Mariner 150 Mag Low on Power when cold

[badbrad358]

Guys,
I'm new to the board for posting but I've been reading for awhile. I love this site, a lot of good info here. I have an older Mariner 150 MAG 2.0L on a '87 Stratos 179FS hull and am having a strange runability issue. When I took the motor out of storage this year after proper fall winterizing it ran great. Also, because I just bought this last year and had never checked the timing, throttle pickup, etc. I went through the full Merc synchronizing procedure and everything is set to factory specs.

The issue I'm having is the motor is low on power when it's cold and you first make a run across the lake. BTW, I never hammer a cold engine, I let it get up to temp first idling around the dock and getting past no wake zone. However, it is low enough on power that it won't reach above 5000 RPM and takes awhile to plane. The interesting part is you can go out with it low on power, let it run a few minutes, then shut it down and let it heat soak. After this it runs like it did last year, revs up to nearly 6000 RPM at WOT and planes off very fast. I'm running a new prop this year which is a Laser II vs. the High Five I ran last year, same pitch. I thought the prop was the issue at first but now I'm convinced after two times out it's something else.

This was happening earlier in the spring and I haven't had it out since due to us moving which is consuming my life :-(. Anyway, my father seems to think it might have just been condensation buildup due to a lot of temp swings in my pole building and maybe spark was weak or something. The odd thing for electrical components is I have typically experienced them failing when they get hot, not when they're cold.

I plan to check this out further and look at the connections, dielectric grease the coil/plug terminals, etc. But I was wondering before I waste a lot of time if this is something observed very often by anyone on Merc V-6's? Does this sound like a typical item or component failure for these engines?

[wrechin2]

I have had 3 engines that would run on 5 when cold then pick up the 6th after a heat soak, making first run then fish, then would run normal the rest of the day. I had one you could set your watch by. Would run for nearly 3 1/2 minutes then start running normal.

Take a timing light and put on all 6 to see if they are all firing. If so , then see if they are all firing when trying to come up. This will help pinpoint which cylinder it is. There are a few test you can do to elimate it. Like switch the coil to another cylinder. Switch switchbox locations. If you have a DVA it would make it alot easier. 2 were stators and 1 was a switch box. I would have never thought a stator could do that, but I have had two. Glad I didn't bet money on them!!! Just my opinion...

[badbrad358]

I have had 3 engines that would run on 5 when cold then pick up the 6th after a heat soak, making first run then fish, then would run normal the rest of the day. I had one you could set your watch by. Would run for nearly 3 1/2 minutes then start running normal.

Take a timing light and put on all 6 to see if they are all firing. If so , then see if they are all firing when trying to come up. This will help pinpoint which cylinder it is. There are a few test you can do to elimate it. Like switch the coil to another cylinder. Switch switchbox locations. If you have a DVA it would make it alot easier. 2 were stators and 1 was a switch box. I would have never thought a stator could do that, but I have had two. Glad I didn't bet money on them!!! Just my opinion...

So did you pinpoint the stators and switchbox being bad by doing the Merc Service Manual electrical test or just by a "check for spark" method? I have troubleshooted these things before using digital meters, just wouldn't have thought these conditions would point to electrical, but you felt the same as me and yours were electrical. Thanks for the help.

If anyone has any other suggestions I'd appreciate the help. I love this boat and motor, just want to make sure I'm not hurting engine lubrication due to a lean condition, but it acts more electrical because when it first did this it was misfiring a little too, but not severely.

[wrechin2]

I used the timing light to pinpoint which cylinder was not firing.

I also used a DVA to test voltages. The problem with the 2 that were stators are they tested normal with no glitches. You have to remember that the DVA stabilizes the volage so it can be tested. It basicly averages the voltage. Some simple test without a DVA are........For example if you find #4 is doing it, switch the coil to another cylinder. If it is still doing it on 4, then switch positions on the switch boxes. If it is still on 4 then it has been ruled to a stator or trigger. If you don't have a DVA then you can simply switch the trigger wires from 2 to 4. FOR THIS TEST all you need to do is check for spark. Have ALL the wires off and grounded so it will not start and backfire. You only need to be concerned with 4. If #2 is firing and #4 is still not firing, then it is a stator. Just my thoughts....

