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View Full Version : SR Fuel Pressure Drop while during DYNO PULL....

karforty5
10-15-2009, 09:04 PM
Fuel Pressure Drop while on DYNO PULL....

Sup guys, need help tryin to figure this one out or seeing if someone had a similar problem....

At the dyno the other day and during a pull @ 12 lbs of boost, the car began to lean out.. At about 5500 to 7k RPM, fuel pressure gauge decreased from about 55 to 40 and my tuner saw that the car was leaning outon the computer..

Here are the mods!!!!!!!

- s13 coupe with SR20DET no internal work to bottom end, cams up top
- Garret SC61 T3/T4 turbo with peakboost topmount/tial 38mm WG
- Aftermarket intake mani with tomei 740cc side feed injectors and
nismo FPR
- AEM management system with wideband
- Walbro 255/z32 fuel filter

What Ive checked so far:
- No kinked lines underneath car
- Voltage at the pump during idle is 13.2V
- checked walbro pump- screen is clear
- All injectors are spraying

So thats where I am right now.. Im am unable to go up in boost but it only happens after !2 lbs. Any ideeas guys, feel free to post..
junn
10-15-2009, 09:11 PM
maybe fuel filter is clogged...or regulator is mest up
karforty5
10-15-2009, 09:25 PM
Possible but both are brand new..
jspaeth
10-15-2009, 09:57 PM
Drops down to 40, huh?

Perhaps above a certain threshold, air begins leaking on your vacuum line going to the FPR, causing the FP to drop by ~whatever psi your boost is at at that point (like 13 or so)

Seems like maybe it's not a coincidence that your fuel p. goes down by how much boost you were at.
Sileighty_85
10-15-2009, 10:01 PM
Nismo FPR are known for pressure drops, Id invest in a SARD FPR
Ali 556
10-16-2009, 01:39 AM
Nismo FPR are known for pressure drops, Id invest in a SARD FPR

+35746857954795495

there was a thread about this last week, ''nismo'' fpr tend to become lose after time and crap on you...go with aeromotive (SP?) proven on 1400whp supra's..
jr_ss
10-16-2009, 07:20 AM
Put a volt meter on your fuel pump power feed as well. I've seen/heard about people losing/dropping voltage at the fuel pump mid pull.
steve shadows
10-16-2009, 09:15 AM
Your fuel pump either is not upgraded as you say or IT IS DYING>

Get a new fuel pump problem solved
Def
10-16-2009, 10:29 AM
Make sure fuel pump is hardwired to the battery(with an inline fuse).
let5l1de
10-16-2009, 12:33 PM
I'm with Shadows on this. The noise of a fuel pump is often a great way to diagnose a fuel pump that is going bad. Some have the luxury of hearing the pump get louder on its way out, other may net be so lucky.

Make sure fuel pump is hardwired to the battery(with an inline fuse).

hardwired?

Use a Relay with switched on power from the ignition switch and full power supply directly from the battery.
GSXRJJordan
10-16-2009, 12:52 PM
All great suggestions in this thread ~ Nismo FPRs have a spotty performance record, and/or your fuel pump could certainly be dying.
robertftw
10-16-2009, 03:35 PM
Check fuel pump for sure. I have had 6 out of the last 10 brand new walbro's be no good they would drop pressure while tuning on the dyno.
Def
10-16-2009, 09:31 PM
hardwired?

Use a Relay with switched on power from the ignition switch and full power supply directly from the battery.

Yea no shit you don't want the fuel pump to run all the time. Obviously a switched source will need to still be switched. This is 12V wiring 101... :blah:
karforty5
10-17-2009, 10:20 PM
Drops down to 40, huh?

Perhaps above a certain threshold, air begins leaking on your vacuum line going to the FPR, causing the FP to drop by ~whatever psi your boost is at at that point (like 13 or so)

Seems like maybe it's not a coincidence that your fuel p. goes down by how much boost you were at.

Only was at 12 psi of boost
karforty5
10-17-2009, 10:24 PM
Fuel pump was at 13.2v at idle. I have heard of voltage drop on srs and different cars but not that many, possible underlying wirng problem if so.

Also, I will swap pumps and might switch to aeromotive FPR, suggestios? Do they sell a twin fuel pump kit?
jr_ss
10-17-2009, 10:35 PM
SARD FPR.... That's my suggestion, but Aeromotive isn't bad either. No one makes an off the shelf twin FP setup for our cars. It can be done, but custom hanger has to be made and what not. Just go with an external A1000.
ericb382
10-17-2009, 10:50 PM
I agree that it sounds like your fuel pump, however one healthy 255lph pump will out flow your 740's. I say flow test it just to make sure, then just get a new single walbro, unless you're planning on upgrading your injectors...