug. Would I be correct in saying this system uses this to detect enginecranking then engages the fuel pump.No spark at the plug, no fuel pump operation?
The fuel computer gets a speed signal from the ignition computer that tells it if the engine is turning over, then it engages the fuel pump relay which turns on the fuel pump. So if you have no primary ignition trigger, you will have no fuel pump by design.
The sensor attached to the no. 1 plug wire is the equivalent of the cam position sensor in the later cars - with the flywheel sensor only, the computers have no way of knowing whether a cylinder is on the power or intake stroke.
Sound like you should change the cap, rotor and wires, which may solve your problem. If not, look for ignition primary - pulsing at the negative side of the coil. Other common failure points are the flywheel sensor and the power stage. The power stage is the device that switches the high primary current to the coil and is mounted on an aluminum heat sink on the inner fender near the air filter box.
Hi mike no problem ,so it looks like the fpr might be at fault?I get a very good strong spark straight from the coil ht to a ground. the owner says it started misfiring,slowly getting to a stage where it wouldnt start at all.Could the distributor cap and rotor arm failing, have in some way caused damage further down the system causing the no run fuel pump.(I checked for fuel pressure with a gauge on the line taken straight off the fuel pressure regulator,zero psi) The owner has agreed to go and purchase a new cap and rotor arm,fit them and then try with the fuel pump bypass I have jury rigged. But it is only powering the external pump.
If you have spark, but no fuel pump, then it's a high probability that it's the fuel pump relay. It also could be the circuit that turns the relay on inside the fuel computer, the fuel pump, or the wiring to the pump.
hi mike would the fpr be the most likely cause. Do you have any info on procedures for checking the fpr?
The fpr would be most likely.
Apply power to terminal marked 30. When you ground terminal 86/1, you should see power at 87/1. Leave the power connected to 30 and also connect power to 85. Ground 86/2 and you should see power at 87/2. It may be simpler and cheaper just to buy a new one, depending on the amount of test equipment you have. The big problem with these relays is cracking solder joints on the circuit boards, and the jostling a relay receives during removal and installation may be enough to allow a bad relay to pass a low current test such as this.
Mike which is the fuel pump relay,was is it green with a b on the top? Another question do all 760s have an in tank primary pump. The rear side of my tank as far as can see,has no electrical connections(is the fuel level sender unit in the top) fitting a lead from battery to the main pump that I can see, the engine is now running fine.The car is an 1990 model.
Yes, that's the one, green with a B on top. All gas 760s have 2 pumps. The power for the pump is sent in through the top of the fuel tank sender with the wires for the tank float.
connections(is
indicate the in tank pump is powered through a fuse switched ignition supply. The relay passes the test you described.What tests can I carry out with the the pump in situ ,to confirm it is the relay and not the ecu switching or other problem The ecu signal comes from the light gauge red wire?..
I would have to have a wiring diagrams book to tell you the colours. It gets tricky from here, but what you need to do is find the wires at the pumps to see what colours they are. The apply 12V to that wire at the relay end, and see if the pumps run. From what I remember in my fault tracing in the past, the power to the pump comes from the main relay. This power is fed directly to the main pump and through a fuse in the fusebox to the tank pump.
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