Cumminz

Are you thinking AC noise or something alternator related (it is the stock alternator...)? There wasn't an ac noise issue a month back when I last checked it.

wire to wire short?

My truck runs rough at idle, any throttle position, unloaded, under load, doesn't matter. Now it is NOT a cylinder misfire. However, it does seem to sound consistent when i enable 6 cylinder high idle. You can hear it and feel it in the truck during high idle (you can even see it in the mirrors. I have tried to take a video but it doesn't really show up well because the truck is just so loud. Now in 6 cylinder high idle (at 1200) rpms the "miss" is Consistent but about once every second or so. How can this be?! The whole fuel system seems to check out. Fuel pressure is all normal. Still have great fuel economy and power. There is usually a heavy lope when cold, then clears up when driving. If you listen to my truck from about 100 feet away, you can hear it running strange, like its not firing consistenly. When im cruising going 55 and let off the gas SLIGHTLY (so little load on engine), the truck starts sputtering and can be noticed on tach (+/- 50-100 rpm). And when coming to a stop (no throttle), it will sputter the same way until i get to a complete stop where you can hear the truck lope (SLIGHTLY) at idle. I have taken it to the dealer twice, cummins once, shown two other diesel mechanics...and they are stumped. The ONLY thing I can think of is a new harmonic damper. I ordered an ati damper to see if it helps. I hate to throw a part at it but Im at a loss. If anyone has anything I can work with please help me. I can't drive it till i get this thing fixed. Ill try to get SOMETHING for a video but...

Im not surprised. Been there done that. Glad you got it working.

I still have the original I can swap it out in like 20 seconds. lol. Anyhow, I adjusted the lift pump pressure and has stopped the whining noise so thats a plus. I was hoping that would solve my erratic rpms that happen throughout the throttle range but it didn't...That's probably for a different thread.... Anyone want to buy an adjustable overflow valve? lmfao

That had helped a bit actually. It must have been set for a 12 valve because it says on their website that a 24 valve is preset to 15-17 but it was 24-26. The pump is no longer whining...or dead heading my pump. Thanks Me I totally forgot it was adjustable

I beleive it does. Its the new Airdog II 4g system and the sump kit. I just put that on there. I haven't messed with it.

I recently got my much needed gauges and hooked up fuel pressure first to check things out. When i bumped the starter for the 25 second run, it jumped to 24 and slowly increased all the way up to 26! Does this sound like a return line restriction? I have an adjustable overflow valve that is preset at 14 psi. What could be going on here? I think this is the cause of my rough running truck...

Okay thanks

What the title asks? Im looking at doing a conversion and am looking at a good deal for an off-road 838 p pump? Can i make this application work somehow? if so, what do i need to know or do? And could i get this to work with an automatic 47re transmission?

No tank vacuum. As far as AC noise, i have unplugged the alternator and drove down a few blocks with no change. I have checked the connections for the computers. No loss of power or hard starting. Fires right up but it does sound like a gasser with a mild cam but this truck should purr like it used to not sound like a bad lope. Its not even a cool sounding lope.

Ive been chasing down this problem for about 2 years and barely drive my truck because of the issue. So I have upgraded to the newest airdog II, new MWFI vp44, and 150 hp injectors, new head gasket, studs, and timbos apps. If you listen to my truck from about 100 feet away, you can hear it running strange but not picked up well on video. It sounds like a random ticking coming from engine like the cylinders aren't firing all the way or something but it is NOT a misfire (more of a random skip). This happens throughout all engine rpms. When im cruising going 55 and let off the gas SLIGHTLY (so little load on engine), the truck starts sputtering and can be noticed on tach (+/- 50-100 rpm). And when coming to a stop (no throttle), it will sputter the same way until i get to a complete stop where you can hear the truck lope (SLIGHTLY) at idle. This truck is not running smooth like it used to. Something happened and nothing I have done that was mentioned has helped it. I have good fuel pressure. Im pretty sure the cylinders aren't firing the SAME but idk. Its very noticeable to me. Any thoughts or tests?

I actually just saw that video from you before you even posted it lol. But this proves that I DO have an issue with the return from vp44 as shown in my video, the clear plastic hose is return from vp44 and there is nothing coming out when bumping the starter. You did the exact same thing i did in your video. So my new vp44 is have a return flow issue if nothing is coming out when bumping the starter then right? Like the overflow valve is bad on this New pump?

If the vp44 is restricted not only by that small orifice as well as the overflow valve, then no wonder these things have issues with heat. So even with the engine running the injection pump is only trickling out small amount of hot fuel. Terrible design to me. Might as well go with the p-pump then.

