760 fuel pump

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.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

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.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

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.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

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 F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

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.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

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.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)