P38 no fuel to filter but runs???

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Chrispndry

Member
Posts
47
Location
Scottish borders
Hi I have a p38 2
5 diesel automatic the fuel filter was changed 3 weeks ago as it started to struggle after the change it ran for about 3 miles then started to struggle again ..looked at pipe and found air in the clear delivery pipe...I thought these were self bleeding..couldnd shift air ..took it to a local garage who diagnosed in tank pump was shot...replaced pump...still the same he took pipe off to filter cranked engine no fuel..when reconnected it runs but struggled...is it possible the crash sensor could be at fault or inertia switch something is stopping the tip from operating even tied external pump linked to itp supply ran then stopped ????
Thanks in advance
 
Chrispndry said:
Hi I have a p38 2
5 diesel automatic the fuel filter was changed 3 weeks ago as it started to struggle after the change it ran for about 3 miles then started to struggle again ..looked at pipe and found air in the clear delivery pipe...I thought these were self bleeding..couldnd shift air ..took it to a local garage who diagnosed in tank pump was shot...replaced pump...still the same he took pipe off to filter cranked engine no fuel..when reconnected it runs but struggled...is it possible the crash sensor could be at fault or inertia switch something is stopping the tip from operating even tied external pump linked to itp supply ran then stopped ????
Thanks in advance
Click to expand...
Welcome, what year is the car? Nothing to do with the crash sensor but could be the pump fuse or relay. The will run with a dead in tank pump if the tank is more than about quarter full.
The pump only runs under certain conditions and that varies according to year.
 
Chrispndry said:
It's a 2000 year. BMW 2.5 diesel automatic
Click to expand...
So the pump should run with the ignition on; and when cranking, and when the engine is running.
If the pump doesn't run as I said, check the fuse and relay and then the connector to the pump.
With the filter removed and the ignition turned on you should get a defined amount of fuel into a container, I can never remember how much but I think it's in the technical archive.
They do not always self bleed, if the filter was refitted empty there may be too much air to bleed out without loosening the nuts on the injectors.
 
Wonder if the garage diagnosed a duff pump because it wasn't running all the time? Pump runs when the glow plugs are energised, whilst cranking and whilst running on that year. Think that's right.
Remove the tank cap and you should hear it running but it'll stop when the glow plug light goes out.
 
Datatek said:
So the pump should run with the ignition on; and when cranking, and when the engine is running.
If the pump doesn't run as I said, check the fuse and relay and then the connector to the pump.
With the filter removed and the ignition turned on you should get a defined amount of fuel into a container, I can never remember how much but I think it's in the technical archive.
They do not always self bleed, if the filter was refitted empty there may be too much air to bleed out without loosening the nuts on the injectors.
Click to expand...
no fuel when cranking not sure if filter was filled before fitting....
 
Maybe your veg is too thick and/or they fitted a cheapy pump.
Whip the filter off and get a measuring jug underneath. You can jump the relay to run the pump, relay in the fusebox under bonnet.
 
Flossie said:
Maybe your veg is too thick and/or they fitted a cheapy pump.
Whip the filter off and get a measuring jug underneath. You can jump the relay to run the pump, relay in the fusebox under bonnet.
Click to expand...
even tried auxiliary inline pump linked to tank pump 12v supply....runs when ignition on then stops but doesn't deliver fuel to filter even when cranking and open end pipe at filter
 
Flossie said:
Wonder if the garage diagnosed a duff pump because it wasn't running all the time? Pump runs when the glow plugs are energised, whilst cranking and whilst running on that year. Think that's right.
Remove the tank cap and you should hear it running but it'll stop when the glow plug light goes out.
Click to expand...
pump runs till glow plug light goes out but no fuel to open end of pipe after even when cranking...
 
Chrispndry said:
pump runs till glow plug light goes out but no fuel to open end of pipe after even when cranking...
Click to expand...
Datatek said:
Welcome, what year is the car? Nothing to do with the crash sensor but could be the pump fuse or relay. The will run with a dead in tank pump if the tank is more than about quarter full.
The pump only runs under certain conditions and that varies according to year.
Click to expand...
We tried everything relay fuse auxiliary pump the pump runs on turning ignition on but no delivery of fuel at filter ...open end of pipe even when cranking...something is stoping the pump
 
Have you bridged the pump relay?
It does sound like the glow. Plugs could have given up. You only need to lose one or two plugs on this engine and it won't start... ;)
 
Chrispndry said:
We tried everything relay fuse auxiliary pump the pump runs on turning ignition on but no delivery of fuel at filter ...open end of pipe even when cranking...something is stoping the pump
Click to expand...
So, if the pump runs, 4 possibilities, duff pump impeller broken; split in the pick up pipe; feed pipe blocked; as an outside possibility flow and return pipes connected in reverse when the pump was changed.
 
Datatek said:
So, if the pump runs, 4 possibilities, duff pump impeller broken; split in the pick up pipe; feed pipe blocked; as an outside possibility flow and return pipes connected in reverse when the pump was changed.
Click to expand...
Not 100% on this but , from poor memory, I didn't think you could mix up the pipes. It was only 7 or 8 months ago I had it all out but I've still forgotten!
To the OP, stop clutching at straws and diagnose the problem properly.
Get the pump running continuously by jumping the relay, wire from battery to the relay output, if no fuel it is as Datatek says. Cheap pumps can be dodgy, VDO is OE and the best. Dropping the tank isn't a massive job or cut the floor to access which I won't do but it's easier.
 
I wonder if you can blow compressed air down the flow pipe to hopefully clear a potential blockage? Don't know if that will damage the in tank pump though?
 
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