MECHAM

iTrader: (4)

Twin 255 Walbros in tank - hot wired to run all the time
-8 Feed line to LS1 Speed Rails
60# Motos
Aeromotive FPR 1:1 at rails

50psi idle
~13 vacuum
+12psi
------------
75psi fuel pressure during WOT


pressure raises fine but towards 5k the fuel pressure drops and at redline its back to 60 or so psi..


Any1 else having fuel pressure dropping

Boostaholic

iTrader: (4)

How much power are you making?

MECHAM

iTrader: (4)

725hp/765tq

onfire

iTrader: (17)

Wlabros don't flow well at higher pressures. Search for a post I made that compared the Walbros at diffeent pressures to a -044Bosch. I removed my Walbro set-up and installed dual Bosch 044's for the same reason....it would ramp up then ramp back down....044's ramp up to 80psi and hold steady.

2001WS6Vert

You could try a BAP on them.

MECHAM

iTrader: (4)

how noisey are they? my twin 255's when I did the install were pretty loud..but after the shop did the -8 feed line..they quieted down quite a lot. I noticed the sound was gone right off the bat and another member with twin walbros asked why mine were so quiet.

I am having trouble find the post...link plz

I take it these are intank pumps? all you did was just remove the old walbros and install the new bosch pumps. nothing extra was needed? remove..and replace. not remove...replace..but had to replace this..and xxx to get it to work.


I also read on ls1tech that walbros dont like high pressure...and was wondering if I set them straight to 58psi with no vacuum/boost reference..would that let them flow within there rated range?

Boostaholic

iTrader: (4)

****, you can even sell your used 255 setup and recoup some of the cash, thoes things sell good

onfire

iTrader: (17)

If you have a 98 tank 044's would be easy to install. I have a 99 plastic tank and wanted them intank so I went with a custom tank...can;t hear them.

If you have enough injector, you can set them to 58psi and they will flow better...just remember 58psi minus your boost psi = what the injectors see.

2001-WS6

Are you checking your fuel preasure with a mechanical guage or are you pulling it into your boost controller for display purposes?

Is this happening with more than a 1/2 tank of fuel in your stock fuel tank? Just a quick sanity check to rule out fuel pump starvation under acceleration.

You're sure both 255 pumps are really working? They do have a weakness at higher fuel preasures but I don't remember the trigger point for problems.

Are you sure the boost reference source line to the FPR isn't leaking or coming loose?

We've been running at 60psi base fuel preasure on the Mototron 60s with the Weldon boost refernced FPR without any issues at 15lbs boost. We even had a cool day last November where we ended up cranking up the base fuel preassure some more to squeeze out a little more fuel during testing. The injectors didn't have any problems getting pushed this hard.

So I'd lean towards one of the pumps not being happy if the boost reference line looks ok to the FPR.

Rick

MECHAM

iTrader: (4)

2001-WS6


full tank of gas
vacuum line is good (I always have 13psi of vacuum - if the line were to become disconnected or something...I would have 8psi of vacuum)
using a Autometer Cobalt Fuel Pressure Regulator
pumps probably have less than 500 miles on them


also have the racetronix wire kit for single pump

2001-WS6

Hmmm... if the dual setup only has 500 miles on it, what were you running before? Just a single with the wire kit?

Rick

HUGGER ORANGE SS

iTrader: (2)

Ernest..

As stated before.. You sure obth pumps are on? Mine are much louder. Also I did a setup just like yours -8 breaded line all the way to the engine, W/a full return line. Dual Walbro's intank.

He's got a 396 LT1 with 11psi of boost and he's putting down the numbers, + his fuel pumps are quite loud when they prime up..

Maybe 1 pump is not happy, failing.. Maybe your not running both pumps. Like said in the other thread you need to make sure both are on..

Talk to you later.

Clint

MECHAM

iTrader: (4)

i was running the exact same thing....except i had stock lines. i had the shop install a -8 feedline to the rails and move the fpr to the rails also. i figured this would solve my falling fuel pressure...but it didnt.

i will re-inspect the pumps to make sure they are BOTH running.

MIGHTYMOUSE

iTrader: (59)

check
dirty filter on upstream side
damaged/bad regulator
good power and grounds to pumps
good flowing Y block from pumps, no restriction inside the tank.
solid voltage to the pumps
weak pump?

when i was dropping pressure i ran new dedicated grounds to the pumps and re-did he y block and havent had a problem since

kp

iTrader: (34)

63psi is the most my dual 255s will hold after 90% or so injector DC. Like onfire said when pressure goes up, flow goes down with these. I have a dedicated 10ga wire to each pump (including grounds), nice Y in the tank, -8 all the way to the regulater etc and mine did the exact same thing when I boost referenced it. I was going to try a voltage booster but next step is dual external Bosch 420s for me when I decide to make some real power

qqwqeqwrqwqtq

Fwiw we've ran dual walbros with no problems at -

995rwhp through a T400 and stock feed line, 43psi base pressure.

My own car which has made 898rwhp, 43psi base pressure.

And on a few customers cars at 70psi base pressure. (pushing 60's)

I would check the things MM has suggested. Also, does pressure bleed down or stay steady after the key is turned off? A pinhole in one of the lines inside the tank could do it as well.

DJ's Z

iTrader: (10)

I'm planning the same set up...just curious what size injectors are ya'll using for the big HP cars and is the FP boost referenced?

We pm'd each other a few weeks back regarding this issue with stock feed lines...keepin' my fingers crossed!

qqwqeqwrqwqtq

We've been using 60lb motrons on the vehicles running the stock pcm. With as high as 70psi base pressure, 20lbs of boost, and 100% dc. Not an ideal situation, but it works.

We usually run 83's on cars with BS3, up to 1000rwhp.

DeltaT

iTrader: (5)

I'd stick another gauge on there to verify the first. Do you have an Aeromotive FPR and and Autometer gauge? Seen plenty of gauges read bad.

Jim

MECHAM

iTrader: (4)

i turned the ingnition on...waited a sec for the pressure to rise to ~52psi...turned the car....pressure stayed at 52psi...didnt drop any..waited a few minutes.

but if i dont turn the ignition off...the pressure starts to slowly drop.

i take it that both instances i just described are normal?

I am pretty sure the fuel pressure is dropping it evident in my dyno runs where my A/F will start to decrease after 5k and no matter how much i open the injectors/PE vs RPM/VE table...the A/F curve doesnt richen up.