Fuel Pressure Low Or Bad Sending Unit?
 

HELP! I just installed a fuel pressure sending unit on my Quad Commander. It shows that I only have 7-8 psi of fuel pressure at idle, 5-6 psi at city speeds.and will go to 0 psi at W.O.T. I have not checked it at freeway speeds yet. I called Quadzilla and they said the commander unit was configued correctly ( 01 Dodge, 0-40 psi sender, sensor adjustment in the middle ) The truck runs great and has PLENTY of power. Is it safe to drive until I can get a mechanical gauge reading to verify that the sending unit is reading properly? Where should I go from here?

IS THERE ANY WAY TO TEST THIS SENDING UNIT? Quad said it should read 2.48 millivolts at 5 psi. I measure between 2 and 2.5 VOLTS at about 7-8 psi.
When I told Quad about this they said that was normal. Is it VOLTS or MILLIVOLTS? At freeway speed if I am carefull I can keep the pressure at 5-6 psi so I will probably baby it to work tommorow and take it to the dealer after work and have them check the pressure with a mechanical gauge.

Where were you measuring the voltage, Steve?

Have it tested but your numbers are not surprising for someone who just put on a FP gauge, most do it for a reason and find a bad LP and soon IP. Start researching on aftermarket LP's. Drive it like you have an egg under the skinny peddle until you verify the quad readings. I wouldn't buy stock engine mount pumps and watch out for dealer in tank pumps.

Good luck.

I took the reading at the terminal coming out of the sending unit. I used the posative lead of the tester here, with the negative lead on the negative terminal of the drivers side battery.

As for the lift pump, it is I believe, a Carter, and it is mounted on the frame rail in front of the fuel tank.

Well I decided to buy a mecanical fuel pressure test gauge and hook it up to the test ports. Low and behold I had under 10 psi at idle from the Carter 4601 mounted on the frame just in front of the tank. I got a new 4601 from NAPA for $140.00:( and installed it. Still only 8 psi at idle both pre and post filter, and deadheaded right out of the lift pump.[verymad] The only thing I didn't check was pressure out of the lift pump from a fuel container to eliminate the possability of a restriction between the tank and the lift pump. I doubt this is the case though, as gravity alone will give you as long of a diesel bath as you want.[dummy] With the new pump I can hold 7psi at freeway speeds, but W.O.T. will drop pressure to 3-4psi.
The good news is, that NAPA said they would refund my money on the lift pump. [redface]The bad news is, buying a FASS is expensive. [tapdshut]I will have one installed this coming week.

you dont need a fass! get a holley blue and use it as a pusher pump.

you ll get 21-24psi @idle . do a search for a pusher pump or holley blue, if you dont know.

good luck

I think I am done with lift pumps. Besides I like the fact that the fass will take the air out of the fuel. The 6 year warranty doesnt hurt either.

May not have low fuel pressure after all
 

OK guys heres what happened, and what I think is going on. When I deadheaded the lift pump to a manual gauge I only got a reading of 8psi. I believe this was because the lift pump was pumping against a 100% restriction. When I took the reading at the injection pump I got 8psi @ idle. I believe this reading was wrong, due to the test kit fittings not quite matching up to the schrader valves on the test ports, perhaps causing to much constriction. When I took the Quadzilla sending unit out of the special banjo bolt and put the manual gauge in its place I got a reading of 12psi after just bumping the starter, and it held at 12 psi after starting the truck. I reinstalled the Quad sending unit and turned the fuel pressure adjustment ALL THE WAY UP on the Commander monitor, and it to showed 12 psi at idle. After this when I would drive the truck I could only pull the pressure down to 8 psi @ W.O.T.

Has anyone else had to turn the adjustment all the way up on the Commander to get a proper fuel pressure reading?

I will be calling Quadzilla about this tommorow, and I will get another pressure reading from a shop to confirm that the one I got at the vp44 with the manual gauge was correct.

Thanks Steve for all your hard work. MY Commander reads very much like yours. That is 8PSI at idle and would draw down to 0 at wot with just a XZT. I wonder if I have more pressure than the reading I get with the commander.

BTW: many of us are having problem with the sending unit going bad.

Mine started acting a little erratic today. I think I am just going to install a mechanical gauge for fp

You might want to talk to tech support at Quadzilla. I have a commander with the FP option and the original sending unit they sent was a high pressure (0-100 psi, I think), that was inaccurate at lower pressures.

The symptoms were just as you describe, readings of 5-7 psi, 0 psi on occasion, and as time passed , more and more erratic readings.

They replaced the unit with one that had a more reasonable range (0-40 psi?) and now I see 9-10 psi at all times, except WOT, where it drops to 8-9. Immediately after installing the new sending unit, I noticed erratic readings, falling to 0 psi, but after tightening the connections and grounds, it settled down so that I now have confidence in what is being displayed.

Finally, I should note that even with a *very* dark fuel filter, the reading does not drop, so the lift pump must be fairly effective' I have my sending unit in the bottom of the filter canister, due to interference with the vacuum pump near the CP3.

as was mentioned above....i purchased my commander for the FP purposes only to find out that i was running 3psi @ idle and 0-1 psi under normal conditions.....i replaced the pump with a Glacier/walbro system....right out the box the GD system read 21psi with NO adjustment to the commander sending unit...i compaired this figure to a mecanical FP guage attached to the FF test port....i then decided to go for a spin around the block to test idle, normal and WOT numbers...like i said idle both guages read 21psi normal driving both read 20-19 psi and WOT they both read 17-18psi.....

so far so good.....

that was for a few months....then i got very erratic numbers...commander started jumping around would always show 20-21psi right at idle...but on the road it jumped all numbers in the spectrum...except 0...and only for the splitest of seconds...it would flash 6,8,15,9,12,19,4, all random no order to it....i pluged in the mechinical guage and found that it was a ROCK solid 21,18,17 depending on the situation....so i had to be the commander....

well...it ended up being a combo of GROUND and air leak in the newly run hose...

1st....the ground on the sending unit from quad...they said in the instructions to wrap the threads with tephlon tape to insure a tight fit...only problem with that is the unit is a self grounding type....the tape caused interferance with the ground...dont ask me how...i called them and confirmed this...they just never reprinted the instructions deleating this step.....(step is when you screw the banjo bolt into the sending unit) so after disconnecting the sending unit and taking off the tape i noticed a much smoother and consistant FP....

as for the air leak...well that is my own mistake.....dont need to go into that as it doesnt relate to your problem....short version.....i didnt tighten a hose clamp enough.

so i guess i would say try that...check the ground....take off the tape and see if the connection that is made there is better..

NCB

Nor Cal Angler,

I have had the same symtoms as you, and have used the same remedy as recommended, but my problems have not cleared up.

Still having the erratic FP displays, seems a little steadier, but will be ordering a new filter from Geno's.

Will keep u posted.