I have a 1997 5.4 and the engine started missing only when the air conditioning is on. The truck had about 80,000 mi when this started. I took it to the ford dealer and they charged me $75.00 only to tell me that they could find nothing wrong. It still missed only when th a/c is on. When the truck had 100,000 mi. I took it back and had new plugs installed along with air filter and pcv valve.It still misses when the a/c is on. I'm begining to think that it maybe something to do with the vacum. Does anybody have an answer?

 

I was just going to say it sounds like a major vacuum leak in the a/c. It could also be the a/c clutch slipping, BUT that shouldn't be too hard to determine.

Does it miss at idle with the a/c on? If so, all you gotta do is watch the a/c clutch plate to see if it's slipping, although I've never heard of this feeling like the engine is missing. It's a long shot, but worth a look see.

 

Thanks for the come back it doesn't miss at idle as best I can tell.You can really feel it at 50 to 60 mph when under load or increasing speed.

 

Hey janvan,
Mine had the same symptoms but the belt was also squealing pretty bad. I got the dealer to replace the belt and tensioner,and it went away. Well the belt squealed and was replaced two more times. On the last time it would have this vibration/buzzing noise when I accelerated. I crawled under suspecting the trouble and I was right. Loose a/c mounting bolts. Haven't heard a peep out of the belt or a/c since. I'm not saying this is it,but it could be. Cheap fix to check though

 

Janvan,
If what 98screamer says is true about the belt-tensioner pulley, your miss could possibly be caused by the knock sensor. However it should have thrown a code, therefore your MIL light should be on (Check Engine). By the way, is it missing after warm up or all the time. Might want to have the converter (s) looked at.
BJ