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

Fuel Pressure/mileage ?

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Old May 11, 2009 | 01:48 PM
  #1  
Rally Smith's Avatar
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From: East Helena, MT
Car: 91 RS
Engine: 305 TBI
Transmission: 700R4
Axle/Gears: Factory 2.73 (unfortunately)
Fuel Pressure/mileage ?

I put in an adjustable FPR and adjusted it to 14.75 psi. My Mileage has DROPPED big time. I assume that backing it down a ways will help but the thing is my engine could use it. So my thinking is that back it down to around 14 psi or so for now. Then when I get my EBL I will be able to dial it in so it is more efficient and not "waste" a bunch of fuel. Would this be correct?
I usually go about 275 or so on a tank, after I'm not even at 200 and down to an 1/8th of a tank. Granted I've been getting on it a little after the adjustment but for the most part keeping habits the same. Any insight or info would be appreciated.

1991 RS 305, cammed, heads, full exhaust, cold air/ram air.
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Old May 11, 2009 | 02:28 PM
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From: Austria
Car: 84 TA / 89 Formula
Engine: LS1 / L03
Transmission: T56 / 700R4
Axle/Gears: 3.73 / 3.27
Re: Fuel Pressure/mileage ?

if i calculated that right you're getting about 17-18mpg? that's not too bad in my book.. how much did you get before all the mods? also where are you driving mostly, city/highway?
you can dial in your BPC injector constants in EBL, if you alter fuel pressure these values need to be adapted in the calibration.

also EBL will provide a nice lean cruise mode, along with some other small feats helping you save some more gas
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Old May 11, 2009 | 03:35 PM
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Rally Smith's Avatar
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From: East Helena, MT
Car: 91 RS
Engine: 305 TBI
Transmission: 700R4
Axle/Gears: Factory 2.73 (unfortunately)
Re: Fuel Pressure/mileage ?

Originally Posted by ownor
if i calculated that right you're getting about 17-18mpg? that's not too bad in my book.. how much did you get before all the mods? also where are you driving mostly, city/highway?
you can dial in your BPC injector constants in EBL, if you alter fuel pressure these values need to be adapted in the calibration.

also EBL will provide a nice lean cruise mode, along with some other small feats helping you save some more gas
Exactly, that's what I was getting. Now after the FPR adjustment, looks more like 13 mpg. Not good!

Like a dumbass I didn't check the fuel pressure before I adjusted it.
So I don't know what the baseline was before I started adding fuel. I'm afraid of going lean or rich, so where do I error on the side of?

Any suggestions to where I should adjust it to? Or at least start back out at?
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Old May 11, 2009 | 04:10 PM
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Re: Fuel Pressure/mileage ?

set it to 12 until you begin tuning and stay away from WOT until you get a tune(EBL). At 12 you will be at stock FP and should be drivable. If car coughs(lean on AE) when you accelerate move it up to 13.
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Old May 11, 2009 | 04:22 PM
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From: Austria
Car: 84 TA / 89 Formula
Engine: LS1 / L03
Transmission: T56 / 700R4
Axle/Gears: 3.73 / 3.27
Re: Fuel Pressure/mileage ?

oh okay, i read that wrong about the milage. 13 isn't that good yeah, i'll agree with that the adjustment Ronny suggested should be fine imho
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Old May 11, 2009 | 04:31 PM
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Rally Smith's Avatar
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From: East Helena, MT
Car: 91 RS
Engine: 305 TBI
Transmission: 700R4
Axle/Gears: Factory 2.73 (unfortunately)
Re: Fuel Pressure/mileage ?

Originally Posted by Ronny
set it to 12 until you begin tuning and stay away from WOT until you get a tune(EBL). At 12 you will be at stock FP and should be drivable. If car coughs(lean on AE) when you accelerate move it up to 13.
Stay away from WOT???! What, are you high? Just kidding. I can do that. Thanks for the help guys.

Now if I just had $350 for the EBL.... RBob, you having a sale any time soon??
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Old May 12, 2009 | 04:47 AM
  #7  
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From: SE PA.
Car: 92RS
Engine: 305
Transmission: 700R4
Axle/Gears: 2.73
Re: Fuel Pressure/mileage ?

Originally Posted by Rally Smith
Stay away from WOT???! What, are you high? Just kidding. I can do that. Thanks for the help guys.

Now if I just had $350 for the EBL.... RBob, you having a sale any time soon??

What other mods do you have? What rear? With TPI-type CAI, and 3 " catback on an otherwise stock vehicle, I get 23-24 mpg as a daily driver. Routinely go 300 miles on a tank. That's about 40% highway driving. My pressure gauge reads 12 PSI.
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Old May 12, 2009 | 09:00 AM
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From: East Helena, MT
Car: 91 RS
Engine: 305 TBI
Transmission: 700R4
Axle/Gears: Factory 2.73 (unfortunately)
Re: Fuel Pressure/mileage ?

2:73 stock rear-end, comp cam, edelbrock headers, 3" exhaust, 99% driving in town. Non stock heads with a port job.

I changed my pressure last night to 12.25. Seems to be running fine so far. Of course I only live about 8 miles from work and it's 45 to 60 the entire way.

Is it natural to have the needle on the gauge wobble a little?
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Old May 12, 2009 | 05:27 PM
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From: West-Central
Car: 91 Trans am
Engine: built 360 TBI
Transmission: built 700r4
Axle/Gears: 10bolt/3.23
Re: Fuel Pressure/mileage ?

Originally Posted by Rally Smith
Is it natural to have the needle on the gauge wobble a little?
FP should not variate. Your set up sounds like lots of fun once your goin to get the EBL to run it. Keep us updated.
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