My truck: 2002, F150 extended cab, 8ft box, 4.6l, 4x2, 4 speed O/D auto XLT. 160,000km

Randomly on hills or with a load it will start bucking and sometimes taking off from a stop it will surge up and down about 200 RPM. Bucking seems to occur around 1200RPM. There's no MIL and no DTC's. I took it to the dealer and they changed all the plugs, PCV, fuel filter, and cleaned the throttle body and injectors. It runs better in between screwing up now . Transmission shifting seems fine and fluid color/level is normal. Is it possible to have bad data from a sensor that doesn't cause a MIL? ANY ideas would be greatly appreciated.

 

So I just drove 1200km to the east coast on Saturday and the truck was pretty good early - when ambient temperature was low, but got rough during the hottest part of the day and seemed to improve as it got cooler again. Just thought I'd add that in case it gave someone any ideas. I did the MAF cleaning proceedure as outlined on this site yesterday, but no change. I'll be driving that same 1200km back home on Wednesday - wish me luck.

 

Welcome to the forum

Sorry that no one replied to your first post.
Yes a sensor can give bad data but not cause a MIL. Does the MIL self test when you first turn on the ignition? Just want make sure it's capable of working and the bulb isn't burned out or something.
It may take a good tech with a scan tool that reads live data to find the problem.
If you could get it in to your dealer while it's running bad that would help.
Next time it happens try unplugging the vacuum hose to the EGR valve and see if that changes it. Pull the hose off the valve and put a screw or something in it so you don't have a vacuum leak and then drive it. The MIL should come on after doing that but you can clear it by disconnecting a battery terminal for a few minutes.

 

My 99 4.6L had the same "bucking" that you speak of. My mechanic called it torque converter chatter, we changed the fluid in the transmission and he put a kind of additive in the fluid and the problem went away.

 

No need to apologize. If no one has an answer, what can you do?

The MIL circuit works. I'll have to try the vaccuum line test tomorrow since it's raining here today. I would have to pull it off before I started since the problem only seems to occur when I'm driving. If it works , what exactly does that tell me? BTW, I have an OBD II reader, so I can turn off the MIL with that.

The transmission fluid was changed about 20,000km ago, but the problem has only been around for about the last month...

 

I've witnessed the same type of "bucking" in older fords.(1994/1996) It was ussually the torque converter as mentioned above. My Dad's 1998 F150 has done it once or twice while pulling his camper. It only happens when the engine is lugging in overdrive just before it downshifts. If you can duplicate the problem at 1200 rpms when in overdrive try turning the overdrive off and driving at 1200 rpms. I believe the torque converter will still lock-up with overdrive turned off but it's been my experience that the "bucking" will not be as bad or may even go away. If it still happens at the same engine rpm regardless of what gear your in it's probably something else. Good luck

 

Update: Started the truck this morning and MIL came on. P0301 (cylinder 1 misfire) and P0316 (misfire in first 1000 revs).

Looking over my last service, I see on the sheet that the mechanic had in fact found cylinder 1 and 5 misfiring. This is why they did the service I mensioned above. Since the plugs and boots were done, is it likely the COP? It could be the power lead I suppose as well. If it was just an iffy coil or wire that would be awesome, but why didn't the dealership notice it?

 

Finally got around to changing the #1 coil yesterday and I haven't been able to get it to buck/surge since. I guess the coil was borderline and wouldn't throw a DTC. Thanks to those that replied.