# fuel pressure regulator



## 0341TODD (Nov 15, 2003)

Hey does anyone have an aftermarket fuel pressure regulator on their car? If so what works and what doesnt- of course I searched this


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## 0341TODD (Nov 15, 2003)

*redline*

What is the redline for the turbo? I cant find an answer to this anywhere


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## Spongerider (Nov 18, 2002)

0341TODD said:


> What is the redline for the turbo? I cant find an answer to this anywhere


Nismo or SX off the top of my head. And it looks like 6K is redline.


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## JAMESZ (Mar 12, 2004)

Stay away from FMUs. FMUs will give you no extra power. At most they are a cover and will get you nowhere. They are bad!


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## Spongerider (Nov 18, 2002)

JAMESZ said:


> Stay away from FMUs. FMUs will give you no extra power. At most they are a cover and will get you nowhere. They are bad!


What is a FMU?


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## 0341TODD (Nov 15, 2003)

what is an fmu?


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## Zen31ZR (Mar 24, 2004)

JAMESZ said:


> Stay away from FMUs. FMUs will give you no extra power. At most they are a cover and will get you nowhere. They are bad!


If they are bad , then EVERY tuner that uses them is incorrect. And that's quite a lot. Actually , if you think about it , FMUs are NOT bad , in fact it could be the very thing that saves your engine. FMUs prevent too much fuel from being recirculated back to the tank , and much above a low level tuned car that could result in a lean condition. It also helps raise the fuel injectors capacity a bit , which is also not a bad thing if you are running close to the limit. 

James , I know you got that information from Z31.com , but the more I read from that place , the more I'm convinced those guys have no clue what they are talking about. For example , DSM tuners have been using rising rate FMUs for years. DSM tuners are also running 8s on the stock ECUs on 30+ lbs of boost , which is quite far outside the stock ECUs operating range. If you use the proper equipment , you can get a car to do anything you want.


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## JAMESZ (Mar 12, 2004)

Errr I didn't get that from Z31.com actually.


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## Zen31ZR (Mar 24, 2004)

JAMESZ said:


> Errr I didn't get that from Z31.com actually.



Yeah , but they say it too. Common misconception amongst low level tuners. Those of us that have used such things know better.


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## Zen31ZR (Mar 24, 2004)

Let me iterate a few things , before James thinks I'm picking on him. FMUs are useful in a number of ways. #1: They can prevent a lean condition caused by hi flow large turbos that run at fairly low psi , since the stock FMU responds directly to the psi/vacuum present in the intake manifold , or the equivalent location. #2: The extra few psi of fuel pressure gives the injectors that extra "kick" , and through the O2 sensor can actually cause the ECU to close down the pulse width a bit. This is not a bad thing #3: It allows high rpm turbo cars to run deeper into the redzone without the risk of leanout associated with the typical loss of boost pressure at extreme rpms. 
FMUs are fairly useless by themselves , except as in the case of #2. A typical stock FMU/FPR cannot handle the associated increased pressures resulting from increased boost pressure over stock , or even a higher pressure fuel pump. This typically results in what every tuner knows as FPR overrun , and in extreme cases can cause FPR failure and a resulting leanout condition , which WILL seriously damage your engine , especially if you are deep in the heart of the power band at high rpms. Can you say melted pistons? 

FMUs are typically coupled with such devices as Super-AFCs and VPCs , and is a very useful tuning tool. Typical stock ECUs reduce timing after seeing a certain amount of airflow (either lbs/hr or cfm) , but using a S-AFC combined with massive injectors and an FMU can cause the ECU to actually ADVANCE timing , as the S-AFC tricks it into thinking it's seeing LESS airflow than is actually going into the engine , while maintaining fuel flow capacity. I've seen timing advances of better than 40 degrees in DSM applications using the devices listed above. Timing advance is a good thing. 

As I've been trying to explain , FMUs are a part of the whole picture and not very useful by themselves. But used correctly they are an extremely useful tuning tool. Ask any tuner in the 10s or 9s in the 1/4 , he likely has one.


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## 0341TODD (Nov 15, 2003)

Right so a simple answer to our question is Fuel Management Unit- Like my super afc- I'll tell you what, from experience they do work and it is an extremly useful tuning tool when used in the right application.- I used it with nitrous on my nx and Im going to use it on my Z when I start making more boost- Is a fuel pressure regulator really worth it though? I seriously think I need to replace mine- my fuel pressure at idle yesterday was 29 - is that right? I need to order the factory service manual


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## Zen31ZR (Mar 24, 2004)

0341TODD said:


> Right so a simple answer to our question is Fuel Management Unit- Like my super afc- I'll tell you what, from experience they do work and it is an extremly useful tuning tool when used in the right application.- I used it with nitrous on my nx and Im going to use it on my Z when I start making more boost- Is a fuel pressure regulator really worth it though? I seriously think I need to replace mine- my fuel pressure at idle yesterday was 29 - is that right? I need to order the factory service manual


29 is a bit low. Typical is in the 40s , and deadhead pressure (With the FPR fully closed) should be about 60-65 psi. I'd hook up a pressure guage to the accessory fitting on the injector rail (the pressure release fitting) and blip the throttle a few times and see what happens. If it (fuel pressure) spikes higher right as you blip the throttle its likely good , if it drops as you blip the throttle it's likely bad.

