i have been reading up in the 3k stumble. i ordered the perrin fpr. the perrin site says there is no need for a tune with there fpr. i am just trying to find out what the stock pressure is so i adjust from there. thanks for the help ahead of time. in anyone has used the perrin fpr let me know what you think of it.
whats the stock fuel pressure??
- Thread starter m8ttixsti
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Spamby
Meat Product Toy
Another member [MENTION=4684]welaish[/MENTION] used the Perrin FPR to correct an odd positive fuel trim at the 3k mark. Since I'm having a very, very similar situation as him, I've looked into the Perrin FPR. I do recall Perrin stating that no tune is necessary on a stock map but tuning will be needed if you have a custom ecu tune.
Welaish's results were impressive but it looks as if his fuel trims went a bit negative and may need a touch up to his map.
I recently did a fuel pressure test and came out at 33psi idle with manifold vacuum plugged in. With the vacuum disconnected, it was at 43psi, idle. Holycrapitsfast gave the blessing of normal at that range. Further reading states that it is the case.
Welaish's results were impressive but it looks as if his fuel trims went a bit negative and may need a touch up to his map.
I recently did a fuel pressure test and came out at 33psi idle with manifold vacuum plugged in. With the vacuum disconnected, it was at 43psi, idle. Holycrapitsfast gave the blessing of normal at that range. Further reading states that it is the case.
SudoSTI
Member
Any of you GR guys try switching to a series setup? According to Dom former owner of MPS that's what ultimately causes the stumble in GRs:
"Pressure differential is moot and frankly I'm surprised anyone thinks it exists.
Here's why:
1. From the first injector to the last, the amount of fuel being used is less and less in steps. So from the beginning, you have less flow which lowers any potential for pressure drop. The largest demand on the fuel system is the line in the frame rail. Once it hits the first injector, the demand is less, which means flow rate is less, which means pressure drop is less.
2. The fuel system does not flow ONE flow rate through the whole system evenly.
3. The fuel pressure regulator is at the end. So if it sees a drop in fuel pressure at the last injector, it's going to bypass LESS fuel, which therefor keeps the pressure more balanced from beginning to end.
Lastly:
Nobody has ever had misfire issues from Series lines.
Many people have had misfire issues with Parallel lines.
Nobody has been able to prove any benefit with Parallel.
Many people have experienced uneven fueling from cylinder to cylinder with parallel.
The first year subaru implemented parallel rails, TONS of misfire issues. Just look up any 08+ STi.
Parallel fuel rails result in large differences in rail temperature and fuel temperature. Fuel temperature is a very important part of fueling (how important? 50C is over 6% fueling. 6% is a lot when we're concerned over 1 or 2% see the last article http://www.injectordynamics.com/NewsletterFeb2013.html). Someone mentioned that by going parallel you lower the speed of the fuel in the rail by half. This is true, in fact in extreme cases it's more than half. HOWEVER, that's not ideal. You want the highest velocity you can get away with without creating a back pressure and pressure drops. Higher velocity means you do a better job of balancing rail temps. Balanced rail temps means balanced fueling. Nice fat rails with a large quantity of fuel going through them would be nice too, but too big and fuel have such a slow fuel flow that you'd once again establish large changes in fuel temp from rail to rail.
So what you guys are doing is creating a problem while trying to prevent a problem that doesn't exist.
If you go series with injectors in the wrong order, you could have issues. However, our firing order is linear down the fuel rail. Subaru H4 is the only engine ever created to do this. The order of fuel feed should be opposite of engine firing order. This means that the fuel injectors are always firing towards the source of fuel. That means that you aren't going to get any lack of fuel from the load on the rail.
In V8's, I4, I6 etc, the firing order is not in a linear fashion down the rail and it is absolutely important and correct to go parallel with your fueling. Subaru isn't like any other engine out there.
Any lack of fuel is from a pump that is too small or from a rail system that is too small to handle the flow rate. It isn't from being series."
Taken from this thread, post #34 :
http://forums.nasioc.com/forums/showthread.php?t=2162858&page=2
"Pressure differential is moot and frankly I'm surprised anyone thinks it exists.
Here's why:
1. From the first injector to the last, the amount of fuel being used is less and less in steps. So from the beginning, you have less flow which lowers any potential for pressure drop. The largest demand on the fuel system is the line in the frame rail. Once it hits the first injector, the demand is less, which means flow rate is less, which means pressure drop is less.
2. The fuel system does not flow ONE flow rate through the whole system evenly.
3. The fuel pressure regulator is at the end. So if it sees a drop in fuel pressure at the last injector, it's going to bypass LESS fuel, which therefor keeps the pressure more balanced from beginning to end.
