Fuel pump recommendations

Working on my 93 XLT Ranger, 2.3L, 5sp pickem-up truck. Took the silencer out of the intake plumbing, truck gained an immediate big flat spot when driving, both just above idle and out on highway. Checked the fuel pump pressure and it is 0 with KOEO. KOER it's 34# idling, speed up motor and it drops a pound to 33#. Disconnect vacuum to fuel regulator and it holds steady at 43#. I plan on installing 17# injectors, thinking that they will cover the flat/bog that i have gained.
Question: will a Mustang 5.0L fuel pump of similar vintage drop right in place of the present 2.3L fuel pump?
Thanks for the help.

Reported:KOER it's 34# idling, speed up motor and it drops a pound to 33#.

The pressure should not drop when you open the throttle. That will give you a flat spot, as will a dirty MAF. The regulator should, I think, bump the pressure when the throttle is opened and the vacuum in the intake manifold goes closer to zero. That function sort of takes the place of the accelerator pump in carburetors, goosing the fuel to make up for the inertia of liquid vs gas flow.(air goes quick 0->50, liquid, denser, takes more time)
Check the regulator again, it should bump, not drop, when the throttle is bipped open.
tom

tomw said:

Reported:KOER it's 34# idling, speed up motor and it drops a pound to 33#.

The pressure should not drop when you open the throttle. That will give you a flat spot, as will a dirty MAF. The regulator should, I think, bump the pressure when the throttle is opened and the vacuum in the intake manifold goes closer to zero. That function sort of takes the place of the accelerator pump in carburetors, goosing the fuel to make up for the inertia of liquid vs gas flow.(air goes quick 0->50, liquid, denser, takes more time)
Check the regulator again, it should bump, not drop, when the throttle is bipped open.
tom

Click to expand...

All this is correct, but a bad regulator shouldn't jump the pressure like that when the vacuum is disconnected. These all sound like symptoms of the fuel pump not keeping up to me.

Not sure larger injectors without increased air(turbo) will do anything but set Rich codes
Computer bases air/fuel mix calculations on fuel pressure and flow thru stock injectors
It "knows" XX fuel will flow out of a stock injector if it is open for 100ms(milliseconds)

And thats what it bases 0 Fuel Trim on
If XXX fuel flows from a larger injector then computer will have to decrease open time of the larger injectors to get 14.7:1 ratio, if it has to reduce open time more than 15%(-15 fuel trim) then it will set Rich code
And you will still have flat spot

Not sure what the silencer is that you removed??
But if you got the flat spot after removing it then my guess would be removing it caused a turbulence in the air flow or vacuum at the intake ports so less air/fuel mix flow into cylinders for that moment, flat spot.

Generally speaking fuel pressure dropping issue would effect high demand first, i.e. driving up a long hill or sustained highway speeds, dirty fuel filter would be most common cause for this.
But it wouldn't cause a flat spot until vehicle was at higher speed, and it wouldn't be a "spot" it would be a limit, can't go above it.
43psi with vacuum hose off means pump is probably OK.
If you raised RPMs to 2,500 or so and held it there for 30 seconds with no slow drop from that 43psi then I would say pump is fine.
And yes, if it was 34psi and went to 33psi when you opened throttle plate then vacuum INCREASED for that moment in the intake, and that would cause a flat spot, so I would look at vacuum in intake as symptom causing flat spot, not lack of fuel
Your Ranger uses 90lph fuel pump, and it works for 2.3l turbo'ed Rangers, same 90lph pump was used on turbo'ed T-birds.


TPS(throttle position sensor) is more like accelerator pump than vacuum line on FPR.
TPS voltage gives the computer the "heads up" to add more fuel instantly when gas pedal is pushed down.
Using MAF only would be slower to react and cause a hesitation, flat spot, when throttle plate is opened.
If "silencer" was near MAF then removal may have changed air flow thru the MAF making a longer delay

The silencer was halfway between the MAF and the motor. Already have a new TPS and new fuel filter. And my flat spot was a limit out on the road, hit the wall at 65-70 mph and wouldn't go any faster. Once I unplugged the vacuum to the fuel regulator it went faster. The fuel pressure drop with vacuum attached was measured after holding throttle open for a while, not momentary.

