Ongoing FRP issue solved?

As some of you may already know I have been fighting a FRP issue that makes my truck buck and bounce between 45-55mph. It all started after installing ported fuel rails. It looks like they do not play nice with stock pump and injectors. Tried just about every tune out there with no luck on solving the issue. Matt at Gearhead has been looking into the issue and working hard at trying to find a fix with tunning. Awesome guy to deal with. Never expected him to put this much time into it. I was told that unplugging the fuel temp sensor has worked for another member. So on a last desperate attempt before forking out money to put my stock rails back in I gave this a shot. It seemed to work but my engine fan stayed engaged and sounded like a Jet was about to take off from under the hood and of course it threw a code. I got Matt to set the fuel temp at -40 which is where it defaulted at when it was unplugged. So now I could leave it plugged in and it would read -40 all the time. After some testing the issue is still there but only for about the first ten miles I drive the truck. After that she is smooth as stock. I am guessing engine or fuel temp is playing a part in this. Not sure what to make of this. This is a hell of a lot better than before where the bucking was there all the time. So its one step closer to a permenant fix. Maybe someone that understands the stock fuel system better than me can shed some light on what is taking place with the sensor unplugged and how thats effecting FRP

Your changing fuel control, meaning pressure control vs volume control. Atleast that's what I'm assuming considering fueling is based on pressure cold vs volume hot. (I might have bassakwards but I would have to look Into it a bit more as I can't remember 100 percent).

On a side note do you hear any noise from your hp fuel pump when engine gets hot? I have home drilled rails, no surge or drive ability issues, however the pump gets noisy when hot.

Havent noticed any change in noise cold vs. hot.

Btw 08 rails are different then the later rails, 08 rail outlets to injectors are smaller then the later years. Base on job2 rails vs later (silver end caps vs black). The inlet port from the hp pump are both tiny, just difference in depth of orfice.

I know from chem the PV=nRT meaning that pressure and volume have a direct relationship to temp. So as pressure and volume increase then temp increase as well.

Maybe as the fuel cooled it didn't have enough volume or pressure?

IBSTROKIN said:

Havent noticed any change in noise cold vs. hot.

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That's good to know as it's a new pump and I'm thinking I just got a bad pump.

Do you happen to check the port dia. When u installed the rails? Can you watch your Frp, vcv, Pcv readings? You could also have a bad pin fit ment at the valve cover connection / Frp sensor. Perhaps wiggle the harness, any injector miss?

Then again I am not sure what it did when the fuel temp was changed to always read -40 vs. in the 100's

I can watch frp but not the vcv and pcv. The frp sensor was changed when I got all my work done a few months back. No injector miss at all. The issue had only existed right after the shift into OD and only at light throttle. Pressure will swing about 1500psi at this point even with the cruise set

I wonder if ported rails are "hogged out" as I never touched the outlet side to the injectors, just the inlet port from the pump. Left it slightly smaller dia then the injector outlets. No drive ability issues. (stock fuel system otherwise on a stock calibration)

Check your fuel bowl for signs of metal. Any fault codes? You could also check under the air inlet tube to make sure it has not chafed the harness to cyl head connection. (would screw with Frp readings)

Yeah I checked all that the other day. pulled the filter and didnt see any metal. No codes either.

sonic blue l said:

I wonder if ported rails are "hogged out" as I never touched the outlet side to the injectors, just the inlet port from the pump. Left it slightly smaller dia then the injector outlets. No drive ability issues. (stock fuel system otherwise on a stock calibration)

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You drilled out the orifice, correct?
I've seen a few stock injector guys w/ the aftermarket ported rails going back to stock because of the surge issue.
Is there any data showing a gain of any sort w/ the ported or drilled rails on a truck w/ stock injectors?

Not really sure why it works but I figured it out when I had dual fuelers. Mine would only surge when the fuel temps would get above 120 degrees. I don't have a factory fuel Birk so my furl temp reads on the inlet side where you guys with the factory bowl reads outlet temps so it reads hotter faster.

Glad Matt got it resolved for you. the rails must do something weird just not sure what.

Yeah Matt has been a huge help. There are over 35 reponse emails about this issue so that should tell you something. I couldn't even get KEM to look into the issue. That the main reason I ditched the H&S

As my rails are being swapped.....LOL

Glad you got it figured out man.

Haha. I wouldnt say its totally figured out though. But it did bring a smile to my face to finally drive my truck and talk at the same time with out my voice jumping because of the bucking

Matt has always been awesome to deal with and the fan running all the time with the sensor unhooked is a pain in the ars
What i was going to do was just unthread the sensor from the fuel block so it read fuel temp as outside temperature (thats how it was hooked up untill i got dual fuelers from elite)

I really dont understand why the rails cause the issues with the surging and some harmonics with the pump but they do

I will have to look into unthreading the sensor so I can run my spartan tunes as well. Right now I can only run my gearhead tune with out the constant surging. It seems the stock pump has a hard time controlling pressure and volume with the ported rails.

The fuel temperature plays into the gain of the PID control loop that must be getting upset with the ported rails.

powerlifter405 said:

You drilled out the orifice, correct?
I've seen a few stock injector guys w/ the aftermarket ported rails going back to stock because of the surge issue.
Is there any data showing a gain of any sort w/ the ported or drilled rails on a truck w/ stock injectors?

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Yeah I just drilled out the orfice, left it smaller then the fuel ports vs a 09 rail, but closer to matching the size of the 08 injector ports. I only did it because I had the truck a part and was not sure of future plans I may have for it.

At the time when I google it, I didn't find anyone with issues. Considering the orfice is less then a 1/16" i was surprised how much power a 6.4 can make. One could see how injector demand could cause a loss of rail pressure.

I've had no drive ability issues, however I wonder if the rails people buy are hogged out more.

Those with the issue can you explain exactly how you get your truck to do it as so far I've driven in town, on hi way with no issues.

With that said I'm currently doing an oil cooler and a few other odds and ends I can try to duplicate your issue. My truck however is pretty much stock except for egr block off plates, removed throttle plate, ported intake elbo (removed egr feed tube restriction)