1993 90hp intermittantly dies

I've never had issues with this motor before. It has been in storage off and on over it's 20 years but always after cleaning the carbs, it's never gave problems.

This year I started fishing again and about 3 months ago I cleaned the carbs and went "boating". It ran good as usual for about 8 trips (all day bass fishing) and never an issue. I needed 2 cycle oil and got Penszoil syntheic. I used to use lubrimatic 2 cycle oil but couldn't find it at the time. Since I've started using penszoil, I've had issues, whether the oil has anything to do with it or not, I don't know. I still mix 50:1.

Here's how my problem goes:

1st time I was wide open throttle (everything prefect so far) headed to the ramp at the end of the day and all of a sudden without warning, the boat died. It would crank but not hit a lick at all. I used the trolling motor to get to the ramp. I got it home, pulled the plugs and they were black. I cleaned them and checked for a spark and had spark. I reinstalled them and hooked up the water hose and after cranking for a total of about 2 minutes (not continous), it started and ran normal.

I got new plugs and ordered new gaskets for the carb bowls since they may have been leaking a little.

2nd time out on the lake, the boat ran fine.

3rd time out, needed gas and oil. Went to the lake and rode to first fishing spot (5 min ride). Then rode to 2nd fishing spot (10 min ride). Went to start the motor and it would crank but not hit a lick again, just like 1st time. I pulled the plugs right there and cleaned them off (just a little black), put them in and motor stated for about 10 secs and just died instantly without warning as ususal. Pulled plugs again and they were clean. I cranked and cranked but it wouldn't "hit" at all. Got pulled to ramp.

Got home and hooked up the water and the motor did as 1st time. It stated after about a couple of minutes cranking, run for about 10 secs and just dies without warning. After a few minutes it would start and run for about 30 seconds or so and just die. I changed the hose and pump bulb from the tank to the motor and still the same thing.

For it to just die without warning has me stumped. Any ideals?

93 Force by Mercury, Model H090412NX

Re: 1993 90hp intermittantly dies

UPDATE: (If this helps out)

I had to charge the battery last night due to it dieing from working on the boat last evening. This morning it started perfect. Could it be heat related? But then again, one day it ran fine all day.

I disconnected the gas line while it was running to see what it'd do and it ran for about 4 mintues until it went lean and ran out of fuel. Now I know it's not running out of fuel when it dies on the lake because it justs dies instantly when it's having it's issues.

Re: 1993 90hp intermittantly dies

Another UPDATE:

I went out and the boat started right up. It ran for 5 minutes or so and just stopped, and again, would not start. I'm thinking that maybe it's heat related.

With the hose hooked up, I have water coming from both holes in the lower unit and a little spray from the two holes at the top back. My overheat buzzier don't NOT come on.

Re: 1993 90hp intermittantly dies

When it stopped running after 5 minutes, did you happen to check the spark? Maybe check the spark when it is cold, then check again after it suddenly stops.

A spark checker like one of these is a good tool as you can vary the size of the spark gap. Useful for finding "weak" spark.

Thexton 404 Adjustable Ignition Spark Tester : Amazon.com : Automotive

Re: 1993 90hp intermittantly dies

pnwboat said:

When it stopped running after 5 minutes, did you happen to check the spark? Maybe check the spark when it is cold, then check again after it suddenly stops.

A spark checker like one of these is a good tool as you can vary the size of the spark gap. Useful for finding "weak" spark.

Thexton 404 Adjustable Ignition Spark Tester : Amazon.com : Automotive

Click to expand...

When I'm at home and it stops, I do check for spark and I do have it.

Re: 1993 90hp intermittantly dies

If you have sufficient spark, and you have gas, the motor should fire....or at least pop or backfire or do something. Does it pop or backfire when it is acting up? Or does it just crank over and nothing?

Re: 1993 90hp intermittantly dies

pnwboat said:

If you have sufficient spark, and you have gas, the motor should fire....or at least pop or backfire or do something. Does it pop or backfire when it is acting up? Or does it just crank over and nothing?

