Thanks to the great information on this forum, I have solved some problems on my truck. Many thanks to all who post.

I have a 99 F150 SC 4X4 5.4 Auto. 127K miles. It still seems to have a missing problem. Here's what I've done:

Cleaned out EGR valve and replaced DFPE sensor (that cured the CEL & P401 problem) -- wealth of info on this site - thanks again.
Changed spark plugs -- again, great info
Replaced one COP that looked a little burned compared to the rest
Cleaned out exhaust manifold elbow behind the TB -- no carbon build-up

Throws no codes and still runs like crap, only when in gear, so I thought it may be a tranny problem.

Tranny fluid & filter change, and added some 'no-slip' additive -- no change.

All these repairs and results were when the temp was between 93 & 100 degrees outside.

Today, the temp outside was only 80. The truck ran just fine. All day. I noticed this same phenomenon two months ago when the weather was cool & rainy.

Could this be a computer problem? As in the physical computer itself not working well when it's hot? What else has anyone experienced like this, where the ambient temperature affects a component on a vehicle, and what else may be being affected be high temperatures?

I'm stumped

Thanks in advance.

 

Just a shot in the dark, but try cleaning the MAF sensor. Just spray some electrical cleaner on it, don't touch the wires. From what I understand they're fragile as heck. Just an idea. Not sure if it'll help or not.

 

I've read many posts referring to the MAF sensor, but I'm still not exactly sure where it is........

 

Maf sensor is the sensor on the intake line from the air box, closer to the airbox itself.

 

 

Thanks, gentlemen.

.......and nice pic. That helps a bunch.

 

Cleaned the MAF -- no change.

I think it's time to get some professional diagnostics done on it.

that sux ($$$$)

 

My 4.2 is doing that Bonking bonking miss and always has.
It happens right ast the PC goes from closed loop to open loop.
It acts (seems to me) like the whole firing cycle is stopped. Like all six did not fire for one sequence.
Then it goes on.
Just about any time the engine has to accelerate from a steady RPM, as in starting up a hill, it will start that 'Bonking'.

I've changed the Plugs to Autolite super sumpinorothers, and changed the fuel and air filters.
This shows no codes.

Has anybody found a reason for this yet? Positively? No guessing?