Questions on fuel pressure. Need ideas

[Ethan12v]

I apologize in advance about what I'm going to put you guys through...

I've been chasing down a fuel pressure issue ever since I bought my truck. Mods are current in my sig. First off my idle pi is set for 21psi, it seems to hold this adequately without much fluctuation. I can accelerate and it will build pressure but once it starts to crest about 1500rpm, my pressure drops down to about 19psi. In here to tell you after reading numerous writeups, TSB's, and searching forums. I've nearly touched every point of my fuel system to look for leaks and restrictions. I have installed a new lift pump.... From orieleys... I know (the brand is Precision). I have a Tork Tek OFV thats nearly bottomed out against the seat to keep my 21psi idle, I've installed brand new 3/8 hose on both ends of the hard steel lines running along the frame (sending unit to hard line and hard line to hard line going into prefilter housing) therefore eliminating the clips. I only have hose clamps now. Ive cleaned my prefilter, I lifted my bed and cleaned my sending unit screen. I looped a 1/2" hose from the pre screen to the lift pump, used hose clamps. I have a brand new fuel filter in the housing. Yet I cannot stop the truck from loosing fuel pressure.

I bought a 14 ft piece of 3/8 fuel line and ran it all the way from the tank to the hard line going to the prefilter housing just to test if the hard steel lines. It mad no difference whatsoever.

I put a sight glass in the rubber line going from the tank to the steel lines, no bubbles

I put the sight glass in the rubber line connecting the steel lines to the hard line on the prefilter, still no bubbles

Ive pressurized my tank with shop air multiple times and waited, no fuel leaks

HOWEVER, when I kink my return line, pressure will shoot up like everything is hunky dory.

Ive taken my OFV apart. Seal seems okay. The seat doesn't "look" damaged. Appears to be all in working order.

My questions are .. Can this be caused by an IP or injector issue?

Does the return line affect fp at all? Say the hose has a loose connection up by the tank

Is it possible that the IP is just flowing more than the stock LP can keep up with at higher rpm?

Anyway, theres my novel... I just really need help

Thanks

[Redrider2911]

Definitely an issue with the overflow valve if your pressure shoots up when kinking the return line. You got a picture of it taken apart? See if we can spot what is wrong. Do you still have the stock OFV? Did you have this problem before the new OFV?

[Ethan12v]

Originally Posted by Redrider2911

Definitely an issue with the overflow valve if your pressure shoots up when kinking the return line. You got a picture of it taken apart? See if we can spot what is wrong. Do you still have the stock OFV? Did you have this problem before the new OFV?

You know, I have no idea where my stock one went or else is throw it in there to check. The thing is that I put my new OFV in before I had a new lift pump so I have no clue what the OFV really did. Im not sure exactly how many miles are on the tork tek one but I've had it for a solid 2 years. I can get a picture of it taken apart for you.

[Redrider2911]

I don't know if those Torq Teks are prone to failure? Or if maybe something was assembled wrong. But I believe that your symptoms point to that as the issue.

[Ethan12v]

Originally Posted by Redrider2911

I don't know if those Torq Teks are prone to failure? Or if maybe something was assembled wrong. But I believe that your symptoms point to that as the issue.

That would be amazing to just throw a new OFV in there and problem solved. Often thought of setting up an actual fuel pressure regulator instead but if there won't be a difference i don't see a need. Maybe I should try the Larry b OFV instead this time but itseems to pretty much be the same design

[CowboyEdition]

Where is your fuel pressure gauge plumbed in?

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[Ethan12v]

Originally Posted by CowboyEdition

Where is your fuel pressure gauge plumbed in?

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The gauge is plumbed into the inlet port of the pump through a tork tek gauge snubber and it is an electronic gauge which I have tested alongside of a known good mechanical gauge

[CowboyEdition]

Any chance the inlet to the pump is the restriction? If it is, injection pump charge pressure could appear to drop under load....

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[Redrider2911]

Originally Posted by CowboyEdition

Any chance the inlet to the pump is the restriction? If it is, injection pump charge pressure could appear to drop under load....

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Either way, with the Torq Tek threaded all the way in, he should be seeing over 60psi at idle...

[Ethan12v]

Originally Posted by CowboyEdition

Any chance the inlet to the pump is the restriction? If it is, injection pump charge pressure could appear to drop under load....

