1982 Merc v150 6010145

[fishingdan]

I am losing spark in two cylinders intermittently. Never seems to lose both at the same time, but it is hard to tell. Looking at the engine from the behind the boat, the problem is with the top two cylinders on the starboard side.

The problem started about on the last trip out. At the doc, the engine was running ok until just before departure. Just before leaving, the engine was noticeably running rougher and I suspected that it dropped one or more cylinders (saw some unburned fuel in the exhaust).

Today I setup the engine in the muffs and tested the spark. Using an inductive tester, I see good (or least visually equal) spark on port bank of cylinders. On the starboard bank, I see what I think it intermittent interruptions in the spark to the top two cylinders. I moved some spark plug wires around one-by-one and didn't see any difference on my spark tester.

I have the Seloc manual and it says that if the problem is in a coil or the switchbox, then one would need a "quicksilver thunderbolt ignition analyzer" to trouble shoot these items.

Is there anything I can do on my own to troubleshoot this? I guess I am hoping it is just a coil since that looks fairly straight forward to replace, However since I'm seeing, what appear to be, some interruption in spark to maybe two of the cylinders, I am wondering if this is a switch box problem.

Am I looking at my inductive spark tester correctly? I am guessing that I should see a steady and uninterrupted pattern in the blinking light (very fast blinking). As rpms are raised, the light gets more constant. I see this on my port side bank of cylinders. Don't see that on the starboard side.

Thanks,
Dan

 

[Barnacle_Bill]

Re: 1982 Merc v150 6010145

You can swap coils and if that isn't the problem you can swap switch boxes. BTW that is no. 1 cylinder at the top right.

 

[fishingdan]

Re: 1982 Merc v150 6010145

One other quick question. Is it possible to loose spark at low rpms and then gain spark on all 6 at higher rpms? The last time the boat was out, I noticed that it stumbled at low rpms, but then took off like a rocket once we got above 3000 rpm or so.

 

[fishingdan]

Re: 1982 Merc v150 6010145

You can swap coils and if that isn't the problem you can swap switch boxes. BTW that is no. 1 cylinder at the top right.

Thanks for the info. What would you test first? Switch coils or switch switchboxes?

 

[Barnacle_Bill]

Re: 1982 Merc v150 6010145

Coils are the easiest. I'd start with them. I recently got rid of a 1983 V150 and never could get that puppy to idle to my satisfaction. 2K RPM or higher she purred like a kitten. I changed everything including the reed valves. I still think to this day I could have got it if it had adjustable low speed jets. I played with different sizes of jets trying to get it smooth. Even went to an electric fuel pump for a while. I had to get a lighter boat due to age so I never did get it perfect. Oh well, I have a 75 now and have it running pretty good.

 

[fishingdan]

Re: 1982 Merc v150 6010145

Mine has idled pretty smoothly in the past. Funny how dropping one or two cylinders will make it idle rough.

Does it make any sense for the engine to intermittantly drop a cylinder at idle and slightly above that, but be firing on all 6 at higher rpms?

 

[fishingdan]

Re: 1982 Merc v150 6010145

bump

 

[Barnacle_Bill]

Re: 1982 Merc v150 6010145

Have you done a compression check?

 

[fishingdan]

Re: 1982 Merc v150 6010145

That will happen tomorrow. Ran out of time today. The last time I did a compession test was, I think last fall. They were all about equal at that time.

I did switch coils between cylinder 1 and the top port cylinder. The port side was still fine after firing the engine. The starboard side was interesting. At first all 6 seemed to have spark and then the bottom right cylinder (#3?) lost spark. I am not 100% sure about see spark on all 6 at the beginning because I was having a hard time looking at my inductive spark tester given the lighting conditions I was in.

 

[fishingdan]

Re: 1982 Merc v150 6010145

I finally got the visiting relatives out of the house and found some time to play with the boat.

As promised, I performed the compression test. I had done it a couple of years ago on a cold engine with all of the plugs still in it. I had consistant results at the time, but the numbers seemed low. This time I warmed up the engine and then pulled all of the plugs. I was very pleased to see that each cylinder was between 118 and 120. I think the higher numbers are the result of performing the test correctly, but also maybe some improvement can be contributed to a heavy decarb that I did about 1 month ago.

Anyways, my focus is now on the switchbox for the starboard side bank of cylinders. I have moved coils around without any change, checked plug wires, and moved plug wires wires without any difference. I plan to switch the switchboxes to confirm, but I will order one now with the assumption that it will need to be replaced.

 

[fishingdan]

Re: 1982 Merc v150 6010145

I'm back. I'm ready to shoot this engine, but I believe it is fixable.

I did change out the switchbox (a known good switchbox that I had) for the starboard cylinders and I'm getting spark on all 6 and, so far, it seems much more consistant. However, it still sounds like it is missing occasionally at idle. I don't see any obvious miss with a inductive spark testor.

While swapping out the switchbox, I decided to do the ohm tests for the stator leads per the Seloc manual. Everything seemed to be roughly within spec except for the ohm test of the blue-white/red-white wire test. It was about 25% lower than the blue/red test. The stator and the trigger look original.

The carbs are spotless and in good shape. I haven't touched the idle screws since nothing has changed prior to the start of the problem (rough idle and originally dropping one or two cylinders on the starboard side).

Fuel system is clean and I change the fuel/water separator once per month.

I could adjust the carbs, but my gut is telling me that there some electrical issue. Are the results of my stator test significant and could that cause my symptoms?

 

[dhsbuckley]

Re: 1982 Merc v150 6010145

Just wondering what you think a smooth idle is? i have never struck a v6 mercury that ever idled smoothly mine has alway been very lumpy at idle and the same with all my mates we have 6 mercury 150s to 200s between all of us and they never idle smoothly until about 1500 revs, i also notice that our octane levels in fuel are a lot higher over here in oz (97 for premuim) yet they still wont idle smoothly.

 

[fishingdan]

Re: 1982 Merc v150 6010145

I know these v6's don't idle very smoothly. I have had a couple of them. This is a rougher than normal idle. Last week it was worse since it was dropping one or two cylinders. Now I have spark on all cylinders, but it still sounds like it is missing a little. I may try adjusting the idle mixture, but I'm looking for feedback on my Stator testing above.