I realize this probably gets much more traction in a JK forum, but I do not have a membership at this time. I'm having a strange transmission issue, it appears to be worsening, and I'm hoping to collect some opinions prior to full-on destruction!
2014 JKUR, 121,000 Miles, Stock Size but 20-30% heavier tires, 3.73 gears, lightly wheeled, running heavy but not overwhelming, just bumpers, winch, a couple of jerry cans, and occasional RTT. The rig spends most of its time in California, so ambient temps around 100-120 are common.
At about 80k miles, it started to exhibit some really hard downshifts during freeway acceleration. One was so hard that I thought I broke a driveshaft or something. It actually yanked the Intake Air Sensor out of its clip, and threw a MIL. I had the transmission serviced (flush, fluid exchange, filter) at a reputable shop using the BG service machine.
The hard downshifts are gone.
The fluid is clean.
The fluid is not overheating (even at ambient of 122 F) based on the dashboard Transmission Temp Display, always between 166 and 172 once operating.
However...
Over the last 40k miles, MPG has dropped from about 16 avg to 14 avg with no change in driving conditions.
The transmission remains in lower gears for much longer before shifting up, sometimes holding second and 4500-5000 rpm for a full minute going up a freeway ramp. It wont shift until you lift off the throttle, even at part throttle. At altitude, the jeep frequently drops into lower gears and won't climb even gentle grades at less than 3500 rpm. While running the freeway, I frequently find myself running 300-500 rpm faster than I would expect for the speed, leading me to believe I'm not in 5th gear, although this rarely happens when I have the scan tool running. Some times it still says 5th gear, but just shows higher RPM (TQ Slip maybe?)
There is an intermittent "burble" or "buzzing" sound from the general area of the trans tunnel during acceleration, it goes away or changes at each shift. It is a new sound within the last 10k miles or so.
It almost sounds like the engine is lugging or the catalytic converters are clogged, but it is intermittent, and the engine will still happily reach full revs if you just mash the throttle, causing a downshift and high RPM.
Sometimes, it jumps out smartly into traffic like the day it was new, sometimes it bogs down and this buzzing noise happens.
I am beginning to suspect that the torque converter clutches are not locking or unlocking correctly. I think that the buzzing sound might be rapid pulsing of the clutches. It goes away in neutral or park, and seems to happen randomly.
I've been using Jscan to watch RPM, TQ slip (desired and actual) and throttle position. The slip seems to vary widely, but I lack the experience to determine if that is normal or not. Most of the time the slip is within 10 rpm desired and actual. I've watched, cleaned, and diagnosed wheel speed sensors as well, there are no issues there. I've changed wheel bearings, as I had one dragging, no real change there.
I have no codes stored at all, no MIL, no intermittent anything, no misfires, no performance issues that I am aware of.
My next plan is a complete engine tune-up, cleaning the intake and throttle body, new plugs and coil boots, a compression test, and bore scoping the inside of the cylinders.
I don't really want to drop $700 and 6-8 hours of time swapping a torque converter, unless I can point diagnostically to that. After reading more than I ever care to about the NAG1 transmission, I have discovered that there seem to be quite a few Mercedes with Torque converter issues, but the internet is sometimes an echo chamber that can lead to false conclusions.
So... any ideas or experiences that might help here? I'm sending out this general cry for help before I start spending big money on chasing ghosts.
Also, any recommendations on highly qualified transmission shops in central California would be appreciated. I would even drive to LA or the Bay if that is what it took to find someone experienced beyond "replace it and hope it all goes to plan". Local dealerships are crap and won't be consulted based on prior contact.
2014 JKUR, 121,000 Miles, Stock Size but 20-30% heavier tires, 3.73 gears, lightly wheeled, running heavy but not overwhelming, just bumpers, winch, a couple of jerry cans, and occasional RTT. The rig spends most of its time in California, so ambient temps around 100-120 are common.
At about 80k miles, it started to exhibit some really hard downshifts during freeway acceleration. One was so hard that I thought I broke a driveshaft or something. It actually yanked the Intake Air Sensor out of its clip, and threw a MIL. I had the transmission serviced (flush, fluid exchange, filter) at a reputable shop using the BG service machine.
The hard downshifts are gone.
The fluid is clean.
The fluid is not overheating (even at ambient of 122 F) based on the dashboard Transmission Temp Display, always between 166 and 172 once operating.
However...
Over the last 40k miles, MPG has dropped from about 16 avg to 14 avg with no change in driving conditions.
The transmission remains in lower gears for much longer before shifting up, sometimes holding second and 4500-5000 rpm for a full minute going up a freeway ramp. It wont shift until you lift off the throttle, even at part throttle. At altitude, the jeep frequently drops into lower gears and won't climb even gentle grades at less than 3500 rpm. While running the freeway, I frequently find myself running 300-500 rpm faster than I would expect for the speed, leading me to believe I'm not in 5th gear, although this rarely happens when I have the scan tool running. Some times it still says 5th gear, but just shows higher RPM (TQ Slip maybe?)
There is an intermittent "burble" or "buzzing" sound from the general area of the trans tunnel during acceleration, it goes away or changes at each shift. It is a new sound within the last 10k miles or so.
It almost sounds like the engine is lugging or the catalytic converters are clogged, but it is intermittent, and the engine will still happily reach full revs if you just mash the throttle, causing a downshift and high RPM.
Sometimes, it jumps out smartly into traffic like the day it was new, sometimes it bogs down and this buzzing noise happens.
I am beginning to suspect that the torque converter clutches are not locking or unlocking correctly. I think that the buzzing sound might be rapid pulsing of the clutches. It goes away in neutral or park, and seems to happen randomly.
I've been using Jscan to watch RPM, TQ slip (desired and actual) and throttle position. The slip seems to vary widely, but I lack the experience to determine if that is normal or not. Most of the time the slip is within 10 rpm desired and actual. I've watched, cleaned, and diagnosed wheel speed sensors as well, there are no issues there. I've changed wheel bearings, as I had one dragging, no real change there.
I have no codes stored at all, no MIL, no intermittent anything, no misfires, no performance issues that I am aware of.
My next plan is a complete engine tune-up, cleaning the intake and throttle body, new plugs and coil boots, a compression test, and bore scoping the inside of the cylinders.
I don't really want to drop $700 and 6-8 hours of time swapping a torque converter, unless I can point diagnostically to that. After reading more than I ever care to about the NAG1 transmission, I have discovered that there seem to be quite a few Mercedes with Torque converter issues, but the internet is sometimes an echo chamber that can lead to false conclusions.
So... any ideas or experiences that might help here? I'm sending out this general cry for help before I start spending big money on chasing ghosts.
Also, any recommendations on highly qualified transmission shops in central California would be appreciated. I would even drive to LA or the Bay if that is what it took to find someone experienced beyond "replace it and hope it all goes to plan". Local dealerships are crap and won't be consulted based on prior contact.