45hp merc, 1989, missing on cylinder #2

[halmc]

The missing is intermittant; i.e., if I go out to the boat today, it may or may not run on #2 (assuming #2 is second from the top) and #2 may or may not continue to miss or to run, as its mood dictates.

I have ordered a shop manual, but do not yet have it.

Here are my observations:
1) very even compression @125psi on each of its four cylinders.
2) when it runs on four, it runs great.
3) very inocasionally, it misses on two.
4) Sometimes when it's running on four, the tach says 4800rpm, other times it says 6000 rpm, tho the boat speed as gps measured is the same (when it's running on three, boat speed is considerably less, of course)
5) starts easily; idles smooth enough unless it's chosen to run on three.
6) spark is observed on all plugs (when out of the enigne) including #2
7) all connections to the switchbox are clean and corrosion free.
8) Sometimes if I shove in on the face of the switchbox, it seems to encourage #2 to begin and continue firing. I'm not entirely sure of this observation, but it seems so

Here's what I've done:

1) R&R'd the top carburetor (removing all jets) Inside was spick 'n' span
2) swapped plug wires, installed new plugs
3) established which cylinder was/is missing by shorting the top of the plug to ground both while runing WFO and at idle.
4) I've done nothing to swap coils #1 and #2 to see if that changes which cylinder is missing. Will do that next, but it's raining like crazy out.

I've searched this excellent forum top to bottom and found this post by J Martin:

Generally speaking, if the stator is bad, all cylinders will be affected, except on a 6, where half will be affected. If a trigger is bad, 2 opposite cylinders (in the timing sequence) will be affected. Switchbox is a crap shoot. Coil affects only one cylinder. You've eliminated the coil with a swap procedure, so that leaves the switchbox as the most likely culprit.
John

Although John was addressing a six cylinder engine, This strikes me like a mavelously succint statement of the issue and prompts me to get my PayPal account ready for a new switchbox, assuming that my proposed coil swap fails to move the missing cylinder.

I would appreciate any comments, prior to my busting out a coupla C notes. The more astute among you will notice that this problem is astonishingly similar to one I'm addressing on a friend's engine, in that instance, a 40hp Evinrude. My merc didn't begin this schennagans until I undertook to help with his. No good deed goes unpunshed, I reckon. Or it's contageous.

As I say, any help appreciated here in rainy Tallahassee.

 

[Laddies]

Re: 45hp merc, 1989, missing on cylinder #2

There are only 2 things that effect 1 cyl on your engine a coil or switchbox swap the wires to 1&2 on the box if the spark changes cyl its the box if it stays the same it's a coil

 

[halmc]

Re: 45hp merc, 1989, missing on cylinder #2

There are only 2 things that effect 1 cyl on your engine a coil or switchbox swap the wires to 1&2 on the box if the spark changes cyl its the box if it stays the same it's a coil

Thankya. Thankyavurrymuch. First thing in the AM.

 

[halmc]

Re: 45hp merc, 1989, missing on cylinder #2

There are only 2 things that effect 1 cyl on your engine a coil or switchbox swap the wires to 1&2 on the box if the spark changes cyl its the box if it stays the same it's a coil

My engine's been consistently missing on #2. Went out this AM to perform the coil test/swap, but first took the boat out to see whether things were the same. They weren't. Away from the slip, she's hitting on #3 and #4; missing completely on #2 and #1. After a while at about half throttle, it starts hitting on three cylinders, so I assume #1 is back on board. WRONG: #2 is back on board!It's now missing on #1. Bust along a half mile or so at half throttle, turn around, engine is still pulling on #'s 2,3 & 4; Missing on 1. Throttle way down to idle to put 'er back in the slip and #1 comes on line. Turn around, head for the open lake, throttle up to WFO and she runs great on all four cylinders for a mile out and a mile back. Coudn't do any more testing 'cause she's running perfectly.

