dewmanshu

iTrader: (4)

ahhh must be a 2000 thing (along with fpr). My radix/3.0 is getting 7.9 and my fp gets to 67psi at WOT. I am on my second stock pump, second magna inline that came with kit(the second stock pump wasn't the problem, it was the magna inline) and oh about my third fpr. I am still confused cuz at 0%TPS and anything over 15mph my fuel pressure will F-ing drop to scary levels(anywhere between 39 to 57 usually 49 to 52)...touch that right pedal in the slightest and back up to 57psi. CRAZY!

Mort

At idle my pressure is 50-52 psi and usually 52 psi. If I get off the throttle when the vehicle is moving the pressure drops to 49 psi. When I give it a little throttle it goes to 58 psi immediately. At higher TPS angles fuel pressure goes to 62# or so and at WOT and 6 psi boost I see 67+ psi fuel pressure. All of this is normal and a direct result of engine vacuum/boost. The fuel pressure regulator works on engine vacuum/boost. When my engine is at idle, with a stock cam and not at too high an altitude, it will produce 9#-10# vacuum ( 52 psi fuel pressure ). When I lift off the throttle when the truck is moving the momentum of the truck keeps the engine turning a little with the throttle closed and the vacuum drops to 11#-12# ( 49 psi fuel pressure or less ). When I give it a little fuel the vacuum in the engine is reduced to 8#-6# or less ( 58 psi fuel pressure ). At higher TPS angles the vacuum is 3#-0# or so ( 62 psi fuel pressure ). At 6 psi there is no vacuum and the FPR is boost referenced and the fuel pressure is 67+ psi.

At least this is the correlation that I find between engine vacuum/boost and FPR operation and resulting fuel line pressure.

TG02Z71

iTrader: (2)

I get about 55-60psi out of my stock system now.
When I first installed my STS base kit it was overboosting to 10psi but I had no fuel delivery issues until I took it up to about 120mph three or four times. Then it just fell on its face bad! I don't know if the computer had to learn at these type of extreme conditions or something else happened.
At the time I had no fuel pressure gauge so I was in the dark.
Either way be happy your seeing so much pressure I guess, that is if your getting the volume you need as well.
Where are you getting your pressure signal from?

Oh ya, I love the new ***** Wonka quote!!
What happened to Miles Davis??

Wilde Racing

iTrader: (26)

Hey vanillagorilla, are you using a autometer fuel gauge? I've posted about a high fuel pressure problem a few times in here, but it turned out to be the sending unit on the gauge.

vanillagorilla

iTrader: (1)

It's an autometer sport comp guage, and its mechanical with a pressure isolator. I'm getting the pressure from the schrader valve port on the rail. And the manifold signal is coming from the little nipple on the side of the manifold.

My pressures are right on par with what Mort is seeing. But I'm sure they'll drastically drop when I really crank up the boost using bigger injectors.

parish8

iTrader: (6)

most of this was said above but it is worth saying again. if you have a return line then the fuel presure is refrenced off of the intake presure. the BASE presure is around 58psi. if you pull the vacume line going to the regulator you should see around 58psi. the regulator seems to add about 1psi of fuel presure per 1psi of boost. when i am over 20psi i see about 80psi of fuel presure.

the regulator will also pull fuel presure when under a vacume. at idle it will pull a little fuel presure and under decel it will pull even more(more vacume=pulls more presure). the whole idea is to keep the presure across the injector constant so if there is a vacume on the intake side of the injector you have to pull fuel presure to keep it around a 58psi and if there is boost it will need to add fuel presure to keep it at a 58psi diference.

the stock pump will push 70psi easy but the flow rate goes down as the presure goes up. every set up i have been involved in the stock pump will support 400+rwhp before you have to worry about it. watch the gauge at the top of 2nd or 3rd gear and if the presure doesn't dip then it is fine. it will dip prety drasticly if it is out of flow. i was seeing it go from 70psi down to 50 just before the shift and then snap back to 70psi after the shift.

02sierraz71_5.3

iTrader: (2)

Ive always wondered about the accuracy of comparing one engines fuel pressure to another. Imagine the same pump on two engines with one with smaller injectors and another with larger inj. The one with smaller injectors would have more pressure at the rail but not be able to support the hp numbers larger injectors would even though the pressure is higher.

What is the pulse width of the stock injectors?

parish8

iTrader: (6)

i think you are missing a few things about how the fuel system works but it is kind of hard to explain. first thing is injector size will not effect fuel presure at all. if you take 2 identical motors both making 400rwhp but one with 42lb injectors and one with 75lb injectors they will both have the same fuel presure. the 75's will be open less of the time than the 42's but they will both flow the same amount of fuel if tuned to the same a/f ratio.

once you turn up the power the larger injectors can and will flow more fuel and will eventualy outflow the fuel pump. at that time the fuel presure will dip hard at the shifts. the regulator will attempt to maintain a certain fuel presure based on manifold presure and is not effected my injector size untill the pump just runs out of flow. it happens all at once, not something you can see at part throttle or low boost.

i have seen stock injectors on a 6.0 motor run at over 80% on a stock motor. the stock injectors are just big enough to run a stock motor and not much more. you can talk pulse width or duty cycle. 16ms at 6000rpm is 80% duty cycle.

i dont know much about what fuel presure numbers to expect on one of the new fuel systems without a return but on the old set up's you definately can compare fuel presure with other people to see if you might have a problem.

vanillagorilla

iTrader: (1)

Yeah, pulse width is pulse width. I've already established I'm at a 100% duty cycle. I just had no idea we were privelaged enough to have boost referenced fpr's. It makes sense why the pressure rises. I thought my fp was rising because of the restriction the injectors were producing. I can sleep now. However my fp will drop though with a stock pump with bigger injectors and more boost. Or will it?

parish8

iTrader: (6)

no, the fuel presure will be dependant on boost and nothing else, if you up the boost then the fuel presure will go even higher. that is right up until the fuelpump flow is maxed out and then it will dip hard.