Fuel pressure

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Fuel pressure

Post  MattEll on 4th February 2013, 12:38

Hello.
I've got an interesting situation with my car, which I'd be interested in your views on:
Standard Metro Turbo Bosch EFI fuel pump, Malpassi regulator & HIF44 carby fitted, with return line to tank.
The standard pump output seemed WAY excessive, and was noisy, so a mate and I rigged up a resistor pack to slow it down.
Seemed to work well, and a recent trip to the dyno shop suggested that mixtures were factory correct throughout rev/boost range.
However with a fuel pressure gauge fitted, it shows only 4psi coming in from tank (ign. only, no engine running).

So the question is, how can the engine work properly (as it does) under boost, when anything more than 4psi of boost should be sending fuel back to where it came from!?

As for a solution, my current plan is to remove the resistor pack to restore full fuel pump performance, and go from there.

Thanks,
Matt


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Re: Fuel pressure

Post  benjamin on 4th February 2013, 12:50

the fuel pressure from pump should be high , you need at least 3-4psi above max boost , i recomend lots more to be safe .

i believe a vl comordore external pump is same as a metro turbo.

So that should output around 45psi , which the adjustment on the regulator will bleed off some to the carbie (3-4psi at idle) The rest goes back through return to tank.

the air pressure feed should increase fuel pressure 1:1 , so once you reach 7psi boost fuel should be at 10-11psi.

Id assume it was working correctly as it should die on boost if boost went higher than fuel pressure.
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Re: Fuel pressure

Post  MattEll on 4th February 2013, 12:56

Thanks Benjamin.
45 psi is a LOT of pressure, when only 10-11psi is needed!

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Re: Fuel pressure

Post  benjamin on 4th February 2013, 13:05

the metro turbo regulator is designed for it , The pump is capable of that but im not sure that the lines will see it as it is just returned to the tank.

Just make sure your rubber lines and clamps are EFI rated !
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Re: Fuel pressure

Post  MattEll on 4th February 2013, 22:53

Thanks Ben. It will be interesting to see how much pressure develops, given the return line.
Good advice re: EFI lines & clips.

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Re: Fuel pressure

Post  MattEll on 19th February 2013, 13:01

Bit of an update. I swapped the return line for 10mm, and now have the pump running at full tilt. Not really noisy at all. The feed to the carby is set to 4psi, and I think 4psi on the reg side of the fuel pump (Awaiting a replacement gauge to confirm). I figure this is because there is just a big circuit (tank, pump, reg, tank), with no real resistance other than the reg itself.
So whilst the previous setup worked (pump with resistors fitted, and small bore return line), it would have been marginal, and would have given problems - probably as soon as any power increase was seen.

Still mostly sorting out boring stuff on the rest of the car now, but am currently sorting out a better setup for the air filter at the moment- trying to use 57mm ID silcone (flexible) hose to run between the rocker cover and radiator, to have the air filter hanging next to the alternator. Will be a good use of space if I can make it work.

Matt

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Re: Fuel pressure

Post  benjamin on 20th February 2013, 12:01

4psi between carby and regulator is perfect ! , just make sure its is rising 1:1 with boost and is steady (no crazy fluctuations ) just face gauge through window and go for a drive.

re the airfiter , I have my boost pipe go under the top hose but its only 52mm. I use a rover thermostat spacer (my turbo water return) and have modified the top radiator bracket.

Other option i have seen done is get a flat thermostat cover and go over the top
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Re: Fuel pressure

Post  MattEll on 20th February 2013, 12:03

That's interesting. I didn't know that the hose could go under the top hose.
A pic would be great.

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Re: Fuel pressure

Post  benjamin on 20th February 2013, 12:09


there you go

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Re: Fuel pressure

Post  MattEll on 20th February 2013, 12:41

Nice! Looks like you've relieved the radiator bracket also?
Thanks for that.
I just checked out under the bonnet here, and it looks like the 57mm ID stuff will run over the top of the standard thermostat cover & hose no probs.
Not a whole lot of room around the alternator/oil filter etc. on a roundnose though for air filter- I might have to get a teeny tiny one. But at least it'll be down in the fresh air!
Cheers

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