Thanks phil for the input but unless the belt, the dizzy, the cam, or some other mysterious part come somehow just jump a notch then there should be no reason why it would suddenly be outa time.

So far we have done the compression, leakdown, and vacuum tests as mentioned above as well as a heat check of all four cylinders at the exhaust manifold with a lazer pointer.

Yesterday we decided to check and adjust the valves cuz a dollar bill placed at the exhaust was sucked in instead of blown out. This happened only one time but it may have indicated a sticky valve. While it didn't solve the problem, we did discover that a few of the valves were out of adjustment.

Though I have little experience, I did get intimate with this engine as I've seen it torn down to the bare block and reassembled it to perfect working condition. My troubles began after installing a new muffler. And my instinct keeps bringing me back to the ECM. I mean think about it. There is a straight pipe where the CAT is supposed to be and I'm told there needs to be a certain amount of back pressure with that system. The ECM is operating with the idea that there is a CAT installed.

Let me explain what I'm thinking and you guys can tell me whether I may be on the right track or way out in left field somewhere.

I've discovered that the truck runs without skip on cold start for about 3 minutes. Once it reaches the point where it kicks itself down, the skip becomes evident and pronounced. My thought was that the exhaust is sending mixed signals to the ECM and the ECM is sending the wrong signal to the gadgets (all those darn sensors) that adjust the air-fuel ratio. Then upon further scrutiny, I discovered the open-loop...closed-loop function of the ECM. When the engine is cold, it is running in open-loop cuz there is not enough info with regards to the air sensors to be sent to the ECM. Those sensors need to be up to a certain temp before they report. Once they are warm, the loop then becomes closed (the sensors send their information) and the ECM makes the adjustments according to the data it recieves.

Since my truck runs fine durring cold start and for the first few minutes, I'm leaning towards a bad sensor somewhere in the group that does not function until warm.

Whaddya think? Could I be on to something here? We plan to use another specialized piece of equipment today to test the air-fuel mix being sent to the injectors today. Maybe I will get some good info.

I have to say, though I hate leaving my truck somewhere other than home, I cannot think of a better place to be than at the tech. where I have two really great teachers with a whole lot of patience, willingness to teach, and the tools...not to mention the heat. These guys know I could just send my truck to the garage to be fixed (one instructor owns his own family run garage) but they have implored me to use my truck as a learning experience. I wonder if they've got more confidence in my abilities than I do.