Been doin some basic bolt on mods (headers, cat back etc) Car was showing no improvement at all even after setting pressure to 50lb. Checked pressure at WOT and it was dropping to about 25lb. Replaced fuel pump and diaphragm in regulator. Set pressure at 50 again, it idles at about 44lb, goes to 50 when ya whack it but as the Rpms climb it drops back down to about 44 or so, once it shifts it goes back up then drops with rpm. Car is running much better now than before but still seems like an underachiever...is this type of pressure normal, if not....HEEEELP Its a 91 L98 Z28....like the name says if this thing dont straighten out I may let the kids use it as a BB gun target!

 

Just wondering how your going about setting the pressure.50# seems awful high for a basiclly stock setup.I've heard some people say that high of a pressure screwed their injectors.Anyway this is out of the FAQ incase your not sure how to properly set.(not saying that you don't just tryiing to help)
Q: How do I correctly set the fuel pressure on my new adjustable fuel pressure regulator?

A: The correct way to adjust your fuel pressure is with the vaccum line of the fuel regulator disconnected. The instructions with many adjustable fuel regulators don't tell you to do this, but it is essential! You must remove and plug the vaccum line going to the regulator or you will be getting false readings, similar to adjusting the timing on vacuum advance distributor. What you are attempting to do is set the maximum fuel pressure. At idle, fuel pressure is reduced due to high vacuum, so the presence of the vacuum line is detremental to fuel pressure. Repeat the process until you have the desired reading.



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1991 1LE Z28 355cu 5SPD (ORIGINALLY 305 BEST E.T. 14.186@99.86mph)NO PASSES ON 355 YET.MINI RAM INTAKE,AFR 190 HEADS,10.23:1cr 24# SVO INJECTORS,BBK 52mmTB,AFPR
FULL ROLLER MOTOR,1.6 rockers MSD 6AL
AUTOMETER A/F GAGUE MARCH PULLEYS,HEDDMEN HEADERS 3IN EXH NO CATS FLOWMASTER,POWER TRAX NO-SLIP LOCKER,3:42 GEARS,LAKEWOOD LOWER CONTROL ARMS HOTCHIKS STRUTTOWER BRACE,COMPETTION ENG.SUBFRAME CONNECTORS
MALLORY TACH W/SHIFT LITE
BLACK, TINTED WINDOWS, TAIL LIGHT COVERS BIG BLOCK COWL INDUCTION HOOD,SHAVED DOOR HANDLES

67RS 327cu 92K ORIG MILES.NEWER GM HEADS HEADERS,650 HOLLEY CARB,CAM, 350 TURBO TRANS W/SHIFT KIT&COOLER 12 BOLT POSI 3.73'S MUTLILEAF SPRINGS
NEW VINYLROOF&CARPET, COWL HOOD,HIDE AWAY HEAD LITES,

 

no prob, believe me I am VERY new at this, but yes it was set with the line off...is a hypertech kit and they said to go with around 48-52 with the line unhooked, so I went right in the middle...is this too much? what really has me puzzled though is why it drops as the RPM climbs??? do they actually start to build vacuum again at higher RPMS?

[This message has been edited by GonnabeatargetZ (edited August 12, 2001).]

 

GBTZ,

The fuel pressure regulator should have a vacuum line on it. The vacuum modulates the pressure by helping to compress the spring. At idle and low throttle angles (low engine load) the vacuum is higher, compressing the spring a bit more. This lowers fuel rail pressure. When the throttle is opened wide (higher engine loading) the vacuum decreases, allowing the spring to exert its full force and raise the fuel pressure. As engine RPM increases, vacumm increases as well. As soon as the transmission shifts, engine RPM drops, and along with it vacuum drops a bit, once again raising fuel rail pressure.

What you are experiencing is pretty normal operation of the regulator - just as it is designed to operate.

Since you have evidently repaired the fuel pressure problem (dropping to 25 PSIG) you should be getting better performance. As for the correct setting, every application is a little different, but I'd tend to set it a the lowest pressure possible. 48 PSIG is probably better for a mostly stock setup, and may even be too high at that point.

Unless the "HyperTech Kit" includes a PROM and they have changed their philosophy, you might not get all the improvements they advertised. Do an archive search, and you might discover that the HyperTechs are not the final answer to reprogramming your ECM. I have one on my desk as a paperweight, since the upgraded GM PROM actually does better than the "performance" PROM from HyperTech. Your experience might be different, but mine wasn't all that positive.

If it isn't too late, you might be able to return the PROM or kit and save some cash if you find that you aren't getting the advertised gains.

Just my 2¢

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Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

I'm not sure why it would be dropping as the rpms go up.It should be going up.(I'm pretty sure)When you take the line off it should go up to where you have it set then when you put it on it should drop a few pounds.when you take the line off this simulates WOT.Because your taking the vaccum away,there's no vaccum or little vaccum at WOT.Maybe you got a faulty regulator,possiablly a bad diaphram. maybe you can exchange it.


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1991 1LE Z28 355cu 5SPD (ORIGINALLY 305 BEST E.T. 14.186@99.86mph)NO PASSES ON 355 YET.MINI RAM INTAKE,AFR 190 HEADS,10.23:1cr 24# SVO INJECTORS,BBK 52mmTB,AFPR
FULL ROLLER MOTOR,1.6 rockers MSD 6AL
AUTOMETER A/F GAGUE MARCH PULLEYS,HEDDMEN HEADERS 3IN EXH NO CATS FLOWMASTER,POWER TRAX NO-SLIP LOCKER,3:42 GEARS,LAKEWOOD LOWER CONTROL ARMS HOTCHIKS STRUTTOWER BRACE,COMPETTION ENG.SUBFRAME CONNECTORS
MALLORY TACH W/SHIFT LITE
BLACK, TINTED WINDOWS, TAIL LIGHT COVERS BIG BLOCK COWL INDUCTION HOOD,SHAVED DOOR HANDLES

67RS 327cu 92K ORIG MILES.NEWER GM HEADS HEADERS,650 HOLLEY CARB,CAM, 350 TURBO TRANS W/SHIFT KIT&COOLER 12 BOLT POSI 3.73'S MUTLILEAF SPRINGS
NEW VINYLROOF&CARPET, COWL HOOD,HIDE AWAY HEAD LITES,

 

Thanks for the help, have my own lil 1/4 mile marked off and the car is defiantely running MUCH better. Found another vacuum leak this morning, helped out the car and now the heater controls work too!!! woo hoo I think Vader is right about the vacuum coming up with RPMS maybe because this thying is finally comin around and running like i expected it to. It likes around 51 lbs by the way played some this morning with that too and that gives me by far the best throttle response. It does have a hypertech Thermomaster chip also....dont know enough to say whether I am really impressed or not with it, had never heard of burnin your own until i found this board(now all I gotta do is get the other half talked into some PC upgrades :-) )Had bought it to disable the VATS as it took a crap on me about a week after I bought the car. Thanks again for the help. Mods to date on car are...Flowmaster back system(no more cat), Edelbrock TES system, Accel coil and module, Holley air foil, gutted air boxes, K&Ns, B&M shift kit, Hypertech fan switch, chip and AFPR. Thinkin next step should be 3.73s is 3.23s now.