OR Mega Cab

On my fuel pressure it is typically at 8psi at idle but when I get after it on the highway it will drop to 4 psi, then go back to 8 psi I when I let back off. Is this normal?

The other fuel pressure issue I have started in the last couple weeks, is my FP will sometimes drop to 0-1psi when I have let off the throttle and am coasting to a stop and the transmission is slowing the truck down. This is more pronounced or occurs more regularly in Tow/Haul with the tranny locked. Does this mean my fuel pump is going out already? The truck has 16K miles, no programmer or downloader yet.

welndmn

For being stockish, you should not be pulling it down that far.
1. When was the last time you changed your fuel filter? (all thought I don't feel thats the issue)
2. Call quad, I bet your FP sender is going south.

rustyshakelford

thats the same thing mine is doing...i dropped it off at the dealer and they said my lift pump is golden? ill crusie down the highway and itll read 0-1 sometimes, then others its right ar 9-11. i dont know whats wrong with it. i even have the rp unplugged for the last month because it makes the truck run terrible. i guess i need to send to to quad to be checked out

brett

louddodge

I had the same problem with my truck. It got to were it was hard to start so took it to dealer they said the lift pump was fine and replaced a couple of other parts, got the truck back and everything was fine for to days and the same thing happened with being hard to start so took it back they started the tests all over again and said the lift pump was going out. They said it would be fine one time then be high then low so double check the lift pump. If it is not that i would go with the injectors.

CTDinMT

Just thinking out loud here, but on deceleration, the CP3 wouldn't be helping the LP draw fuel, which may account for the drop. I know with my Walbro, at constant RPMs I'm getting around 21-22 psi. When I let off the accelerator, press drops to 19. My guess is that the CP3 isn't helping pull the fuel at lower RPMs.

OR Mega Cab

I thought maybe the fuel filter also, but I put one in last Sunday and nothing changed. When I first put the Commander on, the FP would draw down to 4 psi on a hard accelleration, but always say 8psi when cruising or decelerating. I assumed this is normal, and was told this sounded correct when posting my original gauge numbers on this board. It just started doing this within the last month or so. Everything else on the Commander appears to be functioning fine, and I really don't think it is the gauge, but maybe I am wrong.

Quad, any ideas?


Thanks for your help.

qzilla

It could be your lift pump but, these trucks do act a little funny like you described.

The first thing is that the digital is very sensitive and very fast, so you see everything.

What is happening when you let the truck slow itself down is that the rail and other components need to stay pressurized and slowly fall. If you watch your rail pressure when this is happening it will stay up while the fuel pressure falls. If you use the brakes and the truck basically gets shut down to idle then the fuel pressure will not suffer.

Not, what is causing this is that the rail still needs to be fed but, because you are not on the throttle the CP3 is not helping pull that fuel through the filter. Instead the CP3 is in more of an open or pass through state where it allows fuel in but, the pump is not helping pull it.

It is sort of an anomaly with these pumps. A lot has to do with exactly what you are doing with the inputs as a driver like TPS, Brakes, Clutch etc.

Now, on top of that it sounds like your lift pump is ok but, not really strong. Some of these trucks have great pumps and others totally stink. I would put yours in the middle. I have seen stock trucks that are able to suck the pressure down to 0 with little to no effort.

rustyshakelford

qzilla

got a question for ya...when im crusing down the highway, mine will sometimes read between 0-1 psi, then other times be 8-11. i took it to the dealer to check it out, thinking the lp was bad, but they told me it exceeded specs. what do you think is the problem. getting the reading from the fuel filter canister. also when using the rp, it makes the truck idle horrible and stumbles when on the highway..always random...checked the plug numerous times and its tight and installed correctly

brett

qzilla

The only way I can imagine the rail pressure reading causing a problem is if you have a loose pin in the factory sensor??? I have seen it on several 06 and 07 trucks now.

If you want, go to your truck at idle and just wiggle the wires around on the rail plug and you will hit an ugly spot. It is just a loose pin if it goes to idling rough.

I think if that is it and you have another wire on it, the weight of the wire causes it to wiggle around more or something.

OR Mega Cab

http://www.youtube.com/watch?v=PleBgZW90Ks

OK, This is an example of what the truck is doing, it is getting worse. When the video starts I am coasting about 20 MPH, FP gauge says 0 PSI. I give it about 3/4 throttle and bring it up to about 2300 RPM, FP jumps up to 6 PSI and stays there until I let the throttle off and coast again and FP drops to 0 PSI again.

I can't feel anything different with the truck, and without the gauge I would have no idea this is going on.

Truck has 16,800 miles, New 7 micron filter from Geno's is about 2 weeks old. Never used to do this, but started before the new filter was installed.

Luvnacumns

Yeah definately not normal...

qzilla

Weak Lift Pump and getting weaker. Adding throttle is allow the CP3 to suck or draw fuel and raising the pressure artificially, the lift pump is not pushing the fuel properly.

OR Mega Cab

Thanks.

I have an appointment at the dealer on Thursday. I will post here when I know more.

OR Mega Cab

Update:

For the last week or so the Fuel Pressure on the Commander has pretty much always said 0 psi, it will occasionally jump around, but has pretty much stayed on 0.

OK, I start my truck this morning and the Check Engine Light is on. Turn the truck off, key on/off to check code shows: P0191 - Fuel Rail Pressure Sensor Range/Performance. No noticeable difference in how the truck runs.

Take the truck to the dealer and tell them about the new code and low FP on the gauge. They call me about an hour later and tell me that the ECM needs re-flashed and everything should be fine. I give them the go ahead. I pick up the truck and they say that their computer says the FP is fine and that my aftermarket fuel pressure sensor is bad.

I think it is weird coincidence that I get a fault code relating to the fuel system at the same time my aftermarket gauge says I have low pressure, and I am told that this re-flash fixes everything and my gauge is faulty, but whatever.

This is what the receipt says:
Code p0191 flashed ECM to TSB 18-032-07 for code. . 4HR.
checked transfere pump pressure normal in spec. Cust aftermarket fuel pressure sensor bad. . 4HR.

Good news is since the CEL came on today they did not charge me for checking the transfer pump.

Now what???

Quad, do FP sensors go bad that often? What is the process to get a new one or is there a test I can do to check the FP sensor I have?

Thanks in advance.

shortbed rv

I just returned my sender. Called and talk to the QUAD tech. He will give you a return number and send you a new unit ( I received the sender the next day). You must return the old sender or you will be charged.

good luck

Hints: no teflon tape needed. If you will just losen the nut that holds the wire on and then remove the sender. Put the wire on the new sender but leave the wire lose. Go ahead an install the sender and then tighten the nut that holds the wire. Learned the hard way . I kept dropping the nut.