2005, 5.4, 96,000 miles. Running 87 custom tune for last 38,000 or so. Plugs have about 30,000 on them and fuel filter about 20,000.

Truck runs perfectly smooth, accelerates well, no indication of any problem until I punch it to downshift. Then it starts a constant bucking until I let off and accelerate without downshifting. This happens at any speed and downshifting to any gear. If I take off and wind it up through low gear, runs great, so not the fuel filter. I have checked codes and there is no code. Any ideas?

 

Sounds like either your torque converter or the transmission itself is going. Something probably with the line pressures.

Does that Edge EVO with the PHP custom tunes change any shift points, timings or line pressures with that tranny? How about torque converter lockup points?

If that is the case, see what happens if you revert the truck back to the factory settings. If it corrects it, I would talk to Edge or PHP immediately about getting a new "custom" tune done.

 

agree with above. Also I know a guy who had similar issues and one or two of the plug cops were bad. Maybe check that also.

 

is there a certain RPM you can't go over when you downshift?

 

not sure about that Patrick. The first two times I did it I was checking speed and that did not make a difference. The only time I check rpms, it would pulstae from 3000 to 2500 over and over, never get above 3000, never below 2500, just a constant bucking. Again, if I start from a standstll, it will go to over 5000 rpm just fine and do it's normal shift.

Don't see how that can be COPs, or torque converter. Oh, and it is instantly on the downshift, it does not build to it.

 

Our 4.6L Explorer did this same thing, and it ended up being bad COPs.

 

It would drive normal up to 70 mph plus but would not accelerate when you downshift?

 

check the plugs and air filter...

 

check plugs. just had the same problem 2 weeks ago, driving home from work put my foot in it, truck downshifted to 3rd (~2500-3000rpm) and rpms went wild, let off, back into overdrive it stopped. however i had DTC's show up as cylinder #4 missfire. turned out my autolite HT1 with only 30K on it was bad. all i can figure (no expert) is with different loads and timing advances the coils react with more voltage/amperage to compensate and the plug couldn't handle it.

 

My 04 just had this same thing happen last spring. Over the course of a week, it progressively got worse, and still hadn't thrown a code. At the end of the week, when it finally threw a code, it was occurring during normal acceleration also. It was a bad COP...replaced the entire set, since I had 80k on the originals...

 

Thanks guys. I guess maybe I'll change the coils. The plugs are Motorcrafts with 30,000 on them so should be good for a while, though I realize one could fail.

 

I'm thinking that everyone might be right. Sometimes the engine can act up causing the transmission to do wierd things like shift erratically. Especially if one or more of the coils are shot or acting up.

It's rather weird that it only happens at certain situations.

I'd say if you were going to change the coils, might as well change the plugs. The new plugs should come right out.

 

I know this might sound stupid but I didn't believe it till it happened to me. Many moons ago I had a v-8 van with a bad motor mount that did the same thing. When I'd romp on it the motor would lift in one side and the exhaust would hit some wires and cause a short. When I let off it would settle down and run fine. One time the wire welded to the exhaust and finally burned out, that was how I found the problem.
It could happen! That's my 2 cents.

 

Interesting. Have to look at that.

 

Let us know if the COPs solve the problem, Blue!