Bgott- The misfire monitor system looks for a certain number of misfires within a set number of crankshaft revolutions. If the misfire ceases, even momentarily, the counter resets. It is quite common to have a misfire with no codes set, simply because the misfire isn't steady enough to meet the programmed criteria. I would estimate that about one out of every four or five vehicles I work on with a miss don't have a code stored in the PCM.
Derek- Actually the coating on the throttle body isn't supposed to prevent the buildup of sludge, it's just to control it's effects. As the sludge builds up, it can prevent the throttle plate from closing all the way. The idea was to make everything so slippery that the sludge wouldn't have anything to hang on to and the big chunks would just fall away and not pack together like snow balls. At least that's what the engineers told me. It's actually Teflon-based, and I haven't found anything that removes it despite what Ford says we shouldn't do. My previous comment was just to make sure that Stephen didn't think he got cheated because it wasn't cleaned when it was in the shop. And yes, I hear you about fixing other people's problems. I just finished a truck that one of our other "technicians" was working on for over four days (and installed $1100 in parts.) The manager dumped it on me after reaching his frustration point (2004 F150 with 500 miles on it and a really upset new owner.) Fixed in less than an hour. MY reward? I got chewed out because I wanted to leave 20 minutes early to get to my chiropractor before he closed.
Stephen- The demands on the ignition system vary greatly depending on engine operating conditions. During a warm cruise or gentle acceleration, the PCM runs the engine with a lean mixture and high EGR flow. Both of these conditions require a long, hot spark due to the relatively large distance between fuel molecules in the cylinder. If there aren't enough molecules between the gap in the spark plug, the flame won't propagate because the next fuel molecule isn't close enough to pass the flame on. Under harder acceleration, the PCM richens the mixture causing more molecules to be present in the plug gap and this actually allows the mixture to light more readily. Now, if your coil is getting weaker and not giving a long, hot spark and just giving a short little "click" of a spark, it may not be enough to get things going in the cylinder. Of course, you having a weak coil is all just theory at this point and I am just speculating based on my experiences.
If it is a bad coil, the concern will progressively get worse until it finally gives out or the PCM threshold is reached and it sets a code. As someone else stated, a code just tells you what's out of spec, it doesn't tell you the cause or how to fix it. So even if you went to Autozone or some other place to pull the code, it is just another clue in the puzzle, not the solution.
Jay