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You got me thinking now... I can't lead myself to believe that the orifice size in the snubber would be any different than than the factory banjo bolt, but if that was true it would definitely cause a restriction

[Ethan12v]

Originally Posted by Redrider2911

Either way, with the Torq Tek threaded all the way in, he should be seeing over 60psi at idle...

If I completely block it off it will spike to 60psi. I just don't know where else to go to look for an air leak. 25psi is the max I can make before it drops down

[CowboyEdition]

Originally Posted by Redrider2911

Either way, with the Torq Tek threaded all the way in, he should be seeing over 60psi at idle...

Not necessarily. The OFV causes pressure by restricting injection pump outlet flow. If flow is already restricted at the inlet, there may be 60psi between lift pump and injection pump and not enough flow through the injection pump outlet for the OFV to maintain pressure inside the injection pump where the fuel pressure gauge is plumbed.

The fact that the OFV is screwed in so far may be a lack of flow through the injection pump.

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[Ethan12v]

Originally Posted by CowboyEdition

Not necessarily. The OFV causes pressure by restricting injection pump outlet flow. If flow is already restricted at the inlet, there may be 60psi between lift pump and injection pump and not enough flow through the injection pump outlet for the OFV to maintain pressure inside the injection pump where the fuel pressure gauge is plumbed.

The fact that the OFV is screwed in so far may be a lack of flow through the injection pump.

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I really wish I had kept my factory banjo bolt now, I gave it to a friend of mine who had a fuel pressure gauge and needed one to drill and tap for a needle valve.

If the orifice sizes in the Tork tek are the same as the factory than that would mean no restriction right? I wouldn't think they would deviate from the original specs

[CowboyEdition]

Originally Posted by Ethan12v

If the orifice sizes in the Tork tek are the same as the factory than that would mean no restriction right? I wouldn't think they would deviate from the original specs

Agreed. I don't know of the Tork Tek snubber has more or less restriction than stock - you'd think it would be less restriction. But if we're willing to accept a bad OFV valve, then perhaps you could also get a bad snubber. The OFV determines fuel pressure based on flow. So if fuel pressure is dropping when it shouldn't, then you either have a OFV problem or a flow problem. I kinda feel like if the OFV adjuster is screwed in almost all the way, that it's doing its job and you rather have a fuel flow problem.

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[Redrider2911]

At idle I can fill a gallon jug full of diesel from the return line within like 3 minutes (I should have timed it). Maybe see what kind of volume you are getting out your return?

[jwestra]

There is a screen inside the lift pump inlet, which has caused me issues in the past. worth a try taking a look at it.

[Ethan12v]

Originally Posted by jwestra

There is a screen inside the lift pump inlet, which has caused me issues in the past. worth a try taking a look at it.

There's less than 1000 miles on this lift pump. Ill give it a shot and open it up. Would you suggest removing the screen altogether? Theoretically the pre strainer would catch any of that garbage before it went through the LP anyways

[Ethan12v]

Did some experimenting today, I removed my ofv and basically gutted it. Put it back in the truck and pinched the return line until I had 21psi idle. While I was standing there I revved it up to about 1500rpm and pressure raised to 25pi and dropped down below 20 as it always does. Not sure what it means but the problem exists with or without the ofv. I also took my t block off for my gauge and the line to the sending unit and installed a mechanical one, just to make sure it want leaking through those fittings. No difference. Not sure what else to check next. In about to break down and buy the Larry b lift pump inlet 3/8 line fitting. Either that or ill try to find a 1/2 to 3/8 barb fitting and just connect the two hoses together, essentially bypassing the entire prefilter assembly. That way ill at least be able to isolate the prefilter assembly from the rest of the fuel system. If my pressure is in spsp after that, ill know the prefilter assembly is the source of an air leak. In including a few pictures of my ofv as requested as well as my gauge

[CowboyEdition]

Is there an easy way to plumb your gauge into the system between the lift pump and injection pump inlet? If fuel pressure did the same thing, I'd suspect a crummy lift pump, maybe a weak spring or a mushy check-valve... If fuel pressure stays high, the inlet fitting wold be suspect.

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[Redrider2911]

If you kink the line completely what do you see for max pressure? These mechanical pumps are capable of putting out over 100psi. Most guys are regulating between 50psi and 70psi for decent HP applications.