I've had an adjustable FPR on my car since I did heads/cam awhile back. I've got the FPR set at stock pressure (44 lb i think) and have never tinkered with it. I just put larger injectors in the car and now and thinking if by bumping the pressure up maybe I'll see more performance. What's the rule on this??

 

you the afpr is usless on your car (on any fbody 94 and newer). the pcm will correct for it. you could bump it up to 100 psi and it would make no difference. the pcm will cut the pulse width for the injector and compensate for the extra fuel.

you will gain nothing

 

Spend the money to get the car dyno tuned, otherwise you're just guessing at settings and will either run lean and burn up the motor or loose at lot of power and driveability. I had cam surge that I thought I had to live with when I did my heads and cam; Jeff Creech dyno tuned my ride and completely eliminated the cam surge!

An Adjustable FPR does help tune a modified car, but is not very useful on a near stock car.

 

Wrong...theres only one way a afpr will help on these cars and thats if you are running the injectors 100% duty cycle and running lean and the pcm cant compensate, and you up the pressure to get your injector duty cycle back down, and to stop runing lean. that is the only way it would at all benifit you at on all these cars. and if your ok with doing that to keep from running lean. you stupid. im not saying your doing that by using yours. but that is the ony way its good fopr anything.

scan your car and watch the duty cycle and the blms, then up your prssure and scanning agian you will see the duty cycle go down, and the blms go down. and this will keep your car a 14.7 the target a/f ratio in closed loop. and if the blms go below 108 you will be runinng rich becuase the pcm will not adjust that far.

im not saying your stupid for getting one, its your money, but if you think its helping its not. and after tuning for almost 3 years now, i know its not doing anything for you or against you. just a wate of money.

and it doesnt matter waht mods youve done your car, if your using the stock pcm, it will still do it.

learn for yourself and do as i said and scann your car, and see

 

When you "did heads/cam", you must have had the PCM "tuned". What fuel pressure did you tell your tuner you were running? He had to know that to set the injector constant in the program. Now that you have changed injectors, you need to adjust the injector constant in the PCM again. If for some reason you feel you need to change the fuel pressure, the tuner would have to know what it is to do that. You can't adjust the pressure "after the fact" without screwing things up.

 

The PCM does not adjust for FP per se. What it will do is compensate, over time, for an overly rich or overly lean condition during closed loop operation. However, an AFPR can be of great use in tuning for WOT when used properly. However, as Fred siad, when you change the FP there are other programming changes that must be made, primarily the injector constant. When the change FP, you change the injector flow rate.

Rich

 

not unless someone installed a wideband 02 on the car when he wasnt looking. those narrow band 02s are only used in closed loop to hold stoichmetric. at WOT they go open loop and the 02 sensors dont do ****.

 

I had the PCM tuned but the only question asked of me at the time was what size injectors I was running. Nothing was ever asked of the afpr. Now that I installed larger injectors I have sent the PCM away for retuning but again nothing was ever asked of the FP so I guess he just assumes it will be running at stock pressure....PCMforless is doing the tuning...

 

In that case, you need to run at the stock FP.

Rich

 

I was wondering, if you have good injectors that can handle higher fuel pressure than the stock rating, is there any difference in combustion by running it at a higher pressure?

Example:
I currently have 42.5# (at 43.5psi) Lucas injectors with the stock fpr and injector constant set to 42.5 in the PCM. If I installed an adjustable fpr, set it to 60psi fuel pressure, and then changed the injector constant in the PCM to compensate for the fuel pressure change, what would this affect?

I assume that the injector would open for a shorter period of time, but the same amount of fuel would be released. This should cause a finer, more accurate fuel mist? Or is the stock 43.5psi already the optimal place to be?

Thanks,
Shawn

 

if some up the fuel pressure to 60 when he wasnt looking and used a wide band o2 on it, they would have to adjust the injector constants to compansate the rise in pressure, and its the same thing the pacm does as well when you up the pressure. except with the canstant table you do it on a larger scale.


the only good it will do is if the injectors are at a duty cycle where they cant get enough fuel. if you raise fuel pressure it will drop the duty cycle and you will gain performace. if its a t 70% duty cycle and you up the fuel pressure it will do nothing, except adjust duty cycle lower becuase it didnt need the exrta pressure.

but the car uses what it learns in close to make adjustments to wot if needed.

and huh the o2s are technicly used in open loop, you can set your car to go into pe mode at idle and you can watch them move, even if you lock the long term blms to 128. if you put a wide band on it you can see it gradualy move. if you want to get technical

 

the cars dont use the (narrow band) 02s in open loop, so at WOT it will make the cars go pig rich if it had a decent a/f ratio at a lower fp. buy a wideband and watch it. wanna borrow one of mine?

 

ok since you have a wide band, program your car to idle in pe mode and lock the lt blms to 128 and watch your fuel when the car goes closed loop you will see your st blms start move and so will fuel a/f ratio. wich means it uses the st blms in wot, now that wot pass dont last that long, the numbers are useless becuase it dont have time to learn.

oh and by the way wot is not open loop, once you go closed loop you are in closed loop even under wot, and if the car could stay in wot for a few minutes it would use the st blms, if you look at your scanner it will show you are still in closed loop at wot, and your in cell 15 that is a closed loop cell, which means it is reading the o2s and applting the value

 

on a stock pcm setup WOT is most certainly open loop. hell, even after the pcm4less reprogramming my car goes open wot. in closed the a/f hovers around 14.7:1. right where the narrowband 02 can sense. at WOT w/ stock fp my car runs between 12.9-13.1:1 based on the readings of my widebands. when i turn the fuel pressure up it gets fatter. wanna go for a ride? if it were still in closed loop at WOT, it would never go richer then 14.7:1 because thats all the narrow band stock 02s can read. its a different story if its gen 7 or FAST or something that allows you to set a predetermined a/f ratio in closed loop with a wideband. we have a couple of those systems on some mustangs here too.

 

i agree that if you up the pressure it will get fatter,

but wot is not open loop, look at the cell your car is in wot, it is in 15 thats a closed loop cell. 16 17 18 are the only open loop cell and idle cells.

yes it will get richer in closed loop at wot becuase it looks at differnt tables for the a/f ratios. and thats why the o2s show 900+ mv showing rich. yes your right the o2s are only good at 14.7 but they will show you rich or lean at any other ratio.

download datamaster and it will tell you when the pcm is in open or closed loop, and it will tell you when your in wot, and when your in wot you are still closed loop.

i can email you several datamaster files to show you if you would like.