Click to expand...

It dies just like if I turned the key off. And trying to start it, it does nothing. But it seems if I wait an hour or so, it'll start right off like nothing happened.

Re: 1993 90hp intermittantly dies

Bad/ water in fuel. Try running from an external fuel tank and see if you still have a problem.

Re: 1993 90hp intermittantly dies

I would suspect that you might have an ignition system component that might be failing after it gets warm. My initial "guess" would be the switchbox, or something related to the switchbox, but that's not a cheap item and you need to do some checking to confirm. You need some basic testing equipment, like the spark checker that I referenced in post #4 above and a meter. Do you have a meter?

Re: 1993 90hp intermittantly dies

Yes. I have a meter. I'll have to get the spark tester. All I did was "look" for the spark when it wouldn't start and I had spark.

I did take it to a machanic this morning and he said the compression was 130/150/150 on cyclinders 1/2/3. He said the low compression on cyclinder 1 was causing the problems. Would that cause my issues? It runs perfect until it seems to get hot (no buzzer) and just dies like I switched it off, then a while later it'll start again and then die.

Re: 1993 90hp intermittantly dies

I don't think that I would go back to that mechanic. While number 1 cylinder is low, it's highly unlikely that it is the cause for your problem.

I would start by checking your stator windings with the meter. Not saying that I think your stator is bad, but it needs to be checked. You should have a Blue and Red wire that comes out from under the flywheel. These are the stator windings that supply voltage to the switchbox, which in turn supplies the voltage to the ignition coils. Disconnect the Blue wire and read the resistance between the Blue wire and ground (engine block). It should be 3250 - 3650 OHMs. Now do the same thing with the Red wire. It should read between 75 - 90 OHMs and ground. If the reading you get are opposite of what I've stated, then I've got my color codes reversed and you should be OK. If the resistance reading don't match up either way, then the stator is probably bad.

If it checks OK the next thing to check is the switchbox.

Re: 1993 90hp intermittantly dies

pnwboat said:

I don't think that I would go back to that mechanic. While number 1 cylinder is low, it's highly unlikely that it is the cause for your problem.

I would start by checking your stator windings with the meter. Not saying that I think your stator is bad, but it needs to be checked. You should have a Blue and Red wire that comes out from under the flywheel. These are the stator windings that supply voltage to the switchbox, which in turn supplies the voltage to the ignition coils. Disconnect the Blue wire and read the resistance between the Blue wire and ground (engine block). It should be 3250 - 3650 OHMs. Now do the same thing with the Red wire. It should read between 75 - 90 OHMs and ground. If the reading you get are opposite of what I've stated, then I've got my color codes reversed and you should be OK. If the resistance reading don't match up either way, then the stator is probably bad.

If it checks OK the next thing to check is the switchbox.

Click to expand...

Thank you very much for giving me a place to start. I'll be going to get my boat tomorrow hopefully and I'll check the stator out. I'll let you know what it reads.

Re: 1993 90hp intermittantly dies

I got the boat back home today and did a quick check of the stator wires. I didn't try to run the boat so I'm not sure if it will start or not with the below readings.

I got 3915 ohms on the blue wire to ground and 109 ohms on the red to ground. Good? Bad? (my meter showed 3.915k and .109k so I'm assuming that's 3915 and 109 ohms.) I also get a spark tester today if needed.

What next?

I ordered a manual but it won't be here until next week sometime.

Re: 1993 90hp intermittantly dies

OK, looks like the readings are slightly higher than normal, but not off by much. Did you happen to disconnect the stator wires when you were measuring them? At this point I would assume that it is probably OK....at least for now. Next test you really need a DVA adapter to get accurate readings, but I've found you can usually tell if the voltages are good or bad without one.

