Flex Fuel sensor readings drop when in boost

[dreksnot]

Originally Posted by Greenhornet2

Where is the fuel pressure read from? Before the rail? If you have 29psi before the rail you have to be basically using all the fuel that's getting to the rail, essentially running out of fuel and there's no fuel in the return line to get a proper reading. Just a guess, i have no idea how your system is set up just thinking out loud.

FP sensor is after one rail.
So here's the setup:
Triple Pumps > Fuel Filter > split Y then going to each rail as supply > (FP sensor) > combining split Y then going to the boost reference FPR > FF sensor > return to tank via OEM supply line

I have no FP issues. Idle it's set at 58psi. At 25psi boost the FP is reading 83psi.

[dreksnot]

Originally Posted by Big Biscuits

This is why I find it hard to believe it’s flow being so close to the FPR. Is it facing the correct way? Mine had arrows for flow route.

The FF sensor is omni-directional for flow.

[stevieturbo]

Setup sounds fine.

[Big Biscuits]

Originally Posted by dreksnot

The FF sensor is omni-directional for flow.

Emkay, maybe I was wrong Could have sworn I had seen arrows, could just be crazy. Any who. I’m still thinking power or ground. Engine loads pulling power or ground away from the sensor. Being a diesel tech for GM, John Deere and now Cat, 20 years this month to be exact, I have seen similar problems. It would be an easy check just to put the sensor on a separate circuit with its own chassis ground. If it doesn’t change then put it back.

Can data communication circuits have had this problem in several applications. Duramax was a prime example. GM put ecm, tcm, ficm, and glow plug module on the same can circuit. Glow plug module would crack from vibration and heat, short internally just enough to pull can leg voltage down from 2.5 volts to below 1 volt. This would shut the engine down and nothing would communicate to each other. Unplug the gpcm and engine would start and run. Point is, if a circuit has a strong enough current draw, voltage will be pulled away to find ground.

[eLeSthree]

Ok here's a new theory. It only happens when you run high boost, right? You are running a boost referenced FPR, so when running high boost you're also running higher fuel pressure. Maybe, when the FPR see's that much boost on the diaphragm, the orifice is restricting the return line flow in order to maintain that much fuel pressure, and the return line is seeing less or no fuel.

maybe...

[stevieturbo]

Originally Posted by eLeSthree

Ok here's a new theory. It only happens when you run high boost, right? You are running a boost referenced FPR, so when running high boost you're also running higher fuel pressure. Maybe, when the FPR see's that much boost on the diaphragm, the orifice is restricting the return line flow in order to maintain that much fuel pressure, and the return line is seeing less or no fuel.

maybe...

That could only happen if your overall fuel flow is very inadequate, which with a triple setup is unlikely, and if there was a no flow situation out the return, the chances of fuel pressure not also having dropped massively is also nearly zero.

With a return system, the reg always needs an excess of fuel through it to work properly, I'd doubt it could ever maintain stable pressure if fuel out the return was extremely low or nearly zero.

[Greenhornet2]

Sorry i thought you were having fuel pressure issues as well i thought it was dropping to 30psi. I'm pretty much out of ideas other than changing out the ff sensor or trying to put it before the rail.

[JMI]

My FF sensor is at the feed line and my fuel pressure regulator is on my return side.
We always hook the FF sensor on the feed line. Fore did an article about FF sensors on the feed does not cause enough restriction to be an issue hooked up on the feed size.

[eLeSthree]

Originally Posted by JMI

My FF sensor is at the feed line and my fuel pressure regulator is on my return side.
We always hook the FF sensor on the feed line. Fore did an article about FF sensors on the feed does not cause enough restriction to be an issue hooked up on the feed size.

Did you read the whole article? Snippet below.

http://foreinnovations.blogspot.com/...ensor.html?m=1

Affect on Return Fuel Systems
Built return fuel systems take a "ground up" approach to maximizing fuel delivery, and the measured losses are definitely a problem if used in the feed line on our high end fuel systems. The alternate sensor location is the return line, which could potentially induce a regulation error. Good news: we tested this sensor on the return line from an F2i regulator and picked up zero additional regulator error over a 240-1200 lph bypass range. FYI, here is the regulation error of our F2i, which is excellent. (don't expect these results from other brand regulators)

[dreksnot]

Originally Posted by eLeSthree

Did you read the whole article? Snippet below.

http://foreinnovations.blogspot.com/...ensor.html?m=1

Good article. I don't have any regulation errors ASAIK, but my E% does lower when getting into high boost. So, I am not sure if moving it to the supply line will help any. More troubleshooting necessary, I reckon.

[stevieturbo]

Around 4:30....obviously settings wont apply to OEM ecu users, but they are noting odd behaviours


https://www.facebook.com/HaltechEngi...4992425048400/

[Big Biscuits]

I wonder if heat is a factor? Higher pressure=higher fuel temps going into the return line.

[FasNuf]

Originally Posted by Big Biscuits

I wonder if heat is a factor? Higher pressure=higher fuel temps going into the return line.

Are you thinking the fuel is boiling and the bubbles are passing the sensor skewing the %?

[Big Biscuits]

Originally Posted by FasNuf

Are you thinking the fuel is boiling and the bubbles are passing the sensor skewing the %?

No not at these pressures, but going from 70* to 120* changes sensor readout sometimes. I’m digging deep, just thinking of some weird problems I have seen in the last 20 years. Heat has caused sensor parts to expand and skew data.

Another thing to think of is return line sucking air. Small pin hole in the regulator pushing high boost pressure in the return...like I said digging deep. Clear hose on the return line would test this theory. Would need a dyno and people around to verify.