I have a 98.5 24v cummins with ~190K miles on it. Pretty stock except for a FASS system recently installed. It is a 5 speed manual transmission, long bed, basic work truck.

At about 185K miles the truck would start to slightly sputter or "miss" when I would come from high speeds down to a stop and let it idle at a light. First thing I thought was fuel pressure as it still had OEM lift pump. I installed gauge and it ran around 9 or 10. I wasn't happy with that so I installed the FASS system with the 2 filters that goes directly from fuel tank to vp44. It now has about a 14psi, but that didn't change the situation at all.

The truck fires up just fine, drives just fine, it just sputters when it comes to idle once warm from high speeds/rpm (doesn't sputter that hard, but it does) for a couple minutes and eventually stops if I let it idle for a while. Even while sputtering, if I give it fuel it will accelerate like normal and you can't tell it's doing anything weird until you come to idle again. Any thoughts on what the issue might be? I hate the idea of the VP44 being bad because everything still runs fine, MPG hasn't changed (roughly 18-21 MPG). Is this to be concerned about? I've put roughly 5k miles on and the it hasn't gotten worse or better. Over the 5K miles, I've put healthy amounts of diesel cleaners in it with no symptoms change.

There are no codes being thrown.

 

You should be getting more than 14 out of the fass system. You might need to pull the return line spring out and stretch it to get your pressure up. As for the miss, Im not sure. Maybe get your injectors pop tested to see if they are firing under the correct pressure.