1984 Mariner 115 wil not rev past 2,000 rpm

[bainer1290]

Have had this boat for a few seasons, has ran great, had it out for about 45 minutes today, ran well, then swapped the kids in the tube, went to take off and it had no power. The engine starts and idles just fine but when you give it throttle, it shifts like normal revs up a little but after that has no go, I could not even nurse it over 2,000. Oddly enough though with it in neutral, I can raise the fast idle lever and get it easily up to 5,000. So the issue any appears under load. I also noticed the tach bounces all over the place when I tried to go, it would jump to 9,000 then 1,000 then 4,000, and so on all while the engine is only turning maybe 2,000.

When I got home I pulled the plugs and checked for spark, all seemed well, the rest of the engine appears fine nothing looks out on place. The carbs are all opening and closing as they should and the advance/retard mech for the trigger stator is also moving like I think it should.

I am at a loss as to what to look at next any advice? Thank you

 

[bainer1290]

Tried a few things today with no luck, we out in a new primer bulb, fuel filter, took apart the fuel pump and all 3 carbs to clean them all, everything appeared normal. I checked all the wiring connections and they all look good too.

What else could be causing the trouble?

 

[Chris1956]

Well, you could be overpropped. Try it again with a light load. If it still won't rev up, maybe the high speed windings of the stator went bad. They can be ohm'd out for a test of sorts.

 

[bainer1290]

I think the prop should not matter as I have been running it for a couple of years just fine, have not really changed anything on the motor for a couple years also so something failed...

Yesterday we hooked a fuel line directly from the fuel pump to a primer bulb to an aux tank, just to eliminate the entire fuel system in case it had some sort of a clog or air leak but the engine reacted exactly the same could be on get it over 2,000 and at 2,000 it does not sound smooth, sounds like it's missing, coughing, sputtering and the tach continues to jump all over the place, this still leads me to think it is electrical. I did check the resistance of the stator and trigger and both were within specs, but not sure if that rules then out completely.

Next step is to take the boat home from the lake tomorrow and I can do a compression test and also hook up a timing light as I suspect it is miss firing at higher rpms or the stator/switch box is cutting out above 2,000. What is the best way to check all the cylinders for spark/timing at a higher rpms, should I mark the flywheel when each is at tdc and check with the timing light for each or ?

 

[bainer1290]

I checked the compression, all cylinders are within a few psi of 115, so good there. However, I did find that the #5 cylinder is loosing spark at about 2,000 rpm so it looks like this is the culprit. Next step will be to try to isolate the problem between the trigger (ohm'd out good), or the switchbox or the coil (also ohm'd out good) so most likely the switch box but its odd that #4 and #6 seem to fire fine but maybe this is common? Any help is appreciated. Thanks

 

[emckelvy]

ADI coils are known to crack, so be sure to inspect the ign coil for cracks/arc marks. You may need to purchase an inexpensive "DVA adapter" to be able to take peak-voltage readings of the ign circuits, in order to troubleshoot the problem.

Here's a couple of links for that:

http://forums.iboats.com/forum/engi...-dva-adapter-for-standard-multimeter?t=374544

http://forums.iboats.com/forum/engi...ed-a-dva-meter-make-an-adapter-for-5?t=434738

http://www.iboats.com/Piercing-Prob...age-Adapter-CDI-Electronics/dm/view_id.336045

http://www.usatoolwarehouse.com/usatoolwarehouse/ESI-640.html

Here's a link to some excellent troubleshooting information for ADI motors, from CDI Electronics:

http://issuu.com/cdielectronics/doc...t.xml&backgroundColor=000000&showFlipBtn=true

Merc ADI info starts at page 70.



HTH........ed

 

[bainer1290]

Thanks for that ed, here's my plan for the next test:

No Fire on One Cylinder: This can be caused by a defective blocking diode in the other switch box. Disconnect the White/Black jumper between the switch boxes and retest. If all cylinders are now firing, replace the switch box that was originally firing all three cylinders. To verify this condition, swap the trigger leads on the switch box that was originally firing all three cylinders. If the misfire moves to another cylinder, the switch box is bad.
OR
I can swap the 2 switch boxes to also see if the problem moves from #5 to #2.

I can also check the coil by swapping it with another cylinders to see if the problem moves. More to come thanks again!!

 

[bainer1290]

Did the 2 tests today, swapped coils #5 and #6, still had the issue with #5 loosing spark so I am confident the coil is good now.

However, I swapped the switch boxes and all the wires today, I was expecting the problem to move to #2 but it actually moved to #1 and the rpm that it cuts out at now is around 3,500. Now I am scratching my head again is it the switch box or something else?

 

[snider7]

Hello, I'm having the same problem with my 1995 Mercury 115. How did you test your stater?

 

[bainer1290]

The link from Ed above has all the info needed for testing.

I think I am going to find a pair of used switch boxes and give them a try. I swapped the boxes back on mine and #5 is still cutting out above 2,500 rpm. Hopefully this solves the problem.

 

[Chris1956]

Gee, I think it could be the high speed windings on the stator. Did you ohm it out?

 

[bainer1290]

Yes the stator and trigger both ohmed out good... Odd that it changed from the #5 to the #1, even though the switch boxes were swapped so that was a different switch box controlling #1,3 and 5 the second time around. Maybe I should get a used stator too? Both the low and high speed sides all ohmed out within specs.

 

[bainer1290]

I had always thought a bad stator would affect more than just one cylinder? I was leaning towards the switch boxes and the trigger because of this, but I did test the stator and it was withing the range for ohm's but don;t have a DVA at this point to test that way.

 

[Chris1956]

A stator with a bad high speed winding will cause the motor not to rev up under a load to more than 2500 RPM. A bad low speed winding will cause a no-idle condition.

 

[bainer1290]

That makes sense, I think I will buy a new stator too, being that the one on there looks original, its probably close to being done if not already the problem, if it is ok then I will have a spare... Thanks again

 

[bainer1290]

As a follow up I installed a new CDI stator, 2 used mercury switchboxes and a used trigger, the boat is now running normal again, not sure exactly which part caused the problem but it was one of them. Thanks for the help.