I posted this earlier in the forum for 2000 f-150's. I haven't gotten a response so I figured I would copy it here too:

I replaced the heater core in my 2000 f-150 over the weekend. I got it all back together and it works good. I now have a miss in my truck though. It's like a coil pack has went bad or something. I have had to replace a couple of coil packs over the last year so I am hoping that it's just coincedence that one went out right as I was changing the heater core. My question is, is there something that I could have left unhooked under the dash that would cause my truck to start missing a cylinder or something like that? I could see leaving something undone making the truck not start or run. I wouldn't think that leaving something unhooked would make it miss though. Any thoughts?

 

id make sure you got all the grounds tightened up good on the side kick panels. make sure you got the pcm connections tightened up good and that none of the wires are loose going into the back of it or got pushed back into the connector. maybe you hit a pcv valve elbow taking the heater core hose connections..just some advice help it helps..course you could be right about the coils too. check your battery cables that you cant twist them loose.

 

Thanks for the help. I checked the grounds and connections under the kick panels. They all seem ok. I am starting to think it may not be coil packs. I've driven the truck to work for three days now and it still hasn't thrown a code. Any advice on what to check for on the pcv valve? I changed the little elbow and the valve a few months back. Is the tube that runs from there to the engine plastic? It seems stiff. Is it possible that plastic might have cracked or broken? I could look into replacing that whole tube?

 

Well, I pulled the pcv valve off and stuck my finger over the end. It had a good bit of suction coming from it. Can I rule out the pcv tube from that?

I'm really at a loss here. I hate to take it to the dealer and tell him I don't know what is wrong with it. If I tell them that I took the dashboard out and then it started messing up... I might as well walk in the door backwards and bent over.

 

Well, I think I found the problem. I hooked a code reader to it today and it is giving that error about not having run long enough and it's also giving an error about a misfire from cylinder 4. Turns out I was right to start with... I guess. We will see tonight. I'll change it out and let you guys know if it fixes the problem. One more question though. My check engine light never came on. Because it wasn't on, I haven't bothered to check for codes until today. Is that because of the "not running long enough" thing or is there a problem with the light?

 

sometimes with the ford you can have a misfiring coil and it wont set a check engine light. if you have an expensive scantool you can get into mode 6 data test 53 and watch the misfires as they happen. that will cost you a few grand though not available with cheap scanners.if you suspect the number 4 coil you can swap it to another cylinder and clear codes and see if it resets to the cylinder you changed it to.

 

Well, the coil pack was the problem. It's running great now and my heater is working too. Thanks a lot for your advice and help Tim.