Greetings! My buddy came to me with his '99 f350 auto with the 7.3l.
Here's a little history. He ran an errand, came home. Went to leave again, and the truck wouldnt move. We trailored it to a tranny shop. They flushed the tranny and changed fluid and filter. Truck drove great for a week. He went up hunting, and the torque converter started puking atf. Back to the tranny shop. They put in a new torque converter and seal. He opted for the upgraded TC but I don't have any other details on that. Month later, he was pulling a large camper for another buddy, one of those big triple axle jobs. Going up a good sized hill, the o/d light started flashing and the truck would no longer shift into o/d, until around 30 minutes down the road. He took it to another tranny shop, they pulled codes, none written down, they did a flow test, removed the bypass valve, did another flow test. It was improved but not great. The temps were also higher than the tranny guy preferred. So he and I put in a bigger tranny cooler yesterday. We added about a cup of tranny fluid, let the truck idle about ten minutes, checked fluid. We went for a test drive to get it to running temp, checked it again, added another cup to get it to the top of the hot hatches. Driving around normal, the truck shifts great. If you get on it, the tach red lines, the tranny hesitates for about two seconds before going into gear. About the time it goes into gear, the service engine soon light does a quick flash. So, after all that, any body have any insight?

 

My insight is that you need to know what codes have been stored.

 

Aside from that, tell "you buddy" to stop towing heavy loads until he gets a decent transmission oil cooler. He keeps overheating (puking fluid) and hurting his 4R100.

 

Like I said, we put in a bigger tranny cooler yesterday, about twice the size as the old one, and better flow rate. I tried to pull codes with my odbII but nothing came up on that. He'll have to go to a shop to get anything more. The od light quit flashing after he went to the tranny shop. It's the SES light giving one flash, so quick that you can't read it, when the tranny drops into gear at WOT. I haven't been able to find anything similar here or on the net.

 

You still need to get the codes read. Without the codes all you can do is buy parts and hope for the best. The SES won't flash a code, it comes on to tell you that a code was set.

 

He's going to take the truck to get codes read in the next few days and I'll get back to you when we find something out.

 

Well, he took the truck to the dealership and no codes, and everything checked out great. So, in other words, we still don't know anything. I have owned one vehicle with an automatic tranny, and it's my plow truck which gets about 50 miles a year. Reading other threads about the automatics, I get the impression that the torque converter frees up, the tranny shifts, then the tc locks up again. Someone also mentioned a high stall tc...what exactly goes on when the tranny shifts, and can you "feel" these things happening?