90 HP early 80's 6 cylinder starting without key

[katch_me]

I have an early 80's Mercury 90 Inline 6 cylinder, tower of power. I am troubleshooting a starting problem which seems to be no spark on 3 cylinders. It's hard for me to turn over the motor with the key and look for spark. Is there a way to jump some wire at the motor so that I can turn over the motor and look for spark by myself? Thanks

 

[Chris1956]

Sure, put a clip lead on the starter solenoid yellow/red wire, and apply battery power to it to crank the motor.

BTW, that motor has two switchboxes that create spark, each for 3 cylinders. Perhaps one is bad?

 

[roscoe]

Or you have a broken wire going to one of the switch boxes. Either one from the stator or the ground.

 

[Scott Danforth]

on a 2-stroke outboard, the key is used to kill the ignition (the off position grounds the coils)
unplug the controls and jumper the starter and it should be running.

 

[katch_me]

Sure, put a clip lead on the starter solenoid yellow/red wire, and apply battery power to it to crank the motor.

BTW, that motor has two switchboxes that create spark, each for 3 cylinders. Perhaps one is bad?

Thanks Chris. So maybe you can help with my no spark issue. Let me give you some background. So this motor always gives me starting trouble, after it sits for a couple weeks. I sort of nailed it down to a weak battery. If it doesn't start (it floods the motor) I either charge the battery over night of put a booster pack on and then it starts. I sort of figured that a weaker battery just doesn't create enough torque to spin the motor fast enough. And a new battery does that. At first I thought I had an electrical drain causing poor battery performance. Which I still might but this time I left a light on. But now I think it must be something else. Again, it won't start. And I'm trying to pull it out of the water.

So, now I checked. No spark on #3,4 and 1. It looks like my switch boxes fire odd and even cylinders. So it doesn't look like a switch box. I switched wires from the switch box to the coil and the problem stays the same. Which sort of points to the coils. But I find it weird the 3 coils go bad at once. It is possible to drive the boat if it misses one or two cylinders without noticing?

I have thought of something else. Does each cylinder have a dedicated magnet in the flywheel? Last year my starter seized and the pinion gear total stripped away. So maybe metal has gotten attached to the magnets.

The stator and trigger is relatively new (ten years) but I know I can test them out.

Thanks again. At least I don't need a second person to crank the motor!

 

[Chris1956]

Generally an Inline 6 will not flood when cold. So that is strange. I also think it strange that 3 coils would go bad.

Ground wire corrosion could cause weak starter and since starter spins slow, spark can be weak. Maybe check ground wires on the coils and switchboxes for corrosion. On Inline sixes the main battery ground is often on the lower cowling. There are ground straps from cowl to block. You should check them for corrosion. If they are corroded, ground on block will be weak causing slow starter spin.

Obviously check wires from switchboxes to coils.

Inline six motors will run pretty good on 4 cylinders, but will be down on power. I would expect you to notice it running on 3 cylinders.

Not sure about the magnets on the flywheel. You can pull the 8 5/16" bolts and remove the outer flywheel. You can easily see the magnets and test them for strength.

 

[katch_me]

Generally an Inline 6 will not flood when cold. So that is strange. I also think it strange that 3 coils would go bad.

Ground wire corrosion could cause weak starter and since starter spins slow, spark can be weak. Maybe check ground wires on the coils and switchboxes for corrosion. On Inline sixes the main battery ground is often on the lower cowling. There are ground straps from cowl to block. You should check them for corrosion. If they are corroded, ground on block will be weak causing slow starter spin.

Obviously check wires from switchboxes to coils.

Inline six motors will run pretty good on 4 cylinders, but will be down on power. I would expect you to notice it running on 3 cylinders.

Not sure about the magnets on the flywheel. You can pull the 8 5/16" bolts and remove the outer flywheel. You can easily see the magnets and test them for strength.

When I say flood I mean I see fuel come out of the exhaust. This is (I think) because I am cranking for a long time and using the enricher a lot. I have learned my lesson over the years and I use the enricher less.

I do find it weird because I would have noticed if it ran on 3 cylinders for sure. Im pretty good, I would notice 5 cylinders also (I think). I still reach top speed.

When I first tried to start I noticed no spark (on one of the cylinders I tested). Then I connected a booster pack and I noticed spark. Again leads to my theory of weak battery and not spinning fast enough.

I will check the flywheel for sure. Do you need a special puller to get it off?

 

[racerone]

I believe one switch box fires 1 , 3 , 5 cylinders.----The other fires 2, 4 , 6 cylinders.

 

[katch_me]

I mentioned that my battery would always drain. Well earlier in the year I found that my battery was not charging. So I got a new rectifier to solve the problem. But after that my battery was overcharging when I would drive. it would keep climbing to 18 volts. I read that this could be caused by maintenance free/AGM batteries. Which I do not think I have. It's a marine starting/cranking deep cycle. But I did read that this high voltage could blow something, like a switch box. Is that right?

I have also read that when troubleshooting the switch box to disconnect the black/white wire between them because the bias circuit could cause a problem on one box from the other box. That might make sense why 3 cylinders went out.

 

[Chris1956]

Have you checked your fuel pump? If the diagram has a leak, it sill allow raw fuel into the crankcase. This causes cylinders to miss at low speed, but run at high speed.

As for overcharge of the battery, the charging system is at best 9Amps. It should not seriously overcharge the battery. Make sure all wires are clean and tight, so your battery can act as the load on the charging system as designed.

 

[katch_me]

I never thought about that regarding the fuel pump. But it has been rebuilt a couple of years ago. I do feel it could be battery related. I went down this path before with no spark and only a fully charged good battery would resolve the spark issue. It was just recently that I found the rectifier problem and replaced it.
I actually might have the wrong battery. I am using a deep cycle 800 CCA battery. But I read that those don’t like that vintage Mercury charging system and can cause funky stuff with electrical accessories. But I don’t know what to believe. I will be buying a new battery for the weekend and give it a try.

 

[katch_me]

I know this thread went off topic with all my problems! I appreciate the help. To make my problems worse I dropped my motor cover cowl in the lake when troubleshooting. Yeah... I know. I want to try and grab it with a magnet, but is that thing aluminum? There is no rust on it at all.

 

[katch_me]

A new battery got spark back in two cylinder. The third cylinder needed a new coil. Why it didn't start... well my battery died. Water slightly flooded over the fuel tank and I guess water got into the fuel. New fuel got it going. Thanks for the help!

 

[Chris1956]

Gee, you might have mentioned the water in the boat. Motors run really bad on a water/gasoline/oil mix.

 

[katch_me]

Gee, you might have mentioned the water in the boat. Motors run really bad on a water/gasoline/oil mix.

No kidding! I thought my connections were good and also thought my fuel level was the same. That’s why I didn’t check earlier. Lesson learned.