I recently bought a 85 f150 302 FI, at least that's what the data plate and the VIN says. I was doing some tune up on the truck and bought spark plugs (motorcraft ASF32C.)
The data plate on the truck said this was what went with the motor same with searches at the auto parts store. Tried installing them and they won't fit. I checked the part number on the old spark plugs and they were autolite AP104.
From my searches it looks like that's a plug for a ford 4.6, and that they are not for a 302. Am I wrong, and is it possible someone did an engine swap and kept the old intake? This is my first ford and I have no clue how to tell the difference between the different ford v8s. Any help would be awesome, thanks!

 

Shoot a pic and post it here. We might be able to tell the difference, especially since I doubt they put the FI system on the 4.6L.

 

There's no way to confuse a 4.6 and 5.0. The 4.6 has plugs in the top of the head, with 8 individual coils (no dist), while the 5.0 has the plugs down by the exhaust manifolds, and has plug wires coming from the dist.

 

Aftermarket heads?

 

Why do you say they didn't fit?

The ASF32C has a 5/8" hex, 14mm thread, with a .460" reach;
the AP104 has a 5/8" hex, 14mm thread, with a .708" reach.

So the main difference is the reach (how long the threads are - or how far the plug reaches into the head).

So why didn't it fit. either plug should have threaded right in as they are the same size threads. BTW- the reach is important. Too short, and the electrode won't protrude into the head (so the spark will be up in the head/threads), too long and carbon will build up on the exposed threads and you will/may strip the threads trying to get it back out later (and it could hit the piston).

 

Heres the pics of the motor.

 

That what I figured, I wasn't sure but I didn't think the old FI system would work for a motor that would have a more modern ignition system.

Not sure if they're aftermarket they don't quite match the wear on the motor so they might be.

I believe they're not long enough, it seems like they might be bottoming out before in can thread anything in. Exactly, that's what I'm a little worried about is if the last guy who owned it screwed up the motor putting the wrong plugs in.

 

It looks like a stock 5.0L (302) to me. If the heads were changed at some point, my bet is they went back with stock. The engine doesn't show the external modifications that someone would be expected to do if they were putting on a set of performance heads (like upgrading the air intake).

I think the last guy installed the wrong plugs.

You may want to run a "thread chaser" to clean up the threads. Perhaps there is carbon build up making the plugs thread in hard.

You could check the plug reach with a bent piece of wire. Insert it into the cylinder and then catch the back side of the threads. mark the outside of the wire where the threads start, then remove the wire and measure from your mark to the bend. If you do this be sure to use a long piece wire (like mechanics wire) so if you drop it, it doesn't end up in the cylinder where you can't retrieve.

 

Aright, I'll give that a shot when I get a chance. Glad its still the 302 that's the one thing that sold me on the truck.

 

Was doing some looking around and it looks like the gt40 heads use the same plugs, just wanted to double check if I'm right. If they do is it possible the old owner took some used heads and put them on there and is there a way to tell the difference between the original heads that would've been on and the gt40 heads?

 

Ford, with their infinite wisdom, put the head ID's for the run-of-the-mill heads where they are only visible when off. Seems to me the GT40 heads have markings on the end to ID them. You can do some Googling to find out. (Hint, hint)

 

Yea I did a little digging and it looks like there are 3 vertical bars on the end of the gt40 heads

 

That fits with what I remember. But, I didn't think all the GT40's had the bars. There was something different about some of them.

 

Maybe a "quick and dirty" check would be to determine the plug reach as discussed a few posts back. Based on the plug research you did, the GT40 heads have a plug reach of almost 3/4" where the stock heads have a reach of under 1/2". It shouldn't be too determine to see what "plug reach" your heads have.

 

Aright, I'll try that wire check and try poppin off the valve covers to see what's stamped on the heads