Make sure the battery is fully charged. Try starting the engine to make sure that it does start and runs. Only have to run it for 30 sec. or so. Basically what you're going to do is to take some voltage and resistance readings while the engine is running normally, and then when it heats up and no longer runs, take the same voltage and resistance readings.

Now to do this test, you have to crank the engine over with the spark plug wires attached to the plugs, but the spark plugs removed. The threaded portion of the plugs should be grounded to the block. Disconnect the Black/Yellow wire from the switchbox. This is the ignition Kill circuit. Set your voltage on your meter to read at least 400V. If it has the auto ranging feature, you don't have to do anything. Crank the engine and measure the voltage between the Red stator wire and ground. Next do the same thing with the Blue stator wire. I forgot to mention that the wires should attached to the switchbox. Write down the voltage readings. All of these readings are important to determine if the switchbox or stator is bad later on. Next, check the readings on the primary wires on the switchbox that go to each ignition coil while cranking the engine. These wires should also be attached to the switchbox. I believe they are Green, Green/White, and Green/Red. Write down these voltages too.

Next step is to hook the Black/Yellow wire back up, and re-install the spark plugs and wires. Make sure the Black/Yellow wire is hooked up, otherwise the motor will not turn off with the ignition key. Fire the motor up and run it until it dies, and will no longer start. While it is in the "non running"state, remove the Black/Yellow wire. If it starts, then the switchbox is bad. If it still will not start, take your stator wire and primary coil wire voltage readings again while cranking the motor. If there is more than a 10% difference in the readings, then the switchbox may be bad. One other thing to check while it is in the "Non-running" state. Disconnect the Red and Blue stator wires and measure the resistance to ground again. They should read exactly the same as you read before. If they don't, then the stator windings may be shorting out when they get hot.

NOTE: Forgot to mention....While the motor is in the "non-running" state, and the motor starts after you remove the Black/Yellow ignition Kill circuit wire, you cannot turn the motor off with the key. Just choke it until it dies, or put your hand over the carbs.

Re: 1993 90hp intermittantly dies

I may have made things worst.

I went out and started the boat. It started fine so I switched it off to start taking the readings and this is what I got.
137.6 on the blue wire
23.5 on the red
3.5 on all 3 wires going to the coils.

I ungrounded the plugs and put them back and hooked up the black/yellow wire and now the boat won't start. As of now, I'm not getting any spark to the plugs.

I'll go out later to see if the boat starts but this time I think it won't.

Any ideals on what to check now?

pnwboat said:

OK, looks like the readings are slightly higher than normal, but not off by much. Did you happen to disconnect the stator wires when you were measuring them? At this point I would assume that it is probably OK....at least for now. Next test you really need a DVA adapter to get accurate readings, but I've found you can usually tell if the voltages are good or bad without one.

Make sure the battery is fully charged. Try starting the engine to make sure that it does start and runs. Only have to run it for 30 sec. or so. Basically what you're going to do is to take some voltage and resistance readings while the engine is running normally, and then when it heats up and no longer runs, take the same voltage and resistance readings.

Now to do this test, you have to crank the engine over with the spark plug wires attached to the plugs, but the spark plugs removed. The threaded portion of the plugs should be grounded to the block. Disconnect the Black/Yellow wire from the switchbox. This is the ignition Kill circuit. Set your voltage on your meter to read at least 400V. If it has the auto ranging feature, you don't have to do anything. Crank the engine and measure the voltage between the Red stator wire and ground. Next do the same thing with the Blue stator wire. I forgot to mention that the wires should attached to the switchbox. Write down the voltage readings. All of these readings are important to determine if the switchbox or stator is bad later on. Next, check the readings on the primary wires on the switchbox that go to each ignition coil while cranking the engine. These wires should also be attached to the switchbox. I believe they are Green, Green/White, and Green/Red. Write down these voltages too.

