Resolved Fuel pressure high at 52 new FPR same thing

[afjLX]

Ok on to the next problem. Plugs fouling looking like soot around the edges. Decided to start at checking fuel pressure.

Fuel pressure check showed it at 50psi. Looked like the original FPR so I replaced it with one of those adjustable units from LMR. This one reads 52psi and I’m not able to get any adjustment out of it. Can’t lower it at all. I replaced the fuel filter with a K&N unit about a month ago when I replaced the fuel pump. It has a walbro 255lb fuel pump and 24lb injectors.

Not sure where to go next? Bad injectors? Could the bigger fuel pump cause this?

UPDATE:

So I disconnected the return line at the fuel rail and dropped the tank and disconnected it at the pump. I inspected the fuel line closely from the engine to the tank and there is zero damage to the line. I blew 120psi of compressed air through the disconnected line and it blew through the no issues. Pulled the fuel pump and checked the return line and it was clear. I did end up pulling off the little rubber backflow duckbill cap/valve off the return line as it looked warped on the tip. I figured I could replace it later and test flow with it off. I reinstalled the pump, tank, and reconnected the lines. Hooked up my pressure gauge and it still reads 50psi. Zero adjustment with the regulator. So now I’m wondering could I have a clog at the injectors and testing it by dumping the fuel at the supply line disconnected was just the path of least resistance, thus allowing me to adjust the FPR.
One thing I will do first. Replace the shrader valve at the supply line test port. It looks old and kinda beat up. I also want to get another pressure gauge for a sanity check. Do this first before I go replacing injectors. Thoughts?

UPDATE 2:
I’m starting to wonder if I should step down to the walbro 190? The 255 is too much for my application?

UPDATE 3:
I’m stepping down to a walbro 190. Will report back.

UPDATE 4:

Well, installed the walbro 190 and cranked it up. Fuel presssure was at 30psi and I was able to adjust it to 40 without vacuum. So it does appear the 255 was overloading my return line. Maybe I got a really well built 255 that was pushing 99% efficiency and flowing every bit of its rated flow?

The Walbro 190 is on and I can now adjust fuel pressure. Thanks to everyone for their help!!

 

[AeroCoupe]

I ran 24's with a 255 pump and had zero issues getting the fuel pressure down to 39 psi. At idle (where you are setting the fuel pressure) the regulator doesn't care if the injectors are big or small the motor is going to use the same amount of gas at idle so the fuel system will need to return the same amount of fuel no matter the injector size.

My guess is you have a kink or some kind of blockage in the return line. Time to put it on a lift of get comfy on your back under the car to do a visual inspection. If it checks out then the next thing is to use compressed air to blow the return line out back to the tank.

 

[General karthief]

You need two fuel pressure readings, vacuum line attached and vacuum line removed/plugged.
I would get a FPR from the parts store and see if the pressures are better.

 

[afjLX]

The fuel pressure reads 50psi with the vacuum attached and disconnected. This is the stock unit and the adjustable unit from LMR.

I disconnected the return fuel line and shot compressed air in it. Tested it again after and still see 50psi with vacuum connected & disconnected.

Another thing I noticed. Fuel pressure bleeds off pretty quick. From 50 to 20 in less than a minute. I was expecting fuel pressure to be static with the engine off for a few minutes.

 

[General karthief]

Ok,, don't try another FPR

 

[AeroCoupe]

Do you trust the pressure gauge you are using?

 

[afjLX]

Do you trust the pressure gauge you are using?

Well, it’s the second one I’ve put on it. First one I ordered from an Amazon kit and it showed 50psi on the original fpr. When installed the new adjustable LMR unit it started bouncing around all over the place but showed over 50psi for the most part. So I went to harbor freight and bought a fuel pressure test kit and it is solid as a rock but shows 50psi. When I loosen the screw all the way or tighten it all the way the pressure does not change at all.

 

[AeroCoupe]

What brand is the adjustable FPR?

 

[afjLX]

What brand is the adjustable FPR?

Standard Motor Products brand sold by LMR.

 

[AeroCoupe]

In two of the reviews (both this year) one could not get below 73 pso and the other just said adjusted all the way down and it still flooded the motor. I’d say the General is on something here.

