Plug gap on a 78 F150

Justaguy · 12-01-2010, 09:39 AM

My boss has a 78 F150 with a 300 I6. In all of his shop manuals the tune-up specs are said to be located under the hood, and are not in the book. Well the problem is the truck is 32 years old and a lot of the pieces under the hood have been replaced. He has no tune-up specs. He is unsure what to set his spark plug gap to. I suggested .035 because thats where I used to set them on my 67 about 15 years ago, and he sets them at .054.

Does anyone have the specs that they would be willing to share with me? I would appreciate the help. It would also help with getting a good review a little later.

Thanks

Zephyrman · 12-01-2010, 10:05 AM

Spark plug gap on a 300 six should be no more than .040 and no less than .035. Setting them at .054 is way too much, you won't get a complete burn and fuel economy will suffer, plugs will likely foul and I imagine drivability will suck too.

Dominick · 12-01-2010, 10:07 AM

Gap is 54 except California Heavy duty which is 44
054 (In thousandths of an inch)

Caution! Gap is not adjustable on certain plug brands

Zephyrman · 12-01-2010, 06:50 PM

I had an 80 Bronco with the 300 and the sticker under the hood said .035 to .040 plug gap, you sure that's right Dom? Or did something change from 78 to 80?

Justaguy · 12-01-2010, 07:44 PM

I've always set that era truck plugs to 035. Dom, where did you find that?

Dominick · 12-01-2010, 08:34 PM

That's what I thought also.
I found that Info at autozone their info may be wrong but i searched tune-up.

Dominick · 12-01-2010, 08:36 PM

That's what I thought also.
I found that Info at autozone their info may be wrong but i searched tune-up

Stymees'mont · 12-01-2010, 09:02 PM

usually .044 is correct.

Justaguy · 12-01-2010, 11:41 PM

I went to wikiask, and found that in 78 motorcraft recommends .054 for their plugs in the 300 with the exception of california they are set at .044.

So thanks for your responses fellas. I would like to know why they recommend a smaller gap for california, and again in later years cuz in 96 their plug gap for a 300 calls for .044.

Thats what I found.

c-ya I gots to go to work now, b back in the am.

Zephyrman · 12-02-2010, 02:31 PM

Crazy, that gap seems way huge to me, but if that's what Motorcraft specs out to, then I guess that's what it is. learned something new today I suppose.