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Author Topic:   1998 Mercury 90-HP Electrical Problem

blade posted 10-27-2010 03:50 PM ET (US)
I need help. This last summer I was running a 1998 Mercury 90-HP two-cycle motor at 4,000-RPM, and everything was great for hours--then it died all sudden. I attempted to re-start. [The Mercury 90-HP two-cycle motor] would not turn over, but the starter was working well. [The Mercury 90-HP two-cycle motor] had recent re-built carburetors, new fuel and water filter. I switched fuel because it sounded like it was starved for fuel--Not the [cure].
I was convinced [the cause of the motor not starting] was the power pack.
I tried to start [the Mercury 90-HP two-cycle motor] 20 times over the next hour to no avail.
Soon as we got it back to the trailer, my uncle suggested to check for spark. He pulled wire, put in his plug to view spark, and the motor started right up! I started it several times since August, but have not taken it to the lake to run it around to failure. I was told that if the power pack fails that it fails completely not intermittently.
I am not mechanically inclined so I discussed this matter with the mechanic and he said there was not much to do until it refuses to start up. Intermittent problems are trouble. I don't want to take the boat out without being confident that it will bring us back. Good thing the boat came with a kicker.
[Do readers have] any ideas [what is causing the 1998 Mercury 90-HP to occasionally not start]?
Or, [should I try to remedy this problem by] just replacing all the electrical [components in the motor]? Blade
Tohsgib posted 10-27-2010 03:54 PM ET (US)
Could be anything from Key switch, neutral safety switch, safety lanyard, a chafe in the wiring harness, stator, trigger, CDI or Powerpack, etc. Since you have a kicker, take her for a spin then start diagnosing if it happens again. Replacing electronics is gonna cost more than the engine is worth.
jimh posted 10-27-2010 10:08 PM ET (US)
The term "Power Pack" is usually associated with OMC engines. On Mercury engines the spark ignition module is often called "the switch box."
Electrical components can be very intermittent. They often change with temperature. It can be very difficult to diagnose a problem with an intermittent electrical component. You must be patient, and you have to be ready to test and diagnose the problem as soon as it occurs, as often these problems cure themselves after a short rest time.
If you are not a good mechanic or a good electrical diagnostician, it may be difficult for you to locate the source of the problem, and particularly so if it occurs only occasionally.
As far as beginning to replace components without really doing any diagnosis or testing, I recommend you start with the least expensive components first. Replace things that do not cost much. Work you way upward in costs. It would be very effective if you could isolate the problem to be either:
--confined to one cylinder, or
--affecting all cylinders
before you start your program of part replacement. If only one cylinder is affected, you will replace only parts associated with that cylinder. If all cylinders are affected, you will replace only components that affect all cylinders.
Given the price of outboard motor parts, it may be more cost effective and consume much less time to just take the motor to a good mechanic for diagnosis and repair, provided the motor can be consistently put into a no-start condition. If the no-start happens only once in a blue moon, the mechanic will not have much chance to find the problem
Also, for any outboard motor which has been running well and suddenly refuses to start, the first thing to check is the Safety Lanyard and Kill Switch.
Also, I do not understand at all your description of the starting problem, to wit:

quote:
"[The Mercury 90-HP two-cycle motor] would not turn over, but the starter was working well."
You need to be more precise in your description. If the electric starter motor is turning and the engine is not turning, this is a completely different problem than a Crank-but-no-Start problem. Try again to convey to us precisely what you mean about the starting situation. Precision in your description of the problem will also be very important if you hire a mechanic. You will need to tell him precisely what has happened so that he can begin his diagnosis on a proper basis.
blade posted 10-28-2010 12:32 PM ET (US)
Thanks for the imput guys. Yes it was a crank and no start problem now it is working fine but I need to take it out for a couple of hours to see if it quits. The best scenario is if it dies and stays dead to bring it into the shop. Is that too much to ask for?
When I touched the rubber lead that connects to the spark plug I got a shock is that normal? The other two leads did not shock me.
Brian
Stevebaz posted 10-28-2010 03:34 PM ET (US)
The one time I had an [electrical problem] like this [the cause of the electrical problem] was the main wiring harness plug where it meets the engine harness. Mine had worked loose. I separated the connection, checked the connecting pins, took a small screwdriver, slightly spread the split pins, and reconnected the harness. That cured the problem for me. I would also check for a loose ground, and check all connections. That’s all free stuff you can easily do. The other times I had [electrical problems it was because I would] walk away from the helm and pull the safety [lanyard]. [An engine with its KILL switch activated] will crank until the battery dies but won't start. After sitting around for a few hours with a no-start in the middle of the pond you learn to check the safety [lanyard] first whenever the boat won’t start but still cranks. Intermittent failures really cramp your style. You don’t [know] whether to stay or go. Lack of trust [is bad].
Steve