Next step is to hook the Black/Yellow wire back up, and re-install the spark plugs and wires. Make sure the Black/Yellow wire is hooked up, otherwise the motor will not turn off with the ignition key. Fire the motor up and run it until it dies, and will no longer start. While it is in the "non running"state, remove the Black/Yellow wire. If it starts, then the switchbox is bad. If it still will not start, take your stator wire and primary coil wire voltage readings again while cranking the motor. If there is more than a 10% difference in the readings, then the switchbox may be bad. One other thing to check while it is in the "Non-running" state. Disconnect the Red and Blue stator wires and measure the resistance to ground again. They should read exactly the same as you read before. If they don't, then the stator windings may be shorting out when they get hot.

NOTE: Forgot to mention....While the motor is in the "non-running" state, and the motor starts after you remove the Black/Yellow ignition Kill circuit wire, you cannot turn the motor off with the key. Just choke it until it dies, or put your hand over the carbs.

Click to expand...

Re: 1993 90hp intermittantly dies

I doubt that it was anything that you did. Most likely a coincidence. Maybe your intermittent problem is no longer intermittent. Try disconnecting the stator wires and measure to ground again. If no difference than first time you measured the resistance, then you can probably assume that it is good. Disconnect the Black/Yellow wire again. See if spark returns. If you get spark, then you have a short to ground in you ignition Kill circuit (Black/Yellow wire).

If still no spark, then check the resistance between the plate that the coils are mounted to and the engine block. It should read a dead short. There is usually a black wire that is attached to the coil mounting plate and the block. It needs to be making good contact on both ends. This is the ground reference for the whole ignition system.

Also check all of the "bullet" connectors on the ignition components. Make sure that they are all in good shape and pushed all the way together.

Do you happen to have the "candy bar" adapter between the stator wires and the switch box. Pictured below is the adapter that I'm referring to.

Mercury Force Outboard Stator Adaptor 834949A3 834949A1 8M0021546 Works Perfect | eBay

If all of the above checks out OK, then I would begin to suspect that the switchbox itself is bad.

Re: 1993 90hp intermittantly dies

The stator wires were the same, blue 3918, red 110.

I disconnect the black/yellow wire and still no spark.

Coil mounting plate to ground was a dead short. Black ground wire checked good too..

All the bullet connectors looked good too.

I don't have the "candy bar" as far as I could tell. I looked everywhere and didn't see one.

What now?

Thanks ALOT for your continued help!!!!!

Re: 1993 90hp intermittantly dies

Try one last thing. Disconnect the leads from the stator to the rectifier/regulator. I believe you have two yellow leads that go from the stator to the rectifier/regulator. If spark returns, then replace the rectifier/regulator. If still no spark, then I would say that from a process of elimination, the most likely culprit is the switchbox itself.

Does your switchbox have threaded posts with nuts to hold each wire in place, or do you have wires coming out of the swtchbox that connect to the harness?

Re: 1993 90hp intermittantly dies

I disconnected the yellow wires from the stator and I still had NO spark.

My switchbox has threaded posts. If I do need one, all I've seen are ones with wires coming from them. Can you please suggest one if I need one at this point since all I've seen DON'T have post.

My motor is a 93 Force, model H090412NX, Serial number 0E010171.

Thanks again.

Re: 1993 90hp intermittantly dies

IBoats has them. I'm guessing, but I'm pretty sure this one matches the one you've got. Take a close look at the pictures to make sure they match yours. Your serial number looks to be in the 1991 range, but the model number indicates like you say, 1993. I've seen a lot of mistakes in the documentation on line and in manuals regarding S/N and year of manufacture. The type of ignition setup you have looks to be a 1991 though, if it has the threaded posts.

CDI P/N 114-7778, Sierra Ign. P/N 18-5775, Mallory Ign. P/N 9-25100.

Force Switch Boxes - iboats

Here's one. Used, but with a guarantee.

Switchbox 90 HP Force 908F92C Outboard Powerpack Ignition Control Module | eBay

Here's another one. P/N 114-7778. Cost a little more, but brand new.

Chrysler or Force CD Ignition