The question about fuel pump capacity has turned into a non-starter, just checked on Rock Auto and the ratings go from really low to good and high, all for the same application. I didn't realize that there would be that much variety, so I will choose something useable.

Thanks for your replies.

Thats odd that unplugging vacuum from FPR would allow you to go faster?

That would mean the pump can supply enough fuel, so my eye would be on FPR, but it seems to test ok

The fuel pump just spins, only has 1 speed, and yes they can get weak and you would expect to find that out at high demand, highway speeds, and limited power.

The FPR spring is set for 40-45psi, add vacuum assist and its 32-37psi
If fuel pump had reduce flow then fuel pressure wouldn't change, just less fuel would be sent back to the tank on Return line, until..........fuel pump flow dropped enough, so 30psi wasn't possible, then you would see that even at idle and with vacuum unplugged.

Just trying to get my head around it

So, here are my thoughts (rightly or wrongly).
1. Since the fuel pump won't hold pressure when the engine is off, it is getting worn.
2. By taking out the air silencer from the intake tubing, because it is just a big plug in effect, it allows more air to get to the motor. So the motor needs more gas to balance the more air, which pushing the injectors harder accomplishes. And of course then requires a touch less throttle to get the same hp.
3. I plan on using new 17# injectors along with a new fuel pump to restore the balance and hook my FPR back up. I already know that actual horsepower is going to be very little difference, but I am expecting the truck to run okay once again. And since we are talking about a naturally aspirated 2.3L motor in an extended cab truck, every half of an horsepower I can free up helps.

I just minutes ago re-set the computer and took it out on a drive to let the computer re-calibrate itself and it now runs about the same as before. Of course that is with the fuel pressure regulator unplugged from vacuum, which is pushing a little more gas through the injectors because of more pressure.

If silencer was between MAF and intake then you have created a Ported Vacuum leak.
All air going into the intake must go thru the MAF sensor or computer doesn't "see" it, so same a regular vacuum leak, loss of power

No N/A 2.3l needs larger injectors, it is not possible to use more than 2.3 Liters of air in that engine every 2 RPM.
At wide open throttle thats what that engine can pull in, 2.3 LITERS of air, thats what displacement means.
A 5.0l engine can pull in 5 LITERS of air every 2 RPM
5.0l engine has more power because it can pull in more air
Turbo forces in more air so engine has more power

Fuel injector size is calculated by duty cycle at MAX air flow for an engine

Its your money, but you won't get results you want, injectors are NOT the same as JETS in a carburetor

A good upgrade for any vehicle is an electric cooling fan instead of the mechanical fan
Not expensive if you use junk yard parts
And it is one of the few upgrades that gets you more power at the rear wheels and better MPG while doing it.

Mechanical fan draws power from the crank the whole time engine is on.
Electric fan draws power from the alternator but ONLY when driving slow or stopped, when you are driving faster the air flow thru radiator is more than any fan can provide so electric fan would shut off, no power draw, mechanical fan just keeps on sucking out that power

the air silencer is just a muffler between the MAF and throttle to get rid of the loud 4 cylinder intake pulses, they have about a 1" hole in them so they do help a touch when removed and are not a vacuum leak when removed (there's an article on this in the tech library, you take out the center part or replace the straight part with a piece of tubing).

I have heard that the injectors are a touch on the small side on 2.3L's, I've tried to fight that fight Ron... if you go up a couple LPH or GPH or however they are known it really isn't going to affect how the computer works, once it's in closed loop it will get the fueling back where it needs to be unless a large step is made...

Update: Installed slightly larger injectors, 18 gph from a 2002 Focus with regular motor. They are EV6 variety, not strictly plug and play. I had to slot the brackets on the fuel rail so that it would slide down further since the Focus injectors are physically shorter. And use adapters to on the pigtails to match them to the injectors. But, got rid of the flat spot, so slightly better power and about the same mileage, it may be up by a couple of tenths. Haven't done anything to the fuel pump yet.