Joseph1967

hello well here whats up... i have 1993 3500 hd 6.5 turbo diesel,with the 4l80e auto- trans.2 days ago it started to hard shift from 1st to 2nd ,but if you turn off the truck and wait about 20 seconds then start the truck it shifts nice and smooth. but at 60 miles an hour im pulling about 3,000 rpm,s at 55mph im pulling between 2400 and 2900 rpms im not very well vrested in this area .pleas help thanks

Sabino56

I have a 93 C1500 suburban with 5.7l and 4L60E. On it, the ECM/PCM controls the shift points. I think this around this year is the transition to electronically controlled transmission from mech/vac controlled. Do you know how your transmission is controlled?

Also, I’m not sure what you mean by the description of RPM @ various speeds. You’re saying it’s unusual, erratic, what?

you probably have an obd1 ALDL connector where you can check for codes. There is a way to short two of the pins together and count flashes of engine check light to read codes. This link describes how. https://www.chevytalk.org/fusionbb/s...php?tid/273660 when something odd is going on, it’s always a good first step to see if the computer thinks anything is wrong.

Another simple, basic thing is to get under hood and check if any vacuum lines are broken, any ground wires are broken or loose.

Irish_alley

93 would only be the 4l60 not the 4l60e 94 was the crossover year that could have either or. the 4l80e is computer shifted the 4l80e came out in 91 and even then it was computer shifted
a little more on the OBD1 codes
Obd1 code retrieval and decoding

ive heard about getting a dealer to the computer reflashed solving the issue but i dont have any more info on it

Sabino56

I bought my 93 C1500 Suburban new and still have it. K code 5.7L L05 with a 4L60E (M30 option). It has a ECM/PCM controlling the transmission.
On mine, it gear selection moves the input gear selector on transmission but the gear selected is sensed by a pressure sensor in the transmission and sent to PCM. I know as I've had to go in there and replace it once. I've also tracked down shifting problems with TunerPro and logging data.

I've heard that later models had a sensor outside the transmission somewhere so I just assumed that the 93 year was a transition year but have no facts on that. Only thing I know for sure is 93 Suburbans came with a 4L60E and were computer controlled. I have the HELM shop manuals for the year and it shows a 4L80E on some models.

I think the official introduction of something and the production introduction are sometimes two different things - but again, no facts, just heresay on that too.

Irish_alley

Sab, is it the round plug or square on yours? i was under the impression that the 4l60e only came out in 94 as when i went to replace my trans in my 94 it was asked which plug it had.

looking it up now it does appear 93 was the transition year and 94 the 4l60 was phased out. im guessing in the early 94s it could have came with either. sorry about that.

Sabino56

I’ll check when I get home this weekend. I can’t remember, or which pan is on it. No worries on a discussion on what year what had what! I appreciate the aggregate knowledge everyone brings to these forums. Thanks