1988 Merc 9.9 stator question

[wtinnr2]

First of all, let me start by saying thank you to all of you fellas that share your knowledge to help out us average Joe's. This is my first post, but have
gotten lots of good info by reading others questions.

My question.....1988 merc 9.9 starts and idles fine (with a sputter here and there) , but loses power, misses, and smokes in the higher rpm range. The switchbox was changed by a guy that I had work on it but same problem and now he won't return my calls. I'm now thinking it may be the stator. Took a DVA reading at idle with the kill switch wire removed (blk/ylw) as directed. According to the info I have, the high side (blk/wht) should read 20v and the low side (blk/ylw) 180+v. My readings were 10v high side, 38v low side. Did I measure these correctly or should the readings be taken under a higher rpm?


Thanks, Scott

BTW, readings were taken from each wire to engine ground while idling.

 

[presley2]

Re: 1988 Merc 9.9 stator question

Not to indicate you are doing this wrong you may be testing your engine perfectly but I have listed the specs and set up below from the Factory Mercury Service Manual for your engine.

Note the set up is geared more towards the Mercury analog DVA meter your setting may be different with a digital meter but specs and meter lead locations remain the same.

According to the Mercury service manual for a 9.9 engine the DVA specs for a black plastic coated stator are as follows:
(All test done with meter set on the 400 DC volts DVA scale and leads in DVA test ports.)

Switch Box output at the Coil primary terminals (Brass Nuts on coils)
Red meter lead to negative coil terminal and black meter lead to positive coil terminal
300 to 1000 rpm (125 to 260 volts)
1000 to 4000 rpm (200 to 360 volts)

Low Speed Stator Coil Circuit (Switch Box stop circuit)
Red meter lead to a good clean engine ground and black meter lead to the black yellow wire
300 to 1000 rpm (150 to 300 volts)
1000 to 4000 rpm (250 to 360 volts)

High Speed Stator Coil Circuit
Red meter lead to a good clean engine ground and black meter lead to the black white wire
300 to 1000 rpm (10 to 75 volts)
1000 to 4000 rpm (50 to 300 volts)

Depending on the year I will try and side the black meter lead between the clear plastic and the metal on the bullet connectors at the switch box to take my readings while the engine is running.

If you did your test as above it looks like your low speed stator coil is bad and out of spec. My guess is that if you have the DVA specs you might have the resistance specs for your stator. To double check that the stator has failed unhook all wires and test the leads per your manual going to the stator using an ohm test this should also indicate a failed stator.

If the stator is out of spec replace it. The little engines will sometimes start and run even with a bad low speed stator coil.

From your specs and your info it does seem like you are on the right track but consider these items.

Was the engine running fine and then did it just start missing at slow speed and stalling at high speed?
If the problem occurred all of a sudden it is more likely to be ignition.
Are you sure the problem is ignition related?
Another test you might try is to hook up an in line spark tester or a timing light and see if you lose spark at higher speeds or see if the timing light quits flashing. This would indicate no spark at higher speeds.

Problem is most likely in the carburetor if it is not ignition related.

Hopefully this information is helpful.

 

[wtinnr2]

Re: 1988 Merc 9.9 stator question

presley, thanks for the reply and great info. Especially for making me realize that I'm a total loser and was taking my voltage readings with my leads switched. ( OOPS!!! )

Now for the correct readings you suggested....

low speed stator.... 240v @ idle
270v @ highest rpm that can be achieved

high speed stator.... 60v @ idle
200v @ highest rpm

switchbox output @ coil primary.... 95v @ idle
130v @ highest rpm

trigger ohms...... r x 100.... 7.57 ( taken between leads)

stator ohms..... r x 1000... 2.9... blk/ylw to ground
r x 1.........137.. blk/wht to ground
r x 1000... 2.6... blk/wht to blk/ylw

I should note that the switchbox in place is a model #mpp 491/1. I'm not positive if this was a new part or one that he had on hand at the time. He worked on it where I keep the boat docked, and I wasn't present at the time. Like I said, he wouldn't call me back even for money for the part.

Also, this motor had sat for several years in my brother's shed due to lower unit issues which have since been resolved. Even though it sat for so long , it started right up. Changed plugs, cleaned carb, and switched fuel tanks but still same problem.


thanks again for your reply and sorry for the wrong info in my first post. Any other input would be greatly appreciated.

 

[wtinnr2]

Re: 1988 Merc 9.9 stator question

Forgot to mention that voltage steadily climbed when measuring the stator on both wires while increasing throttle. It did however fluctuate when taking measurments at coil terminals. Hope this info helps.

 

[wtinnr2]

Re: 1988 Merc 9.9 stator question

Shouldn't the output of the switchbox to the coils be equal to the input from the stator? Any help?

 

[wtinnr2]

Re: 1988 Merc 9.9 stator question

ttt

 

[presley2]

Re: 1988 Merc 9.9 stator question

Sorry, to leave you hanging I do not have much free time these days.

Having the lead reversed would have only made a difference if you were using an analog meter. With a digital meter the reading would be the same but the meter would place a minus sign in front of the reading.
Yes the output voltage from the switch box should be around what you are seeing as stator output voltage. However, even though there is a high speed and low speed stator coil they both provide voltage to the switch box for ignition operation all the time. The low speed does more work at slower speeds and high speed does more at upper rpms but for basic argument sake the electrical output power of both stator coils is combined in the switch box to feed power to the ignition coils. But I have seen small engines like yours run with a bad high speed stator coil. None of that really matters.

The readings you are providing shows that the output voltage from the switch box is below spec and the stator output from both stator coils seems to be in spec. If ALL the wires for the ignition system look to be in good condition and all grounds are clean and tight (Black wires). I would say you have a bad switch box.
Two Questions:
1) My guess is you are taking the readings while running the engine. If you are that is good you are getting the most accurate reading that way. If you are pulling the engine over by hand or using an electric starter with a somewhat discharged battery your readings could be off some.

2) Are you sure the gentleman you had do your repair actually replaced the switch box?
I would think he would have at least wanted to be paid for the part. A new switch box from Mercury for your engine list at about $180.00 and dealer cost is well over a hundred dollars. Aftermarket switch boxes are sometimes cheaper but not that much cheaper. I would say if the guy was out of pocket for over a hundred dollars in parts he would not give that away.

I did not spec out your ohm readings but I have seen enough of them to know yours look to be ok.

That?s a lot of typing to say I think you have a bad switch box, but I feel it is import to justify why it should be replaced. I hope this information is helpful.

 

[wtinnr2]

Re: 1988 Merc 9.9 stator question

Presely, Thanks again for responding.

To answer your questions: 1) Yes, all readings were taken with the motor running. Also, was using homemade dva adapter from plans I got from this site. Seems to work pretty well. All grounds were clean and tight.


2) As far as the switchbox, no I'm not sure if it's new used or even the sme one that was on the motor before he worked on it. All I can say is that it looked new. Wasn't dirty or scuffed.


Well, to bring you up to date, I replaced the stator last week. Not much change. I hate being a parts changer , but after mulling it all over I figured what were the chances of both switchboxs being bad? I am learning alot though and to be honest , I enjoy working on it myself. I guess there's no such thing as a free education.

Going to order a new box tomorrow. Will let you know how it turns out.

Scott