I would ask for a refund and the cheapest adjustable I would get would be a Kirban and this is because they are a great regulator and still somewhat reasonably priced. I still have one and would still have it on the car but I got a smoking deal on an Aeromotive which is pretty much the top end of regulators but they are pricey.

1987-1990 1991 1992 1993 Ford Mustang GT 4.6 5.0 Shelby Cobra BILLET ALUMINUM ADJUSTABLE FUEL PRESSURE REGULATOR

www.kirbanperformance.com

Also, the fuel pressure in my car drops pretty quick when the key is shut off. Running a Walbro 255.

 

[afjLX]

Thanks! I will try the Kirban and report back.

 

[Mcmahst]

Is there any chance you have a bad enough vacuum leak that the pressure regulator thinks it sees a lower vacuum reading associated with WOT? I think you said vacuum line ot not, you’re getting excessive pressure. Just a thought.

 

[afjLX]

Is there any chance you have a bad enough vacuum leak that the pressure regulator thinks it sees a lower vacuum reading associated with WOT? I think you said vacuum line ot not, you’re getting excessive pressure. Just a thought.

Would a vacuum leak cause Fuel pressure to be high?

 

[Noobz347]

What injector MAF combo are you running?

 

[afjLX]

What injector MAF combo are you running?

MegaSquirt no MAF. Ford 24lb injectors and walbro 255.

 

[Noobz347]

Is this fuel pressure issue a recent development or has the car been running rich for a while? Is there any recent maintenance associated with this issue?

What I mean is... What made you check fuel pressure?

 

[afjLX]

Is this fuel pressure issue a recent development or has the car been running rich for a while? Is there any recent maintenance associated with this issue?

What I mean is... What made you check fuel pressure?

I just bought the car a few months ago and have been going through it trying to fix issues. I noticed the plugs were fouled pretty bad. I installed a new set and checked them a week later and saw a lot of soot on them. Figured it was running a little rich. So that’s when I decided to check the fuel pressure. When I first got the car, it had an intermittent start issue. Replaced the fuel pump and fuel filter (k&N and walbro 255) while troubleshooting the start issue.

 

[AeroCoupe]

Regardless of any other components on the car when you set the fuel pressure with the engine idling and the vacuum disconnected that will be the pressure the injectors “see” at all times. This is a good read if you have a few minutes:

https://cdn.shopify.com/s/files/1/0806/0275/9468/files/EFI_engines_with_Bypass_Regulators_TB-_202-_Understanding_and_using_vacuum_boost_reference..pdf?v=1702570237

What I am driving at here is unless the car was tuned for a higher fuel pressure you need to get the fuel pressure down to 39 psi at idle with the vacuum disconnected as this is what an OEM ECU is expecting.

Your situation is a little different with the with the Megasquirt ECU. I’m pretty sure they want the fuel pressure at 43.5 psi or 3 bar. You also set the injector size in the software and then tune the motor with a wide band O2 sensor.

With all of this said I would think you need to get the pressure down to 43.5 psi.

 

[afjLX]

Regardless of any other components on the car when you set the fuel pressure with the engine idling and the vacuum disconnected that will be the pressure the injectors “see” at all times. This is a good read if you have a few minutes:

https://cdn.shopify.com/s/files/1/0806/0275/9468/files/EFI_engines_with_Bypass_Regulators_TB-_202-_Understanding_and_using_vacuum_boost_reference..pdf?v=1702570237

What I am driving at here is unless the car was tuned for a higher fuel pressure you need to get the fuel pressure down to 39 psi at idle with the vacuum disconnected as this is what an OEM ECU is expecting.

Your situation is a little different with the with the Megasquirt ECU. I’m pretty sure they want the fuel pressure at 43.5 psi or 3 bar. You also set the injector size in the software and then tune the motor with a wide band O2 sensor.

With all of this said I would think you need to get the pressure down to 43.5 psi.

That was my big concern, not being able to adjust the fuel pressure. I have the MS and wideband running. So I’m going to check the fuel lines for any damage to see if it’s kinked somewhere. I’ve already shot compressed air through the return line and I can hear air moving very slowly.

 

[AeroCoupe]

The air should move through the line at a high rate. When you do this remove the gas cap so the tank doesn’t build pressure.