Fuel Starvation Problem

I've been lurking on this group ever since I bought my 1998 Dodge Ram 2500 new in 1999. It has a B5.9 Cummins 12-valve diesel engine coupled to a NV4500 5-speed manual transmission. The fuel injection pump is Bosch P7100. The truck currently has ~66,000 miles.

The problem I have started abruptly last Saturday while it was cruising along at 57 mph on the highway then slowed to a stop because the engine stalled out. The engine re-started with great difficulty but it revved up and I went through the 5 gears and again set it for 57 mph on cruise control. The same problem recurred after less than one mile further down the highway.

I got it re-started and drove to a gas station to top off the fuel tank by adding 10 gallons. The engine started but ran roughly for a little while then I attempted to drive it home on the back roads. The truck won't drive at normal speeds and has to be limped along in a very low gear. When going up a hill, I have to downshift to 2nd gear and nurse it along at less than 1100 RPM going uphill or else the engine will stall out then it won't re-start unless it sits still for a few minutes then only re-starts with great difficulty. I used the hand-operated fuel transfer (lift) pump primer a couple times to get the engine running again after it had stalled out and refused to re-start.

Eventually, I got it home and immediately replaced its fuel filter. The old fuel filter had less than 2000 miles on it but it had been installed for six years. I pumped the hand-operated primer button about 100 times but it never really gets hard to pump as before after a fuel filter replacement. Regardless, the truck engine still stalled out both on the backroads and again on the highway during a test drive.

As for troubleshooting completed today, the engine started up immediately when I re-positioned the truck for inspection. When I removed the fuel cap, air pressure hissed audibly as I unscrewed the cap from the fuel tank. I don't know if the diesel truck's fuel tank is equipped with an atmospheric vent. Maybe the fuel tank's vent is built into the fuel cap? There also appears to be an atmospheric vent valve mounted on top of the fuel tank module. It seems to have a valve disc which moves up/down.

I used an air compressor to pressurize the fuel tank to less than 10 psig in an effort to discover if it has any vacuum (air) leaks on the lift pump supply line, the fuel heater, the fuel transfer pump and at the fuel tank module where the fuel lines connect and where the module threads onto the top of the fuel tank.

I observe no fuel leakage on the steel fuel lines which are routed along the top of the frame rail nor do I see any fuel leakage at the lift pump, fuel heater, fuel filter housing or where the fuel lines connect to the fuel tank module. I verified the fuel line quick-disconnects at the fuel tank module are secure. I used a small hammer and chisel to try further tightening the fuel tank module screw cap onto the fuel tank but it is already very tightly secured. There is evidence of fuel seepage on the top of the fuel tank where the fuel module screw cap threads on but it doesn't look freshly wetted.

I have a replacement fuel transfer pump in-hand but I'm reluctant to install it because it's not a Cummins OEM. Perhaps my fuel starvation problem is associated with the air hissing noise I heard today when releasing the fuel tank's screw-on cap?

 

I have seen some rare instances where the vents clog and it causes a vacuum in the fuel tank, I would try driving it around with the fuel cap loose or off to make sure the tank cant be under vacuum or pressure.

 

66k miles on a '98, 2k miles and 6 years on a fuel filter. That is a lot of siting, old fuel in the tank. It might have sludge enough to clog the module screen. I think I would drop the tank and inspect it.

 

I inspected the fuel tank screw-on cap. It has a spring loaded over-pressure relief valve built into it. I sprayed it with some carb cleaner and actuated it. It is not stuck and it does spring open. The original fuel tank level transmitter (sending unit) failed. The Dodge dealer installed an OEM replacement unit several years ago. This is the fuel tank module installed on my truck. #ad
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Depending on what is several years ago, it might be okay. Pull the feed line off the injector pump and pump the lift pump to see what kind of flow you get.

https://www.genosgarage.com/product/pump-4988747-kit/fuel-pumps

 

Based upon what I read on a thread regarding fuel tank cap hissing noise when un-screwed, I removed that red cap from the hose barb on the fuel tank module then I took the truck out for a test drive... The truck made it about two miles down the road (downhill) then I turned around and about half-way up the incline the engine stalled out and would not readily re-start. I loosened the fuel tank's screw-on cap and could not hear any hissing noise.

After several tries, the engine barely re-started, ran extremely rough. I could hear a kind of clicking sound coming out of the engine which gradually went away as I limped it home in second gear at ~1100 RPM.

 

The fact that you filled up the tank on your trip and nothing improved tells me it is not tank vacuum/pressure related. The tank was neutral at this point, it didn't have time to change.

 

Lift pump bad?

 

Dylan, welcome to the TDR. First, to me, your blue font is hard for my old eyes to read. Is the standard size and black color a problem?

I would start by doing as @NIsaacs has suggested, remove the OFV and hand pump to see what kind of volume your getting. If that’s low, check the screen under the heater, if that’s good, drop the tank and see what you’ve got.

 

Thanks for the help. I read the linked description of the fuel delivery system to familiarize myself with its components. Because the truck starts up readily when cold and after sitting for a few days, I'm thinking that an air leak in the lift pump fuel supply line is less likely; especially since I pressurized the fuel tank to ~10 psi and saw no fuel leakage anywhere on the fuel lines, fuel heater, lift pump, fuel filter assembly or the injection pump.

