Low fuel pressure

[Del09]

Hi,
I'm new to the Cummins world; thought I'd get that out there. My last truck being a 7.3 Powerchoke.... Recently purchased a 99 3/4 24v Cummins with 170k on the odo.

I drove the truck back home about 300 miles with no issue. 2 weeks later, here we are and I'm having a fuel issue.

I was grabbing some lunch at a drive thru and truck was idling for about 10-15minutes without moving. I noticed I was slowly dropping fuel pressure. By the time I made it home it was running on 4psi of fuel pressure and running rough. Almost like a misfire. Im kind of at a loss.... this is a 2 owner truck. Previous owner claimed he had recently installed new injection pump. Im assuming it still has stock lift pump.

Can anyone lead me on the right path or where to get started? Any help is appreciated.

 

[DavidC]

If you have a compressor remove the line from the tank at the pump and blow back into the tank. Reconnect and see what happens. You can also try loosening the tank fill cap to make sure the vent is open and not causing a vacuum.

 

[DavidC]

You can read what happened to me, kind of the same situation
https://www.turbodieselregister.com/threads/fueling-problem.266904/

 

[Del09]

You can read what happened to me, kind of the same situation
https://www.turbodieselregister.com/threads/fueling-problem.266904/

Awesome. I really appreciate it! I'll do that first thing tomorrow morning and get back with my findings.

 

[DavidC]

Where are you reading pressure at, pre or post filter ?. Maybe just a clogged filter ?

 

[BigPapa]

Lift pump failures on the 2nd Gen 24-valve trucks is common. If not caught and repaired it will take out the IP. If this happened to the PO and he didn’t replace the lift pump, it will take out the new IP. A fuel pressure gauge is a must on these trucks for that reason.

 

[Del09]

Where are you reading pressure at, pre or post filter ?. Maybe just a clogged filter ?

I'm reading psi off my edge tuner. Its the edge with attitude. Im assuming the sensor is mounted near the lift pump?

 

[DavidC]

The 99 fuel filter has 2 ports on the top of the housing, one is pre filter and the other is post filter. Mine is post so I can monitor the filter. Maybe your sensor is tied into one of those.

 

[BigPapa]

Personally, I wouldn’t trust the Edge for fuel pressure. Matter of fact, the Edge could be your problem. The first thing I’d do is change the filter. Then, I’d put a mechanical fuel gauge on it just for testing and make sure what your pressure is. Then I would TOTALLY disconnect the Edge and see if it still runs rough.

 

[Del09]

Looks like the lift pump is bad. I replaced the fuel filter. The old filter seemed to be in good shape still. I bump started the starter to prime the new filter in and the pump was having a hard time priming. Sounded weak. Tried cranking and the truck wouldn't start. I repeated the process again and by then i couldn't hear the lift pump anymore.

I tested to see if the pump was getting power. Both batteries are fully charged 12.8v and 11.94v. The pump recieved 11v during a regular prime. So I'm assuming it has failed.

 

[DavidC]

With 170k and if that is the original pump it is very possible along with idle time since 1999 I would say it served it's purpose. I have one of these still sitting in the box for at least 10 years. If the stock pump died I will be installing it but that has not happened yet.
https://pureflowairdog.com/p-35837-factory-replacement-raptor-pump-frrp.html

 

[BigPapa]

Sorry, never mind.