New lift pump, Confused!!!?

[jman]

I had a FP guage installed by a diesel shop at the end of December and noticed about 13psi at idle and could really drop the pressure under acceleration, usually to 0. They mounted the sender to the injection pump and I am wondering if this location gives false readings. I replaced the lift pump (very easy from the top) and I now have 16psi at idle, but under almost any amount of acceleration I am droping to 0psi. Someone said that under hard acceleration the injection pump creates a vacuum and I am wondering if this is playing games with the pressures. I am goin to move the sender to the filter outlet ASAP. I also noticed the sender ground and gauge ground aren't grounded at the same location, could this be a problem? Do I have to remote mount the sender if I put it at the filter outlet?



Sorry so long, but this is driving me crazy!!!

 

[csutton7]

jman--the ground isn't an issue--possibly the location of the sender; most guys locate them post filter, but within inches of the filter--try that and see---what pump are you using and where is it located---have you changed your filter????..... chris

 

[Boost]

When my sender was attached directly to the inj pump I got very erratic readings also. I then attached it to the power steering lines and ran hose to the pump with a fitting in the banjo bolt. The readings are now rock solid at any RPM.

 

[Bigsaint]

jman, are the psi's steadily dropping at full throttle, or are they all over the place when under throttle, i. e. , 13 to 5 to 9 to 0, etc. ? If you are seeing steady readings that are just going down to zero at WOT, I doubt it's the sender. Regardless, a better location is at the bottom of the fuel filter canister, use a snubber line for the sender to be safe.



Scott W.

 

[Steve Campbell]

Another thing you might consider is drilling out the banjo bolts, or for ease of assembly, get a set from Geno's and install them.



In my opinion, it is hard to get the fuel "moving" in the system. The colder the weather, the more dramatic the fuel pressure drop when going to wide open throttle. I installed a "bypass" to the pre-filter port on my 99 with only a "valve" to regulate the amount of by-pass. I teed into the return just aft of the engine. I have only put about 1000 miles on the truck since this retreofit. I was amazed to find that I could open the "valve" all the way without substantially "hurting" my fuel pressure readings.



Idle/cold 10lbs pressure(Guage mounted post filter on top of the filter housing).

Idle/warm 11lbs

cruzin 9-10lbs

WOT 8lbs



Throttle position does not seem to change the pressure at the post filter pickup vey much. I hear the note of the lift pump change (Mounted by the tank) with any throttle application above idle. To me, this is an indication that the pump is not internally bypassing any fuel (IMO) above an idle. The fuel is constantly moving in the "system" and jabbing of the throttle does drop the pressure(very much or very sudden) because the FLOW is always there. The pressure readings above confirm this assumption IMO.

 

[tmacc]

jman,

I originally attached my sender to the inj. pump schaeder valve and had steady pressures. I then got a set of Ray's banjo bolts and drilled out the schaeders and the fittings between the lift pump and the fuel filter housing (BTW 3/16" bit for this). I used one of Ray's tapped banjo bolt w/ a -4AN 90 degree fitting at the bottom of the fuel filter housing and hooked up the sender to it. Works great. PM me if you want the specs for drilling out the schaeders.

 

[jman]

I'm about to snap!!! The pressures drop like a rock when I hit the throttle and as soon as I let up right back to 16 psi. Seems really bad when it is cold out. Today temps in the 50's and on the way home going up a hill I let it slow down in drive with the TC locked and then eased into it really working the engine and it didn't drop below 5 psi. The lift pump is brand new, so if it was a dud I'm going to be p***ed. I also have Rays Banjo bolts installed already.



I am going to move it to the bottom of the filter this weekend and see what happens.



Thanks for the input!!

 

[Bob Cochran]

I also had bad readings when FP connected to schrader on injection pump. I exchanged the banjo with scrader on injection pump with the one on the bottom of fuel fliter. I think I damaged the fuel sender when it was connected on the injection pump as it started out reading good then went weird. Also was weird when I did the exchange to bottom of fuel filter. New sender now all is okay. I got a new banjo so I can put the one with schrader back on injection pump where it was. Don't want to confuse DC or 5 * they are confused enough.



I have a snubber I want to add to the bottom of the filter. Where is a good place to get AN fittings? I need a selection to make the adaption to bottom of filter.

 

[Bigsaint]

Originally posted by Bob Cochran

Where is a good place to get AN fittings? I need a selection to make the adaption to bottom of filter.

Try either Summit racing http://store.summitracing.com/ or Jegs http://www.jegs.com/ . Both have a good selection of -AN fittings and adpaters.



Scott W.

 

[jman]

Well folks, I think I have fixed the problem. I just moved the sender to the bottom of the filter and took it for a spin. At idle 16 psi, heavy throttle lowest I saw was 7 psi. I will try it out real good tomorrow as I live on gravel so I was having to ease up a bit to keep it going straight!! .