The clicking noise I hear after restarting the stalled out engine concerns me. I've read that a failed lift pump will make a clicking noise but I hear this noise for only ~30 seconds after restarting a stalled engine then the noise seems to go away. Also, I don't hear any clicking noise following engine cold-start. Does a failed injector pump click all the time or is it an intermittent condition?

 

Maybe the fuel shutoff solenoid is not holding open? To check the FSS relay, I turned the geyswitch to the RUN position then lifted up the FSS shaft until it clicked and was held by the FSS electromagnet. I was unable to locate any blue wire (with fusible link) connected to the driver's side battery positive terminal.

I located the FSS relay on the firewall but cannot figure out how to remove the relay. There is a tab on the front side of the relay receptacle which I depressed but no amount of pulling upwards on the relay cover or downwards on the receptacle will cause any sort of disengagement of the relay cover, relay or relay receptable.

 

I always figured the fuel shutoff solenoid was either run or not run. However, maybe even if it works fine the adjustment might be off enough to partially hold the linkage shut?

Adjustment instructions:

https://www.genosgarage.com/downloads/InstallPDF/GGInstall-DG-FuelSolenoidAdjust.pdf

 

No one has mentioned the prefilter screen next to the lift pump. It can be reused. Here is how to do it.
Cummins 12 valve fuel filter replacement - Bing video
While you are in there I recommend you take another 5 minutes to delete the fuel heater. It is the source of many air intrusion problems and doesn't really keep fuel from gelling in the winter. An allen wrench removes it and the filter bowl screws into the remaining hole.

 

Dylan,
Several years ago I had what sounds like the same issue you are having. My truck woud do what sounds like almost the exact same thing that your's is doing. It would do this without warning. Other than it acting up on occasion, it ran perfectly. I checked all of the items mentioned here and could find nothing wrong. I visited 2 local shops and they suggested an injection pump rebuild. I wasn't buying this as the truck ran perfectly when not acting up.
The only thing I could deduce was that this only happened when the ambient temperature was above 90 degrees F, and the humidity was high. I know this sounds a bit odd, but it was the best I could come up with. The problem ended up dissappearing as oddly as it had appeared. I have had no issues in several years.
Wish I could offer you a solution.

 

What year is yours? The early p-pumps, '94 and '95 are known to develop sticking plungers when they get hot. The troubleshooting measure is to pour water over them. If the problem goes away it is time for a rebuild.

 

Thank-you for the feedback. My problem was first observed during hot, humid operating conditions. It has occurred on two different days but both days were extremely humid. I'm leaning towards a cause associated with the fuel shut-off solenoid (FSS) becoming de-energized during engine running. This would result in the FSS solenoid dropping out; causing a shut-off to the injection pump's fuel supply.

The FSS function is controlled by a dual-coil relay (FSS relay) mounted at the top-center of the firewall. This relay is allegedly powered by a blue wire which originates at the battery positive terminal but this is not true for my early 1998 Ram pickup truck because my FSS solemoid coil is energized even if the two small leads on the driver's-side battery are disconnected from the battery positive terminal.

I need to determine the source of power going to my FSS relay. My FSS relay's control power wiring may have become corroded which could result in a control power interuption to the FSS relay coil(s) during hot, humid operating conditions. I'm also trying to figure out how to remove my FSS relay from its receptacle because no amount of twisting, pulling, pushing, etc. enables the FSS relay to be separated from its receptacle. Maybe it has become corroded in place?

 

The relay is only energized when the key is in the start position to pull the solenoid arm up. Once you release the key it no longer gets power. The hold voltage is supplied by, IIRC, the #9 fuse. Only '94-'97s have the blue fusible link. '98s have a fuse in the fuse box. It might be labeled spare.

(3) Fuel shutdown solenoid test | Cummins Diesel Forum (cumminsforum.com)

 

Thank-you. My understanding is the FSS has two coils. The PULL coil is energized by the FSS relay function. The HOLD coil is energized by a circuit which originates at the #9 fuse. I need to get my multi-meter onto the leads at the FSS relay's receptacle and the FSS electrical connector.

Would you explain to me how to remove the FSS relay from its receptacle?

I'm thinking it would also be useful to measure the voltage drop from the #9 fuse contacts to the FSS HOLD coil's wire terminal. There may be sufficient resistance between the #9 fuse terminal and the FSS hold coil's wire terminal to lower voltage sufficient for the FSS to partially de-energize, lose magnetic HOLD strength and cause the injection pump fuel shut-off valve to partially close during engine operation.

 

The PULL Relay on the firewall has a connector with a lock tab on the bottom. The connector pulls down away from the relay.
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On the ‘98, there are also two fuses and a relay in the PDC. I have labeled them below.

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Here’s the diagram showing the PULL side, relay on the firewall powered by fuse #9.

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This is the diagram showing the HOLD relay powered by fuse #6.

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While you are chasing the FSS theory, did you ever remove the prefilter screen?

My FSS relay simply pulls from it's socket. No magic there.