Fuel Pump - Updated

[KarlH]

The pump runs consistently every time I can supply 12v to it and when it was running yesterday morning it was ok which makes me suspect electrics somewhere rather than the pump itself. 

its just what I can't figure out! 

[SM25T]

Have you disconnected every plug and socket in the loom ... looked for corrosion

.. spot of anti corrosion fluid as you plug back together. Find any chassis earths and remove and clean cable connectors to bright metal, treat as above.

[Toby S]

"We moved the fuse box" - it isn't a bad connection or something shorting the connection at the back of the fuse box like my previous post

[KarlH]

Checked it all over Toby and all seems fine, no visible issues, wires don't seem damaged etc. Have moved it again tonight and checked again but it's still not working and I get 12v on the right sight of the fuse at key on and if I put 12v on the other side the pump runs so that implies that section is working fine - I think!

[EEK]

Dirty contacts in the MFRU?

[KarlH]

EEK - MFRU is fine, had the cover off and can see the relay working and can measure the right voltage at the correct output pin.

[EEK]

OK - whilst not on a K series and therefore may not be relevant but I had fuel pump stop on my HPC, The problem was in a large Eco seal connector in the engine bay, about 12 wires in it one of which was feeding the fuel pump. On opening connector there was clear overheating occurring on this connection, once cleaned all OK.

So I guess I am saying are you sure there are no other connectors between MFRU and pump that might have been overlooked?

 

[KarlH]

I think I've checked them all but there's a chance I've missed something but don't know what, so far I've checked:

MFRU / Inertia Switch / Fuse Box / Black Plug / Grey plug / Pump plug

 

[Jonathan Kay]

Is this about right... sorry if I've missed something important.

1. Fuel pump sometimes doesn't run.
2. When a new jump is made to the pump's feed terminal it always runs immediately.
3. You haven't found a fault in the normal feed circuit.

Have you had a chance to measure the voltage at various points along that feed circuit when it fails to run? Or to connect that feed jump at various points other than the pump's terminal.

I'd normally advise checking the earth side in detail but 2 isn't consistent with a fault there.

Jonathan

[KarlH]

Yes that's right.

1. Correct, it either fails to prime or stops when running

2. Yes, 12v applied and it runs

3. No, nothing obvious

I've checked at each point there's a plug or connector all the way back to the MFRU, including inertia switch and fuse block. With 12v applied at each point the pump runs, voltage generally has been 3v - so not right but then it randomly started working again. Then stopped!

I've tried two different MFRU's, the relays work and one of them definitely had 12v at the terminal inside.

[Jonathan Kay]

With 12v applied at each point the pump runs, voltage generally has been 3v

You're connecting a new 12V jump feed to the circuit somewhere, and it measures 3V at the pump terminal?

Can you repeat that after disconnecting the normal circuit upstream of where the jump feed is connected?

Jonathan

[KarlH]

No, with the normal circuit in tact I was consistently  seeing 3v at each point - pump plug, inertia switch etc. However, last night I was seeing 12v at the fuse block and inertia switch which the day before had only shown 3v.

With a new jumped supply to each point the pump runs.

I'd have thought that somewhere along the cable I'd see the direct 12v drop and not work if there was a fault but I'm not sure anymore!

[Nick Chan]

Remove the fuse block from the bulkhead. I can recall there being a problem with the connection on the back of the fuse box itself occasionally causing an intermittent problem. Possibly a black and yellow wire (but guessing on that bit!).