Why?

87gtnewtogame · 06-09-2002, 04:46 PM

I was wondering what is this trick someone showed me doing and how or why it works. There is a small vacuum line running into the back of the EGR and one running to the top of the fuel pressure regulator, two different lines, in the elbows of each he installed a BB. It made as much difference as my headers and h-pipe as far as seat of the pants feel. Okay I posted that I had done this trick on a previous post and someone said can't be must be running rich as heck, so I thought maybe it was just the blocking of the EGR so I removed it from the fuel pressure regulator bame it was if someone kick the leg out from under me. It felt as if I were back in a stock 5.0. WHY?

MiracleMax · 06-09-2002, 09:47 PM

Cutting off vacuum to the EGR and the FPR is what you have achieved, not the best choice in either case. Since A. your upping fuel pressure and B. your eliminating exhaust gas recirculation from the process.

The stock Ford fuel map is mapped out to include EGR function and a manifold pressure referenced FPR curve.

cutting off EGR function creates a lean condition when the car reads it as active (since there is more air present). However, the EGR is really only on at high speed part-throttle conditons (it cools combustion temps to inhibit the formation of oxides of nitrogen).

Now cutting off the reference to the FPR is the worst evil here, what you've done is somethign akin to a jedi mind #$%* on the computer which is now trying to frantically adjust the amount of fuel entering the combustion chamber based on what the O2 sensor is reporting (the MAF still thinks everything is hunky-dory and is telling the computer that X amount of air is entering the engine and the injectors should stay open Y amount of time to deliver S amount of fuel. Since the fuel pressure has shot through the roof, the injectors are firing a nice high (for the system) pressure finely atomized spray of fuel which coincidentaly is to much. by the time the combustion event has occured and all the availalbe fuel that can be burned with all the availalbe air is depleted leaving unburnt fuel (which can cool the combustion event BTW) goes out the exhaust and shots past the O2 sensor reading rich. Then on to the h-pipe and the air injection which provides more air to burn the unburnt fuel. Incidentally a rich fuel system will also cause the cats to run hot (made this mistake on an 86 IROC once and burned the carpet in the car). Due yourself a favor and give the computer a breakby opening up the line to the FPR again.

If your making insane power with the BS mod, then look to the fuel system for possible problems (under injected if your modified or low fuel pressure, or clogged injectors, or whatever.)

Stroked408 · 06-09-2002, 10:10 PM

Good points,my only question was how did the car sit? remember a cool car is a powerful car,lot of variables there?

Dark_5.0 · 06-10-2002, 08:08 AM

Trust me with your mild mods you will make the most HP with the stock fuel pressure.

@ WOT there is no vacuum anyways.....so I dont see the point in this BS mod.

I am assuming that your car is still speed density....Most Speed density cars run rich at an idle anyways but your car must be running insanely rich.

I repeat there is no vacuum at wide open throttle so this mod makes no since and does nothing but make your car run rich until you reach wide open throttle. If plugging the line to your FPR really does help your car then you have a problem in your fuel system, most likely a clogged fuel filter.

If you would like to discuss this further PM me.

Later,

06-09-2002, 04:46 PM	#1
87gtnewtogame Registered Member Join Date: Jun 2002 Posts: 9	Why? I was wondering what is this trick someone showed me doing and how or why it works. There is a small vacuum line running into the back of the EGR and one running to the top of the fuel pressure regulator, two different lines, in the elbows of each he installed a BB. It made as much difference as my headers and h-pipe as far as seat of the pants feel. Okay I posted that I had done this trick on a previous post and someone said can't be must be running rich as heck, so I thought maybe it was just the blocking of the EGR so I removed it from the fuel pressure regulator bame it was if someone kick the leg out from under me. It felt as if I were back in a stock 5.0. WHY?

06-09-2002, 09:47 PM	#2
MiracleMax Registered Member Join Date: Apr 1999 Location: Hayes, Va, USA Posts: 798	Cutting off vacuum to the EGR and the FPR is what you have achieved, not the best choice in either case. Since A. your upping fuel pressure and B. your eliminating exhaust gas recirculation from the process. The stock Ford fuel map is mapped out to include EGR function and a manifold pressure referenced FPR curve. cutting off EGR function creates a lean condition when the car reads it as active (since there is more air present). However, the EGR is really only on at high speed part-throttle conditons (it cools combustion temps to inhibit the formation of oxides of nitrogen). Now cutting off the reference to the FPR is the worst evil here, what you've done is somethign akin to a jedi mind #$%* on the computer which is now trying to frantically adjust the amount of fuel entering the combustion chamber based on what the O2 sensor is reporting (the MAF still thinks everything is hunky-dory and is telling the computer that X amount of air is entering the engine and the injectors should stay open Y amount of time to deliver S amount of fuel. Since the fuel pressure has shot through the roof, the injectors are firing a nice high (for the system) pressure finely atomized spray of fuel which coincidentaly is to much. by the time the combustion event has occured and all the availalbe fuel that can be burned with all the availalbe air is depleted leaving unburnt fuel (which can cool the combustion event BTW) goes out the exhaust and shots past the O2 sensor reading rich. Then on to the h-pipe and the air injection which provides more air to burn the unburnt fuel. Incidentally a rich fuel system will also cause the cats to run hot (made this mistake on an 86 IROC once and burned the carpet in the car). Due yourself a favor and give the computer a breakby opening up the line to the FPR again. If your making insane power with the BS mod, then look to the fuel system for possible problems (under injected if your modified or low fuel pressure, or clogged injectors, or whatever.) __________________ 2002 5M GT (99% stock) 1991 5M LX (30% stock) patiently awaiting my satin silver 07 Mach 1, and don't forget the shaker

06-09-2002, 10:10 PM	#3
Stroked408 Registered Member Join Date: Jun 2002 Location: Southwest Posts: 131	Good points,my only question was how did the car sit? remember a cool car is a powerful car,lot of variables there? __________________ Deeper,Harder,Faster Stage Deeper Launch Harder Go Faster

06-10-2002, 08:08 AM	#4
Dark_5.0 Registered Member Join Date: Apr 2001 Location: Staging lane Posts: 4,337	Trust me with your mild mods you will make the most HP with the stock fuel pressure. @ WOT there is no vacuum anyways.....so I dont see the point in this BS mod. I am assuming that your car is still speed density....Most Speed density cars run rich at an idle anyways but your car must be running insanely rich. I repeat there is no vacuum at wide open throttle so this mod makes no since and does nothing but make your car run rich until you reach wide open throttle. If plugging the line to your FPR really does help your car then you have a problem in your fuel system, most likely a clogged fuel filter. If you would like to discuss this further PM me. Later, __________________ 92' LX-Big brakes, Lots and lots of suspension, GT40X heads, Ported cobra intake, stock cam, Vortech SC trim. 00' Lightning-Stock 88'CRX-13 second ego killer Last edited by Dark_5.0; 06-10-2002 at 08:19 AM..