tranny trouble

[crazygspguy2010]

Hello, i just purchased a 94 c3500 turbo diesel. How do i kn Orlandiniw which tranny i have? its auto but no numbers i can see. Also when its first driven it wants to stay in first and second. Once its been driven a ways it shifts fine when going slow. Under power it stays in 2nd when first driven. I changed speed sensor on tranny, fluid is nirmal n octavot burnt or dark. I was told it could be the prom and tcm? any help would be great thankyou

 

[NVW]

Welcome to TTS

You have the 4l80E trans, it should be controlled by the ECM. I don't know what the problem is though.

 

[crazygspguy2010]

Thankyou, i thought that was the one. I drove it tonight after it was shifting normal, got on it a little and was stuck in 2nd again. I shut it off for a minute, started up and shifted normal again.. Quite a pain

 

[ak diesel driver]

any codes?

 

[crazygspguy2010]

The light doesnt come on but im going to try getting it scanned.

 

[THEFERMANATOR]

No need to have it scanned. You can pull codes by shorting the 2 pins together in the diag plug(can't recall which off the top of my head, but I think it's a and b), then count the flashes of the check engine light. 2nd gear only is limp mode for a 4l80e, so it probably has codes stored(obd1 trucks don't turn on the light for trans codes).

 

[crazygspguy2010]

Ill try that today thankyou

 

[crazygspguy2010]

Havent run codes yet but just replaced both speed sensirs, changed nothing. I was told my prom might be bad? or my computer? how or where do i find these?

 

[crazygspguy2010]

These are the numbers but dont know where to get tested or replacement? was told i may need updated prom?

 

[THEFERMANATOR]

Without codes, you're wasting time/money doing anything. If the wnfine runs fine, then my bet is the prom is fine. There was an updated prom to fix a 1-2 shift issue, but you're describing limp mode. It shouldn't take you more than a m8nute to short the 2 pins with a paper clip, and count the flashes of the check engine light. Until you do this, ANYTHING else you do is a waste of time. Throwing parts at it is doing nothing but wasting your money, and many times I've seen people swap in "new" parts that were bad, and created problems they didn't have to begin with. Electronics are not that hard to work with, but guessing and playing spin the wheel of diagnostics just wastes money.

 

[crazygspguy2010]

Ok codes are 34, 78, and 87

 

[ak diesel driver]

First 2 are engine codes the last is an EPROM error?

 

[Will L.]

DTC 34 - Injection Timing Stepper Motor Fault
DTC 78 - Turbo Wastegate Solenoid Fault
DTC 87 - Transmission Gear Ratio Error

Remove and clean ground wires for ecm/vssb and on engine especially tranny dipstick location. Also main battery cable. This has solved 5% of my electrical problems of the last couple decades.

Address the 2 engine codes seperatly and FIRST. They can cause it. Transmission and eprom might be fine and they are reacting to engine issues.

After that:
You already replaced the output speed sensor, did the old one have shavings on it? Did you use the 0.010" spacer for it? Ohm test the new one- bad new elctrical parts are not uncommon.
Any damage to the harness to that sensor outside he trans?

Has the tranny pan recently been removed- if so pull t down- I pinched the inside harness once and had the fight for a year until i found my error- same code.

Once you go through all that then maybe swap new eprom. If anything is wrong with above a new eprom wont fix it and may add more problems.

 

[crazygspguy2010]

Map sensor and wastegate solenoid. Read that map can cause shifting issues. Says pcm reads input and output speed sensors or ignition switch issimue, or could be the pedal sensor?

 

[crazygspguy2010]

The truck runs perfect, whats a stepper motor? Dont see it on autozone site. There were no spacers on sensors. Just the bracket and oring. Neither had any metal shavings at all. Im very new to this diesel. First one i ever had.

 

[ak diesel driver]

Stepper motor is on the injection pump. Does it still have the factory waste gate? If some turbo mastered it you would get those codes from out of range boost. Etc.

 

[crazygspguy2010]

I believe its all stock. Could be the map sensor also? Will wastegate solenoid cause shift issues too? I will be cleaning all the ground wire connections next. One by battery was very loose.

 

[THEFERMANATOR]

Code 87 is high ratio error meaning it is detecting slippage. From your description of it doing it when you get on it supports a slippage problem. I doubt a wastegate or timing control problem would lead to a slipping trans problem. There was isdues with code 87 that were fixxed by a prom change, but those had to do with the 8nitial 2-3 and 3-4 shifts taking more than 2 secondsbecause of cold fluid and trapped air in the hydraulic circuits. The prom chang changed the shift errortome from 2 to 4 seconds. This does not sound like your problem though. From what you've goven us to go on, it sounds like you beed to get a scanner and a pressure gauge on it and diagnose the trans. Low line pressure could easily cause slippage, but if ot's been driven for long slipping, then the clutches will be burnt/glazed, and need replacing. Time to diagnose, but I would prepare for trans work on one that is over 20 years old.

 

[crazygspguy2010]

But it will shift normal if i dont get on it. If i take off fast or jump on it it will kick down to second or first and stick there. Pull over and shut it off for 30 seconds and restart it and shifts fine again. Wouldnt it just keep slipping if that was the case?

 

[Will L.]

On 87 possible cause of the other 2 is based on db2 set ups that had bad or out of adjustment tps causing the messed up shifts. Ive seen that happen a couple times, but it was signaling tiss and toss sensors. Iirc it was 87 on those.
My thought was if stepper motor is off & dumping power from dropped boost, it could cause the same drop of rpm right at the shifting time.

THEFERMANATOR is the expert on transmissions not me.