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Discussion Starter #1
So obviously a fuel pressure regulator manages the pressure at the fuel rail...

the 'j' tube is a 'fail safe' in case the stock afpr fails...

now, when the fuel pump is upgraded to, for example, the walbro 255, the 'j' tube needs to be removed... (that's what I read)


my question is, why does the stock fpr need to be upgraded? I see alot of people with the upgrade, but I don't know why they do it.



the fuel pump is upgraded because the stock one doesn't flow enough, the 'j' tube is removed cuz its to much resriction.... why upgrade the regulator?
 

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Adjustability is sometimes desired. That's it in a nutshell.

Insofar as need, it depends. Pete H ran a T-61 @ ~480rwhp on stock FPR, & I ran my TO-4E @ ~400 on stock FPR & there was enough fuel left over to bottom out the VPC/GCC controls. Personally, I'd start looking for an AFPR once a T-66 meets peak efficiency, but others may disagree. For some reason, I've seen many guys at much lower power levels feel the need to upgrade...perhaps for future needs, dunno.
 

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Discussion Starter #5
Thanks larry, I always look forward to your replies.


I guess Maf/t+Emanage+550's won't be needing a new FPR as I won't be anywhere near that type of power with that setup
 

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i tune the crap out of my afpr. i do 70% of my tuning using it. the reason i like it so much is you can move the entire fuel curve rich or lean w/o any effects on timing like an afc. on the afc when you start tuning leaner it reduces the air flow signal which in turn effects timing.
when i tune i use the afc to get the a/f flat then make the big changes using the afpr then fine tune w/ the afc. at the most i have maybe 10-15% pulled on the afc on the top end.
it just comes down to what you want to have at your disposal for tuning. like i said i like the afpr the best b/c it has a drastic effect on the entire fuel curve without any timing concerns, not because bigger injectors need more pressure. but as master sensei (larry a) says it is not req'd by any means.

dave
 

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dbsupra said:
i tune the crap out of my afpr. i do 70% of my tuning using it. the reason i like it so much is you can move the entire fuel curve rich or lean w/o any effects on timing like an afc. on the afc when you start tuning leaner it reduces the air flow signal which in turn effects timing.
when i tune i use the afc to get the a/f flat then make the big changes using the afpr then fine tune w/ the afc. at the most i have maybe 10-15% pulled on the afc on the top end.
it just comes down to what you want to have at your disposal for tuning. like i said i like the afpr the best b/c it has a drastic effect on the entire fuel curve without any timing concerns, not because bigger injectors need more pressure. but as master sensei (larry a) says it is not req'd by any means.

dave
You make a compelling argument for owning one, as long as you're a tinkerer- & you are quite the tinkerer, LOL.

Ironically, I wish I'd had an AFPR to lower the pressure so I could get some VPC/GCC knob back, but not much since some of the knobs were cocked toward the richer end of the scale. Heh, people say MkIIIs are pig-rich, but I've seen it can depend where on the curve you look.

Anyway, your sell on the AFPR is as good as it gets.
;)
 

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dbsupra said:
i tune the crap out of my afpr. i do 70% of my tuning using it. the reason i like it so much is you can move the entire fuel curve rich or lean w/o any effects on timing like an afc. on the afc when you start tuning leaner it reduces the air flow signal which in turn effects timing.
when i tune i use the afc to get the a/f flat then make the big changes using the afpr then fine tune w/ the afc. at the most i have maybe 10-15% pulled on the afc on the top end.
it just comes down to what you want to have at your disposal for tuning. like i said i like the afpr the best b/c it has a drastic effect on the entire fuel curve without any timing concerns, not because bigger injectors need more pressure. but as master sensei (larry a) says it is not req'd by any means.

dave
^^^^^^^ Agreed!
I got mine because after installing the Walbro, my base FP shot up to 7PSI higher than the highest recommended pressure. That put me beyond the +/- adjustability that the stock ECU counters with (closed loop) and had me running wastefully rich. The AFPR simply brought me back down to a reasonable recommended FP. I believe that all fuel tuning starts there. The other adjustments flatten the curve as pointed out by DBSUPRA. Everyone's case is unique though and what works for one doesn't always suit the other but with adjustability, you know where you stand.
 

