I have searched this forum for posts relating to this issue, but haven't found any. 95 Max SE AUTO 191000 miles; just had EGR and EGR tube replaced. Car is running fine until it tries to shift from 3rd to 4th with light acceleration at about 40mph. Car starts bucking until I give it more gas or take it out of O/D. No CEL and I haven't looked for codes yet, but I thought I might get some ideas by posting this problem.

 

I guarantee it's a coil pack. They typically throw a code at some point, either a knock sensor code or cylinder misfire code. Do you notice any bucking or hesitation at idle? Either way, I have over 220,000 on my max and 90% of my engine issues have been from the coil packs. I suggest buying two brand new coil packs, 1 front and 1 rear, to always have on hand. Try swapping out each coil until the problem is gone.

Or, you can do what I did. I ignored the same advice and spent a every weekend one month doing compression tests, changing the fuel filter, cleaning the injectors, and checking every electrical connection you can think of. I had first diagnosed it to be a coil pack problem but I had switched it out with a used, what I thought was a good, coil pack. Needless to say, had I used a brand new coil pack I would've saved a ton of time. Hope this helped.

 

Damn coil packs!!! I didn't notice any hesitation/bucking at idle, but I do remember some slight "missing" at higher acceleration. In the "ol days", missing at high rpms meant new spark plug wires!!! I'll check for codes, then price out the coil packs. Thanks.