Fuel Pressure

[boostedclipse97]

I just put in a bolt on kit for my 420a.. everythings been running fine but a few days later the check engine light came one.. im pretty sure it might be the fuel pressure.. i already have a fuel pump and a fpr.. but the fpr wasnt adjusted and the fuel pressure is at 50psi. Can anyone tell me if im running lean and what psi i should be running.. IM runing 7.5 pounds of boost on my turbo. I dont wana drive the car until i know whats going on
thanx

 

[rstare]

Idle fuel pressure should be 53psi, what is your rising rate set to? If your rising rate is set to low you might not be getting enough fuel under boost.
Ryan

 

[boostedclipse97]

Idle fuel pressure should be 53psi, what is your rising rate set to? If your rising rate is set to low you might not be getting enough fuel under boost.
Ryan

never set a rising rate.. can u tell me how to do it

 

[rstare]

First of all do you have a fmu or a sfmu, its possible that you cant even set your rate without buying a recalibration kit. Is it a vortech? Where exactly did you get the turbo kit itself, or did you peice it together?

 

[cs82685]

sounds to me like you're running a regular 1:1 fpr. If that's the case, you need to stop boosting immediately until you get a fmu (12:1), sfmu (largest disk/dark spring) or hahn fpr. I would aim for idle fuel pressure between 53-60psi on stock injectors.

 

[tcavenger99]

i am having the same problem. i can ajust my fuel preasure by tightning a screw ,yet i am unsure what presure i have under boost ,i can only ajust idel presure and its at 55 now and still cant get it right

 

[rstare]

Okay, i think i misunderstood the OP, some places call fpr and fmu the same thing. What my question is to both the OP and Avenger is what are you guys using for regulating your fuel pressure. Are you just using the stock fpr, or did you buy something aftermarket? If you are using the stock fpr, stop boosting right now. If you bought something aftermarket, then what was it you bought?

 

[cs82685]

i am having the same problem. i can ajust my fuel preasure by tightning a screw ,yet i am unsure what presure i have under boost ,i can only ajust idel presure and its at 55 now and still cant get it right

yeah you might want to invest in a fuel pressure gauge. Even a cheap $20 under the hood one is better than nothing. Then you can check to make sure your fpr is working by using a compressor to blow air into it while watching to see if your fp gauge goes up. Saves you from having to actually boost to test the fpr this way if it's not raising pressure you don't run dangerously lean just testing to see if it's working right

 

[boostedclipse97]

Okay, i think i misunderstood the OP, some places call fpr and fmu the same thing. What my question is to both the OP and Avenger is what are you guys using for regulating your fuel pressure. Are you just using the stock fpr, or did you buy something aftermarket? If you are using the stock fpr, stop boosting right now. If you bought something aftermarket, then what was it you bought?

i have an aftermarket fpr and it is adjustable.. but i havent had time to figure out how to adjust it.. I also have an fmu.. but i never installed it on the car because i figured if i found out how to tune it with the fpr i wouldnt need both.. the cars sittin in my garage now n i was gona bring it to a shop to get it checked for free b.c the check engine light is on. the fpr also has the fuel pressure on it and its reading about 40 when the cars idle

 

[rstare]

i have an aftermarket fpr and it is adjustable.. but i havent had time to figure out how to adjust it.. I also have an fmu.. but i never installed it on the car because i figured if i found out how to tune it with the fpr i wouldnt need both.. the cars sittin in my garage now n i was gona bring it to a shop to get it checked for free b.c the check engine light is on. the fpr also has the fuel pressure on it and its reading about 40 when the cars idle

When you say the fpr is adjustable you are saying you can change the idle fuel pressure right?

 

[boostedclipse97]

When you say the fpr is adjustable you are saying you can change the idle fuel pressure right?

yea i should.. thats what it said in its description when i bought it.. its adjustable.. just havent played around with it yet but it is under the hood.

