I have an '89 F150 4x4 with a 5.0. Lately it's developed a random miss when under load with a loss of power. It runs smoothly when cruising at highway speed, but when I reach a hill, or when I need to accelerate it starts to miss and looses power. It has less than 5,000 on a tune-up (cap, plugs, rotor and wires) and I checked the timing and it's still at 10 BTC. Yesterday, since I had a spare coil laying around, I switch that out too and there's no difference.

What would be the next most likely reason(s)?

 

What brand tune up parts did you use? I've seen a lot of plug wires fail in no time.

 

Vaccuum leak?

 

I got decent quality from a local independent parts store, but I went ahead and followed your advice anyway. They are within spec according the information that I found on this thread...https://www.ford-trucks.com/forums/2...e-testing.html

 

Since my last post, I've checked all of the vacuum lines, the fuel pressure, etc. without finding any problems. I finally decided to go back to the plug wires and take a closer look. Even though the ohms tested ok, I found where 7 and 8 were arcing near the dist. cap. I found a good diagram here ( 1983 Ford Bronco TSBs & FSAs (Recalls) for '83-96 Broncos & F150s pictures, videos, and sounds | SuperMotors.net ) along with a ton of other useful information about my truck and installed a new set of MSD's. The thing runs great now.

Thanks for the help, bashby!

Here's the diagram...