Losing spark for brief second at 2800 RPM

DesertDawg

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Aug 24, 2016
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Hi All, I have '93 OMC 7.4L HO with King Cobra (Cone Clutch). Model # 744CPEJVB. It has the Spitfire/EEM ignition system. Earlier this season my boat started to cut out just for a fraction of a second at around 2800 RPM. As if it's losing all spark. When I back off the throttle a little it stops and the more I try to get on the throttle, the more frequent it cuts out. I noticed whenever it happens the voltage meter pegs high and it trips one of the breakers on the exhaust riser. I had the alternator checked and it is fine. I recently changed all the shift cables thinking it might be the shift interrupter, they were all original afterall - not it. I'm thinking it has to do with the ignition system. I tested the coil, it's within spec. I'm wondering if it could be a bad sensor or the module. Which would be more likely to fail, all being original? Is there something else I should try/test? Thanks in advance
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Hi All, I have '93 OMC 7.4L HO with King Cobra (Cone Clutch). Model # 744CPEJVB. It has the Spitfire/EEM ignition system. Earlier this season my boat started to cut out just for a fraction of a second at around 2800 RPM. As if it's losing all spark. When I back off the throttle a little it stops and the more I try to get on the throttle, the more frequent it cuts out. I noticed whenever it happens the voltage meter pegs high and it trips one of the breakers on the exhaust riser. I had the alternator checked and it is fine. I recently changed all the shift cables thinking it might be the shift interrupter, they were all original afterall - not it. I'm thinking it has to do with the ignition system. I tested the coil, it's within spec. I'm wondering if it could be a bad sensor or the module. Which would be more likely to fail, all being original? Is there something else I should try/test? Thanks in advance

Howdy,

Welcome aboard!

Well, I am sorry to say that you have an ignition system that is no longer supported by anyone. The module for that engine is not available from anyone anywhere, I don't think you can buy the crankshaft sensor either (I did find the knock sensor though) .

Now having said that, if you have circuit protection activating(CB popping) , you have a short (to ground) someplace, and/or a poor connection in a ground or crimped wire connection that is coming loose or is severely corroded.

If it were mine, and I wanted to continue running that engine and drive, I would remove the entire ignition system and replace it with an Volvo Penta, MSD, Mercruiser Thunderbolt V or other aftermarket marine ignition system. (although I am not sure how well the shift interrupt switch would interface)

You probably know that OMC went out of business in the late 90's. That particular engine and drive were only produced for a few years and (the drive) is NOT "the same" as a Volvo. Evidently, OMC went all alone with the Spitfire ignition system as the ECM's weren't common to any of the Volvos that followed and very few OMC parts are left.

Sorry about that,

Regards,


Rick
 

DesertDawg

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Joined
Aug 24, 2016
Messages
2
Thanks for the fast reply Rick.

I am very familiar with the availability (or lack there of) of parts, support or knowledge of my powertrain. Unfortunately, I only learned all this after buying my boat.

Luckily though the engine and the drive are both operating great, with the exception of this issue, so I will be changing the ignition system. Does anyone happen to have part numbers for a system that will cross over and work? I'm waiting to hear back from a local marine shop that told me they have switched similar setups to an ACDelco system. Any thoughts on that?

John
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Hi John,

I haven't done that Delco [Est?] distributor but many here have and I hear it's a good one. My experience was removing the points type dist from my previous (87 OMC 460 KC) engine to go on a 90 460 with a Spitfire that also failed.

I seem to remember that he didn't connect the interrupt, but it did work long enough to use the rest of the Summer. And then he sold it I think.

I don't know how well shifting works with the interim cone clutch drive without torque interrupt.

Can't do that with a dog-clutch. They won't come out of gear at all without torque interrupt if coming out is not tension on the lower shift cable. (You can pull pretty hard on a cable. But you can only push so hard on a jacketed cable)

If you really like the boat, you're not all that far away from a swap to a Mercruiser or a Volvo. I replaced my previous 87 460 King with a 97 Mercruiser 7.4+ Bravo III

You could use you engine. Your drive is actually pretty valuable and there's a guy here on iboats with twin 93's I think that needs a transom!

I sold all my Cobra stuff including the engine for about $3600 over a 3 or 4 year period on Craigslist eBay, word of mouth etc.

I am sure you know all this! In the mean time, I think switching over to an EST or other distributor ignition system will get you going again. Be careful with the timing though. I am not sure if it will interface with the knock sensor. you may have to retard the timing a tad to prevent pinging.

Take some pictures!

We all love pictures here!


Cheers,


Rick
 
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