So i've had a flooding / rich running issue forever with my M20-swapped 1974 2002tii, and am trying to diagnose WTF is up with the fuel system.
THe plugs are instantly blackened and wet with fuel, and it's running terribly. It's obviously receiving too much fuel. I've installed a fuel pressure gauge in the supply line before the fuel rail, and here's what I get for fuel pressure:
1. Engine On, at idle: ~70psi
2. Engine Off, fuel pump on (jumpered the relay): ~65psi (this should read 43.5PSI, with the M20B25 3.0Bar FPR)
3. Engine Off, fuel pump off (no more jumper): ~40psi, tapering down slowly to 0 over a day or two
Alright, that's pointing to one of two things, right: either (A) the FPR sticking or otherwise malfunctioning, thus not releasing enough excess fuel into the return line to keep the fuel pressure at OEM levels, or (B) a restriction in the fuel return line itself such as rust or some kind of buildup.
The easy way to test for (B) is to unplug the fuel return line and cycle the fuel pump again, this time just catching the excess fuel in a jug through some extra tubing. This eliminates the possibility of a restriction in the fuel return line causing the problem. Doing so yields no difference at all - still ~65psi measured at the gauge. I've also blown out the return line for good measure with compressed air, and it all seems fine.
SO - the problem must be the FPR right? I bought a new FPR to test it out, and upon installing the new FPR, in the same conditions (both with and without the fuel return hose attached), I get the same results - 65PSI on the gauge with either FPR. Hmm.
Wondering what's up with that, I also decided to see if I can "bench test" both FPRs using pressure-regulated compressed air and see what happens. Not sure if this is a valid test since one is air and the other is fuel - but, if I dial up any amount of air over 45 PSI and introduce that to either the old or new FPR, the pressure will hold exactly at 43.5 PSI, as if they both are working just fine.
One would think that the FPR would work the same way regardless if it's got air or fuel under pressure, would it not? How come both FPRs seem to perform just fine with compressed air, regulating to 43.5PSI as expected, but as soon as they're connected to the car's fuel supply and pressurized (with or without a return line attached), they both malfunction and regulate to 65PSI?
Any ideas as to what's going on? Is there any potential cause of high fuel pressure in the system OTHER than the FPR and/or return line being clogged? Is my methodology flawed somehow? Do I just need to keep buying new FPRs and see if I can get one that works? Or, maybe try an adjustable FPR and see what happens....
Any suggestions would be appreciated. Kind of at my wits' end on this...
THe plugs are instantly blackened and wet with fuel, and it's running terribly. It's obviously receiving too much fuel. I've installed a fuel pressure gauge in the supply line before the fuel rail, and here's what I get for fuel pressure:
1. Engine On, at idle: ~70psi
2. Engine Off, fuel pump on (jumpered the relay): ~65psi (this should read 43.5PSI, with the M20B25 3.0Bar FPR)
3. Engine Off, fuel pump off (no more jumper): ~40psi, tapering down slowly to 0 over a day or two
Alright, that's pointing to one of two things, right: either (A) the FPR sticking or otherwise malfunctioning, thus not releasing enough excess fuel into the return line to keep the fuel pressure at OEM levels, or (B) a restriction in the fuel return line itself such as rust or some kind of buildup.
The easy way to test for (B) is to unplug the fuel return line and cycle the fuel pump again, this time just catching the excess fuel in a jug through some extra tubing. This eliminates the possibility of a restriction in the fuel return line causing the problem. Doing so yields no difference at all - still ~65psi measured at the gauge. I've also blown out the return line for good measure with compressed air, and it all seems fine.
SO - the problem must be the FPR right? I bought a new FPR to test it out, and upon installing the new FPR, in the same conditions (both with and without the fuel return hose attached), I get the same results - 65PSI on the gauge with either FPR. Hmm.
Wondering what's up with that, I also decided to see if I can "bench test" both FPRs using pressure-regulated compressed air and see what happens. Not sure if this is a valid test since one is air and the other is fuel - but, if I dial up any amount of air over 45 PSI and introduce that to either the old or new FPR, the pressure will hold exactly at 43.5 PSI, as if they both are working just fine.
One would think that the FPR would work the same way regardless if it's got air or fuel under pressure, would it not? How come both FPRs seem to perform just fine with compressed air, regulating to 43.5PSI as expected, but as soon as they're connected to the car's fuel supply and pressurized (with or without a return line attached), they both malfunction and regulate to 65PSI?
Any ideas as to what's going on? Is there any potential cause of high fuel pressure in the system OTHER than the FPR and/or return line being clogged? Is my methodology flawed somehow? Do I just need to keep buying new FPRs and see if I can get one that works? Or, maybe try an adjustable FPR and see what happens....
Any suggestions would be appreciated. Kind of at my wits' end on this...
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