1988 C2500 Transmission Problem

[Rod_Lei]

I've got a 1988 C2500 with the 5.7 TBI 350, it has a 4 speed Auto. So I was driving to work this afternoon and I noticed some weird vibrations at around 38 to 40 MPH. At 30 it shifts into 4th gear, at around 38 to 40 I believe the Torque Converter shuts down or "locks up". When the Torque Converter locks, the truck starts shaking something awful, and it just gets worse with the more gas I give it UNTIL I press it hard enough to turn the Torque Converter back on, then it's smooth ridin', UNTIL the Torque Converter locks up again. the vibration only occurs in LockUp in 4th gear at low accel, any ideas what this is? It only got worse on my ride home.

[ChevLoRay]

to our world!!

Sorry you're having trouble, but I believe we have some of the sharpest members around and they will be happy to offer some suggestions to help and guide you.

Is your Service Engine Soon/Check Engine light on? Do you know how to access the ALDL and pull the "all knowing ones" respond.

[Rod_Lei]

Thanks for the welcome! Nah the light isn't on, which surprises me because it'll turn on instantly with a hard shift. I'm gonna try throwing half a bottle of tranny fluid at it, the dipstick swears I have too much, but the truck leaks and I haven't added any for about 6 months. I suspect the dipstick is from another vehicle.

[Rod_Lei]

And of course, it responds to a bottle of ATF, the vibration is less intense but STILL there!! Is anyone already just plain sick and tired of these trucks?? I can't believe I got this thing, it's a joke! Does Chevy make anything good?? I mean seriously, all this thing does is break!! Ugh, enough rants.

So anyways, got the truck out, the vibration is less intense. However, the problem is spreading. It is now doing that revup while shifting thing, a hard shift when the Torque Converter locks up. I have now noticed a significant loss of power and torque.

So all the irregularities, I've noticed that at startup, it hasn't started with quite the umph that it has a few weeks before, it takes a few more cranks to get up and going too. Oil Pressure has been a little higher than usual, and Voltage seems to be lower too, but, this could be a result of a pully slowly dying, no I have no idea which pully it is, I just know it isn't the Compressor, nor the Idler Pully, so this could all be due to some extra work that the engine is having to do. But I have no idea why this thing is acting up so bad, please, someone help me out, I am a good mechanic, but ya'll know these trucks much better than I do.

I wonder if it could be a vacuum issue, or some electronic shift control issue, or just another Chevy joke Transmission slowly dying.

[Rod_Lei]

By the way, tried the whole paperclip to the ALDL deal to pull codes. I got:

32 EGR Circuit Fault
45 Oxygen Sensor Rich Exhaust

So I replaced the O2 Sensor a while back, that should be old, maybe I dunno about how this system works.
But, I don't know what an EGR Circuit Fault is, could someone please explain it? Maybe it's just a chip I need to replace that is feeding my transmission some mixed messages.

[Rod_Lei]

Well thanks a lot to everyone who posted, meaning ChevLoRay. Yeah the transmission fluid ended up solving the vibration and the loss of power was the EGR Solenoid.
Again, thanks for the insight, at least I learned how to pull codes.

[ChevLoRay]

I can't tell that anyone did anything but you. You pulled your codes and you fixed the things that seemed to be wrong.

I guess that your problem wasn't one that caused many folks to add their 2-cents to help.

But, when you least expect it, another issue may arise and you'll be flooded with replies that will be helpful. Hope your truck is squared-away for a long time.