Fuel Pressure Help
Turbo Mini Forums

I'm trying to get my 998 build to run nat asp before I try the turbo and to get it though MOT emissions easier (I have no needles suitable for a turbo).

See my build thread linked below for more details.

Basically the problem is that the fuel pressure is too high (7psi) and it's pissing into the engine. I'm running standard size feed and 10mm OD return pipe.

I was under the impression that the standard feed would reduce the flow if anything and so the regulator would be able to cope with reducing the pressure down to about 3 or 4?

Any advice appreciated.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Is your regulator known good?

it was brand new, mg metro turbo one (off ebay tho)

I've tested it with air from the compressor and it seems to work like it should.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Do you have a kink in the 10mm copper return pipe - it's horrible to bend accurately, even with a proper microbore tube bender........

Been there myself.....

Try just putting a bit of fuel hose from the regulator return into a fuel can (missing out the return line) and see what pressure you get.

BUT BE CAREFUL, don't blow yourself up :)

Schrödinger's cat - so which one am I ???

Rod, that's what i've just been and tried. Used a 12mm id clear pipe as a return into a container. It still poured past the carb needle and the flow out the return was massive. I would say about 1 litre in 30 secs.

I'm thinking the fuel pump is flowing far too much and the reg just cannot return it.

I was told on the build thread that it looked like a cheap rip off of the original.

Anyone within driving distance of Wootton Bassett got one I can pick up tonight or first thing tomorrow. Got MOT booked for 11am.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

The Bosch (or Bosch copies) do flow a lot of fuel, they are meant for injection systems that work at 3 bar plus.

But a decent regulator should still spill back the majority and if you've tested it with a pipe straight into a container and the pressure still doesn't drop it sounds like the regulator is at fault.

2l/min (1 litre in 30 seconds) is about right for the Bosch pump, my "copy" does a bit more but still regulates nicely at 3bar for my injection system, the low pressure (carb) regulator should easily deal with that amount of flow IMHO.

Schrödinger's cat - so which one am I ???

Is there a procedure for testing the regulator?

The flow just seems far too extreme tho. It's like turning a garden hose on.

I've just read on another thread that the metty pump ran at 9V. could i be running it too hard?

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Even with 10mm feed and return and putting a fat light bulb in series to reudce the pump voltage i'm still seeing 6 psi at the carb.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Have you adjusted the regulator?

Sorry, this isn't meant to be patronising. You've just not mentioned it above.

In the 13's at last!.. Just

No worries, yeah put it all the way out.
6 psi min and goes up past 15 when i screw it in.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

do you have one of the blue ebay pumps?, i found mine was really powerful, i stepped the feed down to 6mm just off the bump then back up to 8mm with a 10mm return

what does the return line do back at the tank?, does it go into the top of the tank or T into the feed to the pump?, that could be the problem,

Yes i moved to the darkside

Instagram @jdm_brett

As a temporary "fix", rather than stepping the feed down (which will tend to overload the pump motor and shorten its life) Tee off the pump outlet and run some of the fuel straight back to the tank (or back into the pump suction if you have done it that way).

Run this through a slightly smaller diameter than your feed to the engine/regulator so most still goes to the engine or make part of it a copper pipe and squash it partially flat, by trial and error, until you get the right flow.

It sounds like your pump is at the very top of the performance range and a bit too much for the regulator to cope with.

Schrödinger's cat - so which one am I ???

Yeah ebay pump.

This morning I went to the scrappy and got a renault 5 pump which people on here have said they've used with success. It's physically smaller than the ebay one. about 2/3 the size.

Fitted it and no luck still far too much fuel and pressure.

Tried t-ing the feed so that some returns to the top of the tank and still no change. even clamped the feed pipe so the majority went to the tank and still get 6 psi and fuel pouring out the carb.

The renault 5 pump still seems quite high capacity despite its size. I tested it and it pumps more than 58 psi (the limit of my gauge).


Anyone coming to combe fancy stopping off to lent their 2 cents? I live 30 mins east. By junction 16 of the M4

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Well it really does seem like the regulator is fooked then or, sorry to ask, is it plumbed in right ???

The Metro Turbo one should discharge (spill back) from the bottom - if you look from underneath you should be able to see the spill back valve up the brass tube. Is there anythng restricting it like a piece of crap over the seat ???

The only other obvious things are if the spring is too long or the diaphragm split but you say it's a new regulator......

Final test I would suggest is just connect your supply line to the return line in the engine bay with your pressure gauge Tee'd in (ie, remove the regulator from the equation) and see what pressure you get with all the fuel going straight back to the tank (should be near zero...).

Schrödinger's cat - so which one am I ???

Thanks for help Rod.

ok, so I plumbed the feed into return and with the gauge. Works fine. The pressure is under 4 psi. (not quite sure what because my gauge is slightly damaged and the needle sits at 4psi when no pressure is applied.)

So gotta be the reg. Took it apart and tried it without the spring. It is a lot easier to blow through. I think the free length of the spring is too long. It basically shuts the return valve.
Must be that when i tried it with the air line it seemed ok because i blocked the carb output and so it had nowhere to go but out the return. When it's connected to the carb it must be easier to bypass the carb float shut off.

I'll get on at the company who sold it to me. Trouble is I bought it a year ago. It was SMC trading on ebay.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

If something is worth doing, it's worth doing half of.

:) Have you tried them yet John? I suggest just try it over a bucket. Mine can't get the pressure down.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

I've got one too. Maybe we should test them on the van one day...

^ Agreed!

If something is worth doing, it's worth doing half of.

The spring should shut the spillback valve, but only just, when the tensioner/adjuster is wound to minimum. From then obviously the more you compress the spring, the higher the pressure should be.

Having a pressure gauge that doesn't work right at 4psi downwards doesn't help...... it may be the regulator is OK (but you're reading it wrong) and the carb has a dodgy float needle valve failing to hold the pressure.

If you can't get a decent pressure gauge, there is an old skool method involving a long length of open-ended clear plastic small bore tube and ladders to tape it up the side of your house.....

I can't remember the exact figures (I think Joe C has posted them before) but assuming the SG of petrol is close to water, 10 foot up the tube (above the height of the regulator) is about 5psi.

But, like I said earlier, when playing with petrol, be careful.......

Schrödinger's cat - so which one am I ???

Problem solved!
I was following advice from the pic below and blocking off 7 (I have nat asp carb).



However, turns out the problem I had was that the float in the bowl wasn't floating because the the trapped air couldn't escape and so the fuel poured out the jet .
Now the air is out I assume it shouldn't return unless i dismantle the carb. So do I need to block this float vent pipe off again otherwise when on boost the fuel will come out of it?

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Random question but what fuel tank are you using?.

i brought a alloy tank with what i thought was flow and return outlets but they were'nt they were flow and a breather so when i started the pump it just presurised my fuel tank and made the pressure mega high.

could this be your problem?

works now thanks turbo22.

Standard tank FYI

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Right, Actually sorted now.

Turns out that on my carb (I think it's a maestro or metego one, it has the casting in place for auto choke system) the drilling between plenum and carb to pressurise the float chamber was plugged.

So when I blocked off the vent connection there was no vent at all in the chamber and so fuel dribbled up the jet.

It also meant that trying to come on boost was like hitting a brick wall. There was no fuel at all at anything near or past atmospheric.

Drilled out the blank and problem all fixed. No dribbling fuel, able to boost. Fantastic!


Note also my woes here (presumably caused by that same drilling).

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=384648

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo