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Author: Subject: Fuel pump issues
mcramsay

posted on 22/4/17 at 09:02 PM Reply With Quote
Fuel pump issues

I have noticed in my marlin that after driving / having the car on idle for 30mins plus the fuel pump starts to buzz louder and louder and eventually starts squealing quite loud to the point you can hear a high pitched squeak when driving. It sounds like the pump is cavitating but I can't work out why.. Suspecting the pump was on the way out I changed it for a new one today with the exact same results. My set up is the following

I have a non baffled tank, with anti roll shut off and vent fitted
A facet gold flow fuel pump with a pre filter delivers fuel to an engine bay mounted swirl pot.
The swirl pot has a 14mm gravity feed to the main injection pump mounted in the engine bay.
The injection pump outlet is filtered and carries on to the fuel rail which has an integral regulator.
The rail returns to the swirl pot. The swirl pot then returns to the tank.


As I have said I have changed the fuel pump and filters.

When the noise starts occurring I have opened the filler cap just to make sure I'm not pulling a vaccum in the tank, and I can hear a lot of fuel returning to the tank.
The engine doesn't miss or cough like it's having a fuel supply issue. I thought perhaps the fuel or pump was getting hot enough to vaporise the fuel but the pump is cool to the touch.

Not really sure what else to try, all the lines are clear, something is not correct though.. any suggestions?

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motorcycle_mayhem

posted on 22/4/17 at 09:38 PM Reply With Quote
Sounds like cavitation to me as well... sounds like you've pretty much centred on that, replacing the usual.

OK... no mention of a prefilter to the pump feed. If there isn't one, you'd have to be pretty lax with fuel system cleanliness to upset two pumps (assume roller vane, Bosch type?). If there is one, try the system without. I had cavitation issues with a 55 micron stainless mesh prefilter (Bosch 979 pump).

Other things. If the pump is serious overkill, let's say a Bosch 044 type thing, it'll be heating the fuel greatly if all it's doing is pumping the stuff around the system for a small engine to sip when needed.

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mcramsay

posted on 22/4/17 at 09:48 PM Reply With Quote
I have a pre filter on the lp pump, but nothing before the HP. I initially thought it was temperature related but the swirlpot is not getting hot enough to cause any problem, perhaps 20-25 degrees and constantly gets cool fuel from the tank which is half full. The pump is a fairly beefy one as I'm running the m3 engine which runs at 5 bar. The pump is a roller vane type and is literally out the box this afternoon. I was thinking if the pump is overkill and hoofing loads back through the return line that might act as a restriction... but I would expect this to happen instantly and not over a longer period of time..
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gremlin1234

posted on 22/4/17 at 09:52 PM Reply With Quote
quote:
Originally posted by mcramsay I can hear a lot of fuel returning to the tank.
I think you may need a restrictor on the return from swirl tank to fuel tank.

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coozer

posted on 22/4/17 at 10:06 PM Reply With Quote
Sounds like some air in the pump, they squeal there heads off with no fuel in them.





1972 V8 Jago

1980 Z750

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mcramsay

posted on 22/4/17 at 10:16 PM Reply With Quote
I did think of loosing prime on the pump.... but I don't know how that could happen, the system is completely leak free, all new rubber hoses, the injection pump has a good 40cm of head on it and fuel is returning to the tank indicating the swirlpot is full to the brim.
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gremlin1234

posted on 23/4/17 at 12:01 AM Reply With Quote
is the returned fuel just dumped into the top of the tank (and getting aerated) or delivered directly back into the rest of the liquid fuel?
(since you said you can hear the fuel return, I guess after half an hour there is a fair amount of air mixed into the petrol in the tank)

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motorcycle_mayhem

posted on 23/4/17 at 08:30 AM Reply With Quote
Rate of return isn't an issue, unless you're getting aeration. If I can pump MeOH with two Bosch 044's pulling 28 amps in total...

One other thing, I stopped the screaming on the Bosch 979 (pumping pump fuel) when hot, by removing the non-return valve on the pump head. Simply heating the thing up removed the plastic retainer, and then a drill bit opened up the passage. It's had the added benefit (for my racing circumstances) that if you shut off the power to the pump, the rail pressure falls immediately.

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40inches

posted on 23/4/17 at 09:59 AM Reply With Quote
quote:
Originally posted by gremlin1234
quote:
Originally posted by mcramsay I can hear a lot of fuel returning to the tank.
I think you may need a restrictor on the return from swirl tank to fuel tank.


I fitted a 0.8mm welding tip in the return hose from the swirl pot,I can't hear the injection pump at all now!

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40inches

posted on 24/4/17 at 11:56 AM Reply With Quote
You say the rail has an integral regulator?
It may not be a regulator, but a pressure modulator. Used to smooth out the pulses, I believe.
My fuel rail is from a ST200, it has what looks like a regulator, but still needed an actual regulator.
I think the regulator has a vac connection on top, the modulator doesn't?

[Edited on 24-4-17 by 40inches]

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mcramsay

posted on 24/4/17 at 04:37 PM Reply With Quote
The noise is definatley temperature related. It's vapour lock caused by the heat in the engine bay. The noise got really bad yesterday after a long drive I parked the car up for 20 mins, the noise was really loud until the fuel in the pot had cooled down by getting fresh cool fuel from the tank.

Time for a tank mounted pump I think!

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40inches

posted on 24/4/17 at 05:12 PM Reply With Quote
Have you ever felt the bottom of your fuel tank, after a long run? I was gob smacked how hot they get
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