1984 Mercury 115HP In-line 6 lost sparks, keep idle stabilizer?

[justchecking]

During the last outing on the lake I noticed I lost 1 cylinder. It would come in and out so I figured it had lost spark.

By the time I got home and tested with a spark gap tester I found I had lost spark on 1,3,4. I then prepared to check the compression on all cylinders before isolating which electrical parts I needed. By the time I confirmed my kill circuit was working correctly I also lost spark on 2 (so no spark on 1,2,3,4). My compression was 110,110,110,110,110,105.

I performed all the recommended checks from my Mercury manual and the CDI checks with a DMM and did not find any problems with the electronics. (I don't have a DVA yet.). By switching trigger leads and coils around I found that all trigger leads and coils fire. Problem seemed to be isolated to the switch boxes.

The stator was replaced about 3 years ago by a marina due to deteriorated wiring (wish I had known about iboats then!).

I decided to purchase both switch boxes, and since they were 27 years old, the trigger (the wire insulation looks a little deteriorated) and rectifier.

Question 1: Should I remove the idle stabilizer and not hook it up to my new switch boxes? Is there a test that can be performed on it? Although I think it is good I don't want the idle stabilizer damaging my new switch boxes.

Question 2: The 3 lead harnesses from each switch box to the coils are also 27 years old and insulation looks 'ok' not new. They are kind of expensive and the admiral hasn't approved replacement. Are they as special as the price suggests, or can I make up my own replacements?

Thanks way in advance for any advice!

 

[CharlieB]

Re: 1984 Mercury 115HP In-line 6 lost sparks, keep idle stabilizer?

'Float' test the idle stabilizer. When it fails it can send a rod right out the side of the motor.

Coil harnesses are simply three green wires with trace colors.

You can build a DVA adapter very simply and quite cheaply, diagram and parts list are posted somewhere in this forum. Using a peak reading meter will not give reliable results, DVA is the definitive testing method.

 

[justchecking]

Re: 1984 Mercury 115HP In-line 6 lost sparks, keep idle stabilizer?

Removing the idle stabilizer was an easy decision - see picture. This wasn't apparent until I removed the switch boxes and related wiring.

Also it was very easy to remove the flywheel nut. I bought a very nice strap wrench at sears and got out my 1/2" breaker bar and 15/16" socket, attached it all, got ready to really PULL to untorque that 100FtLb nut, and discovered it was barely finger tight. LOL.

Oh well, at least I can use that procedure when I tighten it back up.

I double checked all my other wiring, and decided to keep the green switch box to coil wires. Also will keep the ground wires. I cleaned all connections and thoroughly checked each wire for insulation problems and also continuity checked them. Replaced the trigger, switch boxes, and rectifier.

Last thing I have to do is double check my kill switch wiring on the boat side (following the CDI procedure) before hooking it back up then I can start my link and sync (and double check my 464 mark). I practiced checking it before I pulled the flywheel.

I'll check out building a DVA adapter also.

 

[justchecking]

Re: 1984 Mercury 115HP In-line 6 lost sparks, keep idle stabilizer?

Double checked my 464 mark (about 10 times) and determined it was a little over 1 degree off so I decided to adjust it. Good thing too because THAT bolt also wasn't quite tight! After resetting it I double checked (again about 10 times) to make sure it was right. I completed all the before water adjustments and confirmed I have great spark on all cylinders. Also rebuilt the fuel pump. Found the diaphragm to be very brittle (stiff) and corrosion on the check valves. How can the check valves corrode when there is oil in the gas? Anyway that was an easy clean up.

Finally started her up on muffs to see how it runs and it runs GREAT. Idle is pretty fast (1100 RPM), but I hope that is only because it is out of water.

Tomorrow I hope to complete the link and sync in water.

 

[CharlieB]

Re: 1984 Mercury 115HP In-line 6 lost sparks, keep idle stabilizer?

Corrosion is from the ALCOHOL in the fuel. Anywhere there is alcohol there is also water, the alcohol will absorb water from the air until there is an equality 50:50 alcohol and water.

Same reason for the fuel pump diaphragm stiffness, alcohol in the fuel.

Fast idle is from the lack of water back-pressure in the exhaust.

 

[justchecking]

Re: 1984 Mercury 115HP In-line 6 lost sparks, keep idle stabilizer?

Well CharileB I took it out on the water today and finalized my link and sync. In the water I decided it was idling too fast so I idled it down (a little too far, 600 RPM), decided that was too low so I took it back up to 800. Tried the hole shot and opened carbs up to about 1-7/8s each. Might go a little more next time I take it out. Full throttle it ran great and idled smooth.

Unfortunately I got a little excited while I had it idling a little too low and may have damaged my Commander Classic Panel Mount Control! The throttle only button is sticking/jamming now. Anyone have an electronic copy of the Commander Classic Panel Mount manual or some instructions on inspecting it? I did search this forum and found a link to what I think is the online parts list.

I also gathered the parts for a DVA tester, but doesn't look like I need to build one now, thanks for that tip. At least I'll know how to build one in the future if I need it.

 

[justchecking]

Re: 1984 Mercury 115HP In-line 6 lost sparks, keep idle stabilizer?

Rebuilt my Quicksilver control last week and posted my experience in the "Boat Topics And Questions" Mercury Quicksilver Control Repair post. A few hours, $10 and it is good as new.

Next I rebuilt all 3 carbs. Someone had been there before me and buggered up the slot in most of the brass plugs. A few I couldn't get out. The carbs were pretty clean inside so I decided not to fight them. Also found the slot in one of my jets buggered up. I was just about to the beyond hope point when it came free and I was able to replace with a new one. Also, even though I bought 3 carb rebuild kits of the same part number the parts inside each had several differences kit to kit. Oh well, in a year or two I'll buy all new plugs and kits and redo them.

I did a Sea Foam decarb and it appears that Sea Foam works. When I was doing my compression check I looked inside each cylinder and saw a LOT of carbon build up. I did the 15 minute on, 15 minute off, thing a few times then let it sit overnight. I started that procedure after I checked my idle timing. I noticed the water in my test tub getting dirty/oily while I ran on gas/oil, but when I started the Sea Foaming I saw billowing soot/carbon in the water. Next morning I took it out and ran WOT. I rechecked my compression (no change, about 110 on each cylinder) but 3 of the piston tops were pretty clean and 3 were about 90% clean of carbon. I think I'll let it go and decarb again next year.