Found the problem..now how do I test it ???

[country cadillac 48]

My 1979 70hp Merc..serial #5352752 # 3 cyl. is not firing and I'm guessing is the problem I've been having with lack of power getting to wot . Once it does start firing, after lugging around for 10 minutes, it runs fine. Could someone tell me how to test the coil and or power pack, or direct me to the thread that must be in here somewhere. I know I'm not he first guy with this problem........thanks again guys.........Ray

 

[country cadillac 48]

Re: Found the problem..now how do I test it ???

Laddies..thanks for the reply.....It's got to be tough dealing with all of us out here that don't know the names of all the parts and what they do.....like DVA, inductive tachometer, triggering circuit, to name a couple...sure shows how limited I am.....anyway mine runs on two cylinders at idle, then after a while and some cussin' it will pop a few times as I lug along and take off and run good the rest of the day, but not always. Today I started it on the muffs and it was on two cyl. so I took my timing light and found no spark on #3 cyl. I disconnected the the plug wire and tested the resistance and it checked out fine. Put it back on and it started up on all three cyl. The plug wires seem to be the original set, so I'm guessing that it might be a good idea to replace them or is that a sign of some other issue....what do ya think ?

 

[country cadillac 48]

Re: Found the problem..now how do I test it ???

OK...that I will do and thanks ......hopefully things will get straighten out before the LCI this weekend..............Ray

 

[ajgraz]

Re: Found the problem..now how do I test it ???

I have the same motor. I see in another thread your compression looks pretty good, so I agree that DVA checks on ignition components are the place to go next. I use this device on a basic Harbor Freight DVM:
ESI 640 Electronic Specialties 640 DVA Adapter

But let me ask, do you see any sign of water intrusion into the #3 cylinder (say, emulsified oily/watery wet fouling on the plug, or corrosion on the firing end)? Do you get a lot of nasty snotty-looking exhaust junk out the thru-prop exhaust? Is this something that just suddenly began, or have you had progressing issues with it (like over time, getting harder and harder to start, lugs more and more, etc.)?

Has this motor seen a lot of saltwater running? I see in another post that your rear water jacket is leaking, indicative of corrosion inside the water jackets. There is a baffle between the exhaust and the water jacket on the port side of the engine that, once it corrodes through (and it will eventually, far faster in salt), puts water into #3 cylinder. Ask me and my replacement powerhead how I know all this :grumpy:

 

[country cadillac 48]

Re: Found the problem..now how do I test it ???

ajgraz.....all the plugs look the same, not fouled, no corrosion,no bad looking exhaust junk and no, this motor has never been in saltwater. This started at the very end of last year and never really got any worse. After I found a cracked fitting on the fuel tank and with the new merc primer ball that seemed to take care of the lack of fuel problem. And now it seems there's this intermittent spark to #3 cyl which may just be as usual, operator error in reconnecting plug wires after inspection and testing, but not positive on that one yet. I'll need to test the #3 coil and I guess I'll swap it with one of the others and see what happens. This morning I'll be putting on the new cover gasket. My local merc repair shop said I should use permatex avaition form a gasket...does that sound right ? I really appreciate the help and hopefully this tower of mine will be running as it should be soon....................Ray

 

[ajgraz]

Re: Found the problem..now how do I test it ???

Good news on the no saltwater running, no water on plugs.

When I replaced my powerhead, I used the Permatex aviation form a gasket (brown goo in a jar with brush in lid) on all the powerhead gaskets that are part of the cooling jacket system, thin coat on both sides and let it tack 10-15 minutes.

Sounds good, swap around plugs, coils and plug wires first and see if the problem moves.