Having problem with Mercury 2.5L planeing, trigger out of spec, opinions

[Jim Speros]

My old school approach I'd like to share is. Before you assume you think you know what it might be apply basic troubleshooting first.
Compression , Spark , fuel delivery. It is a reasonable quick systematic approach. Pull plugs, Compression test. While plugs are out spin and check spark. I prefer stevens instruments 8 cylinder spark tester. Allows you to check all at once. Plus you can check for color and consistency of spark . Shows patterns . For example 1 an 4 , 2 and 5 3and 6, act in pairs. A group in the is showing and issue it points toward trigger. A weak side could be a stator issue or switch box on those systems. You quickly test other things too. Like unplug main harness. Loosen, wiggle and secure all coil plate grounds. Check fuel delivery starting with primer bulb. Do any vents weep fuel?

I give little attention to OHM values. really only pay attention to opens and shorts. Confirm with DVA or some other form of confirmation.

If nothing shows there move to ramp under load test while still on trailer. CHeck bulb while under load. Check timing with load. Timing tends to jump around at free idle anyway. Check spark on each cylinder with light under load.

In most cases you will have a specific direction to proceed. Assuming and bouncing from some suspected problem to suggestion can send you chasing your tail.

I hope you find this helpful

[silverfox]

WOW, that does sound like the classic stator problem. The two stage coil winding acts just like that when you increase RPMS. JMO
Bill

[Fishwhisper]

Thanks for all the responses, all are helpful, the DVA should be here Wednesday, I’ll go through more then, I am planning to check compression also. I also ordered a spark gap tester. All plugs were sparking as tested with a timing light. I also ordered a new timing tape so I can check all plugs for specific timing. Any other suggestions would be appreciated.

[Fishwhisper]

This weekend I had my DVA and test harness. With the harness connected to the CDM module and harness, all CDMs tested around .25 volts on the trigger (spec is .2 to 5 volts) except #6 was .18 volts.

All the CDMs tested at only .8 volts for stator output (at cranking) which is way below the minimum 180 volts spec. I then disconnected the stator from the harnessand test the output at cranking, was within spec at about 220volts.

resistance testing the CDMs all seemed in spec except one had very high resistance at the spark boot (secondary coil test) then I removed the wire and screwed it back on and the test was in spec then. Went from 111,000 ohms to about 1010 ohms.

trigger resistance test still low by about half and stator resistance test are within spec.

my plan is to replace the trigger and buy two CDMs to remove and replace the existing CDMs to determine if one is causing the low stator output. Service manual says to do that if the stator resistance test are ok but output is low on all CDMs. Any other suggestions? What fault in a CDM would cause a low stator output? Seems like it would be a short or something.

[OnPad]

Sounds like a bad control module, or trigger, and possibly a coil.

[Fishwhisper]

Yeah, trigger and coil were my first thought, control module is also possible. I will replace the trigger because of the low resistance and erratic timing and replace CDMs one at a time to see if stator output changes, and will retest everything. I forgot to mention I did do a compression check all were within 112-121 psi.

[25two.stroke]

I have a complete electrics system for that motor...stator, control module for carb engine etc. if you want parts at half price to swap out and see if its your problem then send me a message. And if you put a part in and it don't fix the problem you can keep it as a spare or send it back to me for a refund. I can also crank over my motor and get dva readings if that is helpful. The engine I have ran but it had low compression.

[Fishwhisper]

Thanks for the offer 25two, I may take you up on that depending on what i find. I already ordered and new trigger and two new cdms. But i'm also here to tell on myself and my stupid mistake. I decided to try and test the spark gap on each cylinder but could not get any spark at all. New that wasnt right as it does start and idle. So i climb into boat to check the kill switch, its ok. Then I see the ignition key and think to myself, does the key need to be in "run" to spark and does it need to be in run to check stator/trigger output? I was using a trigger switch on the solenoid to to crank the motor over. Well I switch it to run and have spark on all cylinders and they all jump 7/16" gap. I retest the stator and trigger outputs. All stator outputs at cranking are between 240-280 volts, so thats great. Trigger output is around .5 - .85 volts at cranking, within the spec of 0.2 - 2 volts, but still sorta low. So thats good, stator looks ok. Trigger resistance is still low. I test two cylinders with motor running and rev the motor up to 2500 rpms. Trigger voltage is supposed to be 2-8 volts, well as I rev the motor, trigger voltage goes from about 1 volt at idle DOWN to 0.5 volts at near 2500 rpms. Seems like a bad trigger. I also will probably run the bias circuit test tomorrow, supposed to be done at 2500 rpms too, but motor does not like being reved that high, gets all jumpy and rough. So will see how high I can rev it and test the bias voltage. Which is the test for the control module.

