Topic: Fuel Pressure Regulators

[sharpxmen]

I just found this post and I have a few questions as I am trying to learn as I go. Does increasing the fuel pressure at the fuel rail do anything besides increasing the fuel volume being injected into the intake?   What are the befits to an adjustable FPR versus a properly selected non-adjustable FPR? As a follow up, are the adjustments made multiple times or primarily just to fine tune it to your vehicle.

Thanks for the information

Bill

pretty much what Jeffy said but to add to that: if you have a larger throttle body and/or high flow intake/filter you can take advantage of the extra air by increasing the fuel quantity that is delivered - this is only for wide open throttle or close to that or to be more specific where the PCM (fuel injection computer) is operating in open loop without the O2 sensor feedback. It's hard to find a "properly selected" non-adjustable FPR that would match your mods as they are set from factory with a standard pressure for the vehicle they are meant for, the adjustable gives you a bit more flexibility and can be used with stock injectors and also with upgraded injectors like the Ford 19# to correct the resulting flow which would be less than stock in case they are installed in the Jeep (less fuel pressure). Also one thing to mention is that this one is for 91-95 EFI engines, the 96+ FPR is different and located at the fuel tank.

[Jeffy]

Also one thing to mention is that this one is for 91-95 EFI engines, the 96+ FPR is different and located at the fuel tank.

TJ's shouldn't have to worry about low fuel pressure since they are rated much higher then YJ's. 39 psi v. 49 psi

[sharpxmen]

TJ's shouldn't have to worry about low fuel pressure since they are rated much higher then YJ's. 39 psi v. 49 psi

not a worry - i didn't know what Jeep he has (i did see after i posted that it's a 91-95 from his sig). Same goes for the TJ, you can get more flow with a bit more pressure, the fpr is just different than the YJ that's why i mentioned it in case he was asking about that one.

[Jeffy]

not a worry - i didn't know what Jeep he has (i did see after i posted that it's a 91-95 from his sig). Same goes for the TJ, you can get more flow with a bit more pressure, the fpr is just different than the YJ that's why i mentioned it in case he was asking about that one.

The TJ's use that funky fuel filter/FPR on the tank though. Wouldn't it be easier to just change the injectors since most are rated at 43#?

[sharpxmen]

The TJ's use that funky fuel filter/FPR on the tank though. Wouldn't it be easier to just change the injectors since most are rated at 43#?

you need a way to fine tune the afr - it is very unlikely that you will find a combination of an injector + a stock FPR that would be right on the spot with your mods and get you the desired afr in open loop. You could find an injector that is rated at 43.5 which would work well at 49 but the resulting flow would be too much, in that case you want to lower the pressure to get the propper flow.

it's gets more complicated when you get into forced induction as in that case you should also play with your O2 output to alter the afr in closed loop as well (so when you're in boost and your resulting comp ratio goes up you want to be on the rich side and not rely on the o2 feedback which is rather lean for a boost situation) - but that's a whole different topic.

[melbill]

This makes sense. So once you have the adjustable FPR and what should be a proper injector, how do you fine tune it? Is it by ear, or is there a gauge, monitor, or something else to get a read out to make adjustments?

I have a cold air intake and will soon be installing a 62mm throttle body and spacer, a intake cleaned up to 62mm, and a Clifford header.

I am seriously considering boring my engine out .030 - .060. over and a crank and cam to get the most out of it.

My build will definitely be slow and in stages as this is my daily driver. Should I and at what point would I get the most benefit  from  an adjustable FPR.

Thank you both very much for the help and very good explanations.

Bill

[sharpxmen]

This makes sense. So once you have the adjustable FPR and what should be a proper injector, how do you fine tune it? Is it by ear, or is there a gauge, monitor, or something else to get a read out to make adjustments?

I have a cold air intake and will soon be installing a 62mm throttle body and spacer, a intake cleaned up to 62mm, and a Clifford header.

I am seriously considering boring my engine out .030 - .060. over and a crank and cam to get the most out of it.

My build will definitely be slow and in stages as this is my daily driver. Should I and at what point would I get the most benefit  from  an adjustable FPR.

Thank you both very much for the help and very good explanations.

Bill

you can use an adjustable FPR with your stock injectors. If you want to go by the books you would need a wideband O2 sensor that will tell you the exact afr outside of the 14.7 ideal. Or you can go by ear and target a richer afr in open loop and also consider your slightly improved VE by using the high flow intake and larger t/b. the increase in flow should be up to 10% using stock injectors, and probably starting at about 5% if you want to be conservative. In your case considering the mods you can definitely take advantage of a little extra fuel if you have one.

[melbill]

Thanks, I will be watching this thread to see what else comes up. This is quite interesting, not just the effects but the theory behind it also.

Thanks again
Bill

[sharpxmen]

not the best pic but you get the idea

so i finally got around to preset this - i set it at 43psi. Had trouble figuring out why i could not go below 48psi, turns out my return line is plugged. took it out and will ship it over to Jeffy for a review

this is a better picture than the one before

[melbill]

That thing is coming together great. Is it adjusted by the bolt on the end? Also when you were talking about the return line I only see two places for lines, the copper elbow press on fitting on the bottom ant the small silver nipple opposite the bolt. Where does the return line come from and where does it go?

Thanks

Bill

[sharpxmen]

That thing is coming together great. Is it adjusted by the bolt on the end? Also when you were talking about the return line I only see two places for lines, the copper elbow press on fitting on the bottom ant the small silver nipple opposite the bolt. Where does the return line come from and where does it go?

Thanks

Bill

i was talking about the return line on my Jeep that connects to the fuel rail and goes back to the gastank - that is plugged somewhere along that route. the FPR was fine, i had trouble adjusting it so i ended up with a hose on the fuel rail and put the other end in a bottle to be able to adjust the pressure.

yes, it is adjusted by that screw and once adjusted you tighten the nut to secure the screw/bolt in place. Internally the screw is machined down to 3 mm and that end goes into a disk that seats on the spring that regulates the pressure. the brass fitting is the vac port.

[melbill]

Ok, that makes more sense with the return line. and a very efficient and easy way to make changes. I look forward to seeing how this progresses.

Bill

[Sine Deviance]

Same here. I'm going to be needing an adjustable FPR soon and I don't want to spend $130 + core or $200 on one.

[sharpxmen]

ok - i will pick up a couple of stock ones and mod them to be adjustable - $75 plus shipping (it's around $5 US or Canada) and the core charge (was $20 last time i picked one) - i am charged $3 for every parcel i receive in the US so the refund on the core would be $17 - i need back both the fpr and the mounting bracket or you can keep them for the $20.

you guys let me know if this is reasonable and i will go ahead and make 2 of them and have them preset to 43 psi. First come first serve on this so just reply here and whoever commits first gets it. If there are more takers i can make more once i receive the cores back.

[Sine Deviance]

ok - i will pick up a couple of stock ones and mod them to be adjustable - $75 plus shipping (it's around $5 US or Canada) and the core charge (was $20 last time i picked one) - i am charged $3 for every parcel i receive in the US so the refund on the core would be $17 - i need back both the fpr and the mounting bracket or you can keep them for the $20.

you guys let me know if this is reasonable and i will go ahead and make 2 of them and have them preset to 43 psi. First come first serve on this so just reply here and whoever commits first gets it. If there are more takers i can make more once i receive the cores back.

Don't build one for me just yet. I need to see how much of my tax returns I'll be able to throw into this. They come next week.