just recently my 2005 3500 started doing the same. truck was running fine, i needed diesel so i pulled in filled up and then got about a 1/4 of a mile down the road doing 40mph and it started knocking, RPMs were around 1500, when i got home it knocked even worse at idle but if you raise the RPMs above 1500 it sounds fine and you cant feel the knocking. i have a hypertech re programmer and i hooked it up to check the DTCs and it read out P0304 wich means cylinder #4 misfire. i was wondering if anyone might know what is making cylinder 4 to mis fire? sorry 02max that i dont have an answer. maybe we have the samething wrong with our trucks. any information would be greatly appreciated!

 

What brand of fuel filter do you currently have on the truck? Wix33960 or 33960xe?

 

Yes it is a wix 33960
now the hole truck runs rough and has a miss.

 

Sounds like either bad injectors, or a bad Fuel Pressure Regulator (FPR).

I would take it to a dealer, or someone with the right computor to look at the injector balance rates at idle, and the fuel rail pressure at idle, and when commanded to 160 MPA.

Good Luck!

 

I had the same problem a few weeks ago. Sounds like another Wix 33960 defect issue. Search under 911 for "Wix 33960 fuel filter may have defect" You may have to go back a few pages to find it but there is more detail on the issue..
The new wix designed inner seal allows the CP3 to pull dirty fuel past the seal when the filter loads up with trash. You can drive down the highway and not ever know that you have a problem until the motor idles down. Then the CP3 starts knocking like you have several bad rods. The racor/ a/c delco filter has a different inner seal that is positive and as the filter loads up, the RPM's and power drop until you can't drive it. Not so with this new Wix filter seal design, unfortuneately it allows you to keep driving on unfiltered fuel. Do not run the truck until you have installed a new filter and by all means, do NOT put another wix on.
Get a RACOR or a/c delco that has the positive compression seal.
The filters sold by NAPA, Autozone and Discount, all of them have the same defective seal whether it says Wix, NAPA, Luberfiner or whatever, most if not all of those have the same flimsey thin seal.
Racor makes the a/c delco filter.
Change your filter imediately and I hope that solves your problem. If you have a miss, trash may have affected the CP3, FPR or injectors. Perhaps someone with more knowledge in those areas can help you diagnose this further.

Good luck and keep us posted.

 

OK , so I got it back to my buddies shop knocking like a banshee and changed the filter with new racor pff5544, all they had in racor bled all the air out to the blak cap,started it up and ran rough for a while with a knock at idle and quit. Now it won't even run, tries to, almost catches then just crank crank crank. Bled the system 2 more times, no air just fuel but won't start. Can someone PLEASE HELP, give me a direction to go, I need this truck for work.

 

Interesting, mine did almost the same thing. Perhaps someone with a lot of tech experience in this area can help out. I'd like to help but I have virtually the same problem you have. I haven't had the time to start on mine yet, thankfully it's not my main vehicle.
Anybody out there with any ideas or remedies?

 

bump bump guys, a little help please this is my daily driver by the way new injectors 6 mos ago

 

Scanned for codes but found none, what now?

Help please

 

earlier i changed my filter to an a/c delco. started it up and it was still knocking then smoothed out and died as well. it also wouldnt start. i bled it, cranked on it for five or so seconds and it started up... really rough and ran weird for about two seconds then just went back to knocking at idle. i reved it up and it ran really rough. i let it run for a little while and it cleared up and idles fine now. ill post up in a few days if it still runs fine... thank you for the help. good luck 02max

 

Glad you got yours going. I ran the batteries down twice cranking on mine, primed and bled several times, no air. Sure could use some help from someone. No codes, no air in line, new filter, checked for leaks - none, spins over but won't start.
Can someone please help.

 

Somehow you need to check your rail pressure. The fuel pressure regulator might be out.
Same thing happened to my buddy truck LB7 and that's what was wrong with it.

 

How do I do that? Whats the rail and where is it. I've read other posts that mention the fuel pressure regulator, I've built a lot of gas engines but not familiar with this engine.