Hey guys, I hope everyone had a nice holiday season.  I believe that I have another random electrical gremlin but not sure where to start.  So, it started the other morning on the way to the office, the truck started randomly surging as I was cruising down the interstate.  I was traveling between 65 and 70mph, and it feels like the truck is accelerating on it own.  I can hear the engine raise RPM’s about 100 RPM and I can feel the truck accelerate for about .5- 1 sec, then it goes back to normal and then it happens again.  It is totally random, sometimes it happens at slower speeds and sometimes it only happens when driving at highway speeds, and sometimes it does not happen at all.  I noticed this morning that it was still surging even while I was giving it throttle while driving.  So, I’m at a loss here since there is no CEL or codes. The VP is new and has about 6k miles on it, I replaced the APPS last summer, the ECM is new, the batteries are new, the battery cables are new.  I also have not noticed any changes in the gauges, they all still work and seem to always be functioning correctly. Except sometimes the lift pump pressure is low, it stays at 11psi and wont go up to 15 where it normally is, unless I shut the truck off and start it again, then the pressure will be 15, but again this does not happen all the time.  Sorry for rambling and I hope yall can make sense of this.  I’m just not sure what rabbit hole to jump down yet.

@W-Tlearning here. I understand the bd noise filter is not a fix, and basically masks issues which leads to other issues, but if a truck has the WT mod and healthy batteries, alternator, cables, grounds then what can the noise filter harm? 

@Andyba20 The nature of an electrolytic capacitor in the aspect of "uF" or micro Farads level (capacitance) acts slowly in reference to the supplied DC line level. If we have a 5 volt DC rail supplying a variable resistor, which is what we encounter with the APPS device and we change the position of the variable resistor when manipulating the throttle as we drive, the DC voltage changes, which causes the amount of current (milliamps) to vary within the circuit. The misconception of using an electrolytic device in "parallel" with this "variable resistor" as an intended filter for extraneous noise on this purely DC reference line upsets the DC time constant of the APPS device. The true nature of an electrolytic capacitor is to "store an electric charge" much like a regular battery holds a charge for an extended period of time. The purpose of the APPS is to allow a "quick" change in throttle to be calculated by the companion circuits following or tracking this change. The electrolytic capacitor will charge to a peak level of the supplied DC voltage and remain at the present DC level being provided. 

 

Examining the electrolytic cap specifies maximum DC levels from a voltage standpoint and capacitance level in micro-farads. If you introduce an electrolytic cap in this circuit it immediately charges to a given level of DC above ground. This upsets the actual DC level we attempt to set in the calibration procedure of a factory OEM APPS device because the electrolytic capacitance is slow to discharge the initial "bump charge" it was initially charged to.

 

In practice as we drive down the road, a driver will attempt to hold a consistent speed, on occasion a driver will back off the throttle to slow down according to road conditions or any other reasonable purpose the driver deems necessary. This electrolytic in parallel with our foot causes a delay or increased time constant to be in play. It introduces a "sluggish" or delayed response from our variable resistor (APPS device) because even though you let off the loud-peddle the slow discharge of the electrolytic is still commanding the VP44 to fuel. An electrolytic capacitor will appose a change in voltage...as you go down the road at 2 volts and you back off...the capacitor will begin to discharge its self in an attempt to maintain the DC level it had prior to you holding that variable resistor at a desired level. It fights your "let off" by many micro seconds.       

 

Our APPS system has two DC operations or settings. The first is IVS (Idle Validation Setting) where the static setting for low RPM engine operation is achieved. Mike's @Mopar1973Manarticle regarding this setting is very enlightening and I must mention Timbo's aftermarket APPS simplifies much of this due to a brilliant design aspect.

Careful review of what Mike Nelson has presented in the APPS article is excellent foundational knowledge. This poorly thought out "band-aid" fix as a "big fat slow filter" is not the way to do this.

 

The frequency of "fuzz" on the 5 Volt DC rail, most likely being induced by poor ripple effects of a given alternator's rectification process along with poor continuity at critical ground points is a "fast fuzzy" mess and can be served well by perhaps as little as .5 uF or less as a bulk DC filter in regard to cleaning up "poop" on our 5 Volt DC rail.

 

I'm sorry to have never scoped-out the general noise aspects on critical 5 Volt DC rails under the hood of our 5.9 CTD's , perhaps someday I'll have a chance to examine the "dirty fuzz" and provide incite to further harden the excellence of these cult vehicles.

 

My apologies for this most concise dissertation to answer an excellent question from @Andyba20and I shall refrain from going down the rabbit-hole in explanation of uF/resistance time constant in practiced DC theory....though you know I'd like too but, I need to prepare an evening meal and grab a cold beer. 

 

Cheers,

W-T 

 

 

          

W-T, thank you for your excellent explanations of our electrical situations. It's written in a college professor style that I actually can understand, and I understand zip when it comes to electrical issues.

