stumble on acceleration

[Thunder2001]

motor stumbles when under slightest load.  slow acceleration no problem.  video attached explaining everything that has been replaced and tested 

 

[Me78569]

I am assuming it does the same EXACT think on the street?  

 

Any tuning on it at all?  

 

 

[Thunder2001]

Yes it does the same things on the street,only worse. I really am afraid to drive it much. Everything is stock New blue chip Vp44 his best stock pump,air dog Raptor 100 Lift pump,brand new stock injectors and connector tubes,new cam sensor,map sensor,coolant sensor,re manufactured ecm, Beans Diesel sump and lines to lift pump,new overflow valve and all new Banjo .bolts and seals. that's all I can think of Right now but I am sure I will think of more. I took the engine wire harness off and totally stripped all the tape off and checked for continuity on each wire,there were no problems so I resealed the harness and reinstalled. The reason I did this is because the local Diesel shop told me that he thought the harness was bad. Cummins does not currently make or stock a harness for my truck and if they did It when update cost $1200.00. Logic tells me that the Vp44 to be bad wth the exact same symptoms would be pretty low. I just had the clear fuel line on between the lift pump and injections r pump and when it stumbles like that the fuel in the line shows no air at all.

Edited February 8, 2017 by Thunder2001
Miss spell

[Me78569]

 

@TFaoro had 2 or 3 bad bluechip vp's out of the box so odds aren't that low.   I am assuming you used a good code scanner to scan for codes?  I don't think the harness is bad load shouldn't play into that.  What happens if you rev it up and hold a given rpm rather than just free revving?  Will it hold a steady speed without bucking? 

[Hawkez]

Do you know what your fuel pressure from the lift pump is?  Also, how full is you fuel tank? You ought to consider getting rid of those banjo bolts.  They will only restrict fuel flow.  X2 on checking for engine codes.

[Thunder2001]

I have my fuel pressures  set at 20 psi at idle rght now. I just went and picked up a scan gauge 2 and tried it and the MAP is reading 28.6 at idle and when I turn the engine off with key on it reads the same. does this sound normal?

When I throttle it the motor almost sounds like it is hitting a rev limiter. It will just keep stumbling as I hold the throttle down.I just don't want to damage anything by doing this.

[dripley]

The scan gauge II does not read the map well at all. I think mine shows a little higher than yours but still reads the same a idle. I have seen others here saying the same thing about theirs also. 

[Hawkez]

Did this problem exist before you changed out the injectors?  Did the problem get worse or better with anything that you changed?  I would look at getting an actual fuel pressure gauge.  At WOT pressure can drop dramatically, you need to see how much fluxuation you have.  Are there any signs of fuel leaks anywhere?  Do you ever have problems with it starting or losing prime after sitting?  Does it smoke at all?

 

How many miles on the truck?

[Thunder2001]

194,000 miles on truck, owned it since new. Truck seems to run cleaner with new injectors, so it was probably about time to replace. I have no visible fuel leaks anywhere. I do have a shop fuel pressure gauge that I use to check fuel pressure and I have the pump adjusted to 20 psi at idle and it never goes below 10 psi on acceleration. 

Never have any starting problem, starts right up. This problem has pretty much stayed the same no matter what I have replaced. I just feel that it is something that I have missed. I guess it could be another bad Vp44, but I just want to make sure before I bother the guy again.

[Dieselfuture]

10 psi is too low should not be below 14, but I don't think that relates to your problem it would cause damage to the vp in the long run not right away.  did this problem start right after changing the VP?

Nevermind I watched the video again,  sounds like problem started that before you did anything to it. It sure does sound like it's running out of fuel. 

Could fuel be contaminated

Edited February 8, 2017 by Dieselfuture

[Dieselfuture]

It's almost sounds like a car I bought once, it had 2 spark plug wires backwards and it spottered just like that. Another thing is check ac volts coming of an alternator if you havent done it already, maybe it's messing with your vp or ecm? 

