I own a 1986 f-150 with a 1969 429 engine convered to a 460. It has DOVE ported heads and Motorsport roller rockers Cam Dynamics cam and kit, Edelbrock Performer manifold and 750 carb with Doug Thorley tri-y headers. It has a Heavy duty C6 with shift kit behind it and the 9" with 3:55 gears. I feed it 91 or 92 octane Chevron and it really is a strong runner. It started acting up on me a couple of months ago missing so I went through the lifters and reset the clearance. I have new Belden wires on her new Autolite AP45 Platinum plugs set at .044" new glass fuel filter right behind the carb so I can see it, a Carter electric pump that measures 5.5 psi at the carb. I have been through the electronics with a new Wells ICM(this is a DSII factory setup)yellow grommet, new internal resistor coil, and I have cleaned the connectors and put dielectric grease in all of the plug-ins after cleaning them. I am about at my wits end with it. It starts fine runs fine, but you can hear it missing at a low speed around town and you can hear it and feel it missing out on the hiway . Sorry to make this such a long blog, but I wanted to let you know what I have done to it up to now.
I also put a new ignition switch on the column awhile back as it was acting up on me.
So please someone tell me what else to look for. The old autolite plugs I had were the copper plugs and they looked great with no visible defects on them and the insulators were clean as could be.
I live in Winslow AZ so there isn't any place around here that sells any higher octane fuel than the 91-92 that I get. My timing is set at 12 initial with my vacuum advance of another 8degrees and my dist. total at 36degrees all in at 3200 rpm.
Thanks for reading this and hope to hear from some of you Ford Gurus out there. Bud in AZ

 

First I would look for a lean carb issue (vacuum leak). Spray some carb cleaner around the intake mainfold gaskets and carb base and see if the idle speed changes.
How many miles on the engine since the build?
What Camshaft (specs) is in it?

 

Hi Bud,

A couple of observations;

Yellow grommet is altitude compensated.
Finicky sensors and a fairly obscure module to find.
Do you need it???

Go back to the copper plugs.
They're cheap and don't cause issues.