The blue hose is the return from airdog. but if the pump is pushing 165 gph through the supply to the injection pump, wouldn't that fuel need to go through the return so it doesn't keep building up pressure? See when i run the pump for 25 seconds and the supply is primed, the pump no longer sucks fuel from the suction line from the tank to the pump. I thought it still suck fuel and the circulate to the return if it is not needed for the supply. Shouldn't the fuel just circulate through the supply and return if the engine isn't running? The overflow valve on the injection pump should open up to let the excess fuel pass through to the return of the engine still though right?

So here is my update. The blue hose is the 3/8 pump return to tank, the clear hose is attached to the stock 5/16 engine fuel return to tank. The 1/2 inch suction line from tank to pump, and 1/2 inch pump to vp44 are hooked up. If I am correct, the blue 3/8 inch hose should be pouring out fuel that is excess from the airdog, and the clear hose should be excess from the injection pump right? Why would it only be trickling out of both instead of pouring out. I unhooked the line from the injection pump at one point and it poured out into the bucket like a fire hose so supply pressure and volume is good. But how come there is no excess fuel coming out of these hoses? Is there a return restriction or did i even do this test right? Something fishy is going on here... IMG_0028.MOV

So i ordered the airdog pump to have a low fuel pressure light and a mod for the in tank fuel module. My fuel module does not have the pump in the module and the draw straw does have the angle on it. The sensor for the low fuel pressure is mounted on the airdog unit. So it is either the filters or the fuel module itself somehow. But if you think about it, the lift pump has new filters so that only leaves the module left to cause this since it has to be something between the lift pump and the tank. So....I bought a new fuel module (that is already modified) and see if that works. That way I wont have the pre-screen on the bottom and i can also fix my fuel level sensor ( it is empty at half way mark on gauge in dash). So win-win. If this fixes it then it need to be brought to attention the fuel module can be a source of low fuel pressure if it is an old unit. What do you think guys? I will post back with results as "solved" if my idea is right. Thanks to JAG1 for the fuel module idea.

Yeah. Now im thinking that the screen on the fuel module might be plugged up (like JAG1 was saying). I modded the fuel module and added the new airdog system recently. The old fass system had the 3/8 lines and were dry rotting anyway. The OEM fuel canister is removed completely. The injection pump, connecting tubes, and injectors have also been upgraded recently as well. I only have a "low pressure" light at the moment. But when in park it will stumble a little but light will not be lit. Go down the road a few blocks then the light will go on and will stumble worse the more its driven like it is starving for fuel.

As far as the first question, no Im not 100% sure. I WILL check that. The original filter is taken out. the airdog system replaced that. goes from tank, to airdog system, to injection pump. This truck does start and it does fire right up every time. I might buy that pre-modded fuel module from vulcan so I know i won't have issues with that stupid thing haha

for the suction line it is straight draw straw. the return is hooked up to original oe suction port and i drilled a 1/4 hole in that tube for return. So...the module has new suction port drilled with bulkhead and old suction port has airdog pump return, then the return line from tee near engine is at the same original return port on module (not messed with).

The kit did come with a mod for the in tank fuel module. And it did have me put holes in the side of the module. I didn't take out the screen but the straw should be able to suck up what ever fuel flows into the bowl from the sides i would think. I did take it down the road literally today with the cap off (funny you mentioned the cap) and no change.

So i replace my old style 3/8 fass system with a new airdog II-4g model due to no lift pump pressure and couldn't get system to prime and get rid of the air. Now even with the new system in, I go a few blocks down the road and my low fuel pressure light turns on and starts stumbling when going to a stop and sounds awful. What the ;lkjasdf;ljasd;lfkja is going on here? Im getting fed up...ive been so frustrated trying to figure this out the past couple months. I love cummins but this one is beating me up. And don't want to risk trying to drive it to a cummins shop. This is the greatest site ever btw.

Yes. That is just a suggestion. But if you are having hard starts, I would not try just cranking for longer than 30 second intervals and hope for the best. You have an issue and need to test things or you will burn up your starter. Hard starts mean the system is not primed or there is a leak. If there are absolutely no visual leaks (return banjo bolt behind head, tee fitting by firewall, injection pump banjos, or by fuel tank somewhere), maybe air is entering supply. Try teeing a clear tube to banjo on supply side of injection pump and post-filter to see if air is entering system causing your issue. I have done this many times to check for air bubbles.

I would check the overflow valve on the vp44. Maybe stuck open? I still stand firm that it should have no issue running at 10 psi. My truck was running with 5 psi before upgrading to aftermarket pump. Overflow valve on return side of vp44 control low pressure fuel flow. Thats all I can think of other than a fuel leak somewhere whether it be internal (head at connecting tubes) or external.