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HIGH fuel pressure

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1.8K views 21 replies 8 participants last post by  perezrv  
#1 ·
seem to be having a bunch of problems trying to start my car!

i have the fuel pumps wired not through a relay but on a switch (directly from a battery power)
i turned ONE of the fuel pump on and it went up pretty fast after 20psi and climbed as high as 60+psi before i turned it off.

the ignition or the power to the ECU wasn't on or anything. i dont if it's a fuel pressure regulator problem? i recently took it out disassembled it and put it back together.. it seemed like it was fine and i put it back correctly.

any suggestions ideas would be greatly appreciated :)
 
#3 ·
it is an aeromotive regulator the red/pink one. with 6an feed and return

i didn't try to adjust the fuel pressure regulator just yet. i didn't want the fuel to flood the motor (if it would at all). i believe it would be left to lower and right to increase right?

thanks
 
#5 ·
sleeknsilver said:
it is an aeromotive regulator the red/pink one. with 6an feed and return

i didn't try to adjust the fuel pressure regulator just yet. i didn't want the fuel to flood the motor (if it would at all). i believe it would be left to lower and right to increase right?

thanks
Click to expand...

counterclock wise should take pressure away(ie, lower it)...
 
#6 ·
You should be able to just adjust the FPR. If not is it possible that the puimps are stuck on the intial prime mode. I know on some of my other cars the fuel pump will prime before starting where the fuel pressure is high then within a few seconds the pressure drops. Good luck with your car, hope you find what is wrong.
 
#7 ·
Sooco100pf said:
You should be able to just adjust the FPR. If not is it possible that the puimps are stuck on the intial prime mode. I know on some of my other cars the fuel pump will prime before starting where the fuel pressure is high then within a few seconds the pressure drops. Good luck with your car, hope you find what is wrong.
Click to expand...

that may be the case... because i dont have the pumps wired to the stock fuel ECU anymore. just straight power from the battery

how would i unprime it... so you're saying after the car starts the pressure will stabilize?
 
#9 ·
It is not on all cars that the fuel pump primes, I am not sure on a Supra. I just know that my old car primed for around 2-5 seconds then the pressure droped. Anyone know if a Supra primes when you first turn the ignition on? I would just adjust your FPR to change you pressure back to stock levels first.
 
#10 ·
yep it was the fuel pressure regulator.... i turned it all the way out (counter clockwise) and it seemed to drop the fuel pressure down to 35psi

i didn't tighten it to see if it adjusts it but i'm sure it would. so anyway i think i found my problem :) thanks a lot guys
 
M
#12 ·
How will running motor at 2500rpm set your WOT pressure?

You really shouldnt do that. Adjust it to somewhere around 40-45(mine is 43) at idle with the hose pulled to the FPR. When under boost at the dyno you should see that number plus whatever boost you are running. (for instance base pressure of 40psi plus 15psi boost = 55psi total fuel pressure)

WOT has nothing to do with it because you are sometimes not driving WOT under boost all the time.
 
#13 ·
by pulling the vacuum hose, you are running MAX pressure, which i referred to as WOT pressure because as soon as you go WOT this is what the pressure will jump to due to the lack of vacuum. you run it at 2500 rpm so that the motor doesnt buck and want to stall at idle with too high of fuel pressure. i think you are mistaken about how fuel pressure works, it does not go up with boost, it goes up when vacuum disappears, at 0 vacuum you have max pressure. there is no adding boost+pressure to get total pressure, max pressure is max pressure whether your at 2 psi or 60.
 
M
#15 ·
No sir you are totally wrong.

When i adjusted my FPR i did it at idle and had no issues with it stalling. Fuel Pressure goes up with boost. Why ? Because you need more fueling. I guess it could be the same as when vacuum disappears.

Have you ever looked at a FPR under boost on a dyno? If not then you really dont know what your talking about. If your right whatever it was set at is what the FPR would stay no matter what boost your running.

I am sure someone else will chime in on this one.
 
S
#16 ·
Most vehicles will die, or run very rough when the vac line is pulled @ idle, unless there just isn't much vacum from cams/poor tuning.
Sounds like both ways would work. :tag:
I'd say check when the engine isn't running, but the pumps can pull some amps, so better off to be under alternator power.
 
#17 · (Edited)
Mad TKD said:
No sir you are totally wrong.

