do injectors have an effect on fuel psi?

[mr.prick]

specifically injector pulse width,
it seems my psi is inching upward and,
i have been changing the IBPW {B3701} as to try and avoid
making changes to other tables that i have set. (IFR, VE, MAF)
now i am wondering if the IBPW is raising it more
than it seemed to already being increasing or if i`m chasing my tail.

[Bruce Melton]

Never seen a change even with drastic IFR adjustments. Usually run a mechanical fuel pressure gauge on the dyno. I would think if there were a fall off it would be @ higher fuel volume, with min pulse width being insignificant.

[mr.prick]

i am averaging 75psi and have hit 80 psi max.
is that something to worry about?

[Bruce Melton]

All the OSs and tunes done here assume 58-60 psi fuel rail pressure (I believe) so if you are exceeding that your IFR settings and all fueling calculations are skewed. Are you using a stock style pump?

[hquick]

I see fuel pressures of around 75 or so whilst accelerating. Also, sometimes my fuel pressure guage jumps around all over the place...even hitting '0' for a second here and there....but no stumbles or what not???
Quite often as I back off the pedal the fuel pressure will drop a fair way before steadying back to 60.

[Bruce Melton]

Any air in the line before sender or gauge will dampen the response. I bleed out the line at the gauge when using my temporary mechanical gauge.
Amazing how well the fuel pump system maintains pressure given the rate of volume change.

[hquick]

I have a sender permanently mounted on the schrader valve on the rails.
Wonder if I have air in there?
It's been there for a long time.

[TAQuickness]

I have a consistent FP drop at WOT (61 psi to 53 psi). Seems this is the result of the physical location of the regulator (by the tank as opposed to the rail). On occasion I have seen spikes in the FP when I let off the throttle quickly, but nothing over 68 psi.

[mr.prick]

yeah,
i have had this high FP mystery for awhile and
now it seems to be getting higher with out reason.
i just have a walbro, no hotwire kit or anything special.

[hquick]

I used to see the same rises with the Whipple BAP setup but now that is no longer installed.
I recently installed the Walbro...but I used to see the same thing with the OEM pump.
I wonder if the fuel pump voltage offsets have anything to do with it?

[TAQuickness]

I would suspect more a mechanical or physical problem rather than a tune problem. Could be some trash in the line causing a restriction downstream of your sender.

[joecar]

Injectors should not have any effect on rail pressure...

Consider this:
each time an injector fires, the rail pressure drops momentarily... this causes the FPR (at the pump) to reduce it's bleed to the fuel tank, and with the help of the pulse dampner (at the manifold), the FPR should be able to maintain the pressure "constant" to within a few psi (or less) ripple...

if the pressure stays dropped, then there may be problems with supply line restriction, leaky/weak FPR, weak/stuck dampner, pump undervoltage (pump motor problem, power/ground voltage drops), leaky injectors, or something...

if the pressure goes up above the operating spec, then there may be problems with stuck FPR, return line restriction, or something...

if pressure just varies around, then the problem could be anything mentioned including loose power/ground connections...

also, some setups don't have enough pump capacity/flow for the amount of fuel demanded.

It's a hard call... and it's hard to diagnose because the fuel system extends the length of the vehicle.

[mr.prick]

3420
how does this look?

[TAQuickness]

Prick - any chance you could overlay TPS in that chart?

[mr.prick]

i am at idle in that frame. (look at RPM and MANVAC)
that is what my FP looks like pretty much all the time.
in that log i have....
min=58.49 psi
avg=70.42 psi
max=81.22 psi
MANVAC was....
min=0.0 kPa
avg=47.5 kPa
max=75.5 kPa
the 80psi+ is a new high for me,
thus the reason for this thread.
thanks

[hquick]

Hmmm...mine only rises as I put my foot down. At idle it's generally steady at 60-61 psi.

[5.7ute]

Have you verified the pressure with a mechanical guage? Though if your tune was richening up proportionally it would show a pressure issue.
I would think it was a mechanical issue like TAQuickness. A bad return hose, regulator maybe even a blocked tank vent.
How is the system voltage & voltage at the pump?

[mr.prick]

LOL
the mech gauge i had i thought was broken,
it read about 75psi at idle so i got the autometer FP sender.
looks like i may need to drop the fuel tank.:bad:

[joecar]

What is the max psi spec quoted for your pump/FPR...?

[mr.prick]

i have the walbro 255 lph

[Bruce Melton]

i have the walbro 255 lph

I also have the 255 running 50# @58 injectors @~87% max with predictable pressure so my guess is you have a regulation issue with the pump. That is -I doubt you are outflowing the pump which causes the pressure to go---UP ???
Not likely.

[hquick]

I've been trying to get a hold of a 97 Vette adj reg but am having difficulty.

[mr.prick]

I also have the 255 running 50# @58 injectors @~87% max with predictable pressure so my guess is you have a regulation issue with the pump. That is -I doubt you are outflowing the pump which causes the pressure to go---UP ???
Not likely.

oh yeah,
i`m running stock injectors (28.8lbs/hr)
i forgot to mention that.
i had another thread going about high FP,
and now i am see higher FP (after changing IBPW i noticed it),
so i thought maybe by changing IBPW i made the FP go up.
LOL
does anyone know how much FP the stock lines can take?
i haven`t logged IDC yet.

[Bruce Melton]

I am told that that circular device on the crossover of the LS1 rails is a pulse dampener.

[joecar]

I am told that that circular device on the crossover of the LS1 rails is a pulse dampener.Bruce,

That is correct...

altho note that the early C5's did not have the dampner, they had the MAP-referenced FPR instead.

[joecar]

oh yeah,
i`m running stock injectors (28.8lbs/hr)
i forgot to mention that.
i had another thread going about high FP,
and now i am see higher FP (after changing IBPW i noticed it),
so i thought maybe by changing IBPW i made the FP go up.
LOL
does anyone know how much FP the stock lines can take?
i haven`t logged IDC yet.This sounds to me like the FPR is sticking/obstructed, or the return line feeding the FPR is obstructed.

[mr.prick]

This sounds to me like the FPR is sticking/obstructed, or the return line feeding the FPR is obstructed.

:doh2:
well,
i`m still 75% duty cycle anyways.

[Bruce Melton]

Bruce,

That is correct...

altho note that the early C5's did not have the dampner, they had the MAP-referenced FPR instead.

97 and 98s had the return from the fuel rail and the 05s and later did away with the dampner. (at least on C5-C-6s)

[joecar]

97 and 98s had the return from the fuel rail and the 05s and later did away with the dampner. (at least on C5-C-6s)That is correct. :cheers: