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...

Yes it did. Was as though there is some type of electrical interference or grounding leak. Are you sure it's not just normal RPM fluctuation? Cause a lot of guys have that. Like some sensors kicking in.

 

Why don't you like the 2 stroke? The VP was designed for higher lubricity fuel before the ULSD was mandated. The scoring value of the ULSD is too high for VP trucks. So with 2 stroke added, testing showed it placed it back in range for the VP again.

 

I run it all the time in mine anyway,

Edited December 4, 20168 yr by JAG1

Is your initial question about a misfire or skip what we see in the video with the tach needle movement?  If so then I think you have a normal truck.

 

Although I cant feel the shake you're saying is happening at the end of the second video as you hold the throttle at about 1100 rpm.  I did notice that the exhaust is exiting right at the crossmember which will definitely cause a bass like reverberation which can actually shake the vehicle.

 

Is there anyone else you know who has a Dodge Cummins that you can compare against?

 

Edited December 4, 20168 yr by KATOOM

It's skipping not missing. Just the 12 valve across the street that is smoother than a baby's butt...(Lucky basterd!) but i have seen 24 valves where the rpms only fluctuate a FEW rpms with a digital tach. Well the 24 valves do occasionally have a fluctuation in rpms for sampling reasons but they SHOULD stay within 10 rpms or so while idling (unless grids are cycling). Its supposed to use the cam sensor to keep the rpms relatively steady. And the shaking is a result of that rpm fluctuation. THIS IS NOT NORMAL. It shakes even while driving when throttle is steady with fluctuating rpms. If i can't find the cause im gonna be saving up for a p pump. Im not dealing with this anymore. It makes this almost undriveable.

Edited December 4, 20168 yr by Cumminz

Be aware of the thing other things P-pump will create issues as well. Also will not resolve electronics issues like the ECM and PCM. I would do two things... First pull all the injector have then pop tested then do a compression test. This will verify the injectors that there isn't another problem. Then compression test since the injectors are out and have the knowledge of the cylinder health. We've had one member here that had a cracked piston that created a odd miss. Now Once you go back together then do the hot wire test on "Blue Chips" page and see if the skip is still there. If the VP44 is damaged and you do P-pump do realize if you don't fix the problem your ECM and PCM will be next to eat the bullet. In other words AC noise issues.. 

Edited December 4, 20168 yr by Mopar1973Man

  On 12/4/2016 at 2:13 PM, Cumminz said:

It's skipping not missing. Just the 12 valve across the street that is smoother than a baby's butt...(Lucky basterd!) but i have seen 24 valves where the rpms only fluctuate a FEW rpms with a digital tach. Well the 24 valves do occasionally have a fluctuation in rpms for sampling reasons but they SHOULD stay within 10 rpms or so while idling (unless grids are cycling). Its supposed to use the cam sensor to keep the rpms relatively steady. And the shaking is a result of that rpm fluctuation. THIS IS NOT NORMAL. It shakes even while driving when throttle is steady with fluctuating rpms. If i can't find the cause im gonna be saving up for a p pump. Im not dealing with this anymore. It makes this almost undriveable.

 

By no means am I trying to down play your concerns.....but what makes you think the VP is the cause?  Didnt you just assess the VP was "NOT" the problem with the hotwire test?  If not then what was the point of the test???

 

Seems to me that if this problem you're feeling is a problem enough to say its "undriveable" then maybe the cause is coming from either the PCM or the alternator.  Have you tried diagnosing either one of those?  Try disconnecting the alternator and see if the problem you're feeling remains.....

 

Either way, I'd think you'd want to make sure of the problem way before dumping thousands upon thousands of dollars into a p-pump conversion.  We all want driveable but given that your VP is painted "blue" and the injector lines are "red", I'm not being critical but just make sure whomever was under this hood did things correct.

Edited December 4, 20168 yr by KATOOM

Yes, if it went away when hot wired it's electrical then. Check your vp electrical connector for snug pin connections and for any rust /corrosion. Once cleaned and connections are tight again be sure and put some dialectric grease on the pin connections before putting it back in place.

 

If I had a problem that I couldn't track down like this I'd give it a good dose of two stroke every fill up (Break that puppy in with some well lubed fuel... oil, like it used to be, not this solvent)  just go driving everywhere and see what happens. Sometimes a clue will show its first inkling when just runnin around all the time with the problem. If gets worse then it might be easier to diagnose.

