Loosing fuel pressure - Dodge Cummins Diesel Forum
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post #1 of 25 (permalink) Old 07-16-2019, 11:52 AM Thread Starter
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Loosing fuel pressure

I hooked up a brand new isspro Fuel pressure gauge directly to the Fass pump it runs 14 psi at idle and when driving ranges from 14 to 20 now after the truck has been driven and comes to a stop the psi will suddenly drop below 3 psi and take a few seconds before it then jumps above 20 psi again could it be a filter issue I have also installed is the sump Fass kit with bigger fuel lines

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post #2 of 25 (permalink) Old 07-16-2019, 12:01 PM
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Sump sucking air? How much fuel in the tank?

1998 12v, 4x4, Club Cab, Carli, Thuren, BlueTop, Core 4x4, BD Diesel, PDD 5x.012, South Bend
2012 Laramie Longhorn, EFI by Ryan, Carli, Thuren
1995 Dually, Weston's 5x.016, 4k GSK, 5" FloPro, 255/85r16 Toyo M/T, Goerend, ARP, 60# Springs, BW 62/65/14, BW 75/96/1.10, Isspro, Fass 125, BDP Sump, 7mm DV's, 751 HP 1883 FP Torque on NOS
1998 P-Pumped 24v, 4x4, NV4500 swap
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post #3 of 25 (permalink) Old 07-16-2019, 01:25 PM Thread Starter
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Probably a 2/10
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post #4 of 25 (permalink) Old 07-16-2019, 01:29 PM
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Fill tank and see if it continues.

99 2500, Quad cab, 4x4 47RE, BD pressure lock on it, small BD 90/140 chip on the VP 44 connection plug, 17" 3rd gen wheels. 3.55 diffs. Ruenell front bumper and warn winch, Rancho adj shocks. 663k miles.
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post #5 of 25 (permalink) Old 07-16-2019, 03:20 PM
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I know sump is supposed to not have 1/4 tank issues but I never had any issues until I put one of those dang things in my truck. 1/4 tank and stopping it would go to bucking and almost die out.

1998 12v, 4x4, Club Cab, Carli, Thuren, BlueTop, Core 4x4, BD Diesel, PDD 5x.012, South Bend
2012 Laramie Longhorn, EFI by Ryan, Carli, Thuren
1995 Dually, Weston's 5x.016, 4k GSK, 5" FloPro, 255/85r16 Toyo M/T, Goerend, ARP, 60# Springs, BW 62/65/14, BW 75/96/1.10, Isspro, Fass 125, BDP Sump, 7mm DV's, 751 HP 1883 FP Torque on NOS
1998 P-Pumped 24v, 4x4, NV4500 swap
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post #6 of 25 (permalink) Old 07-16-2019, 04:13 PM Thread Starter
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What confuses me is it will idle fine at 14psi but if I drive it for more than a mile and then stop it will suddenly drop
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post #7 of 25 (permalink) Old 07-16-2019, 05:05 PM Thread Starter
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post #8 of 25 (permalink) Old 07-16-2019, 05:48 PM
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I would like to know more about how your FASS is wired because without a doubt whats going on is the fuel pump is intermittently shutting off.

'01 2500 Sport 4x4 5spd w/Fastcoolers, Mag-Hytec, EZ, RV275's, 4" w/o muffler, South Bend, Steering brace, aFe, 2 lo kit, Isspro Boost, FP, and EGT on pillar, Westach Trans/Diff temp gauge in dash pod, Raptor 100 w/ 1/2" line, Pac Brake, Rancho 9000, 285's
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post #9 of 25 (permalink) Old 07-16-2019, 08:26 PM Thread Starter
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Ok so the red and green wire on the pump in to the relay and then the relay splits into the connector going to the block and then the two green and red wires going to the battery
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post #10 of 25 (permalink) Old 07-16-2019, 09:06 PM
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Did you ever put fuel in the tank? I had the exact issue you had when the tank would get low. Itís only when coming to a stop? Where is the sump in the tank?

1998 12v, 4x4, Club Cab, Carli, Thuren, BlueTop, Core 4x4, BD Diesel, PDD 5x.012, South Bend
2012 Laramie Longhorn, EFI by Ryan, Carli, Thuren
1995 Dually, Weston's 5x.016, 4k GSK, 5" FloPro, 255/85r16 Toyo M/T, Goerend, ARP, 60# Springs, BW 62/65/14, BW 75/96/1.10, Isspro, Fass 125, BDP Sump, 7mm DV's, 751 HP 1883 FP Torque on NOS
1998 P-Pumped 24v, 4x4, NV4500 swap
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post #11 of 25 (permalink) Old 07-16-2019, 09:14 PM Thread Starter
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Sump is on the bottom 6 inches fro
The rear of the tank and I filled it to half a tank
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post #12 of 25 (permalink) Old 07-17-2019, 02:57 AM
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If it is happening when you come to a stop it is likely having the fuel to run to the front of the tank stopping (or on a steep hill) and then it sucks air. It only has to suck a bit of air to foul the injection and kill the engine. This is why the original fuel module has a built in small reservoir to prevent sucking air in this situation.
PS we suggested you fill the tank not put in a few gallons.
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99 2500, Quad cab, 4x4 47RE, BD pressure lock on it, small BD 90/140 chip on the VP 44 connection plug, 17" 3rd gen wheels. 3.55 diffs. Ruenell front bumper and warn winch, Rancho adj shocks. 663k miles.

Last edited by bigfish95971; 07-17-2019 at 03:01 AM.
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