[Me78569]

I don't think this is a normal issue we face.  

 

 

10 psi wouldn't cause this.  ac noise would be a all or nothing type of thing.

 

@Thunder2001

 

Would you say it might be related to going on a set throttle position?  IE: if you old TPS at say %10 but increase load will it stumble, or does the stumble happen when you increase throttle beyond a set posiition?

[JAG1]

I know a Snap on scanner can detect flat spots in the TPS.

Did you get the new Timbo Apps to go with new vp? Timbo APPS is a good replacement for the cheaply built factory TPS.

 

Are there any fuel restrictions besides the banjos, Dirt for example, that causes a delay in F/Pressure till it catches up? Or an inlet screen on the inlet side of the lift pump Some did have a screen in there for awhile and should be pulled out. What about the debri from drilling the tank sump is that all clear?

 

Is the lift pump running off the batteries thru a relay and only controlled by the ecm? Too much load from the lift pump, running off the ECM, can play havoc on the electrical system if not run off the batteries.

 

Welcome to the forum BTW. I hear what you are going thru but very much respect guys that don't give up like you.

 

One last thought I have is to slowly remove the fuel cap after a run to listen for any vacuum hissing. Could be your tank vacuum is clogged and hard time getting immediate fuel pressure. Running without the cap will tell too. Just an outside chance.

Edited February 9, 2017 by JAG1

[Thunder2001]

Wow I really appreciate all of your help guys. As far as quitting, I am so deep now that It's got me pissed off now. I will not let it beat me. I wake up at 2 in the morning because I just thought of another idea. as far as the Alternater goes, that is a brand new remanufactured one that I had them test twice before I took it home. The banjo bolts are new but are the ported BD Diesel bolts that supposedly flow better. I am going to try and run it without the alternater hooked up to see if that helps. The Apps is also brand new and the lift pump is hook up to factory connection. Today I will try to note the symptoms a little more accurately with this scan gauge and report back. I was hoping that someone would have heard the noise and said oh yea I have heard that before it's your whatever. I guess this is just my luck but I have never had anything that has been this hard to diagnose.

I have also tested the fuel tank venting and replaced the cap for safe measure.

As far as a fuel restriction goes I would think that if you had one at the pump inlet it would show up in the  clear fuel line test as cavitation bubbles.

[Hawkez]

Maybe take a look at the air filter and make sure there are no flow restrictions. 

[JAG1]

You should not run the lift pump off the factory connection. That factory connection should only activate a relay that lets the L/P run off the batteries. It's too much load on the ECM otherwise.

 

Brand new alternator means nothing when not tested for any excessive levels of House type Current or AC noise as we put it. Say that cause someone once thought we were talking about noise from the air conditioning system.

 

Edited February 9, 2017 by JAG1

[Me78569]

I am getting the weird thought that maybe the IVS switch in the apps or apps wiring is shorting causing hte ecm to think it is at idle state?  

 

@Mopar1973Man thoughts?

[TFaoro]

I'll have to listen to the video later, but the symptoms sound like a bad VP out of the box. 

[IBMobile]

Do you have the ability to obtain live data.  A good OBD 2 code reader will have that function and if it graphs all the better.  You would want the throttle position sensor percentage (TPS %)  along with the calculated load percentage (calc load %) figures. 

Here is some data from my truck.  

Idle cold: ECT 73°F, calc load % 5.5, TPS% 0

Idle hot:   ECT 188°F, calc load % .4,  TPS% 0

Driving no grade:  ECT 190°F, calc load % 25.9, TPS% 34.9, 70MPH

Driving up grade:  ECT 190°F, calc load % 47.1,  TPS% 40.7, 70MPH

 

 

[Hawkez]

That's what I thought.  But according to what he says this problem started before changing the VP and BlueChip sent him another new VP to see if the first new one was bad. Seems unlikely that 3 VPs would be bad with the same symptom.