Engine/Transmission (1998.5 - 2002) Low Fuel Pressure

[KcoleKennyc]

Have a friend with an '02 HO 6 speed. It has been a problem for a long time. The dealer has installed several VP-44's and lift pumps. They finally installed a lift pump in the tank and wired it to a relay. The truck runs great when the pressure is good then falls on it's face when the fuel pressure drops. It has done this with all the engine mounted lift pumps and with 2 in tank units. Is there anything in the tank that could cause this? I don't know what is replaced with the new in tank unit but would think that the new pump would have replaced anything that could cut off the fuel supply. It has really been a problem and if anyone might have had this problem they might could shed some light on this. The dealer doesn't seem to know very much about the Cummins and don't know what to do. Any help would be very much appreciated. Thanks, Kenny

 

[JDiehl]

Does your friend have a fuel pressure gauge? What psi is the lift pump running? I have had new carter lift pumps that were bad out of the box. I fixed my truck by installing an after market lift pump and 3/8 fuel line from the fuel tank to the vp-44. The stock fuel lines often don't carry enough fuel to feed the IP. Sounds like bigger fuel lines and a draw straw would help the truck out. Does the tuck have any codes? keep in mind that the IP my be bad again if the lift up has gone out again. Hope this helps. Seaching the forums will bring up way more info than I can give you.

 

[KcoleKennyc]

He does have gauges but I don't know the exact pressures he has. Doesn't seem like numerous VP-44's and numerous lift pumps would all have the same exact problem. The pressure may be normal and then drop, when it drops the power drops. It may come back up and the power comes up. He had thought about adding a pump as a booster but hasn't done so. This has been going on for 100K miles. Is there a sock in the tank that would not be replaced when the in tank pump was installed?

 

[wlowe]

He does have gauges but I don't know the exact pressures he has. Doesn't seem like numerous VP-44's and numerous lift pumps would all have the same exact problem. The pressure may be normal and then drop, when it drops the power drops. It may come back up and the power comes up. He had thought about adding a pump as a booster but hasn't done so. This has been going on for 100K miles. Is there a sock in the tank that would not be replaced when the in tank pump was installed?

You will find that running a single pump rated for 10-15 psi will allways draw down pressure when fuel delivery is increased. In my opiniion the best remedy for this is to run two pumps in series, or a single pump rated at a higher than required pressure, then use a pressure regulator/bypass to keep pressures within the normal operating range. This keeps the pressure/flow up during high demand. My solution was to add a pusher pump in series along with an aeromotive pressure regulator/bypass. My pressure never drops even at WOT. Other good alternatives are the Walbro or Fass which also use regulators/bypasses.

 

[blacksheepdiesel]

kcole,

Where in the fuel stream is he measuring the fuel pressure? Should be between the filter and the VP because then you know when the filter is getting clogged.

When the in tank lift pump is installed it comes complete with a new module, basically anything that could cause low fuel pressure inside the tank is replaced with new. The problem is the in tank pumps are worse than the original lift pump on the side of the engine. They do not produce near enough pressure or volume to feed even a stock Cummins, let alone one with mods. The answer is AirDog which is a pump and two filters, one water separator and one for particulates. It installs under the bed close to the tank. I have one on my truck and it still produces 19 psi (even at high rpm, loaded, up a long grade) after 300,000 miles on the truck. The Fleetguard replacement filters are less expensive than stock filters. It is the final solution for what your friend is experiencing. You friend will need to install a draw straw and remove the in tank pump for this.

PM me for AirDog dealer contact.

Godspeed,
Trent

 

[mhenon]

Hold on a second guy's. This truck has more problems than a simple "50th" bad lift pump in a row. When you start to see the same problem pop up again and again. . yeah you changed out the part that failed but you never got to the root of the problem.



I would first check the fuel line from tank to VP for ;

A. any kinks or dings in the line that may be restricting fuel flow

B. internal restrictions. Pull the line and blow air through it. You may have a wad of algae or crud in there.



If that checks out OK I would than suspect the ECM for low or intermittent voltage to the LP circuit. I've become very suspicious of the ECM and it's ability to supply a solid 12volts and 5 amps or so to the LP. Mine has done some strange things in the past which smelled like low/no voltage to me.



What you might try (I did this once when a relay failed on me) is to rig up a hot wire directly off the battery (get a 10-20 amp fuse in there). The next time the pump fails connect the hot wire to the LP and see if it runs. If it does your ECM is the culprit.

Good luck on this..... Mike

 

[KcoleKennyc]

Thanks Mike, I have mentioned to him about installing a volt meter on the wire to the pump. I have had problems with an ECM on my 98. 5. It supplied too much voltage to the temp. sender and burned up 7 of them. Dealer didn't have a clue what to do. I told them what the problem was and they flat refused to replace the ECM. Took to another dealer and they fixed it. If this problem would stay, it would be easier to find. It comes and goes. Owner drove it from Al. to Miss. a few days ago pulling a gooseneck. It ran great going over, on the way back the pressure dropped and it ran like a dog. I don't know how many volts it takes to energize the relay but if we hook up a meter it should show up. I will let everyone know what we find. Thanks again, Kenny

 

[Joseph Donnelly]

check for dirt in the fuel tank too.

 

[mhenon]

check for dirt in the fuel tank too.

Good point Joe. I was going to mention the fine mess screen in the tank fuel module but wasn't sure if the '98 even had that.