IROC5.7TPI

My old think tank has been stirring and heres what I've been thinking about:

If you go and put an adjustable FPR on your TPI engine, the ECM eventually learns the added fuel and adjusts the injector pulsewidth to compensate for the increased pressure. So now the advantage of the increased pressure is better fuel atomozation(sp?),right?

So why not just skip doing the AFPR mod and just run the stock one with the vacuum hose unhooked and plugged off? It will increase pressure and the same thing will happen in theory....

Makes sense, doesn't it??

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Mike L.
It ain't pretty.......

1987 IROC Z TPI 350 A4 3.27 Borg-Warner.

Mods: 2300-2500 Stall Converter, Shift Kit(GM parts), TPI Specialties Stage 3 PROM, Modified Airbox w/ K&N's, homemade cold air, Relocated MAT sensor, Gutted MAF, 160* thermostat, MSD 6A, Accel 8mm Wires, bypassed TB coolant, Flowmaster 3 chamber single 3" in/out muffler, 3" MAC mandrel intermediate, custom dual !cat Y-pipe. airfoil, ported plenum. !smog

http://www.MichaelLasiuta.home.att.net

**BOYCOTT LAPEER DRAGWAY**

Grim Reaper

The ECM does not "learn" that way at all. Basically, the ECM stores a BLM value (based on a particular setting within the PROM) but it is still measured from 128.

So if the BLM tends to prefer 120 at a particular RPM/Load, it will store 120 and keep 120 in there, until it notices a difference of 2 (stock setting) from the previous BLM value at a particular RPM/Load.

but, you are limited to a minimum value of BLM of 108 or maximum of 160. If your engine needs to go outside that boundary, it will set an O2 sensor SES code. Further, this ONLY happens in Closed Loop at part throttle. It does not do anything in WOT (or PE) and uses all the table entries with no correction from the O2 sensor as it does in Closed Loop in part throttle. That is why a scan tool always shows 128/128 in PE.

You need to get the eprom tuned to get as close to 128/128 throught out the engine's operating range (rpm and load) without any correction from the O2 to achieve maximum driveability and gas mileage. For WOT, you are in a "whole new game again".

Kyle F

Glen is right, but to answer you question about why you cant just take the vacume hose off is because you set the pressure with the hose off, that becomes you pressure and you can just go out and crank the pressure up.
SInce our cars need a little more fuel after some mods are done it is nice to be able to add a little more, plus get it to mix better by having a better spray pattern. Though since the chip was programmed rich from the factory it is not as simple as more pressure will give me results. In some cases it will hurt you and make you run terribly rich. SO that is the whole idea of the AFPR, allowing you to customize your fuel delivery without having to program your chip after doing some little mods. Its worth it after you do a good intake and a full exhaust with headers because you start to get lean. In my opinion I liked mine and I thought it was a better use of $60 than a damn Air foil.

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89 Trans Am Turbo 3.8L All stock 43,000 miles #1053 of 1555

Past Thirdgen:
86 Trans Am w/ built 355TPI with SLP goodies and too much other stuff to List. One sweet *** car, wish I would have had a good enough Job to pay insurance on three cars so I could keep it, but for a 89 Turbo Trans Am w/ Low miles, I think I made the right choice!

RCR

Also, The fuel pressure goes up when the vacuum goes down. So by removing the line all the time, you've only effectively increased your fuel pressure during partial throttle opening (ie when vacuum is high). Now you'll be running rich for idle and cruise, but no different at WOT.

IROC5.7TPI

Makes sense guys, thanks alot.

I knew it had to be too simple to be effective LOL

So my next mod will be the AFPR. Any recommendations? I had the TPIS on my Vette and it was a piece of junk. The vacuum port came off regularly, and even after putting a drop of locktite on it, it still came off.

I hear good things about the Holley unit.

Thanks for all the insight, guys. I really appreciate it.



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Mike L.
It ain't pretty.......

1987 IROC Z TPI 350 A4 3.27 Borg-Warner.

Mods: 2300-2500 Stall Converter, Shift Kit(GM parts), TPI Specialties Stage 3 PROM, Modified Airbox w/ K&N's, homemade cold air, Relocated MAT sensor, Gutted MAF, 160* thermostat, MSD 6A, Accel 8mm Wires, bypassed TB coolant, Flowmaster 3 chamber single 3" in/out muffler, 3" MAC mandrel intermediate, custom dual !cat Y-pipe. airfoil, ported plenum. !smog

http://www.MichaelLasiuta.home.att.net

**BOYCOTT LAPEER DRAGWAY**

Kyle F

I used the Crane Cams one, I think at the time it was the cheapest one.

Ed Maher

From what i've seen, the happiest AFPR owners have holley's. All the others will accomlish the same thing but they all have had their share of complaints.
If you are gonna get into prom burning you can skip the AFPR and just throw some change under the cover to increase the pressure for better atomization. Actually 'some change' is a misnomer, a quarter should get you about 50 psi which is a nice round number to tune from. a dime and a nickel is too much.
...ed

Grim Reaper

If the "shim" (that's what I call it) can give you a fuel pressure anywhere from 44 - 50 psi; then yeah, just tune the eprom from that point on. By tuning via the eprom, the actual psi is not really relevant as you are going to tune specifically to it anyways.

Anything between 44 and 50 psi is adequate for a good spray pattern yet not so high to prematurely wear out your fuel pump.

So save the money you would have spent on the AFPR and spend it on Prom Burning equipment instead.

IROC5.7TPI

Makes sense. I'm sure you guys can clear up any "confusion" when I get the equipment.

Thanks again. I really appreciate all of your help.


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Mike L.
It ain't pretty.......

1987 IROC Z TPI 350 A4 3.27 Borg-Warner.

Mods: 2300-2500 Stall Converter, Shift Kit(GM parts), TPI Specialties Stage 3 PROM, Modified Airbox w/ K&N's, homemade cold air, Relocated MAT sensor, Gutted MAF, 160* thermostat, MSD 6A, Accel 8mm Wires, bypassed TB coolant, Flowmaster 3 chamber single 3" in/out muffler, 3" MAC mandrel intermediate, custom dual !cat Y-pipe. airfoil, ported plenum. !smog

http://www.MichaelLasiuta.home.att.net

**BOYCOTT LAPEER DRAGWAY**

TruspeedIrocz

whats this quarter thing you guys are talking about? cause my friend burns chips so yeah, it sounds like a good idea to me

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1987 Iroc Z
mostly stock

JoelOl75

Take off the regulator cover and toss a quarter in, re-install.