Alright guys, it's been some years but I'm back in the Ford game.

My family's 97 350 (which as some of you know, is still an eec-iv truck) had some issues, and they gave it to me to sort out. They took it to a shop and were told it needed a new transmission. (e4od, as stated.)

However, here's where it's interesting. This transmission has fewer than 30k miles on it, and is the 3rd one this truck has had. Engine is also a new 460, just as a side note.

So - issues:
They reported hard shifting, and some occasional CELs.
Ran the code, showing stored 628 - excessive slippage. Reset the code, and the truck shifts perfectly as it always has, until you run it on the highway for an extended period of time, then it has the issue below.

​​​​​​Here's the kicker - did the cruise test (tap on brake while cruising) TC works as intended.
Third brake light bulb was jacked up, fixed that.

So, now I'm having a new issue. When accelerating from a stop with half throttle, truck hangs at approx. 1500 rpm, no acceleration, no shudder, just sits there. RPM does not increase. Give it more gas, it kicks down and accelerates normally, albeit in 1st gear until you get above 4000.

No noise from transmission, fluid is new and very clean. Shifts fine everywhere else.

Almost seems to me like the converter is locking up in 2nd, but truck isn't above 20 mph, if that.

New MLPS, no other codes thrown. This is fairly intermittent, but it's bugging me. Sorry for the long post, but have been beating my head against the wall with this truck for weeks and have tried to cover everything at once. Wiring looks OK on most of the sensors, again no other CEL except the 628.

Haven't ruled out the TPS or speed sensors yet, but speedo and tach work fine, and it shifts fine 80% of the time.
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That sure sounds like an engine problem to me. I don't see how the trans could cause that.

 

Ah, I should have specified. The truck accelerates when you press the gas, it just stops accelerating at 1500. Ie, truck will get up to approx 10 - 15 mph, and then hang there until you press the gas past half throttle, at which point it downshifts and accelerates normally.

Engine has no known issues, only has 10k on it currently.

​Honestly feels like the converter locks around this time, and the WOT unlocks it and it feels like it downshifts twice to accelerate.

 

Yes, that sounds like the engine isn't making the proper power at 1500 RPM. The converter should not be locking at those speeds. But if it did, the truck would accelerate or the engine speed would drop.

 

That does make sense. I'll take a look at it tomorrow, it runs through that range without issue in all other circumstances.

My only thought is that this issue only occurs after the 628 code has been thrown. If you reset the code, issue is gone for a week or so.