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Author	Topic: 1998 Mercury 90-HP Electrical Problem
blade	posted 10-27-2010 03:50 PM ET (US) I need help. This last summer I was running a 1998 Mercury 90-HP two-cycle motor at 4,000-RPM, and everything was great for hours--then it died all sudden. I attempted to re-start. [The Mercury 90-HP two-cycle motor] would not turn over, but the starter was working well. [The Mercury 90-HP two-cycle motor] had recent re-built carburetors, new fuel and water filter. I switched fuel because it sounded like it was starved for fuel--Not the [cure]. I was convinced [the cause of the motor not starting] was the power pack. I tried to start [the Mercury 90-HP two-cycle motor] 20 times over the next hour to no avail. Soon as we got it back to the trailer, my uncle suggested to check for spark. He pulled wire, put in his plug to view spark, and the motor started right up! I started it several times since August, but have not taken it to the lake to run it around to failure. I was told that if the power pack fails that it fails completely not intermittently. I am not mechanically inclined so I discussed this matter with the mechanic and he said there was not much to do until it refuses to start up. Intermittent problems are trouble. I don't want to take the boat out without being confident that it will bring us back. Good thing the boat came with a kicker. [Do readers have] any ideas [what is causing the 1998 Mercury 90-HP to occasionally not start]? Or, [should I try to remedy this problem by] just replacing all the electrical [components in the motor]? Blade
Tohsgib	posted 10-27-2010 03:54 PM ET (US) Could be anything from Key switch, neutral safety switch, safety lanyard, a chafe in the wiring harness, stator, trigger, CDI or Powerpack, etc. Since you have a kicker, take her for a spin then start diagnosing if it happens again. Replacing electronics is gonna cost more than the engine is worth.
jimh	posted 10-27-2010 10:08 PM ET (US) The term "Power Pack" is usually associated with OMC engines. On Mercury engines the spark ignition module is often called "the switch box." Electrical components can be very intermittent. They often change with temperature. It can be very difficult to diagnose a problem with an intermittent electrical component. You must be patient, and you have to be ready to test and diagnose the problem as soon as it occurs, as often these problems cure themselves after a short rest time. If you are not a good mechanic or a good electrical diagnostician, it may be difficult for you to locate the source of the problem, and particularly so if it occurs only occasionally. As far as beginning to replace components without really doing any diagnosis or testing, I recommend you start with the least expensive components first. Replace things that do not cost much. Work you way upward in costs. It would be very effective if you could isolate the problem to be either: --confined to one cylinder, or --affecting all cylinders before you start your program of part replacement. If only one cylinder is affected, you will replace only parts associated with that cylinder. If all cylinders are affected, you will replace only components that affect all cylinders. Given the price of outboard motor parts, it may be more cost effective and consume much less time to just take the motor to a good mechanic for diagnosis and repair, provided the motor can be consistently put into a no-start condition. If the no-start happens only once in a blue moon, the mechanic will not have much chance to find the problem Also, for any outboard motor which has been running well and suddenly refuses to start, the first thing to check is the Safety Lanyard and Kill Switch. Also, I do not understand at all your description of the starting problem, to wit: quote: "[The Mercury 90-HP two-cycle motor] would not turn over, but the starter was working well." You need to be more precise in your description. If the electric starter motor is turning and the engine is not turning, this is a completely different problem than a Crank-but-no-Start problem. Try again to convey to us precisely what you mean about the starting situation. Precision in your description of the problem will also be very important if you hire a mechanic. You will need to tell him precisely what has happened so that he can begin his diagnosis on a proper basis.
blade	posted 10-28-2010 12:32 PM ET (US) Thanks for the imput guys. Yes it was a crank and no start problem now it is working fine but I need to take it out for a couple of hours to see if it quits. The best scenario is if it dies and stays dead to bring it into the shop. Is that too much to ask for? When I touched the rubber lead that connects to the spark plug I got a shock is that normal? The other two leads did not shock me. Brian
Stevebaz	posted 10-28-2010 03:34 PM ET (US) The one time I had an [electrical problem] like this [the cause of the electrical problem] was the main wiring harness plug where it meets the engine harness. Mine had worked loose. I separated the connection, checked the connecting pins, took a small screwdriver, slightly spread the split pins, and reconnected the harness. That cured the problem for me. I would also check for a loose ground, and check all connections. That’s all free stuff you can easily do. The other times I had [electrical problems it was because I would] walk away from the helm and pull the safety [lanyard]. [An engine with its KILL switch activated] will crank until the battery dies but won't start. After sitting around for a few hours with a no-start in the middle of the pond you learn to check the safety [lanyard] first whenever the boat won’t start but still cranks. Intermittent failures really cramp your style. You don’t [know] whether to stay or go. Lack of trust [is bad]. Steve