A non-diesel-specific mechanic recently told me there are many problems with my 5.9L, and one of them was that I'd need a new ECM because they saw some codes.
I had him replace a rear U-joint and the passenger upper+lower ball joints, and then I got the truck back as I did NOT
have shifting issues before it went to him.
Now it can't seem to stay in 4th gear even at 70mph, and the truck has 315k miles on the truck.
Shifting Issue 1
If I start slow from a dead stop (start rolling real slow with no load), I get what feels like a clutch shudders around 5-10mph (just barely after turning through a turn from a stop light).
I back out of the accelerator, then throttle down on the accelerator at about 25-30%, and it picks up without that shudder.
Shifting Issue 2
It seems to shift through gears 1-3 without issues (48RE).
However, I won't start thinking about 4th gear until I push it towards 50-55mph, and the tach is around 2800-3000.
Once it jumps into 4th (even at 55+ mph) won't take long, and it downshifts to 3rd.
I haven't been driving much with these issues. But I did take it down the hwy at 70mph, and it shifted to 4th around 55mph, but when I got to 70 and let up to cruise there, it downshifted into 3rd, and RPMs are WAY high.
I heard that some shifting issues might be due to a faulty TSS sensor, so for $35, I replaced that, but it didn't resolve the problem.
Tranny oil level looks fine, and I have engine oil leaking out of the rear main seal because of crankcase pressure (I replaced the seal twice).
I figured out the cause is that cylinder #2
has pressure loss and cylinder #1
is just behind it.
It must be time to replace rings or more. But that's another issue.
This is all stock, and the tranny was rebuilt about 80k miles ago, and the valve body springs were upgraded about 20k miles ago.
I've had guys tell me it's an ECM or TCM issue, but not anyone who knows these 5.9L & 48RE systems.
What are the thoughts of the community here?
Does anyone have experience with this?
Is it an ECM issue?