What have we learned today?



DO NOT MOUNT FP SENDER TO INJECTION PUMP INLET!!!



Thank you to everyone that replied, I appreciate your input.



jman

 

[RADdodge]

So What's the Difference

Help me understand this. If you install the sender (hopefully with a snubber line, (i. e. 1/8" NTP 2' grease gun hose or similar) any where from the bottom of the fuel filter to the injection pump, what difference is it going to make? If it's past the fuel filter, the hydraulics will be the same. If you install the line pre filter, then the filter will isolate the sender somewhat, depending on the backpressure. Then you will be reading the pressure the injection pump is "seeing" minus and drop in pressure across the fuel filter. I would think that tapping into the fuel line anywhere on the injection side of the fuel filter would produce the same results. In other words, it shouldn’t matter where you tap into the fuel line post filter. Is this correct?

 

[csutton7]

RADdodge--nope--you get it to close to the VP44 and you get weird readings--the VP44 causes the readings to fluctuate due to it's working habits--chris

 

[lberch]

I currently am driving around with two mechanical guages hooked up to the factory schrader valves and my readings are steady... . a little low, but steady.

I agree with RADodge, it should not matter where, post filter you hook into. So what gives?

Is it that a mechanical guage can take the inj. pump pulses and an electrical sending unit can't?



LB

 

[Neal Cassady]

If you mount the sender on the VP44 remotely, that is with approx. two feet of fuel rated line you shouldn't have any problems.



If you mount the sender directly on the VP44 the fuel pulsations may give erratic readings and beat up the sender. The engine and pump vibrations may shake the sender to death.



Dave

 

[Bob Cochran]

I don't have the answer why but do know when I mounted mine directly to the VP44 with sender mount remotely using stainless steel flex I had made up without snubber I had a problem. Moving to the botton of fuel filter with no other change but moving it corrected. Mine still jumps around some say up or down 4 to 6 psi I think the snubber will help that.



Forgot to say mine is electronic not mechanical.

 

[Challenger-II]

Sorry for the ignorance here..... but what is a snubber? Is it a hose that mounts the sender unit remote of the test port?

 

[RustyJC]

A gauge snubber is a device that dampens pressure pulsations in the media being measured by a mechanical gauge or electrical sending unit. A grease gun hose may, in some cases, suffice if it "flexes" slightly to dissipate the pressure spike seen by the gauge/sender. In other cases, a needle valve in the line to the gauge/sender might suffice. After knocking out two (2) sending units in 1000 miles, however, I went with a Sun Hydraulics gauge snubber available through WWGrainger (the industrial supply house). My remotely-mounted sending units are plumbed with braided stainless steel hose, so there was no flex to dampen the pressure spikes.



Rusty

 

[dresslered]

A snubber can be either a rubber hose (easiest) or a fitting with a tiny hole in it to take out the "water-hammer" effect from the injection pump. However, you also want to get the sending unit off of the engine to avoid the engine vibrations. When the sender is mounted at the fuel filter, the small rubber hose between the fuel filter and the injection pump does offer some snubbing. It is best if you come off of the fuel filter with some additional hose and the pulses should then be dampened enough for proper gauge readings. I even left some air in the line up to the sending unit for additional snubbing.



P. S. Also, an -AN fitting does not make a reliable seal on the schrader valves although many people force fit these. I would buy the tapped banjo from Geno's or make your own fuel lines with proper fittings.

 

[Challenger-II]

Thanks for the info... ..... I have my sending unit mounted on the firewall with a stainless braided line (teflon tube core) going to the post filter test port on my '99. I have been seeing some wacky intermittent pressure drops when cold and I think my sender is flaking out. Is this arrangement good enough or would you suggest a snubber? The line to the sender is 18". I like your idea of leaving some air in the line to act as a snubber. I put a tee at the sender and have one side capped. I use this to bleed the line of air up to the sender. Maybe I shouldnt purge the air???

 

[RustyJC]

Originally posted by Challenger-II

[BI have my sending unit mounted on the firewall with a stainless braided line (teflon tube core) going to the post filter test port on my '99. I have been seeing some wacky intermittent pressure drops when cold and I think my sender is flaking out. Is this arrangement good enough or would you suggest a snubber?[/B]

Sounds like you have the same arrangement as me although I use 2 senders, one pre-filter and one post-filter. Mine are plumbed to Ray's banjo bolts, one on the rear (firewall) side of the filter housing (pre-filter) and one on the bottom of the filter housing (post-filter), but mine is a 2002 model year.



As I posted above, I lost two (2) Westach post-filter sending units in 1000 miles. Since adding a gauge snubber, I've had no more problems.



Rusty