47 minutes ago, Max Tune said:

W-T, thank you for your excellent explanations of our electrical situations.

  DITTO

 

 

5 hours ago, Max Tune said:

W-T, thank you for your excellent explanations of our electrical situations. It's written in a college professor style that I actually can understand, and I understand zip when it comes to electrical issues.

W-T thank you for the detailed explanation.  I went out and checked last night and my truck does in fact BD noise isolator. I will remove it this weekend while performing the ground mod.  I still have not had the surging issue again, but i did notice something else on my drive into work today.  My boost pressure was spiking while on the freeway cruising at 65mph.  It would bounce from 4psi to 16psi on my Quadzilla monitor.  I will look at pulling the MAP sensor and replacing it with a spare i have to see if that fixes that issue.  

Kick in a bit more for the APPS Sensor...

 

3 pins are the rheostat.

1. +5V
2. APPS Signal
3. GND

Then there is 3 other pins which is the IVS (Idle Validation Switches)

1. Idle
2. Throttling
3. GND

Now the stock APPS has a tag value of voltage on the back which is the point the logic chip flips those two idle validation switches. Only one leg at a time will be hooked to ground. If the throttle side is grounded then the ECM follows the APPS signal voltage. If the idle pin is grounded then all APPS voltages are ignored and the Cummins Idle Software is used. Some time ago someone on CF posted about doing voltage adjustment to fix shift issues and such. This went down a huge rabbit hole that had all kinds of bad results. Typically the end user attempted adjust to exactly that voltage and the sensor would rock back and forth between idle and throttling causing all kinds of other issues, idling high, shift changes, possible error codes. Hence why all documentation on the stock APPS sensor says "DO NOT ADJUST". 

 

I've removed a ton of these crappy noise filters and ground wire mods even the dealer today still doing. I will give it to @W-Tthe ground wire mod does indeed work very very well. I just done one not to long ago with shift issues had the BD noise filter and the APPS wire mod. This particular truck would not shift to 4th gear period. After pulling all the wiring mods off and returning pure stock electrical now it shift into 4th gear normally. I even informed the owner I needed to do a W-T ground wire mod soon to keep this straight. I even showed him on my own truck of what is removed and how its wired. I done at least a solid dozen W-T ground wire mods and 100% success rate too. Always a solid fix and no longer AC noise problems.

 

Now as for APPS sensors I would only suggest the Timbo's APPS being its a completely mechanical sensor and there is NO ELECTRONICS. Life pan of the sensor is about 7 to 9 years of daily driver. Do bother with OE replacement, or Wells APPS both of these are back to using electronics to toggle the IVS to idle or throttling and back to fighting with adjusting voltages and people always screw that up. Timbo's you can literally install, start and drive without even adjusting or doing a APPS reset. I know this isn't optimal but I know it can be done. The whole voltage adjust is all about that IVS switches only on Wells and OE APPS its critical of the voltage where on the Timbo's is actually the bellcrank angle voltage isn't even a issue.

 

As you see there is no electronics and the angle of the bellcrank will set the idle or throttling IVS legs. This why you could install and forget and never think about it again. Just when you do the install as instructed from Timbos you actually setting the slack space from the screw stop so your closer to the breaking point of the IVS. 

 

@Mopar1973Man is it age or mileage that ends the Timbo apps…you’re driving your truck a lot more in 7-9 years than I am. I’m now at 7 years on my Timbo, but probably 70,000 miles. 

4 years and 72,000 miles on mine...

 

 

- John

I was doing about 1,100 miles a week. So time spans will vary. Mileage will vary depending city vs highway use. Now not as much for me either.

I am wondering if the Timbo APPS will have a longer life for those who have a manual transmission and use cruise control a lot (I would fit into that category).   The reason I mention this is because the ECM does not use the APPS signal for input when cruise control is selected on manual transmission trucks.

 

My OEM APPS lasted for 290,000 miles before I got the dead pedal and the APPS trouble code.  I use cruise control a lot.

 

What do you think, @Mopar1973Man?

 

- John

W-T mod is complete and BD noise filer is removed.  I haven't had any issue since, seems the truck runs better and feels smoother while at idle. Not sure if it's just me or not but I'm not sure why I waited so long to do this upgrade. Now on to other electrical problems.

On 2/4/2022 at 12:03 PM, Tractorman said:

I am wondering if the Timbo APPS will have a longer life for those who have a manual transmission and use cruise control a lot (I would fit into that category).   The reason I mention this is because the ECM does not use the APPS signal for input when cruise control is selected on manual transmission trucks.

 

My OEM APPS lasted for 290,000 miles before I got the dead pedal and the APPS trouble code.  I use cruise control a lot.

 

What do you think, @Mopar1973Man?

 

- John

My last timbo APPS lasted quite awhile not sure how many miles I would say over 250k being I got it just before @MoparMom went down with kidney failure. So in my case I did the same thing used cruise a lot but then once in the city lot of light to light driving though.