Well i put a new cap and rotor on my 97 f350 sunday and took it around the block and everything seemed fine,but monday it rained all day and when i took it out i noticed that it was missing.It would take off fine and accelerate fine but cruising 55mph or above it began to miss badly,so i figured it just got wet but when I got home i pulled the cap and everything was dry,so I began to trouble shoot.I found that number 6 the plug was loose to i pulled that and the plug was white so i put it back it and put on my old cap and went around the block and same result so I put the new cap back on checked my wires etc and went around the block and noticed the engine was spark knocking badly and had no power or torque so i got home pulled the cap and it was covered in black soot or carbon or whatever.So I guess my question is did I get some bad gas and it just happens to be a coincidence that I happened to change my cap when this happened or could my distributor still be wet?I'm hoping it's just bad gas but i'm gonna pull the plugs tomorrow when she cools off.Thanks for any input as this is getting me frustrated

 

I doubt bad gas is the cause of the problem.

The fact that you had black carbon build up under the cap so quickly is the result of a short- and it's either in the new cap or rotor. Take them both back to the parts store and exchange them- then install them and see what happens. It's rare but not unheard of for a new cap or rotor to be defective.

Make sure that the cap is sitting squarely on the mounting base. Sometimes they can be tricky and not be squarely mounted but look and feel like they are.

 

Check wiring around the cap and plugs as well - I have FHS (fat hand syndrome) and have been known to dislodge wires, vacuum hoses, and all kinds of other stuff when working on unrelated systems

Probably what DB says, you're the lucky guy who got the cap and rotor that slipped through Q/A at the factory.....

 

Check the plug wires too to see if one is arching out.

 

did you put the wires on in the correct 351 order?

 

Yes I do have the correct order.I put the old cap and rotor on and it is still running the same.It idles fine no miss or nothing but under load it has a terrible shudder.What about a weak coil.Wires are fine to.

 

Weak coil could be a contributing problem but not likely the primary. Now if your coil was putting out too much voltage, that might be another story.

Try replacing the cap and rotor again and see what happens- keep us updated.

And BKS72- how big is that catfish? 40-50 pounder?

 

85 He's from last year, 75 was big fish this year. Rod and reel, all catch and release - I'm just in it to see how big of one I can catch. I pretty much live on the river during the summer when I'm not working.

97FRD, check your timing. Any chance you knocked the dizzy around when you were working on it?

I'm not a big believer in coincidences - if the only thing that changed between it running well and now not running well was the tune up, then I'd bet it's either bad parts or something got bumped/broke/loosened during the tune up. Just a thought.

 

If the wires are old, maybe during the process of replacing the cap and rotor one or more of them now has a bad connection inside.

 

man i hope not damn 60 dollar ford motorsports wires but i guess it's worth a try

 

I'd replace the cap and rotor first as others have said but I bet it's the wires. Go with the more expensive Ford type. I had two brand new NAPA Beldon wires sets not be able to handle the juice, missed in the rain, rough idle, glowed blue in the dark etc.- drove me nuts. Many in this forum said repeatedly to change the wires to Ford but I resisted (no pun intended). As soon as the wires were changed- presto. Ford wire composition is noticibly diffferent - and they just work - bottom line. It's been over a year with no ignition problem irregardless of the weather.

 

When you say Ford Motorsports wires, do you mean the 9mm Ford Racing wires? I have had them on my truck for years. I have replaced them a time or two, but never had any issues with them. How old are your wires?

 

yeah mine are the 9mm wires too.I have had them roughly 2 to 3 years,visibly i can't see anything wrong and i popped the hood at night just to see if i could see anything arcing and nothing.I haven't touched the damn thing since thursday so i might mess with it tomorrow.Thanks everybody for your input though

 

Did you route your wires correctly to prevent cross sparking in the harness? 351s and 302s are very picky on how you route the wires on both cylinder banks. In particular 7 and 8 can not be near one another, 5 and 6 should not be as well.

https://www.ford-trucks.com/forums/6...e-routing.html

 

If those wires are only 2-3 years old, they probably are not the problem. However, what alxsnmr said could be the problem.