I'll try to be to short and to the point with this. I posted about this about a year ago. A year ago the truck would get sluggish when it warms up outside, gas milage would go to 11mpg, and temp gauge would rise above halfway. It seemed like it is working too hard just to keep up with traffic. I brought it in to the Dealer, they had it two weeks and replaced the cat, pcm, and some sensors. Well it still gets sluggish but the gas milage stays around 15mpg(mixed driving) but the temp. gauge will go above halfway (sometimes). The dealer claims that everything checks out ok. I'm thinking it could be a couple of things and want to see what you guys think.

1. Flowmaster 50 could have gotten some debris from clogged cat and causing too much backpressure.
2. Surpintine belt slipping when AC is on.
3. Clutch fan putting too much stain on motor on a hot day.
4. FM TB not correct diameter. This was the last mod I did.

Anyone's input would be appreciated. Remember this happens when it gets warm outside (at least 80 degrees). It runs great in the winter. Also, I have never gotten an average above 16mpg with all highway driving.
Thanks in advance.

 

How many miles are on it?

1. Flowmaster 50 could have gotten some debris from clogged cat and causing too much backpressure.

I am gonna rule this out, correct me if I am wrong, but I dont think there is packing in these exhaust, which I cant see anything sticking inside of it or clogging it up.

2. Surpintine belt slipping when AC is on.

Not sure why you think this would make it sluggish. Its possible but not likely unless you have a ac clutch going out but the belt would be squeeling.

3. Clutch fan putting too much stain on motor on a hot day.

This is normal. Clutch fans do drag some hp out of the motor when they are on. I would say switch to an Electric Fan if its t, hat much of a problembut I havent noticed much of a draw from mine to say it makes the truck sluggish for a DD

4. FM TB not correct diameter. This was the last mod I did.

What diameter did you go with? Even anything that should have made it room smooth and easier. Did you ever reset your PCM?

 

Also, sluggishness could be a result of not dropping gears with an increase in throttle...is the trans doing what you want it to?

 

My meows were clogged and replaced by a dealer.

 

how do u reset ur PCM? my O/D off light came on and now it suddenly wont shift out of first. i replaced with another used one and the light still doesnt go off but it shifts into overdrive. also it sounds like its running rediculously high rpm's. my gas mileage is at about 5 mpg. no im not kidding it really is. any one ever have this promblem or kno how to fix it?

 

The trans does feel that it doesn't drop a gear if I increase the throttle. I good example is when I go around a turn, I ease into the gas and the truck seems like it struggles, like it doesn't have much torque. I have to give it more gas and then it jumps down gears and gets going but I shouldn't have to do that.

The truck has 64k on it and I did reset the PCM when I installed the TB. He gave me one that works best with the 4.7 but I'm not sure what dia. it is.

 

Have you tried seafoam, or carb cleaner, or fuel injector cleaner?

 

I would suggest not shooting carb cleaner in or around the engine...they have throttle body cleaner that is less aggressive towards the sensors and plastic. Fuel injector cleaner is a good idea. Ever replaced the plugs?

 

I've cleaned the TB with Tb cleaner and changed the spark plungs 10k ago.

How could you tell if the ac clutch is going bad other than the belt sqeaking?