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1994 Chevy k3500 4x4

R

retired09

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rving across U.S.A.
Truck has been in limp mode for three months. Couldnt find mechanic that wasnt too busy to diagnose truck. Pulled camper to friends house in Memphis,Tn. and found mechanic. He first thought problem was computer and he hooked his extra computer up replacing mine but problem wasnt computer so he put mine back in. He checked optic sensor in injector pump and it wasnt reading signals properly. Told me to get new os. Found one on ebay and changed it out. Truck came out of limp mode has full power but on starting engine dark grey smoke coming out when accelerating. Drove truck and transmission not shifting into overdrive. When accelerating to go faster dark grey smoke coming out until get off gas pedal. Truck finally shifted into overdrive after driving 10 miles. Let truck sit about 30 minutes in driveway and started engine again after checking to see if air in fuel lines. No air no lines leaking fuel all way back to tank. Dark smoke coming out again and transmission still wouldnt shift into overdrive until driven about 10 miles. Need help guys. Was told by another member to have timing checked since I changed optic sensor. Am mechanic and changed os out properly made sure scribed mark so new os would be in same spot as old one. My mechanic has gone deer hunting for awhile. Only code showing now is 49 service throttle soon circuit fault ?? Would changing sensors on transmission make it shift properly? Truck starts like new no hard start like before. Does feel like timing is off little. Thanks
 
I would def check TDCO timing. You'll need a scanner GMTDScantech from Engh. Also check your fuel rates at idle to see if OS is positioned properly. IIRC Buddy said it should be around 8mm3 at idle. Also need to verify if your temp sender in the coolant crossover is working properly. TCC lock up won't happen until 170*. And as always check and clean all grounds. I'm sure others will chime in with more suggestions also.
 
x2, the TDCO should be done anytime the OS is changed. Even the thickness of your scribe line can change idle fuel rate 2-3 mm3.
 
Here is something I had posted in another thread for OS replacement. I emailed shellieman and he reports that his truck is running awesome since he performed the adjustment.

OS adjustment: eyeing up a scribe line is not good enough for this one

First you need to have a scanner. And you need to read the warm idle fuel rate in park. You adjust the position, laterally, of the OS, put it back togther, fire it up and want to see about 7mm3, give or take 1mm3. If it is out of range adjust the position and repeat.

Once that is done, you must run the TDCO relearn. You can initiate this with some scanners, or there is the key on key off (KOKO) method for OBD2 6.5 trucks. You still need the scanner to verify the final value is where you want it. TDCO is a value, but it represent a timing in some ways. You want a TDCO of like -0.75 to -1.5. A lot of people shoot for the max which is -1.94. Stock they set them to -0.25 to -0.75 TDCO. Setting the TDCO is setting the base timing, and in some ways it affects the fueling.

If you need a reference for the OS here are a couple, obviously youve already successfully swapped it. When adjusting the OS, pictures and info on the "optic bump" are helpful, because they bump it (move it laterally) to fool the PCM on how much fuel it is commanding. This is why the idle could be lopey, because its bumped too much and the PCM is probably sitting around 0-2mm3 of commanded fuel at idle, which makes it lopey, because of a poor feedback loop. When its around 6-8mm3 at idle the PCM can control idle smoothly. The bump also can make the fuel pedal more sensitive, put in lots of extra fuel and make smoke.
http://www.mamut.net/royh/newsdet9.htm
http://www.dieselplace.com/forum/sho...ic+bump&page=2
 
there is the key on key off (KOKO) method for OBD2 6.5 trucks. You still need the scanner to verify the final value is where you want it. TDCO is a value, but it represent a timing in some ways. You want a TDCO of like -0.75 to -1.5. A lot of people shoot for the max which is -1.94. Stock they set them to -0.25 to -0.75 TDCO. Setting the TDCO is setting the base timing, and in some ways it affects the fueling.

What is the key on key off (KOKO) method for OBD2 6.5 trucks?
 
