1989 Merc 90HP 3 Cylinder Power Problem

[WildWillJAX]

This engine is still experiencing the same intermitent power loss problem after many hours of troubleshooting and I am stumped.HELP!<br />Problem: After throttling up on plane (3,000 - 3,500 RPMs)and running for a approx 5 minutes the engine experiences an intermitent power loss of one cylinder. The engine will bog, lose RPM (500-1000), for an abitrary amount of time, then power will return and run fine for about 2-3 minutes then the engine power/rpm's droops again. This occurs at any power settings between 1/4 to WOT. Problem seems to be less dramatic after engine is warmed up and ran for awhile.(but never goes away completely).<br />I have performed spark testing, fuel system testing, and compression testing, with the following results.<br />Fuel system appears A-OK, no leaks, clean fuel, new filter, and clean carbs.<br />Compression=110 on all 3<br />New plugs, plug wires and trigger assembly installed.<br />IN ADDITION:<br />When troubleshooting, At idle and up to 3,000 rpms when attached to muffs in the driveway disconnecting the #1 spark plug wire from the plug does not affect the engines performace or rpm's significantly ? However, a crisp blue spark is present when the #1 wire is held near ground but it appears that number 1 cylinder is not contributing power.<br />Periodically as the engine runs at idle for extended periods, there will be an "after firing" (pop) out the exhaust port (center prop hub) with a stumble of rpms.<br />I suspect, that water is entering the combustion chamber of the number 1 cylinder and fowling the spark plug because the spark plug electrodes (number 1 only) are clean and free of carbon deposits. Furthermore, that this air/fuel/water mix is not igniting under most conditions resulting in only occasional power production.<br />Is this assumption reasonable?<br />Is there any way to verify my suspicion that water is getting into the air/fuel mix due to a bad gasket on the head or exhaust plate without pulling it apart?<br />Any other suggestions/troubleshooting tips greatly appreciated. THANKS in advance.<br />Will

 

[rabidfish]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

What color is the stator?

 

[WildWillJAX]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

Not sure of the stator color, why is this relevant? The stator has passed it's resistance and continuity tests IAW the Clymer manual.

 

[rodbolt]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

cause the stator can do weired and funky things on a merc. the next two steps will require a timing light anda peak reading ANALOG meter. hook the meter upon the #1 coil primary. index all 3 cyl at TDC on the flywheel using numbers painted with fingernail polish. while observing the needle on the meter and watching the marks on the flywheel run the engine atthe RPM the miss occurs. if the timing light shows anyother marks than the cyl you are on the switchbox is cross fireing. also if the meter needle starts bouncing its cross firing. from there its a matter of elimination. the black stators procuced some funny problems and would blow smoke rings out the exhaust. the switchbox can do some funny things as well and both will pass every test in the book and still not work correctly, usually water will leave very tiny green spots on the ground electrode, takes a good light and a magnifying glass to find them.<br />take a dirty plug and install it to see it it gets cleaned. a new plug that stays white can indicate that its being fuel washed.

 

[prolinews]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

My father has the same engine on his boat . Zero problems until november cranked ran fine 20 minutes later nothing .I checked the stator fine no problems .checked everything on the motor it all checked out Went to the shop for advice my buddy gave me another stator and told me just to try it . I thought he was crazy until it cranked up. been running great ever since It was the black stator .By the way that flywheel is going to be fun to get off with a gear puller buy or borrow the merc puller $90 bucks. but if you use the gear puller put a good amount of pb blaster on the key torque the puller tap the woodruff key with a punch . remember to replace the key.

 

[WildWillJAX]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

I will procede to test/inspect the stator as recommended to determine it's color. If it is black, I will replace it, however, what color is the APPROVED stator assembly? Replacing a poorly designed black stator with another black stator of the same design would be senseless. Does the redesigned stator assembly have a new/specific part number?<br />Thanks

 

[rodbolt]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

I dont think the black stator has been availible for some years. the last red stator kit I bought was about 460 and was on revision a26 or so.<br /> but if all tests are good its time to replace a stator or a switchbox. I know that sounds like tossing parts at it and I hate to say it but mercs are notorious for passing every test in the book and a few that are not and still not working. years ago most merc manuals said do this test, if the test passes and ther unit does not work, replace with a known good unit and retest.

 

[rabidfish]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

It is possibly unfair to say that the stator is bad, just because it's black. However the new kits do not seem to fail at quite the same rate.<br /><br />The "black" stators are available, but you would be putting it back together only to have not done anything about the root of the problem.<br /><br />The new style is red.<br /><br />I would recommend you change out the whole system to the "KIT". It converts the charging system from a 9 amp system to a 16 amp system.<br /><br />There is a service bulletin.<br />Send your email & I'll get you a copy.

 

[WildWillJAX]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

Email address is WildWillJAX@aol.com<br />What does the Red stator "kit" contain? Does the red stator "kit", include an upgraded voltage regulator or is the voltage regulator used with the black stator compatable with the upgraded red stator.

 

[WildWillJAX]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

I have confirmed that my engine has the Black Stator assembly. Although it passes all resistance and voltage checks, I will initiate a upgrade to the Red Stator. I have found a source for a Red Stator P/N 398-832075A3, the parts book identifies the Red Stator Kit as P/N 398-832075A5, what if any is the difference? Will I have to upgrade my rectifier and/or voltage regulator when upgrading from black to red?<br />In addition, I have found no evidence of cross firing using the voltmeter and timing light tests as suggested in an earlier posting.<br />Thanks in advance.

 

[rabidfish]

Re: 1989 Merc 90HP 3 Cylinder Power Problem

If you have a black stator, then you need a kit. The (A3) is a stator alone and cannot be used without the adapter module. <br /><br />The (A5) kit has the module ( and other misc. parts )and upgrade installation instructions.<br /><br />The (A7) kit includes the voltage regulator also.<br />( I recommend this option. The voltage regulators are the weak link in the charging system anyway, you may want to replace it while you are installing related components )