When i adjusted my FPR i did it at idle and had no issues with it stalling. Fuel Pressure goes up with boost. Why ? Because you need more fueling. I guess it could be the same as when vacuum disappears.

Have you ever looked at a FPR under boost on a dyno? If not then you really dont know what your talking about. If your right whatever it was set at is what the FPR would stay no matter what boost your running.

I am sure someone else will chime in on this one.
Click to expand...
This is correct, The only way you would see an increase in fuel pressure is when the FPR is with a Rising Rate FPR. In the end set a fuel pressure, record that then go tune your car, that way it won't really matter if you are off by 1-5psi. assuming you don't go lean, or too right at idle.
 
P
#19 ·
Mad TKD is right. The speed that you are running the engine is of no consequence when setting your fuel pressure. The engine will be near max vaccum whether you are at 600 or 2500 rpm. The only way that isn't true is if the throttle is open in which case you're not going to be at either speed for long. Unplug the FPR and set your base pressure. Plug it back in and your fuel pressure will drop. As you get on the gas, the manifold pressure will go from max vaccum to atmospheric (Fuel pressure will go to base setting) and fuel pressure will go up 1:1 with boost pressure after that (base setting + max boost pressure=fuel pressure at max boost).

Rene
 
P
#20 ·
Why do you think the fuel pressure regulator has a vaccum connection anyway? By lowering the pressure at low throttle positions, it gives the engines computer finer control of the air fuel at low consumption rates. By increasing the pressure with manifold pressure it gives the ability to flow more fuel.

I forgot to mention in my first post about the original fuel pressure problem. If I read it right, it sounds like you are running multiple fuel pumps at full speed. With a setup like that, you may be seeing back pressure form the return line on your fuel pressure gauge if your return lines and fittings aren't big enough. At idle, your engine is using almost zero fuel, which means that everything that the pump is sending forward must go back through the return line. As you start getting on it, your engine's fuel demand will reduce flow through the return line and its corresponding pressure drop. This can result in setting your fuel pressure regulator too low and your pressure may actually drop as you get into the throttle. It might be a good idea to check your fuel pressure under load to be sure, especially since you were having a high pressure condition and adjusted your reg down.

Rene
 
#21 ·
yep i believe my fuel pumps are running at a constant speed... they are connected by two switches (one for each pump). dont ask me why i did this :)

it seems like i'm flooding the motor too with the pump/s on starting the car... i set the fuel pressure to about 40psi.

i have the stock return line.. do you think that is causing a back up? how would you go abouts resolving this issue with the constant speed fuel pump/flooding of the motor? would you say, 40psi at idle (with the vacuum hose off) is good?

thanks a ton for the informative reply! :bigthumb:
 
P
#22 ·
Per the manual, fuel pressureshould be between 38-44 psi with the vaccum line disconnected. With the vaccum line connected it should be between 28-34 psi. As far as your oe return setup, with both pumps running at idle, you can be pretty sure that you are going to have a backpressure problem in low demand operation. If you only run one of the pumps it will alleviate the problem somewhat. I would put a pressure gauge and install it near the regulator in the return line. The pressure in that location will be the amount of backpressure that you are getting from the return line. I am only guessing at this, but I would be a little concerned if the pressure was more than about 5 psi. You can run this test in one and two pump operation and see how big of a difference it makes. Also make sure that the line is not obstructed (pretty unlikely). It will probably be a big difference when you start the second pump. I have'nt done any pressure drop calcs on it to figure out what it's supposed to be. At the very least, you are going to have to add this backpressure to the base pressure when you are setting up your FPR in order to have adequate fuel pressure under high demand situations. If you want to keep the existing fuel pump setup, you should modify your fuel return system by increasing the return line size. I am assuming that your FPR is big enough to handle the fuel load (Full bypass, low demand). Doing this will allow you to maintain normal idle fuel pressure and proper full speed fuel pressure. You may want to reconsider the twin pump, constant speed arrangement. If you are running the stock rail and injectors, it seems like a bit much. The cheapest, reliable way out of this is the return line size increase to handle both pumps at full speed. As long as you're at it you can go to the SARD 800cc low impedance injectors in the stock rail with a piggyback fuel computer or go all out and get a new rail/injector setup with the piggyback. This will at least give you the benefit of being able to make more power. Problem with that is that the addiction just gets worse...bigger turbo better clutch new engine broken rear end out of money. You understand.
Good luck,
Rene
 
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