ok, vacuum hooked up, and guage shows pressure lowering about 2 PSI when revving engine. also it jumps around ALOT (about 5-6PSI) as soon as i open the throttle. should it raise, stay the same or lower when revving? without the vacuum connected it shows 44 PSI.


EDIT: 44 PSI with the hose NOT connected. about 36 WITH it connected.
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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series Muffler added to Unkown CatBack, Ported Intake

http://www.geocities.com/david_angel_16

[This message has been edited by breathment (edited November 14, 2001).]

 

Should raise, maybe 10-15 psi from idle to full throttle.

-Reno

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"We are the middle children of history. Our Great War is a spiritual war, our Great Depression is our lives" - T.D.

 

when engine is in neutral? if it doesn't raise then whats that mean.

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series Muffler added to Unkown CatBack, Ported Intake

http://www.geocities.com/david_angel_16

 

Fuel pressure regulator maybe. Vaccuum problem possibly at WOT. Since the fuel pressure and the vaccuum to the fuel pressure regulator are all connected in a way, there's a good chance that's your problem.

 

but vacumm at WOT should be very low right? meaning it would be as if the Vacuum hose wasn't even connected to the intake. is there any rule as how much pressure should rise based on vacuum?

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series Muffler added to Unkown CatBack, Ported Intake

http://www.geocities.com/david_angel_16

 

Yes, the pressure at the regulator will vary with maifold vacuum. It will change directly proportional w/ manifoldd pressure. Meaning, if the engine is making 20" of vacuum at idle, thats 2/3 of a perfect vacuum. Atmospheric pressure at sea level is 14.7 psi. Ths, the rail pressure will drop by 2/3 of 14.7psi, or about 10psi. FPR design is such that this never works in a perfectly 1:1 linear fashion, but a pressure drop of 8-10 psi on a stock cam,med (~20" of vacuum engine is about right)
44psi at idle w/ vacuum connected is way high unless you're into the PROM and have adjusted the injector constant. I'd bet $1 you're bottoming your BLMs running that high/rich (meaning your computer is outside it's ability to compensate for the extra fuel in closed loop, and simply runs grossly over-rich in open loop)

 

On my stock 305 TPI engine, the fuel pressure dropped 10 psi from idle to WOT.

Basically from what I could translate out of the Ed's post, your fuel pressure regulator is probably not working to it's full potential and you would probably benefit from A. a new fuel pressure regulator OR B. an adjustable fuel pressure regulator.

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1986 Trans AM
305 TPI
Well over 200,000+ miles (speedo/odometer non-funtional! Odometer reads 142,000)
4 Wheel Discs
9 bolt Borg Warner Rear (2.77's....oh joy) :P
Completely Stock
Current Project: upgrade to a 355 TPI, 6" rods, 9.7:1 Compression, Stock TPI ported, 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech hot coil.

 

ED. im an idiot, I ment to say its 44 PSI NOT connected. and like 36 PSI with vacuum connected. Im sorry That kinda changes stuff

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series Muffler added to Unkown CatBack, Ported Intake

http://www.geocities.com/david_angel_16

 

If you are reving the engine in park and looking at FP guage you are not getting the right reading.You have to tape the FP guage to the winsheld and drive the car.The engine needs a load on it to get the correct reading.Just reving it in park the FP will raise then start to drop, it wont raise and hold the engine neeeds the load on it.

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89 350 TPI,comp cam,edelbrock intake base,SLP headers,highflo cats,flomaster cat back,accel 300+ ign,ported plenum and runners,ported maf,auto w/shiftkit,cold air induction,AFPR,custom chip,3.23 posie best ET 14.011@98.72mph without cam/New best 13.926@98.27mph

 

Mine used to drop under full load. Finally figured out the problem when the pump died. I had a hole in the rubber line between the pump and the hardlines. Under load the pump couldn't keep up, so pressure would drop. The line finally failed after two years. New pump, new hose, no problems.

[This message has been edited by RCR (edited November 15, 2001).]

 

that's a commomly overlooked problem.

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'88 RS (originally 2.8)
-350, .040 over, vette alum. L98s, stock tpi.
-305 injectors & chip
-TES headers & edelbrock cat back
-3.73 gears, 700r4.
Best with 2.8-17.4@77mph
Best with 305-15.0@93mph
Best with 356-13.7@101mph
on a 2.050 60 ft.
(Damn the 2.8!)