I have noticed lately that when I am cruising around 65 and nail it to pass some one that the instant my truck downshifts it studders like it is loading up then it takes off like a banshee. It makes a wierd popping sound through the exhaust and puffs a little black smoke. It was doing this with the stock tune, TP tunes and now just started with my Roush tune. I have replaced the O2 sensors, new plugs, new COP's and have changed out the fuel filter. does anybody have any idea of what they think it my be? It is something mechanical or sensor related I believe since it happened with all the different tunes. Could it be that ny maf is dirty or that maybe I had some dirt in the tank and it is clogging my fuel filter? Thanks in advance.

 

Try posting this question in the SC&Tsection as well. I've hung around there for good reading and those guys know what they're doing.

 

My thoughts go to your torque converter. Remember, at 65 and cruising, you are not asking much of the engine and trans. You are running in 4th gear, RPMs are around 1800-1900, and the load on the engine is fairly low. When you nail it, your trans does a 4-2 downshift and you are immediatley asking for everything the power train can deliver. In actuality, you should hit the OD switch before nailing it. I'll bet you see a different result.

The very first thing I would do is have your trans flushed; but, I wouldn't let the dealer just flush it. Buy a couple of extra quarts, have them power flush first. Then have them drop the pan and replace the filter. Then, they should top it off until the stick reads full. When they drop the pan, have them clean it and examine the magnet. It will show you if any excessive wear is occurring.

I have tuned my truck to not allow the torque converter to lock except under WOT. Ford has quite a number of locks and unlocks built into the factory tune in an attempt to get better fuel economy. Also, talk with Mike Troyer. His 93 Tune does a real nice job with the downshift in the situation you described.