Stumble and Backfire during accel

Most likely the thing that hasn't changed is the engine manual, The specs for the basic Ford and Chevy motors was basically the same for a long time so they didn't update the manual for many years. The additions were usually just an added section so the 83 manual looks pretty much the same as the 93.

If you search engine rotation there is a thread that has all the PLR/PLL ect broken down. I keep a pic of my tag on my phone so I can remember what spins which direction so I don't have to guess at it when I'm not around the boat.

Go to the reference section , click on manuals, page down to the bottom, find PCM service manual page 4 has the code break down.

Ah HA! Beautiful! Thanks very much. Page 4 of the service manual does indeed have the model number decoded.

I had written down "PLP", but that page does not indicate that "P" is one of the options for that third space. Maybe I misread my engine badge, and the character is really a "D". I'll check the next time up at the boat.

Meanwhile, however, my gear ratio code is definitely a 12, which is, strangely, not one of the options listed in the service manual. So I wonder what my gear ratio really is (not that I need to know).

The missing gear ratio code makes me wonder whether my "PLP" really is a "PLP" after all, and the "P" horsepower code exists, but is also missing from the manual. Again, I'll double check the model number next time I'm at the boat.

I can't find a date on that service manual.

Thanks. I'll try that. I thought about trickling a bit of water onto it, but was afraid the temperature differential might cause it to crack.

Why brake cleaner?

When I was having troubles with my '85s coil I used a wet rag with ice wrapped in it.

It's been a few weeks since I last made an entry here. Since then, I have NOT, in fact, replaced the coil. Rightly or wrongly, my mechanic talked me out of it, saying that the coil isn't getting hot enough to be the problem. Meanwhile, the severity of the problem has diminished substantially. There is still some occasional hesitation, but that's all.

What's changed? When I put the boat away, I now prop the engine cover open a bit to let the engine have a bit more ventilation. I also leave a bucket of moisture absorbent on the cockpit sole next to the engine.

I also find that, when the engine acts up, I open the engine cover for a minute or two, to let it either cool down or dry out (or something, I'm not sure what), and then it runs fine for a while until I have to do this again.

I've also noticed that, when the engine is hesitating, the tachometer bounces around quite a bit.

All this suggests to me that moisture is causing a problem somewhere in the portion of the electrical system that's under the engine cover. But where exactly? I find it hard to believe that the problem is with a connection. I've checked the connections under the engine cover, and they all seem fine.

Any more ideas?

When I experience the hesitation, I stop the boat, open the engine cover, and put my finger on the coil. It's hot to the touch, but not so much that I can't keep my finger on it for five seconds or so. This, according to my local mechanic, strongly indicates that the coil is fine.

You disagree?

When a coil fails, usually the insulation on the windings starts to break down, which is accelerated by heat (expansion). So it would make sense thst the tach would be affected since the coil resistance would change as it starts to short out.