 

A question... have you checked for tank vacuum by slowly removing cap and listening for suction hiss? I ask even tho you most likely have electrical issue.

 

For the Record... I very much appreciate how you are so vigilant in solving this problem. It's commendable. Hang in there Dalton, we all appreciate it too  

Edited December 4, 20168 yr by JAG1

I have swapped injectors out with my other ones...no change. The injectors in it have only a couple hundred miles. I did a compression test. They were all above 450 psi. Is that good? im sure it is...I have disconnected the alternator fuse and drove around. No difference. A/C noise is less than .01 volts. What circuits from the PCM should i look for? Yes the VP is "Not" the issue but it runs off the computer. When it is hot wired and not connected to the ecm it runs fine. It is a good pump but p pumping will eliminate my wiring issue...wherever it is. I don't own a lab scope to check all these connections. It has a 12v power and a good ground from ecm to the pump and connections look fine but something is causing it to run this way. And there is a HUGE lack of diagnostics for the other pump wires....Im feel very knowledgeable about how these 24 valves work but it theres no real way to test the signals going into the pump from the ecm (i don't think).

There was a guy on the Cummins forum that was running his lift pump off the ECM (not supposed to do that) and the lift pump was pulling too much load and affected how it was running by effecting  the electrical system and rest of the emgine sensors.

 

You are supposed to run the lift pump off the battery thru a relay. The relay being controlled by the ECM. Running the lift pump directly off the ECM has destroyed ECMs'. You can get the plug and play harness from Vulcan Performance or Geno's Garage. Plug right into the ecm factory lift pump connector

@Cumminz Is this what yours sounds like?

 

That sounds like a cold engine on high idle to me Tyler, is it not?

All I hear is an engine that sounds like it needs some 2 stroke.

 

Only difference I noticed between the two videos was a significant lower charge rate on the volt gauge in the second video.

Edited December 5, 20168 yr by JAG1

@TFaoro That does sound like my truck when in high idle. Hard to tell but does yours make that weird noise about every 1 second in high idle too?

  On 12/7/2016 at 12:57 AM, Cumminz said:

@TFaoro That does sound like my truck when in high idle. Hard to tell but does yours make that weird noise about every 1 second in high idle too?

Yup. I figured that's what you were hearing. 

The only thing that has made any difference was valve lash. As weird as it is, nothing else has made a difference. 

 

I was just like you and did everything I could to make it stop. Best advice I can give you is QUIT WORRYING and don't spend any money on trying to fix it as your efforts will be wasted. 

Well my valve lash is good. but the fluctuating rpms doesn't sound good for the valve train...or the crank for that matter.

  On 12/7/2016 at 1:24 AM, Cumminz said:

Well my valve lash is good. but the fluctuating rpms doesn't sound good for the valve train...or the crank for that matter.

That little bouncing of the tach? That's normal.... RPMs aren't fluctuating that much. You'll need a live data tool to see what the RPMs actually are. 

Even though your tach appears to be acting totally normal, a little "lope" isnt harmful in any way and could just be a result of timing due to a box or cold weather.  After installing my 275's I'll occasionally get a little idle lope.

Edited December 7, 20168 yr by KATOOM

I have the same occasional idle lope as Katoom after installing my 275's. As far as the needle bounce, I have seen it since new. I added a scan gauge a couple years ago and my rpm drifts around from 798 to about 808. It is un noticeable to my ears though.

This is noticeable to everyones ears. "Is that a rod knock?" "Do you have a bad cam?" "Is your truck misfiring?"

About 15 yrs ago,  on my first gen, I thought there was a rod knock. I forgot about it and still running the same unrebuilt motor that's approaching half million miles. Still driving the old girl every day for over 20 years now. Been a great truck is all I can say.

 

2 stroke oil will quiet it down. My trucks love that stuff.

If i have good fuel pressure and no air in the system and it fires right up (no leaks in return). Could this issue be my new vp44? When i put it in drive it shakes and feels like it may die. I have been in denial about my pump but everything else has been checking out like you guys have said...Could the pump be faulty without throwing a code? would that be likely?