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Hey wait a minute...we're assuming that people actually know their fuel pressure!? ;) Good fix on the pressure Will, & can we assume you dumped the J-tube during all that too? Mods begetting mods, LOL. Before I removed the J-tube & after the Walbro, FP was 13psi over max, yikes; but dropped back to ~2psi over max once J-tube went away. My FP went up an additional 2psi when I removed the FPD, so that's another item to keep an eye on if you're dicking around with fuel.
 

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Discussion Starter #10 (Edited)
Very good argument, and I didn't think about that... i am alwas forgetting timing when adjusting fuel

my base FP shot up to 7PSI higher than the highest recommended pressure.

recommended pressure for what?



what happens when your fuel pressure is to high? Too low?



I'd be mroe than happy to look this kind of stuff up but i don't know where to look.... and you guys are more than helpfull :)



I removed the FPD
what's FPD?
 

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Discussion Starter #12
Stock pressure level... does that stay constant regardless of mods or does it increase with more mods?

Do you want your pressure to stay the same with bigger injectors and more flow?
 

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i got my aeromotive brand new for $105. I can now increase fuel cut considerably with stock injectors and a lex or stock afm with backed out screw, for less than 550 injectors. Plus, all the adjustability mentioned above
 

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Larry_A said:
Hey wait a minute...we're assuming that people actually know their fuel pressure!? ;) Good fix on the pressure Will, & can we assume you dumped the J-tube during all that too? Mods begetting mods, LOL. Before I removed the J-tube & after the Walbro, FP was 13psi over max, yikes; but dropped back to ~2psi over max once J-tube went away. My FP went up an additional 2psi when I removed the FPD, so that's another item to keep an eye on if you're dicking around with fuel.
Yeah Larry, I dumped the J-tube "before" I got the AFPR and the 7PSI over was that result. I still have my FPD though.
You were 13PSI over? You must have been covering those white lines in the road with that black smoke. :) Wow!
I have the VPC/GCC combo but ditched the GCC for an AFR thinking that was going to help but the AFPR was the one. AFR didn't help me in closed loop.
 

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Justin said:
Stock pressure level... does that stay constant regardless of mods or does it increase with more mods?

Do you want your pressure to stay the same with bigger injectors and more flow?
1] FP [fuel pressure] is a function of injector size versus demand.

2] At the same FP, larger injectors flow more fuel. At this point, answer #1 applies again.

So, the bottomline on fuel pressure is, it depends. Just know the rule of thumb established long ago to not substitute fuel pressure for the properly sized injector.

BTW:

F - uel
P - ulsation
D - ampener

It's the knobby-looking thing on the rear of your fuel rail where fuel enters.
 

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Heh, I got mine because i think my stock fpr went bad...and I couldn't check my pressure...
Then again I have a standalone and changing the fpr just to put a fp gauge (yeah, what an expensive fp gauge) seemed to cure my probs...stock pump still too...
 

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animantoric said:
Heh, I got mine because i think my stock fpr went bad...and I couldn't check my pressure...
Then again I have a standalone and changing the fpr just to put a fp gauge (yeah, what an expensive fp gauge) seemed to cure my probs...stock pump still too...
I was checking my pressure with a cheap FP gauge I bought from Pep Boys plugged into the cold start injector access. Couldn't have been no more than $25-30. But rest assured, your FP adjustability is worth the expense.
 

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I've been doing research on this before. However, I still really haven't found the answer I'm looking for. How exactly do you go about removing the J-Tube restriction. I have a walpro and a J-tube block off plate, but I'm a little unsure how to go about it. Sorry for hijacking the thread. Thanks.

Mo
 

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The return line from your FPR goes directly to the J-tube. Just take the J-tube out of the return line, connect the two hoses together and replace the area where it was mounted with the block-off plate.
 
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