Another 4L80 problem

[bison]

Pulled a trailer load of Bison to the Butcher yesterday, truck ran and pulled good and shifted good but halfway in the trip and going 95 km the truck started bucking out of the blue so i let of the throttle a bit and the bucking disappeared till i put the pedal down again and the bucking started again.
To make a long story short i narrowed it down to what i think is 3th gear locking and releasing constantly.
I made it to the butcher OK(thank the lord) I checked for codes, didn't find any,Checked the oil and such(was all good) and crossed my fingers that i would not get stranded on the way back(250 km in the dark at 30c below and hardly any traffic to speak of( prob due to the bad road conditions with lots of ice and packed snow ).
Drove the whole trip back mainly in second just under the shifting point of 3th but could at times access 3th and TCC lock for as long as it lasted or the road allowed.
Most times the truck would run smooth as long as i kept my foot in it but the moment i eased off the go pedal the bucking would start again and forced me to back off to second gear
I got home OK but i was plumb wore out. :agreed:


I have a repair manual that lists a whole stack of trouble shooting points by condition but the one i encountered ain't in there.:nonod:
There are no codes or idiot lights on.

Any idea anyone??

 

[WarWagon]

Fuel gelling? PMD? Just has fuel starvation written all over it.

I have had transmissions not hold a gear and fall back to the lower gear rapidly. Generally 4th falls back to 3rd on me.

 

[bison]

Nothing wrong with the fuel supply,Pressure stays at 3 to 5 psi. I never have a gelling problem,.. we run winter diesel up here
Engine never missed a beat.

I do have to go over 2200 rpm to get into 3th gear, as soon as it locks in the bucking starts.Running in second is smooth as silk.

BTW this is my 98

 

[WarWagon]

Check the wiring for the speed sensors on the trans. Insulation likes to fall off near the trans. 2 sensors front and rear of trans with 2 wire connectors. You can pull the sensor and check for metal fouling the magnet in it.

 

[Will L.]

I would think if ISS/OSS he would get codes.
You don't like this idea, but last time I had that it was in my transfer case.

I wiped teeth on sleeve some how (which chewed up other parts being fulltime 4wd) and had very similar problem. The rotational speed in the tcase was causing slipping once worn and gearing was trying to disengage, as it would do that the output load dropped and would allow engage. It would speed up 1 mph then try to disengage again. Very rapidly, 30 times a second rapidly. Hopefully mine was abnormal and WW is right.

Try low range and see if it changes occurrences by speed / rpm.

 

[bison]

Low range has never worked yet in this truck, only 2hi and 4hi.
It happens the moment it engages 3th unless i keep my foot in it,but when i easy off on the go pedal it starts bucking till 3th disengages. No problems in 1 and 2.

Come to think of it 2 years ago it happened a couple times when cruise control was on and i was climbing a hill and it shifted back to maintain speed it started bucking
When I cut the cruise and took over with my foot it stopped.
Been good till now.

When i have more time and the outside temp is more agreeable i'll hook up the scanner and go for a drive.
It's to nasty out there right now.

 

[Burning oil]

Im sure you tried to manually shift the gears? not sure that would tell you anything anyway?
First thing I thought of was fuel delivery too. Got another PMD to try? They present all kinds of wierd issues.

 

[bison]

Im sure you tried to manually shift the gears? not sure that would tell you anything anyway?
First thing I thought of was fuel delivery too. Got another PMD to try? They present all kinds of wierd issues.

And that in the end was the culprit.:agreed:
That's why i changed the IP hoping that it would do the trick,..ehh not so, same problem persisted with bucking today when hauling a load uphill :agreed:
And THEN it dawned on me when i watched the fuel gauge closely when stomping on the throttle,.. the gauge's needle never got below 4 PSI, at idle it is 7.
For awhile allready the fuel gauge never hitted zero even with the engine shut off for a week and it never rung a bell:nonod:
The gauge is shot and cause of that i could not tell that the filter is plugged.:agreed::agreed::agreed:
It was as simple as that

 

[Burning oil]

Glad you fixed her up. Its to cold to be messing with those problems.