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TBI Throttle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.

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Old 09-22-2002, 04:34 PM   #1
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How to adjust fuel pressure regulator?

How do i precisely adjust the fuel pressure regulator? If i want to adjust it, say 2 psi, how do i go about adjusting it exactly two psi. Thanks guys
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Old 09-22-2002, 08:16 PM   #2
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At the risk of sounding obvious, you will need a fuel pressure gauge. If you install it in the engine compartment, keep in mind that each 30 degree rise in gauge temp will cause the gauge to read 1psi lower than it really is.

An alternative is but a TBI fuel pressure tester at a parts chain store of your choice and splice in a fitting to hook up the gauge.
HTH.
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Old 09-22-2002, 10:22 PM   #3
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What's stock? and what's a good number to run at?
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Old 09-24-2002, 01:04 PM   #4
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Okay, when you adjust the fuel pressure are you adjusting the fuel pressure at the injectors or the fuel pressure in the fuel lines. Whatever the answer is, what kind of fuel pressure are you guys running?
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91 RS 5.0 TBI, Auto, 14x3 open Element K&N, cat removed, Flowmaster 80 series <--- shes about to make her triumphant return to the road
91 Ford F-150, 4.9L I6, 5-speed

"Not enough time, not enough money, and just too many mustangs in the world"

Kills: 81 T/A 4.9L w/ cam & exhaust upgrade
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Old 09-24-2002, 08:02 PM   #5
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AFPR?

Have you checked out teh tech articles? Look for how you make your fuel pressure regulator adjustable

Or just go to turbocity.com and buy teh AFPR - its like 70 bucks - i may do this cuz i dont trust myself
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Old 09-24-2002, 08:07 PM   #6
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seriously guys, this is an easy mod to do. i did a slightly different method that i found on the board around here somewhere. used a bold that hangs down. that way you can see it and adjust it easily witha wrench. i still have yet to put in my guage though...
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Old 09-24-2002, 09:08 PM   #7
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Im not asking how to make it adjustable, im asking how to precisely adjust it. How am i suppose to now how many psi up or down i am adjusting it by.
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85 Berlinetta Auto, 2.8L MPFI<--w/ overhead console AND flashlight
91 RS 5.0 TBI, Auto, 14x3 open Element K&N, cat removed, Flowmaster 80 series <--- shes about to make her triumphant return to the road
91 Ford F-150, 4.9L I6, 5-speed

"Not enough time, not enough money, and just too many mustangs in the world"

Kills: 81 T/A 4.9L w/ cam & exhaust upgrade
79? Camaro
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Old 09-24-2002, 11:03 PM   #8
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Quote:
Originally posted by Berlinetta
Im not asking how to make it adjustable, im asking how to precisely adjust it. How am i suppose to now how many psi up or down i am adjusting it by.
As PaulD said, you will need to plumb in a fuel pressure gauge. When you first do this, write down the stock pressure so you can revert to it if there is a problem. When you turn the screw (or body, etc) one way or the other you will see the pressure go up or down.

You should probably make your adjustments with the car not running. Make sure that you have an ABC fire extinguisher right near you just in case a fire starts (turn off the engine to stop the fuel pump if that happens). To be safe, you might also want to do this in the driveway rather than in the garage. A lot of people have burned down their homes while working on fuel systems. Carry that extinguisher around with you for at least several days -- until you know that nothing worked itself loose (check the engine regularly).
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Old 09-24-2002, 11:18 PM   #9
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Does the gauge measure the fuel pressure in the fuel lines or does it measure the fuel pressure at the injectors? BTW, where the hell do you plumb the gauge into?
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91 RS 5.0 TBI, Auto, 14x3 open Element K&N, cat removed, Flowmaster 80 series <--- shes about to make her triumphant return to the road
91 Ford F-150, 4.9L I6, 5-speed

"Not enough time, not enough money, and just too many mustangs in the world"

Kills: 81 T/A 4.9L w/ cam & exhaust upgrade
79? Camaro
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Old 09-25-2002, 12:03 AM   #10
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Quote:
Originally posted by Berlinetta
Does the gauge measure the fuel pressure in the fuel lines or does it measure the fuel pressure at the injectors? BTW, where the hell do you plumb the gauge into?
The gauge is meant to measure the pressure in the feed line from the pump to the injector. Ideally, the pressure in the line will be constant so you could measure at any point in the fuel line.

