I had the joy of replacing the injector and lift pumps back in March, I relocated the lift pump to the rear frame and installed a FP gauge at that time. Turns out the NAPA lift pump was NFG out of the box and was replaced under warranty. All was good, solid 10+ at WOT and ~15 @idle. Totally stock engine btw. A couple of weeks ago the gauge went to the high peg and sat there while running. Back to the NAPA/Mechanic and mechanical gauge indicated normal pressure. I have been trying to figure out if it is the sender or the gauge (likely since it's harder to replace and more expensive) so I can feel relatively comfortable with it. Today the gauge barely came off the low peg, maybe 2 needle widths at idle and half that under load.

FWIW it goes to 15# when the key is turned on, drops to nil as usual then to the high peg upon start and ~15 sec running it is down to just off the low peg. Voltage appears to be ~.25vdc at the high peg and ~.02vdc on the low reading.

Does anyone have the voltage from the sending unit at various pressures to help me trouble shoot? I will be back to the Mechanic tomorrow morning to have the mechanical gauge put on it again and will be loking for one to buy and take along (I'm leaving Thursday to visit grandkids in South Dakota)

Thanks for any help y'all migh have to share

 

If a fuel pump fails they dont generally pump "to much" pressure but usually the opposite. Because your gauge started reading higher than normal indicates that you're sender is bad. And its probably shot from either the dynamic fluid pulses from the VP or the additives now used in diesel fuel compromised the seal in the sender. What gauge manufacture are you using and where are you reading the fuel pressure from?

 

Thanks KATOOM, it's a westach gauge http://www.genosgarage.com/prodinfo....ber=WM-FPKT-30 and is sensed from the schraeder valve test port on the side of the VP44 with a Vulcan fuel line kit

I'm with you, I dont know how any of the pumps could fail to an excess pressure situation

 

I put in an Air Dog and put the sending unit in the back away from the harmful pulses of the injector pump. I have a electric sensor to the cab and tee off with a mechanical one at the pump. My electronic one is off and reads high but the mechanical on is at about 20#. I do like the mechanical back up. ED

 

Coming directly off the VP is the hardest on mechanical gauges and electric senders because you're coming right off the source of the pulses. Moving the tap location as far as you can from the VP but still staying on the post side of the fuel filter is the best spot. If you're using the OEM fuel filter canister then thats as far away as you can get. Since I have dont know what year your truck is, you could either have to tap in the outlet line or use the port on the top of the canister. Then from that location, running another 3'-4' line to the sender or isolator or longer line if you're running directly in the cab. No matter which way you choose, you NEED to run a fuel snubber. http://www.genosgarage.com/prodinfo....er=RLT-SNUBBER

If you get a new sender and use a snubber, you'll probably be back to normal. But I'd still consider relocating the tap.

 

Thanks gents, I should have mentioned that the truck is an 01, QC 4x4

After checking pressure with a mechanical gauge we discovered that the lift pump is (gasp!) failing, that's #3 since April or May. As soon as I get home I'm going to one of the direct drop in Air dog or FASS or something pumps, to hopefully regain some reliability. Seems strange to me that I ran one for 4 years or so and since it and the injector pump failed in March we have put 3 Napa replacements in it.

The sending unit needs replacement too I think, I'll be sure to grab a snubber when I get the new sender and will look at relocating the sensing point. I wasnt aware of the snubber when I did the gauge install in the springbut now that I am I'll be sure to have one! Thanks I guess that's what I get for following the instructions for a change.....

Thank you gentlemen, I always learn a ton here...

 

Hi guys..I just ordered the 3rd sending unit for my fuel pressure gauge. There was probably 4k on it. I mounted mine prefilter thinking it would last a little longer farther from the pulsation, but it didn't change anything. The first one bounced around a lot right from the get-go. It's the bd x-monitor, if there's one that has any longevity to it, your input would be welcome.

 

I wouldnt suggest taking your FP readings pre-filter otherwise you'll never know you're true FP to the VP or if something happens like the fuel filter plugs up.

If you're sure that the fuel pump is fine and you're using a snubber then the only other thing I could think of is to check all your electrical connections. Maybe your ground is bad. Or maybe the entire unit itself is bad. You might want to contact BD and ask them.