470 missing at speed

[achris]

Most of Ted's problem have been things other than the MPI, like old kill switches, broke/corroded wires etc. The MPI and its associated parts are pretty reliable. I think he's had to replace an IAC, and that's about all... BTW, I have also had an IAC fail. Quick (and cheap) fix....Against the cost of annual points, plugs, rotor, capacitor etc, my single failed IAC (in 13 years) is still much cheaper. Add the better fuel efficiency and I'm a long way ahead. Oh, and in 13 years, I'd have had to strip and rebuild/clean out a carb a couple of times. So yeah, love my MPI...

Chris...

 

[Scott Danforth]

It's a Mallory electronic ignition. Uses original externally ballast coil. The Napa coil is ic12sb, which Google tells me should work...

i have had 3 of the mallory trigger ICM's fail over the years. one lasted about 3 years and was killed when the ballast resistor went bad and I bypassed it, one lasted about 2 years, and the last one that failed was literally 3 hours.. I now keep one in the boat at all times now along with a spare cap and rotor.

if your 3 coils in a row are bad, they were murdered by something.

would you have the specs on the Napa coil, their website doesnt list anything.

the module must see full 12 volts, the coil must only see the 9-10 volts after the ballast

the coil for the mallory YLM series of distributors and the conversions are the same you would run with points. 1.5 ohm primary.

 

[stonyloam]

Do a compression check.

 

[nola mike]

Do a compression check.

I did, results earlier in the thread. Picked up another coil, and though I couldn't find the specs, Napa lists the 3.0 and 3.7 engines as compatible. Too windy today to try again, hopefully this evening or tomorrow am.
scott Danforth, my module is powered by the post ballast voltage...

 

[nola mike]

New coil, 7 miles out at 3400rpm/32 mph, running perfect. Now victory beer. 'murica. (Actually, my temp gauge suddenly isn't working and the choke on my rebuilt carb isn't closing, but willw worry about those tomorrow).

 

[achris]

How do I subscribe to this post? I have similar problem.

 

[nola mike]

Ok, well,
had been running great since the 2nd coil change. Today took it on a big boy trip- 50 miles with a full load, 5 adults 5 kids. Ran great. Hit a bar, then started acting up about s mile after leaving. Throttled down and put the timing light on. Started missing again, but at least on #1 it looked fine. Full boat +wanting to get home, didn't troubleshoot too much. But then I came back up with the throttle and it was fine for the remaining 15 miles home. Wasn't babying it. 3500 rpm, 32 mph with a full load. Only thing running a bit low on gas and a bit rough water, maybe some crud got kicked up. Will check filters tomorrow, but pretty disconcerting...

 

[salty3rd]

Sounds like success to me. I don’t post much any more since I switched to an MPI so I agree they are a lot more reliable. I will say that again and again I read posts like this and people are always told it’s not the coil, when a lot of times it is. Being extremely familiar with the 470/ 170, i always carried a spare coil and It would have been one of the first things I would have swapped out as it’s a 10 minute job.

 

[nola mike]

Water separator looked pretty clean, maybe a few drops of water but very little. Guess I just cross my fingers and keep boating...

 

[nola mike]

Ok, happened again. This time went about 8 miles, docked for a while, and it again started soon after leaving the dock. This time I throttled down a bit but didn't come off plane. It lasted about 30 seconds or so, and then went away. Drove it back the remaining 5 miles at 3500 rpm, brief runs to 4k without recurrence. Next day went another 5 miles with a couple of WOT runs. Aside from running a bit slow (44 mph at 4500 rpm), it was fine. Any suggestions on how to proceed?

Filters are clean, but could I still be getting some junk to the carb? If so, would you expect it to go away like that?

Is it worth siphoning the bottom of the tank?

Could I have something getting sucked up against the pickup intermittently?

 

[Scott06]

Don't think it's fuel if it goes away like this. To me sounds like something is wonky (yes it's a technical term) with sensor in distributor or ignition module.

Very similar symptoms to a VW fox I had years ago -was eating coils, very intermittent lose of power and bucking, would be days or months in between issues. Ultimately was able to give it to a mechanic who drove it three weeks and when it acted up put an ocilliscope on it and saw coil out put was low... but had a new coil .... ultmimately he reccomended replacing the Hall effect sensor (in distributor) and ignition module ...$100 of junkyard parts ... never had the issue again. Also never bought a VW again.

Your symptoms sound too similar... was a painful experince for me due to intermittent nature and no error codes.

 

[nola mike]

Last time out when I had the timing light on it it wasn't missing (at least on #1). I think that rules out the hall sensor and module. Possible that I'm having an occasional miss on another cylinder due to something else. I'll move the light around to the other cylinders if it happens again. When the coil was acting up I saw it on all cylinders.

 

[nola mike]

Just as an update (since I like reading others' updates), 250 miles since the last post, no recurrence. Guess I just angered (and then appeased) the boating gods. Damn, just jinxed myself for this weekend...