As for identifying the feed line (versus the return line to the tank), it is the larger diameter hardline going to the TBI (correct me if this is wrong, anyone). In the photo below of a 91 RS, it is the circled line. You could plumb the 'T' fitting in here --- BUT ---- before you do, measure the OD of the line and go down to your auto supply store and find out if they have fuel injection hose (very important to get *fuel injection* hose) with the appropriate ID as well as the 'T' fitting, clamps, and gauge, etc.

Now, some stores might have a gauge you could rent that would go in place of the connecting hose (next post).
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Old 09-25-2002, 12:07 AM   #11
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This is a picture from the Haynes manual showing what, to me, would be the ideal solution: a gauge that would bolt-in in place of the feed hose in the left front engine compartment (photo in next post).
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Old 09-25-2002, 12:12 AM   #12
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Here is a picture of the hose that the previous gauge should replace. Make sure you trace the lines yourself in your own car so that you know you are using the feed line.

If it were me and I had another vehicle, I would disconnect the feed hose and bring it with to the parts store so that you could ensure you are getting the correct parts.

Hope this helps!
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Old 09-25-2002, 05:41 AM   #13
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Good info, Kevin.
Stock pressure is anywhere from 9-13 psi. There is little need to bump it up unless you start modding the engine. An alternative to the afpr is to disassamble the regulator and put shims under the spring. Does the same thing as the afpr. Have gaskets ready when you remove the injector pod. I bought a rebuild kit and a sheet of gasket at Autozone for $7 and used the gasket in the kit to trace all I needed.

FWIW,I know guys that run as high as 15# on basically stock engines and start to have troubles at idle.
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Old 09-25-2002, 08:42 AM   #14
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I'll sum up everything since I've done everything above.
First off let me just say that doing an AFPR is cake work so long as you know how to operate a handdrill and have access to a dremel and MAYBE a Lowes or HomeDepot for a different screw (what you turn to adjust pressure).
The FPR is in the return line so any and all pressure that's at the injectors is also everywhere in the supply line. The flex line that kevin posted a picture of above is where you should tap in a FP gauge. Call up Summit or Jegs and order their no-name 0-30 psi gauge for $20 and get the Mr. Gasket t-fitting for $9. All part numbers can be found from my previous post; http://www.thirdgen.org/techbb2/show...highlight=jegs
It's simple but like it was said before, for every 30 degrees in temp change the gauge reads 1psi less. This is a PITA because underhood temps change a LOT so always make an adjustment, turn the key to the on position while a friend looks at the max pressure while the fuel pump primes the line.
I'm running a kind of crazy TBI monster setup so if I give you my pressure readings for my motor you'll just end up going crazy figuring out why your car runs like crap. Long story short, fuel pressure needs to be adjusted with either winaldl and getting the average BLMs to around 128 OR going to the 1/4 mile and getting a best mph = best fuel pressure setting.
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Old 09-25-2002, 06:25 PM   #15
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Quote:
Originally posted by PaulD
FWIW,I know guys that run as high as 15# on basically stock engines and start to have troubles at idle.
Could this perhaps be me?

FYI, I removed the shims that were previously in my fuel pressure regulator and I am back to stock pressure (13 on the dot). Curiously, it idles with BLMs smack down at 108 with your chip, even at the stock pressure!! However, once under way, BLMs are much better (as high as 127 and as low as 115 or so). I think taking this chip and tweaking it further would be a good solution. It still starts hesitantly (too much fuel)....I started my car for the first time (today) since two saturday's ago (when we went to NED) and the tach went up to about 900 and the whole car was shaking...I think it was badly loaded up. Then I revved it to "unload" it and it started idling at 1500 (higher than normal for my car) and slowly came down. I think some tweaking of that chip could provide good results.

I am thinking changing the injector constant is the only way to really affect idle mixture (though I could be wrong) then re-tweak everything else. It DOES have O2 switching events during idle, even with BLMs of 108. But it smells richer than normal and VERY smelly after that stone cold start. So the chip is commanding way too much pulse width at idle.
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Last edited by kevm14; 09-25-2002 at 06:29 PM.
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