[OnPad]

Oops, yeah the key has to be in the run position.
If you don't already know, you'll need a flywheel remover/ lifting eye, in order to replace your trigger.
The older mercs you could check the trigger output at cranking, and they would read 4+ volts, but I guess that doesn't help, as the cdm system doesn't have the wiring labeled to identify what's what.
I also found this tidbit, in my old supplemental manual. Don't know if it pertains to your adapter or not.

[Fishwhisper]

I have the test harness, which lets me test trigger and stator ouput. The service manual says trigger output should be between .2V and 2V at cranking, mine is around .5 to .8volts on all of them. Running the motor at 2500 rpms the trigger output is supposed to be 2v to 8v, but my trigger output actually went down to .5V, I dont know if being i just revved it briefly instead of actually running it for awhile at 2500 rpm makes a difference. But when I revved it, the motor really didnt like it, started running rough and shaking, I think the timing got worst when i did that. Which was my problem originally, couldnt run above fast idle otherwise it would bog down. I have a flywheel puller, figured I was going to need it. Hopefully the trigger will fix the problem, otherwise maybe the control module. I may try and test the bias circuit tomorrow, but the output is stated for 2500 rpms and I'm not sure I want to keep doing that.

[Fishwhisper]

#11Today, 07:51 PM

I received the trigger and 2 CDMs last week. Today I had time to just remove the flywheel, stator and trigger. After removing the trigger and flywheel I noticed some rub marks on the flywheel hub magnet and the trigger as well. The rubbing is light and on the magnet you can’t actually feel anything, on the trigger, you can see a feel where it rubbed. Looks like on one of the trigger points. Again not real bad, is this anything I should worry about as I am swapping triggers. This could of happened 20 years ago when it was started for the first time or recently.




second question, one of the five stator screws snapped off in the motor, I believe I still have a few threads that will hold. How important is it to try and remove the broken screw and use a new screw or just tighten down the one I have with loctite. Such a small screw looks like it will be super hard to remove.

third question, when I was trying to remove the flywheel it was tough and sometimes I was turning the flywheel maybe 1/8-1/4 turn when trying to wrench the flywheel off with the removal tool. When doing this there was some clinking and maybe clanking noises coming from in the motor, not real loud but noticeable. Is it normal for there to be some noise coming from the motor when turning the flywheel?

[OnPad]

Answer#1: Most likely alright, as long as it didn't get to hot.
Answer#2: Better to leave it out vs losing it during operation. Or weld a nut to the broken bolt and remove.

Answer#3 It's hard to tell you with out hearing it myself. Should make no noise with spark plugs out. Maybe a little with them in. A impact would've had me not hearing anything.

[Fishwhisper]

It was barely scraped, didn’t look like it got hot, but I have a new trigger and the magnet I think has a metal ring around it.

Answer 2 was my thought also, the screw is so small and down in the hole not sure could weld anything to it.

Answer 3 Spark plugs were in the motor, when I reinstall I’ll turn it again without spark plugs, and listen, wasn’t using an impact just large wrenches and elbow grease. If it makes a noise again I’ll try and record it.

[LakeFever]

Sometimes a squeaky or clicky sound is a sign of a cracked and/or broken ring. I use a mechanics stethoscope to pinpoint mechanical sounds that concern me. Work great, cheap tool

[Fishwhisper]

Ok, first, clicking sound was just the impeller spinning dry in the housing, duh. So I got the new trigger on and ran link n sync. All seemed pretty normal until I checked idle timing, before the trigger change it was reading 4* ATDC though very erratic but idle was ok. After trigger change the timing was now at 0* so I adjusted the idle timing screw to get it back to 4* ATDC. Did that at cranking with plugs out. Then replaced plugs and started motor and checked idle, idle was at 4* ATDC but the idle
speed was low and bogging. So I recheck at cranking again and still at 4* so I decided to move screw back to spot it was before even though it shows timing at 0* . Run motor at idle and it’s running better, idle speed good, around 750 rpm and no bogging. HOWEVER, when I test the timing while it’s running the timing is showing about an inch before the .462 mark on the timing spec, but the motor is running well, I try and adjust the screw while it’s running to get it back to somewhere close to a normal time and it slowly bogs down and stops. So I turn screw back out to start it again and it’s running but the timing mark is way off, still before the .462 mark, which is like 60-70 degrees BTDC. Turn off motor, remove spark plugs check timing at cranking speed, shows back to 0*. What in the world would cause that, seems like it would not run well if firing that early, my first thought is the control module are a CDM module, I have two new CDMs on 2 and 3 but I think I will one to #1 and see if that makes a difference. Any other suggestions?