Fuel Pressure - Another Thread

[Charles Young]

I am fairly new to TB's and have been reading but would like your opinions of my problem. I think I have a FP going bad.
What I have: 87 GN, new fuel filter, Kirban regulator (I think), hot wire kit and a pump that PO said was a Red Armstrong pump but 10-12 years old. I just installed a new test gauge so I could see FP while driving. I have a scanmaster but no power logger.
FP at idle was about 40-41, vac about 15
FP at zero boost/vac went up to about 49
FP at 5 psi boost was about 52
FP at 10 psi boost was about 58
at about that point, FP starts to drop off. As boost increases, FP continues to drop. It went all the way back down to about 45 psi as boost went in the 10-15 psi range. I got no KR though.
Batt voltage on the SM was about 14v while driving normally.

I am not sure how to check the voltage to the pump while driving but have no reason to think that is a problem.
I know there are tons of posts on FP but after reading about 40 of them I start to get a little foggy and thought I'd ask.
Any ideas?
Thanks,
Charles

 

[87-WE2]

Could be. Check all your vacuum line 3 times first, especially the one going to the regulator (which regulator you using?). Also check to be sure none of your intake piping is leaking.

 

[Charles Young]

Regulator is from Kirbans per previous owner. I have already been replacing vac lines but will keep working on that. Intake piping is good as far as I can tell. Thanks for the info!

 

[we4Mateo]

49 at zero boost is a little high. What chip do you run? It's usually around 43-45 psi car running, warmed up, with vacuum line of off the regulator which should be the same pressure as your zero boost reading. Regardless, you do have either a bad regulator, a vacuum leak on the way to the regulator, or a bad pump. You should be able to make and sustain 70+psi of steady fuel pressure with any pump you run. You can also test it without driving the car. Just put pressure to the top side of the regulator and watch for steady or falling fuel pressure. You'll need to measure the air pressure though to know where you are at.

 

[Charles Young]

Thanks we4Mateo.
I have a Bailey's Extender chip and it says set FP for 45 psi. I'll double check my "line off" setting.
Testing the reg/pump combo by applying pressure directly to the reg would help me rule out the vac leak piece of the puzzle, right?
That's a great idea and I'll give it a try if I can find away to apply a controlled air pressure source.
Thanks!

 

[dynoman]

Use a Mity Vac hand pump to pressurize your regulator. They are good to have for other repairs too, like bleeding brakes . Sam

 

[Charles Young]

I tried the idea of applying air pressure to the reg while in the garage. FP increase tracked air pressure increase pretty close 1:1 from zero all the way up to 70 psi FP and held there. Sounds like pump and reg are OK so I'm off to chasing vac leaks, unless somebody has another suggestion.
Thanks!

 

[we4Mateo]

I tried the idea of applying air pressure to the reg while in the garage. FP increase tracked air pressure increase pretty close 1:1 from zero all the way up to 70 psi FP and held there. Sounds like pump and reg are OK so I'm off to chasing vac leaks, unless somebody has another suggestion.
Thanks!

It still may be a pump. Holding 70psi while the engine isn't sucking any fuel is easier than when it is. I'd first be checking for vacuum leaks. You may have a hose going to your regulator that is bleeding off boost pressure and thus dropping fuel pressure. Once vacuum line is verified good, then you need to check the fuel pressure rise while driving the car again under load; get out of it quick if it doesn't hold pressure then. If it still falls off after that, then you probably need a pump. I change mine every four years or so just as maintenance.

 

[earlbrown]

You may have a hose going to your regulator that is bleeding off boost pressure and thus dropping fuel pressure.

^YEP. Every joint between the FPR all the way to the manifold signal needs to have a zip tie or safety wire clamping it down.


Just for funzies, pop the FPR signal line off the vacuum block and do the same test with your John Holmes pump. If it doesn't track to 70 with the same tool pressure (giggity), you've found your problem.

 

[Charles Young]

Thanks Earl - Will do. It sure would be nice to find the problem in that relatively small length of hose. At one point I noticed a little bit of air leaking by the FP reg adjustment screw. It didn't seem to be enough to affect fuel pressure. Is there anything to do about that?

 

[earlbrown]

Depends on how it's leaking and what FPR it is. Is it leaking where the nut meets the body or past the screw threads.

 

[Charles Young]

I believe my reg is from Kirban and looks much like this one on their site; except I just noticed mine missing the hex nut on the allen screw shown in this pic. I assume that is a lock nut.
The leak I saw on mine was past the threads. In the pic above it looks like there is a little seal under the nut on the allen screw. Is there a seal I'm missing too?

 

[Pronto]

Don't remember but think there is a fiber washer under the lock nut.

 

[TurboTdr3.8]

except I just noticed mine missing the hex nut on the allen screw shown in this pic

You need that nut to lock down your adjustment to keep it from moving

 

[earlbrown]

I believe my reg is from Kirban and looks much like this one on their site; except I just noticed mine missing the hex nut on the allen screw shown in this pic. I assume that is a lock nut.
The leak I saw on mine was past the threads. In the pic above it looks like there is a little seal under the nut on the allen screw. Is there a seal I'm missing too?

Yep, you need to get that nut (giggity) and the plastic seal under it. It doesn't look like it in the pic, but I'd get an 'aircraft' nut with the nylon top threads. You might have to run a tap halfway through it to open up the plastic a little and keep from stripping the adjusting stud. (or replace that stud with a SS bolt too)

 

[DavidM]

Precision Turbo and Engine (PTE) makes one that looks just like Kirban's.
@Charles Young

 

[Pete Revenidis]

Mine was doing the sane thing it was my pump starting to go bad

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[Charles Young]

Update: Did more testing and replacing vac lines, found a major leak at the EGR so I got rid of it but still had the same problem. Vac lines to the FP reg are new and tested, same problem. Ugh. Finally got to replace the fuel pump with a Walbro 340 tonight. Also found that the rubber piece of line in the tank was in very bad shape, probably sucking air. Between replacing the pump and the small piece of line, the problem appears to be solved! I'll readjust FP this weekend and do a little more testing of pressure vs boost but I'm feeling pretty good about it right now! Everyone's input from this board is invaluable. Thank you!!

 

[buickGN3:16]

My fuel pressure drops off instantly aftr cutting the car off aftr having it running, any ideas there? Possibly the same lil hose u had sucking air?

 

[Charles Young]

My fuel pressure drops off instantly aftr cutting the car off aftr having it running, any ideas there? Possibly the same lil hose u had sucking air?

I think I misspoke about the rubber line in the tank. I think it was actually downstream of the pump so it would be bleeding off pressure rather than sucking air. Either way, there is a separate check valve in the system that may be bad on your car.