4L80E cant decide if it wants to be in 1st or 2nd

[Sandracer799]

The 4L80E I swapped into my '87 k5 started acting like the converter was going bad the other day. Like it was slipping. But upon further diagnoses it is not the converter. When you put the truck in first the truck goes great shifts through all the gears. When you put the truck in second, it will start out in 2nd like it is suppost to. (Aftermarket tranny controller from TCI)

However when I put the truck in OD the truck will sometimes start out in 2nd and sometimes start out in first. And if you give it half throttle or more the tranny doesnt know what to do and starts shifting back and forth violently causing the whole truck to shake.


i have replaced both shift solenoids and it is still doing the same.


Also I know there is an actuater screen in the valve body. Could this be clogged, causing incorrect line pressure to the solenoids?

My trans guy doesnt think it is anything major to where it would need to be rebuilt. Also I talked with the TCI tech department and he told me that some mechanics have a "Zoom Box" that by passes the computer to see if the trans if working correctly. Anyone heard of that?


Anyone have any ideas? I am ready to blow the damn thing up.

 

[jcool]

The 4L80E I swapped into my '87 k5 started acting like the converter was going bad the other day. Like it was slipping. But upon further diagnoses it is not the converter. When you put the truck in first the truck goes great shifts through all the gears. When you put the truck in second, it will start out in 2nd like it is suppost to. (Aftermarket tranny controller from TCI)

However when I put the truck in OD the truck will sometimes start out in 2nd and sometimes start out in first. And if you give it half throttle or more the tranny doesnt know what to do and starts shifting back and forth violently causing the whole truck to shake.


i have replaced both shift solenoids and it is still doing the same.


Also I know there is an actuater screen in the valve body. Could this be clogged, causing incorrect line pressure to the solenoids?

My trans guy doesnt think it is anything major to where it would need to be rebuilt. Also I talked with the TCI tech department and he told me that some mechanics have a "Zoom Box" that by passes the computer to see if the trans if working correctly. Anyone heard of that?


Anyone have any ideas? I am ready to blow the damn thing up.

whats the fluid look like (color,smell,level). Have you dropped the pan and checked the filter for being properly seated? Or any metal inside the pan? I would start there before anything. How did you check the converter?

 

[Sandracer799]

The fluid did not smell burnt but it was dirty. The level was full. I put in new shift solenoids and filter while I had it out. I check the converter by driving along and holding the break a little to make the converter unlock, and it did with no shuttering or any other irregular noises.

 

[just a number]

have the shop do a road test to se what the transmission is seeing. mine had a gear hunt issue which turned out to be a simple but expensive TPS. it thought the throttle was half open at idle. last scan I had done only cost me $35. any codes?

 

[docdray]

2nd gear starts can be pcm or quad driver, direct clutch lube feed blocked. any problems with tranny in other vehicle, set up a long time? there is a shop in my town that has scanner that monitors/ pulls codes from tranny real time, might call around for a good ol boy shop that might check for free or small charge.

 

[bk95td]

Does the tci controler have input for 4 -low as the factory pcm does?Or is it strictly input - output-throttle? Input and out put sensors can get gunked up and give false readings.Remove and clean.price= Free Also check output of throttle position sensor. 0-.5 at idle, up from there with throttle. Wiring at the tps should be: 5 volt reference signal from controler,ground and throttle signal.
The factory pcm has a provision for 4wd-low range. Trans. will shift eracticly if it thinks it's in low range and it's not.

 

[Sandracer799]

2nd gear starts can be pcm or quad driver, direct clutch lube feed blocked. any problems with tranny in other vehicle, set up a long time? there is a shop in my town that has scanner that monitors/ pulls codes from tranny real time, might call around for a good ol boy shop that might check for free or small charge.

I got the trans from a junk yard. It had 95,000 miles on it. I had this set-up in my blazer for about a year. The problem did not start out real bad. It started out like the trans was just slipping a lil, and just got progressivly worse.

 

[Sandracer799]

have the shop do a road test to se what the transmission is seeing. mine had a gear hunt issue which turned out to be a simple but expensive TPS. it thought the throttle was half open at idle. last scan I had done only cost me $35. any codes?

In my deep searching I am finding out that TCI is not the best system out there. It is unable to pull codes which is making this even more difficult.:mad2:

 

[Sandracer799]

Does the tci controler have input for 4 -low as the factory pcm does?Or is it strictly input - output-throttle? Input and out put sensors can get gunked up and give false readings.Remove and clean.price= Free Also check output of throttle position sensor. 0-.5 at idle, up from there with throttle. Wiring at the tps should be: 5 volt reference signal from controler,ground and throttle signal.
The factory pcm has a provision for 4wd-low range. Trans. will shift eracticly if it thinks it's in low range and it's not.

The TPS sensor is one thing I have not checked. I will defintly check that tonight.


Thanks everyone for all the ideas.

 

[just a number]

when you check it you have to move it VERY slow to pick up a bad spot. they wear out when you normally have the throttle. Let us know how it goes.