Symptom
When holding steady acceleration between 45-50mph, (rpm 1500-ish), engine seems to want to "downshift" asking for more power. RPM increases maybe 150-ticks (about 1 second) then backs down to normal. Does this repeatedly until I get up to highway speeds, then runs normal.

Conditions: More frequent/noticeable if I'm pulling a trailer (light weight riding mower). Also occurs more often if I'm coming up a hill/ridge (not too many Mts in flat S.Texas). I did pull a trailer couple months ago (est 4K lbs), but no problems.

What I've done:
--codes check with autozone scanner: none
--transmission flush/fill (BG, plus Valvoline synthetic)
--rear diff: drained/filled (synthetic..140weight)...old stuff was "old"
--drained fuel bowl to check for water: none; fuel is clean
--fuel filter --that's next...

Any ideas?

 

Does it feel like a stutter or more like the torque converter isnt locking correctly?

 

Sounds like what my 24v was doing. My truck acted like it was hunting between gears. I ended up cleaning all the grounds and installing a noise filter from genos garage.

 

Sorry, I don't know what "torque converter isn't locking correctly" feels like.

Just happens in the 45mph to 50ish-mph phase if I "hold steady" on the accelerator. (ex: speed limit zone 45mph) The engine seems to "down-shift" for 1 second (rapidly), then steady out again. Does this recurringly as long as I'm holding steady on the peddle. When I come out of the speed zone and begin to accelerate to higher speed, it does not happen again.

 

"Hunting gears"... sorta seems like what it's doing. Described differently, more so, it seems as if the engine quickly down-shifts (as if to gain power), then re-shifts to higher/normal gear almost immediately. (the whole incident cycle takes 1-second or less).

Had not heard of the "noise filter". Where do you connect the ends?

NOTE: When I changed the fuel filter today, I did notice the driver side battery terminal connections were snug, but "movable",... so I tightened them.

Other readings:
Fuel psi: very steady between 14-15 psi

 

While it's acting up on the road, hold up on the brake pedal with your left foot, and see if the problem goes away. A failing or misadjusted brake light switch is one of the things that can cause this.

 

I dont know exactly what you're feeling but what I'm referring to is..... The torque converter on newer model vehicles have a locking clutch inside them. When the torque converter is unlocked you can feel the engine RPM's move as you apply throttle, typical of what its like driving around town. But when the torque converter locks at higher speeds like cruising along the highway then the RPM's will drop a little and stay solid in relation to the vehicles speed instead of varying with the throttle, just like driving a manual transmission.

When the TC does lockup it can almost feel like the transmission is shifting into another gear too. So when or if there's a reason to cause the TC to lock and unlock rapidly then you'll feel and see the RPM's change accordingly.

Also, because today's vehicles are computer controlled and loaded with electronic devices, solenoids, and sensors, that means that any voltage/amperage differences outside normal factory specs will cause interference with other neighboring electronics. So what happens with these trucks particularly is if the batteries are in poor condition they will affect the alternator sine wave output, and/or if the alternator diodes are worn out resulting in a drastic increase in AC voltage output, those electronic variances will affect things like the APPS sensor and the transmission torque converter clutch.

If you're curious if this is the issue you're facing, check around other threads/forums about alternator AC noise, APPS sensor problems, and torque converter locking/unlocking. Here's link about the last one too. https://mopar1973man.com/cummins/art...k-issues-r388/

 

HHmmm........ might be onto something.
Few wks ago I had gooseneck hitch installed. Installer also installed an "in bed" plug connector which T-'d into the existing wiring.

Based on your comment, I'm wondering if tapping into the wiring might have caused the issue...

I will try the "press on the brake pedal" test tomorrow.

Meanwhile, I'm guessing (pure guess) that the TPS or APPS may be either failing or might need adjusting.
NOTE: Please don't assume I know
1) what or where either of these are actually located
2) how to replace them
3) nor cost of each...

 

The APPS is the throttle positioning sensor and its located just above the VP, identified by the black plastic housing with a rounded top.

You can try resetting the APPS by fully disconnecting both batteries from the engine, turning the key to ON, and letting it sit for approximately 30 minutes. Then turn the key to OFF and reconnect the batteries. Then turn the key back to ON and depress the throttle to the floor and back up, and turning the key OFF again. The APPS is now reset.

But that said, usually the APPS doesnt need this kind of attention and is merely a voltage rheostat that can act up. When or if you have to replace it you'll want to look into a Timbo APPS given they're just as good but much cheaper than OEM.

https://mopar1973man.com/cummins/art...procedure-r33/ and https://mopar1973man.com/cummins/art...s-sensor-r432/

 

perfect---thanks KATOOM !
Will try the "reset" procedure above. ((thanks for telling me where to find it too))

Question--does my truck have a TPS also? or just the APPS gizmo? (if yes, where is it, and is there a similar procedure to try on it?)) --or, are TPS and APPS same/same?

 

Yes their the same thing as the APPS is the throttle position sensor. APPS stands for accelerator pedal positioning sensor too.

 

You have the APPS. It is on the top left corner of the engine under a squarish black plastic cover. You should search apps for more info.

I usually go back to the last thing I fooled with. Sounds like your trailer wiring guy may have tapped a wire that shouldn't be loaded....

 

Good advice SIX.

Wire guy was a pro...although that doesn't absolve him from a mistake. Not sure how I'd prove it since I'm not elect.savvy. I suppose I could ask him to "take a look at his workmanship for a possible overlooked procedure" (it can happen to anyone).

Giving him the benefit of doubt (though will strongly consider), I'm inclined toward trying the "noise resistor" option suggested earlier. Seems relatively inexpensive from Geno's. Also saw a reference link on TIMBO's site...was a blog about something called a "SPONGE". From reading, it sounds like same as Geno's noise resistor wire. ... Can't quite convince myself to buy something called a SPONGE tho...

Additionally, I did place a call to Richard @ Glacier diesel (bought a raptor from him and he's very approachable). I may try the APPS (timbo) if the resistor doesn't resolve it.

Appreciate any continued analysis/assessments!

 

You might also take a look at your alternator brushes.

When they wear out they start to arc and make a lot of electrical noise. I usually get mine at Larryb - LarryB's Brushes for Dodge Diesel Denso alternator, 1989-2007

Good Luck!

 

Thanks RAM.
I've decided to replace the alternator with a NEW (not rebuilt) one. Ordered it; should arrive early this coming week.
Considered the "noise filter" but I figure that simply "covers the wound" without healing it. Alternator seems easy to replace, so I'll try replacing rather than rebuilding. Found a NEW one on ebay from reputable seller (with warrantee) for under $150.
Will post results...

Also, looking to replace my battery cables (originals)...any suggestions or does it really matter...are all cables generally same/same?

Tks!