This has sent me on a wild goose chase for a couple days, thinking my new GT500 fuel pump or the dual FPDM setup weren't working right, since the gauge was reading 28-30PSI at idle where it should have been reading 38-39PSI!

the needle keeps fluctuating ~2psi and sometimes drops and generally has an erratic feel to it.

So today while at the bodyshop discussing some work needed on my Shelby hood, i saw one of the technicians pushing around a Ford scan tool. so i asked if he could run a check and see if he could find a problem in my setup.

all systems were go.. evap tests passed, no leaks or blocks were found..
then i noticed where the Fuel Rail Pressure was reading 39PSI on his screen.. it was 28PSI on my gauge!
50PSI on his screen was about 40PSI on the gauge and so on!

now i'm wondering wtf is up.. is it the gauge? is it the sender?
i've just installed this a couple days back, and we bolted the FP sender unit to a little braket we welded at the back of the passenger side fuel rail.
i've checked the wiring and all the obvious..

now what?

 

I have a autometer fuel pressure gauge installed.. mine reads at idle 28-29psi and then almost 40 at wot....

However.... when I slow down using the engine to brake.... it drops really low and sometimes I think air bubbles get trapped in the area where i have the sender mounted (fuel nitrous tap) and then it reads like crap until i turn the car off for a few minutes and then it's back to normal.

i have no idea.... i'm starting to consider it a worthless gauge and similar to a air/fuel gauge...

haha

 

Same here!!
mine also idles between 28-30psi (fluctuating) and drops sometimes below 20, even if i'm revving the engine.
the actual reading was 39psi at idle, and 60-70psi in throttle (ford scantool)

i wonder if it's a faulty sender, or some "design feature" :|

p.s: what makes you say an air/fuel gauge is worthless? had a bad experience with an autometer AFR gauge lately?

 

Unfortunately you are running a whipple.
I don't mean this in a bad way but whipple does some unconventional things with their tune.

The reason I say this is as follows
normally the lowest you'll see the fuel pressure is at idle.

Using a standard Ford, Saleen, JDM, Kenne Bell tune the differential pressure is always maintained at 39psi so at 10psi of boost you should see 49psi on your gauge. At 20"hg of vac you should see 29.18 psi
since
Inches of Hg / 2.036 = psi
20"hg / 2.036 = 9.82
39 - 9.82 = 29.18psi

If you were able to datalog the same way they did with the scan tool you would see that they were checking differential fuel pressure and not gauge pressure.

On any of the above mentioned systems the tune tries to maintain a constant 39psi differential pressure.
I have no clue to what whipple does.

 

In my last car I had an air/fuel gauge (not a wideband 02, just a plain old 50$ air/fuel) and it was not very usefull. I think anyone will agree.

A wideband o2 on the other hand is more usefull and more accurate.


jake

 

For what that Nexus fuel pressure gauge cost it should be more accurate than that. I would contact Autometer about it.
I agree with the comments about wide band vs. narrow band AFR gauges. The narrow band units are pretty much useless.

 

A good way to test the gauge is to turn the key and not start the car.
The fuel pressure should read around 40psi.
I have both the Nexus and a mechanical gauge on mine.
I bet his fuel rail adapter has an additional port for a mechanical gauge.
It's easier to install a $15.00 gauge than to wait 4 weeks for a replacement to find out it wasn't the gauge at all.

 

you think it would have made a difference having the sender unit on the driver side fuel rail?
can you show me another angle of it please? i'm curious how the whole braket looks like

well.. with my GT500 fuel pump, when i turn on the key without starting the engine, i hear the fuel pumps going on and the gauge jumps to ~80 PSI then settles at 50PSI.

then when i crank the engine, pressure goes up to around 58psi then drops back down to 20psi then back up to 28-30psi and stays there.
also when gently revved, pressure goes to about 40PSI and drops back to 28-30, but sometimes it drops further down to 20PSI :\

all in all, i just don't feel right about the way that needle moves on the FP gauge.. there's something about it!
not to mention that with a scan tool, i'm picking 10psi more pressure (Fuel pressure drop across injectors) than the gauge reads.

i just went outside and shot a video of it.. please have a look and let me know what you think of it

http://www.youtube.com/watch?v=8JwWAIcSuYw

 

I just read this on SCT's forums. LINK

 

There is nothing wrong with the gauge.

It is working properly.

Mine does the same thing, but it doesn't sit so high at idle or with the key in the ignition.

I'd say it's the Whipple tune.

Are you running 38 lb injectors or 39?

 

the H.O kit comes with the Ford GT 38lb/hr injectors

 

I know that, but some people have swapped them out for the 39 lb'ers. You may want to look into that...

 

Offtopic: S197_GT... whats your numbers at the wheels with that KB? Just curious..

 

i never doubted you not knowing what comes in the kit S197GT

but i just got the kit a week ago, installed it 3 days back.
now i'm still waiting to get it tuned, and for my bank account to recover before i could even start thinking about yet another mod

so 38lb/hr injectors it is!

 

In August I pulled 423.8 rwhp and 394.0 rwtq with the 2.6L Kenne Bell @ 8 psi, 4.10's, manny tranny, and 16* timing.

Since then I've added mty Aluminum Drive Shaft and my Off Road H Pipe, and I estimate it to be at 440 rwhp and 400 rwtq on an extremely conservative tune.

I know someone selling some 39 lb injectors for less than $150...It's a small price to pay for the proper fuel setup...Don't cut corners on the important stuff if you can help it.

Also, do you have long tubes?

 

nope.. i've put on JBA LT headers when i was N/A and i hated the way they sounded, and the 15hp didn't really cut it.. so i took them off

i love the stock exhaust sound (call me crazy) and i can't stand anything that resonates or drones :\

 

Wow... great numbers!

Was just curious because we're doing install and dyno tune on a very similar setup early next month.

 

Not a problem...I asked because the Whipple tune has been coming up lean on cars with LT's.

Thanks CR...They're still pretty conservative. You could see more or less depending on the setup and/or dyno.

There's plenty more power to be had, but I'd prefer to get it with additional mods first as opposed to throwing more timing at it right off the bat.

I have a great combo of suspension and power mods that make it easy to gain traction, as well as make it easy to break traction when I want to...

For what it's worth, I took down an 11.3 '03 Termi twice last weekend.

I have not been to the track since the blower...hell, since it was bone stock(11/04). Even then, I was only able to muster a 14.096 at 102.24 while spinning through 1st. I've since learned the cars habits much more, and consider myself to be a much better driver now.

Now back to your regularly scheduled Fuel Pressure thread...