FMU is just a fancy name for an aftermarket FPR , its not to be confused with a complicated unit like a S-AFC.


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## 0341TODD (Nov 15, 2003)

Oh, gotcha then- you cant use big words like that in this forum man- we still think like its the 80's here-LOL


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## Zen31ZR (Mar 24, 2004)

0341TODD said:


> Oh, gotcha then- you cant use big words like that in this forum man- we still think like its the 80's here-LOL


Yeah , I'm living in the 80s too. No problem.


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## 0341TODD (Nov 15, 2003)

are you sure that it is supposed to be that high? 60 max? what is it supposed to be at idle? if that is the case then maybe my fuel pump is going.


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## Zen31ZR (Mar 24, 2004)

0341TODD said:


> are you sure that it is supposed to be that high? 60 max? what is it supposed to be at idle? if that is the case then maybe my fuel pump is going.


Nah , thats fuel pressure with the FPR blocked , basically , so you'll likely never see it that high. And FPs don't really lose pressure like that. They either run or they don't. Your fuel filter may be clogged. Did you check the FPR like I said ? :thumbup:


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## 0341TODD (Nov 15, 2003)

yeah dude, and at idle it sits at 30 psi. when I unplug the vacuum line it goes to 43 or so- so the fuel pressure regulator is working- I think its the pump- I posted some threads to see if anyone will help me figure out how to install the Walboro (what needs to be modified etc etc etc) I know that thing is screwy- whenever I start the car it takes a few turnovers to get it going. and my air fuel ratio gauge never even reads anything. wierd.







[email protected] said:


> Nah , thats fuel pressure with the FPR blocked , basically , so you'll likely never see it that high. And FPs don't really lose pressure like that. They either run or they don't. Your fuel filter may be clogged. Did you check the FPR like I said ? :thumbup:


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## Zen31ZR (Mar 24, 2004)

0341TODD said:


> yeah dude, and at idle it sits at 30 psi. when I unplug the vacuum line it goes to 43 or so- so the fuel pressure regulator is working- I think its the pump- I posted some threads to see if anyone will help me figure out how to install the Walboro (what needs to be modified etc etc etc) I know that thing is screwy- whenever I start the car it takes a few turnovers to get it going. and my air fuel ratio gauge never even reads anything. wierd.



Yeah , you're likely running super lean. I'd still be inclined to say the fuel filter before blaming the pump , at this point.


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## 0341TODD (Nov 15, 2003)

I already changed the fuel filter-its brand new.- did you read my post about the air fuel ratio gauge? How even when Im driving the thing doesnt even register fuel.


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## Zen31ZR (Mar 24, 2004)

0341TODD said:


> I already changed the fuel filter-its brand new.- did you read my post about the air fuel ratio gauge? How even when Im driving the thing doesnt even register fuel.


May be other issues at work here. Do you have either the factory or the Haynes repair manual? They should tell you what your idle fuel pressure should be. I have the Haynes manual , its a good source of technical info like that. The factory manuals are hard to come by , I havent even bothered looking for one.


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## 0341TODD (Nov 15, 2003)

I have one and I cant find the stock fuel pressure anywhere. I can get you the number for the company who sells the fsm if youd like it man.


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## Zen31ZR (Mar 24, 2004)

0341TODD said:


> I have one and I cant find the stock fuel pressure anywhere. I can get you the number for the company who sells the fsm if youd like it man.


I'll find it. I'm not anywhere near the manual right now , though , but I'm pretty sure it's in there. , somewhere.


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## 0341TODD (Nov 15, 2003)

I found it bro- 30 at idle and 44 under pressure. It was in chapter 4 of the haynes manual- actually I dont know that for sure- but I did find it. tomorrow morning Im going to check my power and ground again for the air fuel ratio gauge. I just got done wetsanding and buffing half the car and I need to go home(just got it painted)- my g/f is bitching that Im still at my shop


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## Zen31ZR (Mar 24, 2004)

0341TODD said:


> I found it bro- 30 at idle and 44 under pressure.


Still seems a bit low , but I guess I'm just used to newer cars. My Beretta GT was about 40 at idle. When you said 30 before , for some reason I kept thinking that was while it was being revved , which sounded quite low to me. But 44 off-idle sounds a lot better. Me >> :loser:


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