I have an 87' F600 with a 370...

Starting today (drove about 200 miles) it randomly will miss and loose power and then after anywhere from a few seconds or a few minutes it will go back to running normal. There is no in-between, it's either running great or missing really bad. This happened about a dozen times today on the highway doing about 2500 rpm... however it only did It while I was loaded (7 ton). It ran fine the whole way home empty. I couldn't find any consistency in the length of time it would act up or when it would start... but it was like someone flipped a switch.

When I got home I put a timing light on a few of the plug wires and they seem to spark intermittently even when it seems to be running well.

Any ideas? When it comes to this electrical crap I'm lost... but I feel like it has to be something like the coil or computer on the fender. Seems like if it were distributer or wire related it would do it all the time?

The truck has a brand new jasper motor with less than 1000 miles... has new plugs, wires, and the distributer seems to be fine and was replaced last year (before the new motor).

Thanks in advance...

 

Is the coil really hot when this happens?
Like too hot to touch for more than a second?
If not, the coil is okay.

If the engine has a new distributor (and pickup) I would definitely say these are all the symptoms of a failing DuraSpark ignition module.

The module can be replaced in a couple of minutes.
Two electrical plugs and three screws holding it in place.

You can find anything from an AutoZone $35 cheapie to a $100+ genuine Motorcraft part.
I have a NAPA Echlin module in my truck now and it has been trouble free, so far.

 

Thanks for the reply,

Yesterday after work I replaced the coil, distributer, cap, and ICM. It all only cost me about $80-$90 at advance-auto. Since it's not something I could diagnose very easily I figured I'd replace all the "suspects".

My next delivery is on Thursday so I'll find out then...

Austin