 

[Shadow98]

Are you running the stock injectors? If you are, thats your problem along with the A-FPR. If you are not using MS or Portfueler, you need to be running a FMU or S-FMU! An A-FPR has a rasing value of 1:1. So, if at idle you're at 50psi it will 1psi for every pound of boost, hence making you run lean under boost. With an FMU, depending on the disk will depend on how much your pressure raises by. Do you know what disk is in your FMU? You'll need at least a 10:1, but must go with the 12:1 for added safety of not running lean. I have a 12:1 Vortech FMU laying around if you need it. PM me.

 

[rstare]

Exactly what shadow just said. A fpr controlls idle pressure and a afpr has a 1:1 rate so you wont be getting enough fuel under boost. So stop boosting like said previously, get at minimum a fmu. 12:1 is what you need to get. I would suggest a sfmu, and larger injectors, cause you dont want to skimp out on the fuel system. The fmu is looked at by most people as a temporary set up. With a sfmu you can control idle pressure and the rising rate, which allows you to controll injectors. That is what I would suggest at minimum.
Sorry about the confusion, some places refer to a fpr a fmu (bell engineering) so I wasnt sure exactly what you had.
Ryan

 

[boostedclipse97]

Are you running the stock injectors? If you are, thats your problem along with the A-FPR. If you are not using MS or Portfueler, you need to be running a FMU or S-FMU! An A-FPR has a rasing value of 1:1. So, if at idle you're at 50psi it will 1psi for every pound of boost, hence making you run lean under boost. With an FMU, depending on the disk will depend on how much your pressure raises by. Do you know what disk is in your FMU? You'll need at least a 10:1, but must go with the 12:1 for added safety of not running lean. I have a 12:1 Vortech FMU laying around if you need it. PM me.

thanx alot.. i already have a 12:1 fmu but i need help on installing it.. n u have a link or can u tell me how to set it up.. its a jdm universial 12:1 fmu

 

[rstare]

Your fuel system is a "returnless" system. One end of the fuel rail is capped off, (the passengers side). The stock fpr is in the return line and the fmu goes in after the stock fpr. So take the line coming out of the fpr and put it in the the fmu in. Rerun the fmu out line, and run a vac line to the fmu from the intake manifold.
You need a fpr with a fmu.
Ryan

 

[chris712vt]

thanx alot.. i already have a 12:1 fmu but i need help on installing it.. n u have a link or can u tell me how to set it up.. its a jdm universial 12:1 fmu

You must be logged in to view this image or video.

batta bing batta boom, aesthetically pleasing installation diagram.

 

[rstare]

Thanks Chris I looked for a diagram, but couldnt find one so I just explained it best I could, but pictures are always better.

 

[chris712vt]

Original poster - I don't know if you are new to this or not, but in case all these acronyms and ratios are confusing you I'll try to lay them all out here for clarification:



FPR - fuel pressure regulator. Stock, yours maintains about 53 psi.

AFPR - air fuel pressure regulator, such as the aeromotive 1:1. An AFPR will replace your stock FPR, and then you can set whatever you want your static/idle fuel pressure to be, and it will raise fuel pressure at 1psi of fuel for every 1psi of boost it sees. You would use an AFPR if you were running larger injectors, and more importantly a stand alone type of tuning device like megasquirt (MSnS) or portfueler.

FMU - fuel management unit, such as the Vortech 12:1. FMUs are to be used WITH your stock FPR. An FMU would also be used with stock sized injectors. Reason being - the stock FPR maintains your static/idle fuel pressure, then when you get into boost, the FMU adds even more fuel pressure beyond what the FPR is making, specifically at whatever rate your FMU is made for. The rate is not adjustable, so the 12:1 which is most common would supply 12psi of fuel for every 1psi of boost on top of your FPR's 53psi.

SFMU - super fuel management unit, such as the Vortech SFMU. This is similar to the regular FMU, except for two big differences. First you can set different gain ratios using the disc and spring combinations, so you aren't stuck at say the 12:1 rate. Also, more importantly, just like the AFPR, you set your own static/idle fuel pressure, thus you don't need the stock FPR and you can run larger injectors.