IIRC it is hold the throttle pedal to the floor with the key on for like 1 minute then then turn the key off for 1 minute. I believe it needs to be up to temp 170* minimum. You would still need a scanner to read TDCO. And then keep moving the pump until you get the value you want.
 
Morning... Have new problem with my 1994 GMC k3500 4x4 6.5 diesel. Lost reverse and overdrive in trans.. Cant pull my camper or any other utility trailer cause truck sounds like its slipping out of gear when I slow down or stop. Took truck home and parked it. Checked with trans shop and was told that a 2 wheel drive trans wont work in my 1 ton even though it has same motor. was told that my trans is heavy duty just for 1 ton. Another mech said he has a 2 wheel drive trans out of 1995 box truck with 6.5 motor and all he has to do is change out input shaft from my trans and put it in his trans and install his trans in my truck and my truck will be ready to haul. He claims to be trans rebuilder and installer. He said wiring harness will hook up and 4x4 will work too. Anybody know which mech is right? Am retired and dont want to and cant afford to waste money on trans that wont work in my truck. Have to haul truck 100 miles to this guys shop. Need help guys.Trans shop said only have 3 choices, find a trans just like mine, have my trans rebuilt or buy new trans. You guys helped me when my truck went into limp mode and to fix it had to buy and have installed new injector pump. Motor runs like new after that work was done. Thanks for any help....
 
Any 94-96 4l80 should work as long as you swap the tail housing. I know wiring changed a couple times but that's about it besides 99 and newer have slightly stronger input shafts and internals
 
Thanks for the info. Going to pull my 1 ton to this guys shop and have him change out trans. he told me his trans would work. Was worried about 4x4 whether it would work or not. Dont use 4x4 very often except in emergency situations. Dont care what anybody says, you guys know your stuff. Lol. Thanks...
 
tanman_2006 said:
Any 94-96 4l80 should work as long as you swap the tail housing. I know wiring changed a couple times but that's about it besides 99 and newer have slightly stronger input shafts and internals
Click to expand...

Any 4L80E will work from a 2wd You need to swap output shaft and tail housing. Basicaly you have to remove all the components in the trans to access the output shaft, so I'd recomend having it rebuilt/latest updates or atleast new clutches, bushings and seals. Reuse your torque converter unless you know for sure the condition of the donor.
 
Morning guys...Will a 1993 2500 4x4 trans interchange with my 1994 3500 4x4 trans without any major changes in wiring etc? Owner of 2500 trans states it will interchange. Would like to save money. 2500 trans has 132,000 miles on it and was working fine before owner deciced to part out his 1993 6.5 2500 truck. Wondering if 2500 4x4 trans will be heavy duty enough for my 3500 4x4 truck. Cost of 2500 trans is $ 500 compaired to cost of rebuild of $ 1200. Appreciate any help on this. Thanks...
 
What transmissions are you talking about?

Fill out your info.

Manual transmission or Automatic /4L80E?

I'm not sure on the 4L80E/automatic since these vehicles switched from mechanical injection pump to PMD between 93 & 94

The manual transmission would swap



retired09 said:
Morning guys...Will a 1993 2500 4x4 trans interchange with my 1994 3500 4x4 trans without any major changes in wiring etc? Owner of 2500 trans states it will interchange. Would like to save money. 2500 trans has 132,000 miles on it and was working fine before owner deciced to part out his 1993 6.5 2500 truck. Wondering if 2500 4x4 trans will be heavy duty enough for my 3500 4x4 truck. Cost of 2500 trans is $ 500 compaired to cost of rebuild of $ 1200. Appreciate any help on this. Thanks...
Click to expand...
 
93 to 94 will swap just fine. Make sure the donor has the same style plug and your good to go. If not its easy to update the harness in the pan, about $130 for new harness IIRC.
 
I have a K1500 and am planning to put its trans in a 3500 some day. THEY ARE THE SAME, wireing is the main difference between yrs and internal parts change over yrs but a 4L80 in a 1500 is the same as any other 4l80 be it a 2500 or 3500.
 
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