My truck experiences "bucking" while accelerating in the 40-45 mph range on a slight uphill grade with the throttle barely cracked open. If I step on it the bucking goes away. I've tried turning the OD switch off but the tranny won't downshift for a few seconds anyway - I'm not sure if the problem just goes away anyway or if the OD is acting up.

Older posts found using search indicate it may be a TCC "lockup control" solenoid being bad. Unfortunately these older posts generally contain a link to the "solution to your problem" that takes you to a "404:file not found" page.

History. Truck has NO mods of any kind. Trucked owned since new and has original tranny/TC, also has tranny cooler as part of trailer towing package. Present mileage 69K. I've never towed with it. Tranny fluid changed at 33K and 66K miles with Valvoline Mercon V. Used fluid looked and smelled good. No codes shown with my code puller. Problem started IIRC around 63K miles.

Any thoughts on troubleshooting/repairing this tranny?

 

Yea, that's not a trans problem IMO, you have a low grade misfire.

 

What brew said man, sounds like your experiencing lack of a tune up or motor side issue. Do you wash your motor? That could cause the problem, will fry your coils if you get water on them or in the plug wholes.

 

Well shoot. That could be the problem but it sounds odd to me. First of all, there aren't any DTC codes thrown, and it's been doing this for months now. My Miata will throw codes with any minimal problem. Second of all, the general rule over the years has been to expect ignition misfires at WOT rather than at almost-closed throttle settings. The reason: the voltage required to jump a gap increases with pressure, and the cylinder presssure is higher at WOT than near closed throttle.

I don't wash the motor, at least at and above the level of the cylinder heads.

However, I had already bought a set of the proper Motorcraft plugs and eBay COPs. Right now I'd just been waiting for the weather to warm up before spending a day in the garage. At least I have a 2-valve 4.6l Romeo which IIUC shouldn't be so much of a problem when changing plugs.

 

Nah, not the COP ig's in the modulars. Favorite spot to miss is right after the shift into OD accelerating normally. That particular load pics on a weak coil and more often then not,-doesn't produce a DTC.

 

The reason it does it at light throttle and low rpm is the fuel strategy - that's when it's running the leanest. Weak ignition is gonna fart on you when the mixture is that lean.

 

Change your transmission fluid!

 

GLC,
So basically the spark is mostly good but the mixure doesn't completely combust? The flame front peters out - needing perhaps a longer spark duration?

Roadie,
As mentioned in the OP I changed the tranny fluid 3K miles ago, without any change in symptoms.

I'll post back when I get around to changing the plugs and COPs.

 

Well it was a nice day today so I started my plugs/COPs changing. I am going to change 2 plug/COPs at a time so I can find which parts are good and which parts are bad - I'm retired so there's no rush.

I changed the #1 and #2 cylinder plugs and COPs this morning. Might as well start with the easy ones, since I'm a little gun-shy of changing the plugs considering the problems people here have had with them.

Hmm.....after a test drive up that long slow hill it appears that my problems have gone away.

Funny thing. When you change the oil on a 4x2, you have to turn the road wheels all the way to the left to get to the oil filter. When parking in preparation for my last oil change, when I turned the wheels full left the engine almost stalled and threw a code - P0301, cylinder #1 misfire. I cleared it after changing the oil and didn't think anything about it, since it's a load on the power steering pump at idle. But I now suspect the #1 plug and/or COP was marginal.

Well next week I'll change the #3 and #4 plugs and COPs.

 

You shouldn't have any issues with changing the plugs, just do NOT use antiseize and torque them to 28 ft/lb.

 

1) Pull off old COP
2) Use compressed air to blow out the plug well
3) Pull the plug
4) Clean moist debris out with 12 gauge shotgun cotton swab on rod
5) Put in clean dry plug, start with old scrap plug wire, torque to 28 ft. lbs.
6) Dab dielectric grease on COP, reinstall

I added #4 to the typical list. I use an old scrap plug wire rather than a rubber tube to start my plugs.

You guys were right. So much for my diagnostic skills.

 

I actually got what it sounds like you're experience from a fuel pump going out on me. It happend in my 99' with 128k miles on it. It would do everything fine but if I was doing 40-50 and gave it a little bit of gas, it would buck because the pump couldn't keep a stable pressure of fuel going up the lines. Had it replaced and it ran fine.