question about fuel

okietheranger · Mar 15, 2015

Yes it has fpr and a return I would guess and probably cutting short. Around 315 hp at the motor. I have 19# accel injectors. I can only get 15psi with the tank pump only. I and have no idea why

RangerSVT · Mar 15, 2015

Whats the voltage at the pump (with the pump running)? You should be running 24 lb squirters at that hp level...

SVT

RonD · Mar 16, 2015

okietheranger said:
Yes it has fpr and a return I would guess and probably cutting short. Around 315 hp at the motor. I have 19# accel injectors. I can only get 15psi with the tank pump only. I and have no idea why

Does the 15psi stay after engine is off or does it drop to 0psi?

Have you removed the return line from the FPR and turned on the key, not start the engine just turn on the key, so fuel pump comes on for 2 seconds.
If fuel comes out return line port on FPR then replace FPR, it should be closed tight if there is no vacuum.

The fuel pump you mentioned is rated up to 90psi so its check valve(back flow preventer) should hold 40psi
I assume it does have a check valve???

315 x .5 / 6 = 26.25GPH at full throttle
So if pump specs are correct you are fine in that regard.

You can use part of the same formula to calculate injectors
315hp x .5 = 157.5 <pounds of fuel per hour at full throttle

Then divide that by the number of cylinders using that fuel.
157.5 / 8 = 19.68 lbs injector needed
Generally you don't want to exceed an 85% duty cycle with fuel injectors, so divide result by .85
19.68 / .85 = 23.16 lbs

Your 19#'s are OK since this is a Full throttle usage, but RangeSVT has a point that 24# might be next logical move, but it has nothing to do with current issue, unless the 19#'s are leaking like a sieve, lol.

okietheranger · Mar 16, 2015

I know I should of put 24# in to get better results. When I turn the key off with the stock high pressure frame rail pump bypassed fuel pressure drops off right away. The pump in the tank should not let the pressure dissipate right away. It's done this with two pumps. Which is why I'm so confused. Regaurdless of the fpr its brand new. But I have also checked the return side with the the pump on. No fuel. The fuel pump in the tank has the correct voltage. The injectors are not leaking. There brand new. Also I have noticed that when the engine is cold it seems to pop. I would say backfire but it's more like it's making popcorn. Not a whole bunch but a few times. Warm is fine. Timing is also correct I've played with it s bit to see if it changes. Seems to do better advanced. Thinking doesn't advance over 40* when the spout is connected

RangerSVT · Mar 16, 2015

I'm suspecting the pump is faulty. Hook up a fuel pressure gauge, and cycle the key on for 3 seconds (or until pump shuts off), off, then on again for another 3 seconds, several times, taking note of the fuel pressure each time. Fuel pressure should boost with each cycle (though it may not since it doesn't appear the system has a check valve. If I remember correctly the check valve on a stock system is at the framerail pump, not the intank, which is why its bleeding off). You may have to bypass the fuel pump relay (for diagnostic purposes) to run the pump constantly with the engine off. After about 10 seconds of the pump being on consistently the pressure should be at least 35-40 psi. If it is not, replace the pump.

Is that pump new, or used?

SVT

okietheranger · Mar 16, 2015

RangerSVT said:
I'm suspecting the pump is faulty. Hook up a fuel pressure gauge, and cycle the key on for 3 seconds (or until pump shuts off), off, then on again for another 3 seconds, several times, taking note of the fuel pressure each time. Fuel pressure should boost with each cycle (though it may not since it doesn't appear the system has a check valve. If I remember correctly the check valve on a stock system is at the framerail pump, not the intank, which is why its bleeding off). You may have to bypass the fuel pump relay (for diagnostic purposes) to run the pump constantly with the engine off. After about 10 seconds of the pump being on consistently the pressure should be at least 35-40 psi. If it is not, replace the pump.

Is that pump new, or used?

SVT[/QUOTE

The check valve is in the stock pump on the rail. But remember I put a mustang pump in the tank.

RonD · Mar 16, 2015

Snap-tite and others make inline check valves.
Most current(EFI) fuel pumps have a check valve on the output end(back flow preventer), but that being said there is that old saying "never assume anything", lol, you could have a pump that needs a check valve added.

EFI fuel pressure should hold for months and months, 5 to 8psi drop after shut down can be normal as fuel pump shuts off with the key but FPR closes when engine vacuum stops which takes a couple of seconds as engine RPMs drop to 0.
In a 40psi system you should see no lower than 25psi after shut down and that should hold for months and months.

The "popping" could be Lean mix self igniting before intake valve closes, but that should only happen after warm up, the low fuel pressure would, of course, cause the Lean mix.
Cold engine "pop" could be misfire and then that unburned air/fuel mix is ignited in the exhaust manifold by the next firing cylinders hot exhaust

okietheranger · Mar 16, 2015

Well I started off with a brand new stock mustang intank pump. After a while I bypassed the high pressure pump on the rail and the pump in the tank also only out out 15 psi and didn't hold. So I bought the bbk one. Same results. Either I have the worst luck in the world or I'm overlooking somthing. But it's pretty simple.

okietheranger · Jun 6, 2015

Anyone like bama performance? Arg I'm having a **** of a time!!!

question about fuel

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