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fuel problems heeelp!
Posted: Sat Apr 12, 2008 2:53 pm
by gumtree
i cant get my sierra dyno'd until the fuel pressure in the return line is 45 psi (stock) and now its 55/60psi, which means it runs rich. the good fellows at suzisport springwood helped me out a bit and we found out the fuel pressure regulator is not the problem.
so somewhere along the return line there is an obstruction somewhere after the regulator. also i have an arb lg tank but i dont think it a problem as it inlet plug is same size as return line.
has anyone encountered this problem before and managed ti fix it? i would rather fix it and use the metal lines along the chasis rather than bypassing it with a rubber fuel line all the way back to the tank as they are less durable and will crack over time...
Posted: Sat Apr 12, 2008 4:49 pm
by MightyMouse
Fuel pressure in the return line is HOW MUCH.... you mean the supply I hope.
You could run the return line into a bucket for a minute an see if the pressures still high. It it drops its the return line/tank.
Then do the same at the tank - same as above.
Will narrow down the problem.
Posted: Sat Apr 12, 2008 5:06 pm
by lilzook
return line should always be low pressure. since you have an efi conversion your return/feed line diameter is smaller than a factory efi setup. 6.3mm to 8mm. this might be causing the higher pressure reading at the fuel rail.
Posted: Sat Apr 12, 2008 8:09 pm
by gumtree
thats what i meant when we figured out it wasnt the regulator, we ran a hose straight out of the regulator into a bucket and it was 40 psi so its in the line after this point.
i think it was supply, as its meant to be 45psi. i ran a fuel line all the way back to the tank today and it still seemed to run rich. the rubber line is slightly thicker so it should lower some of the pressure. i havent measured it yet as i dont have a gauge.
just a thought, could the fuel pump be pumping to high of a pressure for the car? remembering that after we ran the line in the bucket straight after the regulator it was 40 psi.
Posted: Sun Apr 13, 2008 12:33 pm
by MightyMouse
Its really important to tell us what line has what pressure...... to many vague "its" will get us scrambled.
The pump doesn't control the fuel pressure that's the regulators job assuming the pump and regulator are stock.
So if I understand correctly supply pressure was correct with fuel returning from the reg to a bucket - so its definitely a restricted fuel RETURN line.
The return line should be substantially bigger then the supply line and free flowing back to the tank.
Unless you have done something else we don't know about that would be my bet.
Posted: Sun Apr 13, 2008 4:01 pm
by gumtree
hmmm, underneath the original lines are used but the supply line is bigger than return. are u sure the return line is meant to be bigger? anyways now the rubber return line i put in is bigger than stock but not as big as the supply. will put a gauge on it tuesday hopefully...
Posted: Sun Apr 13, 2008 4:31 pm
by bazooked
what kind of fuel pump are u runnin? also is it the standard reg in the fuel rail for the efi??
Posted: Sun Apr 13, 2008 7:47 pm
by gumtree
fuel pump i dont know, probably standard and standard regulator. there was 40 psi when we ran a hose straight out the back of the regulator so im assuming these are both fine and the problem is in the return line. there doesnt seem to be and damage to the stock one so maybe its too thin.
Posted: Sun Apr 13, 2008 8:12 pm
by zook4fun
check the return line where it meets the fuel rail. that might be a bit blocked and need a clean, so your psi is going up.
had sort of the same problem last year but no fuel psi (elec pump, reg ,1/2 inch lines on a stroker v8) and was using the standed line as the return. no matter what i did i couldn't get pressure. ended just gettin a holly carby jet and putting it where the rubber hose mets the metal line (fitted perfect!) got psi strait away and when i had to change psi (carby car) just swaped the jet and no stuffing around with the reg. never had a problem again
Posted: Mon Apr 14, 2008 11:39 am
by MightyMouse
gumtree wrote: are u sure the return line is meant to be bigger?
Yes - absolutely. The supply line is under pressure so it has no problems carrying the required fuel volume . The return however should be at close to zero pressure and therefore needs to be larger to carry the return fuel.
You have already proven this when you ran the regulator return into the bucket. Just make certain its the line not a restrictive fitting somewhere.
Posted: Mon Apr 14, 2008 10:56 pm
by gumtree
sweet, went to suzisport today and they pressure tested it and 40psi.

.
the rubber line did the trick. cheers for the help all, it was a happy ending.
Posted: Tue Apr 15, 2008 3:56 am
by JrZook
gumtree wrote:sweet, went to suzisport today and they pressure tested it and 40psi.

.
the rubber line did the trick. cheers for the help all, it was a happy ending.
So does it run better now? Was this the cause of your earlier tuning problem?
Cheers Dan
Posted: Tue Apr 15, 2008 7:52 am
by gumtree
yes it runs a little better now but still a bit rich so now its all ready to be tuned. couldnt be tuned before this as pressure needs to be correct and before that the thermostat wasnt working properly.
Posted: Tue Apr 15, 2008 8:05 pm
by suzimad
ahh i thought that was you , thanks for the 6 pack , enjoying one now.
good luck with the tune , should run a lot better after it isnt running so rich.
also now that you know it was a restriction in the return line , i would probably suggest getting another metal return line and replacing the original , lot safer and longer lasting than standard fuel line....
Posted: Wed Apr 16, 2008 12:05 pm
by gumtree
suzimad wrote:ahh i thought that was you , thanks for the 6 pack , enjoying one now.
good luck with the tune , should run a lot better after it isnt running so rich.
also now that you know it was a restriction in the return line , i would probably suggest getting another metal return line and replacing the original , lot safer and longer lasting than standard fuel line....
yeah no probs dave, thanks for the help ay.
thats a good idea actually... i just went and had a look and it looks like it will be a complicated job of puting one in if at all possible without bending it. unless its easy might just leave it for now.