Given the intermittant nature of the problem, I'm really, really on the verge of ordering a switchbox, but one thing in this quote bothers me:

If a trigger is bad, 2 opposite cylinders (in the timing sequence) will be affected.

I do have two cylinders affected, but John was talking about a six, not a four. Should the fact that I occasionally have two cylinders affected deflect my attention from the switchbox to a the trigger, or should I remain focused on getting a new switchbox.

Thanks for your patience in considering my lengthy posts, and thanks for the help.

 

[Laddies]

Re: 45hp merc, 1989, missing on cylinder #2

Have you cleaned the switcbox connection, 1&2 share the same trigger winding so if if only ran on 3&4 the trigger would be bad. However you said at first it was only missing 1 cyl. so if thats a fact then the box is bad and the problem may be spilling over to #1 or running it has damaged the trigger also. Use a Ohm meter and measure between the top 2 trigger wires it should be 800 to 1400 ohms if it does the the problem is the box and not the trigger

 

[halmc]

Re: 45hp merc, 1989, missing on cylinder #2

Have you cleaned the switcbox connection

I'm not sure, which switchbox conncetion? I cleaned and resoldered the switchbox end of the wire that runs between the #2 coil and the switchbox. That's because when I gave it a shove with a screwdriver, it seemed to cause the engine to fire on #2.

1&2 share the same trigger winding so if if only ran on 3&4 the trigger would be bad. However you said at first it was only missing 1 cyl. so if thats a fact then the box is bad and the problem may be spilling over to #1 or running it has damaged the trigger also.

I understand. What about the fact that it straightens out and runs on all four? From my reading/searching the forum, intermittant issues seem to arise more from switchboxes than from triggers, no?

Use a Ohm meter and measure between the top 2 trigger wires it should be 800 to 1400 ohms if it does the the problem is the box and not the trigger

OK, but I am not sure how to identify the top two trigger wires . . . ? Unfortunately, the engine is out at the lake, not at my shop. However, I'm certainly familiar with the s'box layout, and am aware that four wires leave the left side (as you face the s'box) and go to the coils. Where do the trigger wires connect to the s'box? And thanks for your patience. This is were a shop manual would really come in handy, I hope mine gets here soon.

Harold, Tallahassee

 

[holbs10]

Re: 45hp merc, 1989, missing on cylinder #2

The trigger wires go in on the right side of the switchbox. The colors on my 88 4cylinder 100 hp are purple, brown, white, and white/black (which is a bit confusing because this wire is actually all black) I only know this cause i was tinkering with mine yesterday.Hope this helps . I am right now experiencing sort of the same symptoms you describe yet i have no spark on the bottom cylinder. I replace the stator last year with the updated red stator kit but wasnt sure I actually installed it correctly due to the lousy directions that came with it. Now that I still have no spark on bottom cylinder Im quite sure I have the new stator kit installed correctly.

 

[halmc]

Re: 45hp merc, 1989, missing on cylinder #2

The trigger wires go in on the right side of the switchbox. The colors on my 88 4cylinder 100 hp are purple, brown, white, and white/black (which is a bit confusing because this wire is actually all black) I only know this cause i was tinkering with mine yesterday.Hope this helps . I am right now experiencing sort of the same symptoms you describe yet i have no spark on the bottom cylinder. I replace the stator last year with the updated red stator kit but wasnt sure I actually installed it correctly due to the lousy directions that came with it. Now that I still have no spark on bottom cylinder Im quite sure I have the new stator kit installed correctly.

Thanks for the note, holbs10, seems us newbees have to hang together as when the topic gets much more than knee deep, the graybeards run for the beach.

I should be receiving a new switchbox any day and I'll post the results in this thread.

 

[halmc]

Re: 45hp merc, 1989, missing on cylinder #2

A new swtichbox cured all of the ills with this engine. Thanks to all for the excellent suggestions. The engine runs great throughout its entire rpm range.