03 5.4 2x4 lariat, 140k. have a hard miss. Took it to dealership who said it was a loose timing chain, and I should replace engine. Took it to different shop who also said it had a loose chain, but the said if it was a chain it would happen all the time. They replaced the cam position sensor because that was the code. Changed all the plugs, cleaned the IAC, throttle body. still the hard miss and hesitation. Parked it for a couple of weeks. When I started driving it no misses. After the fifth drive it started to have more of a hesitation then a hard miss. Changed all the cops, and fuel filter. no moisture in cop's but 1st and 3rd on passenger side had rust color on boots, so I am guessing they had water in them at some point. Ran great for one day. started missing again. code said cam position sensor. found hole in the 90 of the egr hose. Fixed that, ran great until I put it through car wash and started missing again with no code. Drove in rain today and it started the hard miss and hesitation. SES light on, have not been able to put it on code reader yet. It will run fine for a few miles, then miss, fine for a few more miles and then miss and hesitation. Help please

 

I would first nail down what cylinder it is misfiring on. If it is misfiring on multiple, random, cylinder's it probably isn't water intrusion on any of the COP's. If you are able to nail down a which cylinder(s) is/are misfiring, then you have a place to start. If it is water intrusion, I would try and track down how it is getting in. Inner fender well? Back of the hood? However, I think that would be unlikely.

If I were trying to diagnose this I would first find find out where it is misfiring. I'd then prove out fuel, spark and air. If I have those, I would do a cylinder leak down and/or compression test. I would think a loose timing chain would show it's ugly head on a leak down test. If it is random cylinder's, your compression and leak down come back good, then it is time to start looking at connectors and splices for intrusion/corrosion. That is when the real fun starts.

My $.02

 

Thanks for advice. if it was fuel, spark or air would it do it all the time? I am a newbie, so the fuel test you speak of is the pressure test you do on the fuel rail? I am telling you I can run for miles with it running so smooth. I guess there could be something in the tank that temp blocks the pick-up, but I am not sure how to test for that. Everytime it has thrown a code it has been cam position sensor,(replaced twice) so that would be a good place to start looking for connectors and intrusion/corrosion. I wonder if the wire from the cps goes straight to the pcm where i could just run a new connection. Next week my buddy said he is going to let me drive around with his computer scanner to see if it can capture anything.

 

My 2000 150 had a coil pack that was bad and would work fine for a while then not at all for 2 or3 days. I had it down to the dealer and they had it happen to them the second time I took it in. Took it to my Ford dealer and had the coil packs and plugs changed and one way in the back was messed up and this fixed my issue cost me a chunk of change but it was worth it. May want to look at the coil packs and see if they have been changed or not.

 

Plugs and coil packs changed,

 

SORRY, thought it may help It has me dumb founded at this point some of the other FTE members can hopefully help. I will talk with my brother he is a grease monkey and knows quite abit about these trucks.

 

Did you buy OEM coil packs? I have heard a lot of bad things about the cheapo coils you get online...

 

Yes on OEM for plugs and coils. The wire going into the cam posistion sensor has electrical tape right after the plug. Is this normal? Maybe a splice job gone bad. Will keep you all posted.