4l80e no overdrive

[ailver79]

98 1-TON big block 4wd has no overdrive. Watching the trans data trans fluid temp got to 175* on the test drive. When doing 60 mph, rpm is at 3k, 4th gear selected, ratio says .75:1 , but input and output shaft speeds read the same. 1-2 and 2-3 solenoids both on When calling for O.D. When parked I commanded both shift solenoids 1 at a time and tcc solenoid on and off and can hear them click. Ect was at 190 when parked. Filter and fluid changed and level was good. Old fluid did not smell burnt and no excessive metal in the pan. No trans codes come up. Up stream o2 on bank 1 has a heater circuit fault. Anyone got any ideas where to go next?

 

[Schurkey]

98 1-TON big block 4wd

has no overdrive... ...input and output shaft speeds read the same.

So it's in 3rd gear, (direct drive) and the torque converter clutch works (no slippage.)

Up stream o2 on bank 1 has a heater circuit fault.

Truck is in closed-loop operation?

 

[NickTransmissions]

98 1-TON big block 4wd has no overdrive. Watching the trans data trans fluid temp got to 175* on the test drive. When doing 60 mph, rpm is at 3k, 4th gear selected, ratio says .75:1 , but input and output shaft speeds read the same. 1-2 and 2-3 solenoids both on When calling for O.D. When parked I commanded both shift solenoids 1 at a time and tcc solenoid on and off and can hear them click. Ect was at 190 when parked. Filter and fluid changed and level was good. Old fluid did not smell burnt and no excessive metal in the pan. No trans codes come up. Up stream o2 on bank 1 has a heater circuit fault. Anyone got any ideas where to go next?

You should have a gear ratio error if the PCM thinks the trans is in fourth but the ISS and OSS are spinning at the same speeds. That said, sounds like you have a no-upshift condition which is either faulty solenoids or VB...Since your other gears work seemingly normal I'd suspect the 3-4 upshift valve in the valve body. Check it for freedom of movement and if you have it, use the Sonnax vacuum tester to determine if the circuit is sealing adequately.

 

[ailver79]

As far as closed loop goes, I'll check tonight.
I also think that it should throw a code if there is a discrepancy between realized ratios and selected gear. I think that's odd, but can't figure out why. Is there a known issue with shift solenoids clicking but not engaging?

 

[NickTransmissions]

As far as closed loop goes, I'll check tonight.
I also think that it should throw a code if there is a discrepancy between realized ratios and selected gear. I think that's odd, but can't figure out why. Is there a known issue with shift solenoids clicking but not engaging?

Prioritize drivability symptoms themselves over codes as it doesn't really matter if they set/store or not if you're having a problem...They can be helpful with the diagnosis or not but don't get hung up on lack of DTCs plus the PCM can only place so many sensors/switches for monitoring purposes. Solenoids can fail in two ways: Electrically or mechanically...If they fail electrically, it will throw a code (voltage, continuity, performance, stuck on/off) but if the diaphragm fails a code may or may not be set.

That said, a no-upshift condition is almost always command and control which means PCM, harness, solenoids, valve body. So if your scan tool is showing the PCM commanding the 3-4 upshift ( but it physically stays in third; it never upshifts to 4th gear then neutrals) then the communication is going to the transmission and the health of the OD clutch pack cannot be assessed as it's not being commanded 'on' either electronically or mechanically. And since you have normal up and downshifting from first through third gear (right?) then I'd also rule out shift solenoids, harness, etc as potential causes (though you can always test with a multi-meter just to be sure).

Here's a 4L80E apply chart to help you know what should be working in a given gear and determine the source of the issue. Based on what you've described thus far, I think it's valve body but obviously, could be wrong.

You must be registered for see images attach

 

[ailver79]

"never upshifts to 4th gear then neutrals"
It does not upshift for certain, but has never nuetraled, had it up to 80 mph in od selected but obviously 3rd gear. Thanks for the chart, I'll go looking soon.

 

[NickTransmissions]

"never upshifts to 4th gear then neutrals"
It does not upshift for certain, but has never nuetraled, had it up to 80 mph in od selected but obviously 3rd gear. Thanks for the chart, I'll go looking soon.

Yep, so no 4th gear apply oil is making it to the clutch pack so now just need to figure out where the 'barrier' is (again, most likely 3-4 upshift valve and/or bore in the VB)

 

[yevgenievich]

On earlier 4l80e I had a case where issue with either lock up slip or one of the speed sensors will put ecu in not allowing 4th gear. But should have some codes usually for that condition

 

[ailver79]

Well, while doing all the other new to me truck maintenance, I was thinking about my no 4th gear issue. I thought that should it need rebuild, a new valve body wouldnt hurt. I did a bucket flush before I pulled the pan to move everything through the old filter. Dropped the pan, removed my old valve body, cleaned everything up and reinstalled a new valve body with solenoids and checkballs and filter. No change. Still no 4th gear. Going to recheck fluid level and video the trans data pids in in the morning, but not looking good. Probably going to end up pulling it and decide how much my time is worth to build it myself or not.