F~@kin flapper fuel pump

[corniceman0_0]

Hi,
I need help!
rv8 3.5 efi flapper.
Now on my 4th fuel pump.
engine starts and runs fine then suddenly wont due to faulty fuel pump.
buy new fuel pump,starts and runs a few times then again wont.
each time ive bought one ive tried a better quality one.
have 1st tested new pumps on bench direct with battery and fuel so know they work when new.
have tested electrical system with multimeter and getting power at fuel pump when it should
have swapped afm and ecu with known good ones and still same happens.
i once tried what i thought was an old faulty pump and it worked again but like before only for a short while.
Could the pump be getting too much power and its getting damaged?
i`m stumped,ready to fit body now but this is holding me up for last 6 months.
Desperatly need some opinions,however serious,silly or critical.
thanks.
Gary

[kdavies3]

Do you still have the oil pressure fuel pump cut off on there? Try bridging that out.

[GDCobra]

Must admit I don’t quite see the logic of swapping the ECU or AFM if the problem lies with the fuel pump.

Not too familiar with flapper system but would have thought the EFi system only gives a signal to a relay to supply power to the pump, not powering the pump directly and in any case it can only supply battery/alternator voltage. The only way I can see that being too much for the pump is if the alternator output was too high or if for some reason the pumps you are using are not 12v.

Have you tested the “failed” pumps off the car?

Only other issue I could see is if the pump is struggling to pull fuel from the tank in order to get required pressure but would have thought that would pop a fuse if so

[dinosoar]

Possibly to do with fuel pressure regulation.
If there is faulty or no pressure regulation then the pump will be running flat out in free circuit.

A

[incey1966]

I would also check the fuel pressure regulator.
I had a similar issue with a beemer many years ago. Changed the main fuel pump and the lifter pump in the tank.
It ended up being a 30 quid fuel pressure regulator valve.... 5min job and problem solved...

[GDCobra]

Possibly to do with fuel pressure regulation.
If there is faulty or no pressure regulation then the pump will be running flat out in free circuit.

A

Could be but I’d have thought if that were the case the pump would not achieve correct pressure on the rail and the engine would run poorly or not at all.
Of course when a problem has a mystery cause everything is on the table, also I know there are some “tricks” played with fuel pressure regulators on the flapper system to get different pressures at different load levels, perhaps someone has had a “play” in the past. In any case I can’t help thinking the issue is more likely to be on the fuel side rather than electrical side, if the pump is actually failing.

[tonym]

Been a while since I've dealt with the flapper system but something at the back of my mind is saying the fuel pump only works when the flap moves due to air being pulled into the engine. Could the flapper electric track be faulty?

[aaronjb]

Your memory is right Tony - ol' Edd China did a video on just that recently on YouTube (on a range rover but the same efi system)

[GDCobra]

Your memory is right Tony - ol' Edd China did a video on just that recently on YouTube (on a range rover but the same efi system)

But you’d think a quick bench test of the pump would be in order before condemning it wouldn’t you? Particularly when it got to number 4. I’d have been making sure before I replaced the first one but I am a bit tight.

[corniceman0_0]

Thanks for the interesting replies but im now thinking im just a bloody idiot.
Fully charged the battery today and turned the key,started 1st time!!
(on what is supposed to be one of the faulty pumps)
In the past when i thought the pump was faulty,i took it off and tested it on a seperate battery,didnt work,therefore thinks it faulty.
multimetered seperate battery and showing 11.2ish volts so i think ok.
Now......... epiphany?
Can the battery in the car have enough power to turn the engine but not enough to power to run the pump?
Therefore i think its a faulty pump.?
Am i that stupid that all this time the battery on the car has been too low AND my "test battery" also too low.(test battery now on charge)
BTW i changed the ecu and afm as there was a new pump and the engine was turning over but still no start.(could this be the low power battery?)
I kind of hope im right but at the same time,if i am,im a stupid f@#kinf idiot and banging my head against a wall.
Thanks and please give your opinions...i may deserve them!