PCM Firing Order

[James Evans]

Picked up cheap, runs a tad rough.

PCM 351 with 1:23 Ratio Tranny. I am unsure on the rotation. Its in a 1992 boat.

What is the firing order on this thing? Think the plug wires may be on incorrectly.

[UKandH]

1-3-7-2-6-5-4-8

[James Evans]

1-3-7-2-6-5-4-8 is what is on the engine tag, however it will barely run in this configuration. It runs smooth as butter on the old 302 firing order of 1-5-4-2-6-3-7-8. It was wired 1-3-7 as the tag says, and the number 4 plug wire was unhooked laying in the bilge. Hooked it up and tried to run it on a bucket, but it would barely run. Tried the old 1-5-4 and she fired instantly and purred like a kitten. Either someone has replaced the original motor with a 302, or someone has put a 302 cam in it.1.jpg2.jpg

[UKandH]

Or be optimistic and hope you have the 460 and not the 302

Definitely something wrong there then, even the reverse rotation engine has 1-8-4-5-6-2-7-3

[James Evans]

If I put it as the tag says it pops and wont run unless I open the throttle up some. The old 302 firing order, she fires right up and idles like a sewing machine, and is very snappy on the throttle with no hesitation. Now this is running on a bucket in the driveway.

[chris young]

If you want to be sure, you can grab a vacuum/compression gauge and find TDC for each piston. I know it's a bit of fiddling around but it's the only way I can think of to be sure.

[SquamInboards]

There's definitely been some tinkerin' in that engine bay. Is that an inline fuel pressure gauge? I think the valve covers have been painted, which, on its own is no big deal. But then, the coil looks like it's just sitting there, loose. And that sweet chrome flame arrestor... I'm liking your theory of a 302 being in there with all the original accessories bolted on. And hey, if the thing runs well? Great!

I believe that the 351 has a 3.5" stroke, while a 302 has a 3" stroke. Something like that, anyway. So you could take the plugs out and turn the engine over very slowly by hand, and put something like a long screwdriver very carefully down a cylinder to measure the stroke. Maybe that's a bad idea, I don't know, just a thought.

[mjdean]

James, you may already know this but it threw me on my pcm. The cylinders are 1,2,3,4 on one side and 5,6,7,8 on the other.

[James Evans]

Yeah its a fuel pressure gauge you see. The coil is bolted down. But I have also noticed there isn't a resister anywhere in the wire going to it. I even removed the cover over the starter relay, and there was nothing there. May need to source one to keep from having issues, as it still has points.

I know the stb side is 1,2,3,4 and the port side is 5,6,7,8. I may try the screwdriver/dowel trick to verify what I have.

I do know it runs like a scalded dog!

[SquamInboards]

I am really curious on the identification of the engine, but hey - it runs, don't "fix it" right?

As someone who put the wires on in reverse order after a complete engine rebuild, I have felt the frustration of tracing and re-tracing plug wires, only to then witness the magic of putting them on RIGHT and wow, it runs perfect now!