Ignition help '88 OMC 5.0L

Droopy

Seaman Apprentice
Joined
May 9, 2010
Messages
31
Hey guys,

I'm running out of ideas. Boat is a '88 Bayliner Capri 2150 with an OMC 5.0L in it. It has an aftermarket Mallory Unilite electronic ignition and has been running fine.

Last time out I trolled for a LONG time at idle. Right up to the dock, so never blew the crap off the plugs before pulling out.

Went out again and the engine wouldn't start. Occasionally it would "hit" while turning over, but never more than a single hit.

Took it back home figuring that the plugs were fouled. Pulled each plug, cleaned it (wet and slightly fouled), regapped, and reinstalled. Did them one at a time to make sure I didn't reinstall wires in the wrong order.

No change. Disconnected and ohm'd the Mallory Promaster coil (24990) and it ohm'd out close to the specs (I could wiggle the probes enough to make it go above and below the spec'd ohms by just a couple. Is that close enough?) Think it was 600 +/- 50 on the primary, and 24K or something on the secondary... Anyway, I *think* based on that the coil is fine.

I've got good voltage at the positive and negative coil terminals.

Ohm'd out the plug wires and they are all good. Tested the electronic ignition module per Mallory instructions and the voltages and operation were good. (Cleaned the optics out real carefully)

Visually inspected the cap and rotor. Nothing obvious.

Checked the engine kill switch. It appears to have failed open. Great, I think! Found the problem. Bypass the switch. Still no change... Grr...

With my timing light on any of the wires, I'm rarely sensing a spark. (Even on the wire from the coil).

I hate throwing parts at a problem before I figure out what's wrong. I'm kinda out of ideas and am thinking maybe a new cap and rotor might be the next step.

Ideas?

Thanks,

John
 

shimano

Petty Officer 2nd Class
Joined
Jul 26, 2008
Messages
132
Re: Ignition help '88 OMC 5.0L

I have a 89 3 litre,this happened to me fishing trolled ,for half the day and when I went to head to the dock she quit and would not start(fouled plugs)Cleaning the plugs did not help me ,I had to replace them.Problem for me was a dirty spark arrester(making it run rich)Cleaned it out with brakleens,Havent had that problem since.
 

Droopy

Seaman Apprentice
Joined
May 9, 2010
Messages
31
Re: Ignition help '88 OMC 5.0L

Shimano,

Next time you're in Vegas, let me know. I owe you a beer.

Just gapped and installed 8 new plugs and she fired up on the first spin...

Anyone know what we did to our plugs that killed them idling that long?

Happy New Years,

John
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,956
Re: Ignition help '88 OMC 5.0L

Anyone know what we did to our plugs that killed them idling that long?

Ayuh,.... Gas fouled plugs are Dead plugs,...

Fix yer carb so it don't happen again,...
It's obviously runnin' to rich...
 

HorizonblueDK

Petty Officer 1st Class
Joined
May 27, 2010
Messages
355
Re: Ignition help '88 OMC 5.0L

Ayuh,.... Gas fouled plugs are Dead plugs,...

Fix yer carb so it don't happen again,...
It's obviously runnin' to rich...

That's one of the reasons why I like EFI engines; they can idle the whole day, and when you suddenly hit the throttle, they don't stall.
 

Droopy

Seaman Apprentice
Joined
May 9, 2010
Messages
31
Re: Ignition help '88 OMC 5.0L

Thanks again for the replies. I went and adjusted the idle mixture on my recently rebuilt Quadrajet. For some reason, I thought it was adjusted by the rebuilder, but thinking about it, how the heck would they do that without my motor... And yeah, it was really rich.

Went fishing the other day, trolled for about 4 hours, and when I gunned it afterwards, no hesitation at all...

John
 

shimano

Petty Officer 2nd Class
Joined
Jul 26, 2008
Messages
132
Re: Ignition help '88 OMC 5.0L

That's great .But did ya catch any fish??
 
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