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No spark on a 1988 90hp Merc

F

fivestring

New member
"I have been working all day t

"I have been working all day to find where my problem is to no avail.

I bought this boat last week. The seller started the motor and it started and ran very smoothly.

I got it home and began to clean up the rat's nest of wires in the battery box. I apparently disconnected something that powers the ignition system and I can not find out where it is.

I have good connections from the battery to the starter relay and the engine cranks over well. I get no spark on any of the three spark plug wire leads. I get no voltage from the white or red leads at the switch box. According to Seloc's troubleshooter, that tells me I have something wrong in the harness, ignition switch or battery.

The battery is fully charged. Every connection is clean and tight.

My questions are:
1. Are the safety, neutral and mercury switches supposed to be closed or open in the 'run' position?
2. What wires are supposed to send power to the engine ignition system when you turn the key on?

I know this is somewhat obscure but I need some ideas of where to look. I am certain it is going to be a wire off or a bad switch, etc.

Any help is appreciated."
 
"Mark, Merc's ignition sys

"Mark, Merc's ignition system on this model does not require power from the battery other than to turn over the starter.

However, running it without the battery connected can fry the rectifier which in turn could fry the stator, so always keep the battery connected when attempting to start/run the motor (not that I know too many guys that can pull over a 90 with the emergency rope start)


The safety/mercury/stop switches should all be "open" (no continuity).

Their method of operation is to ground out the ignition power to the block when "closed" to either prevent the motor from starting or to shut it down."
 
"Jim, sounds like you and I ar

"Jim, sounds like you and I are in the same boat. ;)

Graham, thank for the reply.

The reason I started cleaning up the wiring mess in the first place was there were lots of questionable connections, one of which was a bare hot wire connection that laid briefly against the GAS TANK and was sparking away! When this happened the ignition was not on. I hope that didn't fry any components. Both fuses on the engine test ok.

On the safety switches, I am getting sporadic continuity from the deadman (wrist harness) switch. It shows continuity in either position occasionally. Can I disconnect the black/yellow leads at the switchbox to eliminate it and the mercury switch to see if that allows spark?

By the way, I am testing spark with a spark plug tester. With this tester I can adjust the gap the spark should jump. I have it set at around 1/4"."
 
"Yes, if you disconnect the bl

"Yes, if you disconnect the black/yellow back at the switch box you will effectively disconnect all the "kill" switches.

Then you can turn over at cranking speed and check the spark.

If you do start it however, you basically just have to run it out of gas to stop it.

Be careful around the ignition wires if you are playing with screwdrivers or pliers and it's running (or turning over) - these babies put out close to 50,000 volts at the coils - and they bite real hard if you get too close


The 1/4" gap will be sufficient to see if you have spark...."
 
"****Don't

"****Don't sent power into the ign. It blows the switchbox***

Pull the cannon plug from the motor. hit the starter with a jumper. It it works, than rewire the boat.

If not than take the blk/yel lead off the switch-box. That should get a spark, unless the stator or box did just fail."
 
"Thanks for the help so far.

"Thanks for the help so far.

Bandit, I am ignorant on what a cannon plug is. The starter will run fine using the key switch.

I think I found a serial number. This is the only number I can find and it was on the frost plug....B145612....can anyone tell me for sure it is a 1988 motor?

I tried eliminating the black/yel kill switch wires to the switch box, still no spark.

I tried disconnecting the rectifier, no spark.

I tested the stator according to these specs listed in the troubleshooting section...

Between red and blue leads: should be 3.6-4.2 Ohms, I got no reading at all, just a steady "1." on the meter.

Between red and ground: should be 90-140 Ohms, I got 108 Ohms.

Before I go dropping $200 on a stator, I would like your opinion that I really need the stator.

Is it possible for that brief sparking at the gas tank to have fried the stator?

I think this is the stator my engine uses: CDI 174-8778K1. Can you confirm?

Any other suggestions??

Thanks again for all the help. I know time and persistence will reveal and resolve the issue."
 
"Bandit, I believe you were re

"Bandit, I believe you were referring to the main multi-pin plug coming from the wiring harness as a cannon plug. I unplugged it and tried again, again no spark.

It looks like 398-8778K1 and 398-9710K1 will fit, the first being a 9A and the second a 16A stator..."
 
"Ok, after much searching and

"Ok, after much searching and reading, I have concluded that the 9A stator is the one I need if I need one for sure. The 16A version requires a voltage regulator that I don't have.

I would still like a confirmation from Graham or other member who knows this stuff. I have found a good price on a new CDI stator ($157)and am ready to hit the 'buy' button but want to be sure."
 
"Yep, 9 amp was original to yo

"Yep, 9 amp was original to your model and the CDI stators are good quality (I personally like most of the CDI parts better than OEM Force products) and the price is good.

BUY
"
 
"I just found this post for te

"I just found this post for testing the rectifier...

"If the rectifier in question is the standard three post model, then the test is to use an analog ohmmeter across diode pairs. Specifically, that rectifier has four connections including the case, which is ground (-12VDC), since the motor is negative ground. Set the ohn meter to RX1 scale and put one meter lead on the +12V post, the other on one of the two AC (stator) posts. Now switch the leads. You should have no continuity one way, and when you switch the leads, you should have continuity. Repeat the test for the other AC post and +12V post. Now try the same test using the case ground to each of the AC posts. If all the tests show continuity one way, and none the other way, the rectifier is good. If a pair of connections show no continuity either way or show continuity both ways the rectifier is bad."
"
 
"Ya, that sounds about right -

"Ya, that sounds about right - I will post the test flow diagram (don't know how well it will show up).

And yes, a bad rectifier can toast a stator. So for less than 35 bucks, if you even "think you might possibly, kinda, maybe suspect" a bad rectifier, change it...

252183.jpg
"
 
"Got the stator and tool for p

"Got the stator and tool for pulling the flywheel today. I just hooked the new stator up and retested the rectifier to be doubly sure it was good.

I turned the motor over briefly with a spark tester hooked up and...

VIOLA! I have big, fat spark! I will hook the water hose up to the motor this weekend and see if I can get it to start up.

Thanks for all your help! I may be back for more if anything else pops up with this motor."
 
"Got a chance to hook up the m

"Got a chance to hook up the muff and hose this afternoon. I apprehensively cranked it over. It turned over about 4 times (I forgot to squeeze the bulb) and it fired right up! It seems to run very well, although there may be a slight miss until I get to higher rpms. I want to freshen up the gas after letting some more of this gas with sea foam in it run through a little. I ran it about 10 minutes at all speeds."
 
"<[img]"http://www.marineengin

"
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That was an easy one. I probably looked at 3 or 4 stators a day in those years. Or so it seemed. "
 
"The hard part was clicking &#

"The hard part was clicking 'BUY', not knowing for 100% sure I was correct that I really needed a stator! All is well now."
 
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