I am new to this forum, and have found it a great deal of help with a few minor issues. I guess it is my turn to ask a question. I have a 1999 F-150 with the 4.6L V-6. It is a great truck which has 196,000. The top half of the engine was redone 50,000 miles ago. Lately it seems like it is starting to miss on acceleration. It misses and hesitates when I get on it from a stop light, and at highway speeds when I barely push down on the accelerator. Can anyone help me? Thanks

 

A misfire with no CEL is usually a secondary ignition problem

That means plugs and wires, typically.

Steve

 

If it has turned on the check engine light, go to Autozone and pull the code. The code will lead you to which cylinder if it is actually a misfire, which is what it sounds like. The code will start with P030_ The last number tells you what cylinder. Once you know that, you have a starting point. Let us know what you find out.

Robbie

 

The voltage it takes to fire a plug goes up with engine load. The RPMs don't matter at all, it's the throttle position that matters. From your description, it kinda sounds like this. If so, the secondary ignition system (coil, wires, boots, and plugs) is the most like suspect.

This isn't scientific, but it gives me a diagnostic direction at almost no cost. Tune to an AM radio station that picks up nothing but static, the less noise the better (engine off). Start the engine, turn the radio up quite a bit, and put it under load. If an automatic, power brake it. Put it in drive (nothing in front of you), apply the brake, and press the accellerator (sp?) down pretty far. If it's a secondary ignition problem, you'll hear it. It sounds like it looks if you pull a plug and ground it to see if it's firing. You can usually find where it starts by easing in on the accellerator. I'll bet I hear 80% of the secondary problems I look at.

The right way to do it is with a pair of spark testers (I don't think the '99 had coil on plug yet). Connect a spark tester (looks a little like a spark plug with no threads and a ground clip, about $6 each) on the plug wires on each side of the coil pack. Start at the front, connect to the wire from the frontmost on the left side of the coil pack and the frontmost on the right side. Ground the spark testers and start the engine. Both testers should have consistent sparks. If one doesn't, the coil or that wire is bad.

If that doesn't find anything, it could still be a plug. My bet is secondary ignition due to the symptoms and this is how I'd test it without an ignition scope.

 

Thank you all very much!!! I went to Aotozone and got Bosch Platinum Plugs and Pro 8.5 wires and installed them on Sunday. My truck runs better than ever. I took a 4 hour trip today and it used an eighth of a tank less than it usually does! Thanks again...Craig