190e Fuel pump testing

Still have a dead car! (see thread somewhere below)
It's not the relay - tried a new replacement.
So - how do I test the fuel pump electrics - is there a voltage/ampage
target I should be hitting, and for how long?
TIA
Buzby
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It would appear the relay's doing what it should but no power is getting to the pump - there is a good earth.
When I turn the engine over I can hear a very brief (split second) fizz coming from the engine bay somewhere which may suggest a short - are there any known culprits?
Cheers
Buzby
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I can't tell you specifically but consider the relay's function. The relay ensures that the fuel pump will stop if the engine stops - as in a wreck. So there must be something that "tells" the relay that the engine is running, or not. It may be, for example, the crank position sensor or something like it.
The electric pump ought to run - very briefly - before the engine is cranked for starting, to build pressure for the injectors.
Then, after the engine fires, the electric pump should be running.
There's a test point on the fuel rail for a pressure gauge to be attached. There's a specified pressure for your engine; many cars' pressure is about 43 psi, your's may (or not) be one of them. The specified pressure should be in the fuel rail with the key ON, but before cranking the engine to start it.
Some early '90s models had engine wiring harnesses whose insulation failed causing erratic engine performance as wires shorted. Something to consider unless you can affirmatively exclude it.
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What engine and what year?
Anyway, it is most probably fitted with the CIS-E injection system, which uses a fuel distributor instead of a fuel rail.
Try to take out the fuel pump relay and jump pins 7 and 8 on the socket, or even better connect an amperemeter (be careful, pin 8 is always hot). This will apply power to the fuel pump, and you should hear the fuel pump running continously. The current should be around 7 amperes.
If it does not work this way, the fault is in the pump or the wiring to it.
If it works this way, the problem must be in the signals to the relay or the relay itself:
- Pin 8 is always 12 volts - Pin 9 should have 12 volts when you switch on ignition. - Pin 12 should have 12 volts when you crank the engine. - Pin 11 is ground - Pin 7 is output to fuel pump
The relay energizes for a second or so when you switch on ignition. It energizes again when you crank the engine, and finally it stays energized once it gets normal RMM signal on pin 10 (which of course does nor occur in your case, since the engine does not start).
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I believe Jens owns one of these cars so take HIS suggestions.
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:o) Yes, but it still won't start.
I've spend endless hours to troubleshoot, so I have got to know the circuits quite well.
By the way, it should read RPM - not RMM.
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Not in Aylesbury are you ;-)
I think it's time to get a man in!
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Yep... or the car to a man.
As long as I had ideas, I still wanted to try them out. But now I am dry.
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How about hot wiring the pump?
Marty
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In order not to stay dry?
(pump hotwired, pump running, injectors spraying, strong sparks.... but no start)
Jens
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