Fuel pressure loss-Can it be in the tune?
07-19-2005, 10:38 PM
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Fuel pressure loss-Can it be in the tune? I am still dropping from 61#'s to 52#'s of pressure at WOT. I have
checked all the lines-No kinks No leaks
Replaced fuel pressure regulator
replaced fuel pump-Walbro 255
Checked all hoses in the tank
replaced fuel filter
replaced gas cap-I just felt like trying
The only think I have not done is replace injectors. But I cant see a 10# drop from a leaking injector. This all started after a base tune was put in. Is there anything in a base tune that would cause a 10# at WOT. Could fuel pulse not be set right?
Any ideas would be appreciated.
I have a 98 TA with regulator in tank. 30# FMS injectors
checked all the lines-No kinks No leaks
Replaced fuel pressure regulator
replaced fuel pump-Walbro 255
Checked all hoses in the tank
replaced fuel filter
replaced gas cap-I just felt like trying
The only think I have not done is replace injectors. But I cant see a 10# drop from a leaking injector. This all started after a base tune was put in. Is there anything in a base tune that would cause a 10# at WOT. Could fuel pulse not be set right?
Any ideas would be appreciated.
I have a 98 TA with regulator in tank. 30# FMS injectors
07-20-2005, 11:24 AM
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It has to be either forward flow/pressure drop in
the lines, or pump power supply. I would begin
with hooking up a volt meter across the fuel pump
power lines, as close to the tank as possible (to
see the drop most accurately). Some people have
had to upgrade power feed wiring, like run a new
dedicated B+ and GND wire pair, and a new HD relay
out back that has its coil driven by the old one.
If you see that the at-pump voltage at high demand
is sagging away from what you see up at the engine
where wiring is short and tight, look at this upgrade.
Big injectors will offer more of an "exit orifice" against
which to drop the available pressure, across the fuel
line flow resistance. Bigger forward plumbing for the
12 or so feet involved, might help you. So might a new
fat forward run, and using the old forward as the return
and cobbling that in place of the short tank return line
(though I don't know if '98s are the same as what I see
under mine, I'd rather have the return tapping off the
rails than way back in the chain; just not enough to go
and do anything about it).
The PCM tables seem not to know anything about forward
line drops. Have not seen anything (other than PE vs RPM
which is a command, not a calculation) for that. So I figure
you want the delivery to just be as ideal as possible and a
flat pressure profile, like you would get from a rail mounted
or rail-returned, in-tank regulator is that. The reg will work
to null the forward drops.
the lines, or pump power supply. I would begin
with hooking up a volt meter across the fuel pump
power lines, as close to the tank as possible (to
see the drop most accurately). Some people have
had to upgrade power feed wiring, like run a new
dedicated B+ and GND wire pair, and a new HD relay
out back that has its coil driven by the old one.
If you see that the at-pump voltage at high demand
is sagging away from what you see up at the engine
where wiring is short and tight, look at this upgrade.
Big injectors will offer more of an "exit orifice" against
which to drop the available pressure, across the fuel
line flow resistance. Bigger forward plumbing for the
12 or so feet involved, might help you. So might a new
fat forward run, and using the old forward as the return
and cobbling that in place of the short tank return line
(though I don't know if '98s are the same as what I see
under mine, I'd rather have the return tapping off the
rails than way back in the chain; just not enough to go
and do anything about it).
The PCM tables seem not to know anything about forward
line drops. Have not seen anything (other than PE vs RPM
which is a command, not a calculation) for that. So I figure
you want the delivery to just be as ideal as possible and a
flat pressure profile, like you would get from a rail mounted
or rail-returned, in-tank regulator is that. The reg will work
to null the forward drops.
07-20-2005, 04:05 PM
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Thank You Jimmyblue, Thank you for the information. I do appreciate it. The one thing I dont understand is that the fuel pressure issue just started. I have been running this set up for a year and a half with no issues. This started when I was having the car base tuned. A base tune went in and the trans crapped out on the dyno. So I rebuilt the trans and put in a new torque converter and bam I have a fuel problem I can t figure out. Would a voltage problem just pop up?