1989 mercury 115 acting funny at idle

[sutor623]

Sorry it is an 86. a good friend of mine has some strange engine issues. He has had the motor for a few months. Never ran well. Mechanic changed the 2 power packs and when it didn't fix it he said he didn't know what else to do. I rebuilt the fuel pump, the 3 carbs and changed the waterpump for him just because. That helped it under throttle (on muffs) but it is idling very strangely. Sounds like someone is taking the throttle and ramming it up and back. Motor will spike in idle and misfire like crazy. This motor has an idle speed control assembly, trigger, stator, powerpacks(which were both changed) and rectifier. Any ideas what is wrong? I don't want to start throwing parts at this thing because they are very expensive.

 

[sutor623]

Re: 1989 mercury 115 acting funny at idle

Oh and another issue is that when he has it in the water it won't go past 2-3000 Rpms. And battery voltage doesn't climb when the motor changes Rpms.

 

[Laddies]

Re: 1989 mercury 115 acting funny at idle

Disconect the idle stabilizer if that don't help diconnect the rectifier and if that don't help test the stator with a DVA

 

[sutor623]

Re: 1989 mercury 115 acting funny at idle

Thanks for the reply! That's what cdi said. When I disconnected the rectifier it helped a bit. Idle stabilizer didn't change much actually made it worse when I give it throttle. Don't have a dva tester but I checked resistance per cdi an stator checked out great. Resistance in the trigger was 1700 ohms on one wire an high end per cdi is 1400. Another wire had resistance in the same range. I am thinking rectifier and trigger. If a trigger fails does it show visible signs of failure? Also cdi says I need to reset the timing if I pull out idle stabilizer is that true. It says you can scrap the idle stabilizer as it is not needed. What do you think buddy?

 

[Laddies]

Re: 1989 mercury 115 acting funny at idle

The idle stabilizers cause a lot of trouble but when one is removed it's best to check WO timing and re adjust the idle speed and mixture. If you have a voltmeter here's a wiring diagrham for a DVA get the parts at Radio Shack for about $5. A trigger failure will be 1 winding which will effect 2 cyls and again needs to be tested with a DVA. testing with a OHM meter just will not tell you the whole story.

 

[sutor623]

Re: 1989 mercury 115 acting funny at idle

Laddiea I'm making a dva tester this week. Just thought you'd be interested in a video of what the motor is doing.

 

[sutor623]

Re: 1989 mercury 115 acting funny at idle

Ok so I made a dva meter. Trigger resistance was off. Dva readings for trigger were spot on. Marked all 6 cylinders with dial indicator and checked with timing light. Everything fired relatively consistently except cylinder 4 was erratic in Rpms. timing light on that wire showed erratic firing. Cylinder 2 has no fire. Switched coils with 2 and 3 and still no fire at 2 so I am assuming it is a wire issue. Stator dva was low at one point, but resistance was okay. Stator looks good with no melting. Rectifier needs to be replaced.

Here's where it gets tricky. Mechanic that worked on it before me changed or said he changed the switch boxes. So I assuming it is not a switch issue. They are Sierra so I know they aren't factory.

All in all the motor is very erratic. Starts relitively easily, sometimes idles okay and sometimes not. Sometimes hits higher Rpms smoothly and sometimes not. Battery is not taking a charge. Any ideas? I think I have multiple issues here.

 

[aussieflash]

Re: 1989 mercury 115 acting funny at idle

First check resistance on rectifier.It sounds like Stator if DVA reading is low.

 

[sutor623]

Re: 1989 mercury 115 acting funny at idle

As stated, rectifier tested faulty.

 

[CrossCurrent50]

Re: 1989 mercury 115 acting funny at idle

Could be a bad bias resistor in the switchbox. If you disconnect the bias wire from the switchbox and then have spark on #2 The box needs to be changed

 

[sutor623]

Re: 1989 mercury 115 acting funny at idle

Could be a bad bias resistor in the switchbox. If you disconnect the bias wire from the switchbox and then have spark on #2 The box needs to be changed

Wiring from the switchbox on that cylinder is ok. I swapped the ignition coil from 2 and 3 and the problem did not move. I did not swap the coil wire. That's my next move.

 

[quicktach]

Re: 1989 mercury 115 acting funny at idle

Check the mechanical movement of the trigger. Is it binding or moving smoothly? Are the wires from it limited in their movement ? Is the plate on which the trigger assembly moves clean? Is the link to the trigger assembly moving OK? Is the trigger coil securely fastened?

 

[sutor623]

Re: 1989 mercury 115 acting funny at idle

Ok guys so I checked the cdi troubleshooting guide from top to bottom. Idle issue cleared up when i removed idle stabilizer until the motor got warm. Reason it was hard to find was that it was intermittent. Numbers all checked out fine. Once the motor ran for about 5 minutes it started acting up. Then I checked all the test points and found 20vdc coming up for the red wire of the stator. Switched the wires to opposite switchbox and ruled boxes out. Bad stator, period. Ill check back in once I install the new one.

 

[rrumba]

Re: 1989 mercury 115 acting funny at idle

i am having a similar problem. Did you get a new stator and did it fix the problem? any new updates?

 

[sutor623]

Re: 1989 mercury 115 acting funny at idle

Rrumba, you NEED to buy or make a DVA adapter for your volt meter. Google the CDI troubleshooting manual and do it STEP BY STEP!! You will find the issue. You have to check both sides of stator, rectifier, 2 switchboxes, trigger, and remove idle stabilizer assembly. If you start throwing parts at this thing you will go for over $600. The motor I was working on needed a stator, rectifier and trigger, and it now runs like a dream. I also did waterpump, carbs and fuel pump. Let me know if you have questions this project is still fresh in my mind.