93 4.0 two wheel drive. 168000 miles. transmission shifts in and out of gear normally. runs through all gears normally. At freeway speeds, typically 75-80, in OD with cruise on or off when a load is put on the engine, (going up a steep hill) the whole van begins to chatter(shake).It doesn't happen at normal level or slight inclines. when the action begins, if I slow down or floor it to make it down shift the shake stops. It begins again as if I shift it back into OD. The transmission doesn't slip. I can accelerate hard from a standing start as in freeway merging and the problem doesn't occurr. Any Ideas??

 

Just a guess, but I would start by inspecting things like the tranny mounts, motor mounts, tailshaft bushing and drivshaft to see if everything is OK.

 

Sounds to me like the experience my Sister had with her new '99 Crown Vic. The "chatter" on her car was the torque converter clutch locking and unlocking in a very rapid fashion. FOMOCO replaced it free of charge.

 

CFP12. You're not alone. My wifes 94 4.0l 4X4 Eddie Bauer does the same thing (sometimes) when I drive it, but she claims it doesn't while she drives it. It is an intermittent problem and has been doing it since late summer. I think it is a tranny problem, but it's going to have to get a lot worse before it gets fixed.

1994 Aerostar 4X4 Eddie Bauer Extended 4.0l, auto

1992 F150 Supercab SB 4x4 302 AOD 3.55 31x10.5 All Terrain on Ford 15x8 Ralleys

 

I think I'm getting closer. I haven't found it yet, but I'm pretty sure that it isn't the tranny. I say that because I can make it happen just about when I want to. Accelerating hard as in a freeway on-ramp and continuing after it shifts almost always causes it to happen. Any kind of load while at speed will cause it to happen. (ie. cruising along at 70-75 and starting a climb. initially it runs alright, but close to the top of the incline when you would expect the most demand to be put on the elect/fuel/tranny/ it starts to shake) It appears to be an electrical or fuel breakdown when a load is applied in OD. Kind of like lugging the engine with a standard trans. It is accompanied with a lack of power, but no significant rpm increase(as in tranny slip)I'm starting to think plugged injector or bad plug wire. They are new wires, but....... It's still driveable but real annoying!

 

OK! Found and corrected the problem! A couple of things were at work in this case. First, the most obvious was over looked because they were new....plugs and wires!. Bad plug wire on #5 and a loose plug that had detonated the electrode on number 2.
Actually a pretty good endorsement of that 4.0 motor. Slight miss at idle and breakdown under a heavy load. Probably the slight miss was the bad plug and under the load, the bad wire compounded the problem. But most of the time at cruise (70-75) It ran pretty smooth on only 5!! Anyway, check those wires and plugs first, no matter how new they are!!!

Thanks to everyone that had input!