86 merc 115 erratic tach@ idle

[canoemang]

Yesterday i noticed my system wasnt charging but my tach was working. I got home and tested the rectifier and it was bad, swapped it out with a new one. At WOT it charges at 16.5 Volts and the tach works fine.. at idle the tach gets erratic and it sits at 700 which is where i have it set to idle then crawls up to 1500 rpms then drops back to 700, during this the throttle is at idle and the motor doest rev.. just tach climbing..

It didnt do this with the bad rectifier.. New one also tested good prior to installation.

connections are clean and tight.. any idea?

 

[bktheking]

Re: 86 merc 115 erratic tach@ idle

Try switching your tach to the other yellow wire and see if it makes a difference.

 

[canoemang]

Re: 86 merc 115 erratic tach@ idle

I'll give it a try today.. was wondering if it matterd what yellow wire it went on..

 

[canoemang]

Re: 86 merc 115 erratic tach@ idle

Swapped grey wire to other yellow. At idle it was acting the same then it got way worse and my rectifier blew again and my tach went dead.

New rectifier tested bad after this last run, 2 rectifiers dead and no tach.

someone told me its that i have a bad tach and thats blowing my rectifiers.. any sense to that?

Should i try another rectifier and leave the tach (grey wire) disconnected from the rectifier?

Also..for troubleshooting purposes should i try to disconnect the rectifier all together and hook one of the yellow wires directly to the grey wire with nothing else connected to the rectifier and tape off the other yellow and red wire (not together). Or can i wreck anything doing this?

Thanx again..

 

[bktheking]

Re: 86 merc 115 erratic tach@ idle

I can't see the tach doing it, a short in the stator could do it, reversing battery cables will do it. Have you verified the stator isn't shorted out on the yellow wire side, have you inspected the wires going to the rectifier?

 

[bktheking]

Re: 86 merc 115 erratic tach@ idle

Here another guy having similar issues,

http://forums.iboats.com/showthread.php?t=128568&page=1

skip to the end.

 

[canoemang]

Re: 86 merc 115 erratic tach@ idle

Here another guy having similar issues,

http://forums.iboats.com/showthread.php?t=128568&page=1

skip to the end.

Yup read that about 20 minutes ago.

I have looked through the harness and see no loose connections or shorted wires, everything looks to be on the up n up. Ive never reversed the bat cables.

 

[canoemang]

Re: 86 merc 115 erratic tach@ idle

upon further inspection there is a whiteish wire coming out of the harness at the same place as the yellow and black wire for my primer solenoid. It isnt connected to anything, i checked it for voltage with the key off and nothing, with the key on i get 12.4 volts (same as my bat). Im unsure if this has to connect to something, Only elec things is tilt n trim n the starter sole.. It may have hit the case internally somewhere and caused a short, my inline fuse is good.

Any idea where this wire connects?

 

[bktheking]

Re: 86 merc 115 erratic tach@ idle

The only white wire I see in the entire diagram is 2 white , 1 going to each switchbox from the trigger. Can't be that as your 2 white are already hooked up i'm sure. Can you trace it back to the 8 pin connector?



Did you pull the plug apart from the motor to the controls to check for corrosion?

 

[canoemang]

Re: 86 merc 115 erratic tach@ idle

I looked in my manual and also saw there is no white wire that should be coming out there. Tomorrow morning im going to dig into it a bit more.. ill let ya now what i find..

 

[canoemang]

Re: 86 merc 115 erratic tach@ idle

OK it is a tan wire coming out of pin #3. It doesnt show a tan wire for my wiring harness but it does for the V6's where it is also pin 3 and goes into the terminal block then to the water temp switch.

Im thinking the prev owner used a harness for a v6.. it all lines up..

It looks like it was cut clean and then left to hang, I think it mave have been shorting out, would this cause rectifier and tach issues while not blowing my main fuse?

Also i have seen threads about others using a $4.00 25 amp full wave rectifier from radio shack.. is that a better oprion.. atleast until i get this figured out?

 

[bktheking]

Re: 86 merc 115 erratic tach@ idle

Anything is possible, do you see any damage from it rubbing. You can use the $4 rectifier as a permanent solution, they are better than the merc ones IMO.

 

[canoemang]

Re: 86 merc 115 erratic tach@ idle

Anything is possible, do you see any damage from it rubbing. You can use the $4 rectifier as a permanent solution, they are better than the merc ones IMO.

No rubbing, when i found the wire it was tucked up in by the disconnected idle stab.. could have been grounding out.

I found this drawing on this site.. thanx to j-martin.. This is how i should hook it up excluding the voltreg?

Im thinking for the $4.50 for the rectifiers (i bought 3) for testing sake im going to hook it all up and leave the tach disconnected and see how it goes.. then after it runs and charges correctly ill hook up the tach and see if it pops the rectifier.. <-- sound rite?

 

[canoemang]

Re: 86 merc 115 erratic tach@ idle

Cleaned up my wiring harness and retapped everything and Installed the radioshack rectifier, ran for 25 minutes at variable rpms.. charge kept raising.. fished for a cple hours and hooked up the tach,ran it for 20 minutes and tach is stable and working fine and charge is slowly climbing on the bat....

With the merc/quicksilver rectifier it would jump up to 15 or 16 volts while running wot.. this seems to crawl up to 14.9 or so and hold steady.. is that due to dif rectifier?



thanx for the direction..