Lastly:
Nobody has ever had misfire issues from Series lines.
Many people have had misfire issues with Parallel lines.
Nobody has been able to prove any benefit with Parallel.
Many people have experienced uneven fueling from cylinder to cylinder with parallel.
The first year subaru implemented parallel rails, TONS of misfire issues. Just look up any 08+ STi.
Parallel fuel rails result in large differences in rail temperature and fuel temperature. Fuel temperature is a very important part of fueling (how important? 50C is over 6% fueling. 6% is a lot when we're concerned over 1 or 2% see the last article http://www.injectordynamics.com/NewsletterFeb2013.html). Someone mentioned that by going parallel you lower the speed of the fuel in the rail by half. This is true, in fact in extreme cases it's more than half. HOWEVER, that's not ideal. You want the highest velocity you can get away with without creating a back pressure and pressure drops. Higher velocity means you do a better job of balancing rail temps. Balanced rail temps means balanced fueling. Nice fat rails with a large quantity of fuel going through them would be nice too, but too big and fuel have such a slow fuel flow that you'd once again establish large changes in fuel temp from rail to rail.
So what you guys are doing is creating a problem while trying to prevent a problem that doesn't exist.
If you go series with injectors in the wrong order, you could have issues. However, our firing order is linear down the fuel rail. Subaru H4 is the only engine ever created to do this. The order of fuel feed should be opposite of engine firing order. This means that the fuel injectors are always firing towards the source of fuel. That means that you aren't going to get any lack of fuel from the load on the rail.
In V8's, I4, I6 etc, the firing order is not in a linear fashion down the rail and it is absolutely important and correct to go parallel with your fueling. Subaru isn't like any other engine out there.
Any lack of fuel is from a pump that is too small or from a rail system that is too small to handle the flow rate. It isn't from being series."
Taken from this thread, post #34 :
http://forums.nasioc.com/forums/showthread.php?t=2162858&page=2
HolyCrapItsFast
Drinks beer!
Interesting. Not saying I completely agree with this because it shatters some of my own ideas but now that I think of it, When I had my 06 and converted it to parallel feed, I developed a stumble. I was able to tune it out so I attributed it to changes I made to the induction system at the same time. It never occurred to me that it could be the fuel system and perhaps I was in denile.
I never gave much weight to fuel system issues causing the infamous 2500 rpm stumble because I was always able to tune it out.
SudoSTI
Member
Yeah I was pretty surprised to read this as well when I did because I was always told parallel is the end all of of fuel systems but it makes a lot of sense the way he explains it. And I've seen some pretty impressive results come from Dom's shop on very simple fuel systems. He doesn't recommend upgrading the fuel system (aside from injectors and fuel pump) until around the 500whp level. David Buschur says the same thing about the OEM fuel system being that he put down about 750whp on his Evo with just injectors and his double pumper hanger and points out that the Subaru fuel lines are bigger/better than the ones on an Evo.
SudoSTI
Member
Well if the Perrin unit works then you should be golden. I only recalled reading that before and thought I would mention it. I don't have any personal experience with it being that I don't have a GR (even though I want a hatch SO BAD). The Perrin unit just kind of seems like a band-aid to the real problem but these guys with more experience would probably be the ones to ask for sure. I threw that in as food for thought.
[MENTION=2827]m8ttixsti[/MENTION] I bought the Perrin FPR it is well built piece. But fitment is not easy becuase fuel lines are short and if you have any brake brace you will require fabricated mount or another part from Perrin. It came by default adjusted to the stock pressure which as [MENTION=1507]Spamby[/MENTION] mention (43 unplugged - 33 plugged). I guess if you have stock injectors it will work and remove the stumble with a touch of tune. If you have aftermarket bigger injector, I think you need to upgrade the Rails. Thats what i have been reading in a lot of sources.
Check thr pics: https://docs.google.com/file/d/0B6zn_kRV08vAY3hnMjMzNF83ZUE/edit?usp=docslist_api
https://docs.google.com/file/d/0B6zn_kRV08vAb05FNDBnUDBFWVU/edit?usp=docslist_api
Check thr pics: https://docs.google.com/file/d/0B6zn_kRV08vAY3hnMjMzNF83ZUE/edit?usp=docslist_api
https://docs.google.com/file/d/0B6zn_kRV08vAb05FNDBnUDBFWVU/edit?usp=docslist_api
(43.5 vaccuum unplugged - 33 vacuum plugged).Similar threads