I know Bell Engineering has an FMU which has an adjustable rate of gain (you can set it at 2:1, 4:1, 8:1, 12:1, etc.), which would be used in conjunction with your stock FPR, and I've got an extra one of those. Bell also makes the equivalent of an SFMU where you can change your gain rate as well as set your static/idle fuel pressure, which would be used alone. I think there are also FMUs made by Cartech or something like that, but I don't know of any other popular/trusted brands that are used by 420A DSMers.

All in all, I'd say your order of fuel systems would go like this:

- stock injectors, stock FPR, NO BOOST!!!
- fuel pump, stock injectors, stock FPR + 12:1 FMU, up to 7 or 8psi.
- fuel pump, larger injectors (450s or 550s max), SFMU, up to 15-16psi, depends on lots of variables.
- fuel pump, much larger injectors, AFPR, *stand alone tuning*, 20...25...30...psi!



If that was all a waste of time to everyone... sorry. I'm just killing time on my lunch break .

 

[rstare]

What a wasted time, . J/k.
No i was really confused to cause the op kept saying he got a fpr, you have a fpr stock so I figured he meant fmu. But Bell Engineering actually does call their fmu a fpr. When I emailed them asking about their fmu they replyed with a "I dont understand what you mean by fmu" so, idk, i guess this was the real wasted time, .
By the way Cartech and Bell Eng. used to be the same company, so theres are practically the same, cant even tell the difference by looking at them as far as I have seen.

 

[chris712vt]

Isn't cartech what Hahn supplies with their kits too? Or am I mistaken?

Anyway yeah there's plenty of room for confusion when some people call fmu's fprs, then you don't know which they are really referring to, and blah blah blah. You (original poster, whoever else) just need to be aware of what you actually have, what it's function is, and if it is being used correctly for your fuel system.

Edit - I guess the terminology "FRP, AFPR, FMU, etc" isn't worth getting caught up on and confused over. All of them build fuel pressure, some are predetermined, some you can set yourself, and some raise the rate with boost, at what rate and if it is adjustable depends on the model.

 

[cs82685]

Isn't cartech what Hahn supplies with their kits too? Or am I mistaken?

Yes.

AFPR - air fuel pressure regulator

I was always under the impression it stood for Adjustable fuel pressure regulator

 

[chris712vt]

oh maybe it does... that makes sense. haha I had just heard air a long time ago and thought that was it. oh well whatever.

 

[tcavenger99]

OK all this is for sure a mouth full. ( yet great info ) My question is my so called fmu has 3 lines coming off it for fuel , one is blocked off and the other 2 are tied into the fuel system now. I can turn the screw in it and my idle pressure increases. I then hooked my air compressor up to the vac line on it and with 10 psi and my fuel pressure jumps from 55 to 75psi. so is this not a fum after all ? Second off i am running a 95 fuel rail that has a regulator built in the rail on the passenger side , do i need to do anything to that . Last of all i have a fmu 12:1 on the way now , yet the old so called fmu if it is that what should i do with it or can i put it in line with the new fmu so i can tune idle pressure?

 

[rstare]

Avenger,
It sounds like what you have now is a sfmu, because you can control the idle fuel pressure and it is raising your fuel pressure when under boost (2:1). Your fuel pressure went up 20 and you applied 10psi so do the math and its a 2:1. Do you have bigger injectors? Either way I would say your idle fuel pressure is too high if its at 55psi. I would also think 2:1 is too low. What brand is your sfmu, if it is Vortech then they have different disks for different ratios, Bell Engineering can change the ratio by simply turning a knob, those are the only 2 sfmus I know of.
Ryan

Edit: 55psi for idle fuel pressure is ok as long as you have stock injectors, but if you have bigger injectors its too high.

 

[tcavenger99]

Edit: 55psi for idle fuel pressure is ok as long as you have stock injectors, but if you have bigger injectors its too high.[/QUOTE]

ok 55 is good for stock i have 36lb injectors what should i set the idle pressure ?