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Old 05-21-2002, 01:11 AM   #1
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Default Rising Fuel Pressure with Rising RPM?

okay, I have a problem. Im pretty sure its right under my nose and am probably saying the answer but Im just checking with you guys to see if my thinking is correct. I just did the heads intake and cam on my car and in the 3000+ rpm there felt to be a hesitation. I found one of my spark plugs were cracked (porcelain) so I changed my wires and that plug. Now my engine bogs and hesitates at every rpm. I have my fuel pressure set at 40psi w/ the vaccuum off, so at idle it sits at about 32psi. The fuel pressure gauge is mounted under the hood, so I cant tell if it drops when it bogs, but at a stop when I rev it slowly climbing from 900-4500ish rpm the pressure drops to 30psi, but If I take a quick stab at it, it will jump to 40psi. The pressure should be going up as I rev, no matter how slowly I take it up right? How can I tell if it's the fuel pump or fuel pressure regulator? This pump and regulator are less than a week old but Im pretty sure its one of em. What if I disconnect the vaccuum and rev it and the pressure drops? will that tell me there? or have I already found it?
Sorry for the long post, Im sure you guys will come out with the right answer(s). THX.
1993 Grabber Blue Mustang GT
Trick Flow Heads, Street Heat intake, 3/8in spacer, E303, TFS 1.7rr & 6.75 pushrods, Holley 190lph fuel pump, 24# injectors & sample tube, SVO timing chain, Aeromotive AFPR, 180* t-stat, 2 5/8 Auto Meter mech fuel pressure gauge, K&N, March Ram Air & Pullies, 73mm C&L MAF, Edelbrock 65mm TB & EGR, 1 5/8in Equal Length Super Competition Hooker Headers, 2 1/2in H-Pipe w/hi-flow cats & Flowmaster 2 1/2in Cat-Back Exhaust, FlowTech Cut-Outs, Nitto DR's, 3.73 gears, FMS Aluminum DriveShaft, Pro 5.0 Shifter, Pro-Shift Lite, 8.5mm MSD Super Cunductor Plug Wires, PowerSlot rotors, PowerMaster 140amp Alt., LX lights, Cobra R hood w/SVO scoop, Saleen spoiler, Cobra Bumper, 3in chrome tips.
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Old 05-21-2002, 03:49 AM   #2
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Join Date: Feb 2002
Location: Nebraska
Posts: 86
Default plug the line

Sounds to me that your reg is fine simply because the pressure changes. A slow rev will still allow all vaccum devices to operate because the cylinder is not in demand of all of the air entering the system. Where as a snap rev of the throttle will cause the throttle position sensor to go to max or near max volts telling the computer to supply more fuel which in turn requires more air and all off this happens so quickly the air coming into the engine has only time to get in the cylinder and not sight-see on the way in. Nature is lazy and will always take the least path of resistance. Thus the other vacuum operated systems have no air to work with. Dose it backfire at all (intake or exhaust)? Any black smoke after a shift under hard accleration? How dose it idle? You might have a vacuum leak or even a exhuast leak. Either/or will seriously affect performance. A vaccum leak will cause eradic idle due to unmotiored air to entering the system confusing the computer (so to speak), Also a exhaust leak (even a small one) will cause lowered performance due to lower exhuast temps across the given o2 sensor. Because there are two (o2's) the side with the leak will have a lower temp across that o2 and the side without the leak will be higher in temp, my guess is the computer will see this and add more fuel thinking the actual "good gasket" side is running lean. Because the Adaptive Logic computer will always try to make the engine run as well as it can with the given inputs. And will always opt for the conservitive tune (to prolong engine life). And this is assuming all your sensors are working properly. I am so sorry about the HUGE post but sometimes I just ramble.....You can not affectivly troubleshoot something without first knowing how the system works. my .02 feel free to tell me that I am full of S*%# I may have just made it worse..sorry but when I get started.....
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1990 Mustang GT Trick Flow heads,F303,Mac cold air,FMS 65mm tb,73mm ma,FMS 1.6,GT-40 intake,MSD igintion,NOS Big Shot@150,Mac equal shorties,Mac h-pipe,American Thunder flows,Centerforce dual friction,TTC 3550,alm drive shaft, 3.73's, HPM subframes, k-member brace, strut tower brace.. amongst others.
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