I am surprised J-martin hasn't jumped in. He is the man when it comes to this.....

[badbrad358]

I used the timing light to pinpoint which cylinder was not firing.

I also used a DVA to test voltages. The problem with the 2 that were stators are they tested normal with no glitches. You have to remember that the DVA stabilizes the volage so it can be tested. It basicly averages the voltage. Some simple test without a DVA are........For example if you find #4 is doing it, switch the coil to another cylinder. If it is still doing it on 4, then switch positions on the switch boxes. If it is still on 4 then it has been ruled to a stator or trigger. If you don't have a DVA then you can simply switch the trigger wires from 2 to 4. FOR THIS TEST all you need to do is check for spark. Have ALL the wires off and grounded so it will not start and backfire. You only need to be concerned with 4. If #2 is firing and #4 is still not firing, then it is a stator. Just my thoughts....

I am surprised J-martin hasn't jumped in. He is the man when it comes to this.....

Very helpful and simple logical test method, thanks. I'll print out this thread and keep it so once moving stops consuming my life I can work on this.

Thanks again, good forum here.

[j_martin]

I am surprised J-martin hasn't jumped in. He is the man when it comes to this.....

Yer doin' fine.

Like brad says, the trick is to come up with a way to trap the bug. You'll probably have to use a timing light when it's failing to find the mis-firing cylinder, just like he said.

Once you've found it, you can dog it by swapping parts with the goal to move the bug. When you move it to another cylinder, you have the bad part under your thumb. The only part that doesn't apply to is the trigger.

Cleaning and tightening connections is never a waste of time. Might even fix the problem without getting a headache trying to figure it out.

A dirty, oxidized connection can be a semi-conductor. Sometimes it conducts, sometimes it doesn't. sometimes it's predictable, sometimes it isn't. This is the one item that can make a trigger appear to fail on only one cylinder, when the same coil services 2.

hope it helps
John

[badbrad358]

Yer doin' fine.

Like brad says, the trick is to come up with a way to trap the bug. You'll probably have to use a timing light when it's failing to find the mis-firing cylinder, just like he said.

Once you've found it, you can dog it by swapping parts with the goal to move the bug. When you move it to another cylinder, you have the bad part under your thumb. The only part that doesn't apply to is the trigger.

Cleaning and tightening connections is never a waste of time. Might even fix the problem without getting a headache trying to figure it out.

A dirty, oxidized connection can be a semi-conductor. Sometimes it conducts, sometimes it doesn't. sometimes it's predictable, sometimes it isn't. This is the one item that can make a trigger appear to fail on only one cylinder, when the same coil services 2.

hope it helps
John

Agree on the connections and cleaning bit, I have already planned to do that since that is easy. Then I'll proceed through with checking for missing spark, what component is bad, etc. This is the basic approach I was thinking to do, just easier when folks confirm it. Thanks.

[capnzee]

could it be as simple as a spark plug? do the simple things first.

[badbrad358]

could it be as simple as a spark plug? do the simple things first.

Yep, I plan to look over the stator, switch box, coil, plug wires, etc. connections and wiring condition first. I already checked the plugs when I did the timing and synchronizing of the fuel linkage this spring, they were in great shape. I usually find the surface gap plugs to almost always be in good shape BTW.

Like I've said, when I can find the time I'll do the simple stuff first and try to find which cylinder is misfiring and troubleshoot from there, I was just trying to see if this is a common Merc V-6 thing. I've worked on a lot of Merc's but never had a V-6 before, but thrilled to have it and the power it gives compared to the old inlines.

Thanks to all for the help, hopefully I can get this nailed soon.

[capnzee]

Don't just look at the plug and say "it looks great"--make sure all of them actually fire, then move to the next item, I believe it would be the coil--switch a couple of wires and see if the problem follows. Probably not the professional approach, but it has worked for me. Good luck