No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

[Imjus4u2nv]

I own a 1986 Mercury Inline 6, I had an overheat in the #3 cylinder and that cylinder stopped firing. After that the engine ran on 5 cylinders for a while, then dropped another cylinder (I think #1 but dont remember). As I was working on the boat to repair the dropped cylinders (which I thought were ignition coil so I bought new ones) it dropped another cylinder during the ignition coil swap, now I am not getting spark to three cylinders (all odd, 1,3,5 cylinders).
I brought my ohm meter and did test on the ignition coils, the trigger, and the stator.
I thought it may be a switch box issue, especially since it was odd cylinders that were not sparking. I tried swappping the two switch boxes and then i got not spark to any cylinders. I swapped them back to original formation, and only three cylinders. Possibly one bad switch box?
ALso, since I got no spark I thought it could be the trigger (another member on the site had suggested in the past so it was on my mind). I check the trigger for its ohm specs and it all was in range (from 12.34-12.65, specs was 11-14).
I then check the stator and all the specs were within range as well.
I do not know of any specific test to bench check a switch box.
I decided to also conduct test on ignition coils and found this which was odd:
cylinder 1 (NEW IGNITION COIL): 238 ohms (should be 800-1100)- NO SPARK
cylinder 2: (NEW IGNITION COIL): 238 ohms (should be 800-1100)- SPARK
cylinder 3: (cylinder that stopped sparking a few months ago)- NO SPARK
cylinder 4: No measurement, would not register, but this cylinder sparks- SPARK
cylinder 5: WITHIN RANGE- NO SPARK
cylinder 6: WITHIN RANGE- SPARK

I am waiting for a DVA adaptor to test the stator and the trigger. I have the specs but am uncertain how to test for this:
Stator- Low side (20v)
Stator- High side (180v)
Trigger- (4v+)- I believe his is the same test for ohms (Brown/Y to White, White to Violet/Y, and Violet and Brown/Y.

Any help would be greatly appreciated, trying to get it running before I pull it for the season so I can test it in the water and decide whether to drop a deposit on a dock slip.

 

[achris]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

Odd cylinders lost spark is either a switchbox or a stator. Try swapping the stator wires across between the packs (leave everything else as is). Also remove (only for testing purposes) the bias wire between the boxes and the kill wires off the boxes. If you still have the odd cylinders with no spark, it's the switchbox, it the fault moves to the even cylinders, it's the stator...

Chris....

 

[Imjus4u2nv]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

Odd cylinders lost spark is either a switchbox or a stator. Try swapping the stator wires across between the packs (leave everything else as is). Also remove (only for testing purposes) the bias wire between the boxes and the kill wires off the boxes. If you still have the odd cylinders with no spark, it's the switchbox, it the fault moves to the even cylinders, it's the stator...

Chris....

Thanks Chris,
I attached the diagram to make sure I am disconnecting the correct wires.
The stators wires are the blue/red wires.
The bias wire I am assuming is the white/black wire that connects to both switch boxes.
I am uncertain which wire is the kill wire is it the Black/yellow in the diagram?
Thanks again for the help.
View attachment IGNITION DIAGRAM.pdf

 

[achris]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

Thanks Chris,
I attached the diagram to make sure I am disconnecting the correct wires.
The stators wires are the blue/red wires.
The bias wire I am assuming is the white/black wire that connects to both switch boxes.
I am uncertain which wire is the kill wire is it the Black/yellow in the diagram?
Thanks again for the help.
View attachment 216616

Yes, Black/yellow is the kill wire.

 

[Chris1956]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

You had best test compression, since you overheated. #3 cylinder is prone to damage, followed by #1.

 

[Imjus4u2nv]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

You had best test compression, since you overheated. #3 cylinder is prone to damage, followed by #1.

Hey Chris- Do you think it is worth canning the engine? I was uncertain what to take from your post and appreciate you taking the time to respond. Do you agree that is likely the stator, I know someone else indicated a possibly faulty trigger. In the end WWCD- what would chris do?

 

[achris]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

Hey Chris- Do you think it is worth canning the engine? I was uncertain what to take from your post and appreciate you taking the time to respond. Do you agree that is likely the stator, I know someone else indicated a possibly faulty trigger. In the end WWCD- what would chris do?

No Pressure, right? :facepalm:

If you are losing cylinders, and you suspect the pistons (detonation or piston melts). I would remove the transfer covers from the cylinders in question and have a look at the pistons skirts. If you have access to a bore-scope (or one of those tiny USB cameras) then also have a look at the cylinder walls. If there is damage on the pistons (and I suspect there will be) but the cylinder walls are in good shape, I would pull the power-head and rebuild it.... If you really like the engine, that's the way I would go... But if you are 'oh-hum' about the engine, part it out and find a good, late model 3 cylinder 90 to replace it with.... That is WCWD (what Chris would do )

Chris....

 

[Imjus4u2nv]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

No Pressure, right? :facepalm:

If you are losing cylinders, and you suspect the pistons (detonation or piston melts). I would remove the transfer covers from the cylinders in question and have a look at the pistons skirts. If you have access to a bore-scope (or one of those tiny USB cameras) then also have a look at the cylinder walls. If there is damage on the pistons (and I suspect there will be) but the cylinder walls are in good shape, I would pull the power-head and rebuild it.... If you really like the engine, that's the way I would go... But if you are 'oh-hum' about the engine, part it out and find a good, late model 3 cylinder 90 to replace it with.... That is WCWD (what Chris would do )

Chris....

I believe from my other post (the one with 10x magnification of the inside of the cylinders), it appeared to be an overheat from running lien (as I believe you said, or the trigger as another poster suggested). The cylinder walls looks to be decent and seems to be just the top of the pistons, and as you reiterated I have good compression.
I already have the transfer port gasket, just have to get around to taking it off would probably be a good time prior to dropping more money into it.
I like the engine and when I ran it ran like a bat out of a hell (even in five cylinders).
The issue in the past was overheating/lien condition.
The issue now is dropping cylinders which I am assuming is electrical.
So where I only had one issue to address, I am now in the position where there are multiple issues, or it is one issue that possibly caused all the problems (trigger?). I wish I knew more.
Probably time to start pulling some over time at work to pay the mechanic, if the flywheel has to be pulled I don't comfortable with that.
My fear of getting a replacement used engine, is not only the cost, but it may have similar or new issues.
I don't know what to do, but only so far you guys can lead me.

 

[achris]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

ah, ok... That thread with all the video cameras down the plug holes was yours? I liked those pictures so much, I'm buying one of those cameras... So for that, thank you...

Your lean run may be the carb main jets. When I had my boat shop, one of my first customers had exactly the same problem as you appear to be having, running lean, cooking pistons. It's not actually a lean run condition. What it is, is that Merc had the inside of the last of the in-line six engine blocks EDP coated in the water jacket... Helps keep corrosion at bay, but slows the transfer of heat out of the cylinder walls and into the water around the cylinders.... The fix we came up with was to increase the size of the main jet in the carbs. I'm away from home at the moment (and will be for another couple of weeks), so don't have access to my manuals, but I think we increased the jets 2 sizes... That allowed enough fuel into the engine to keep the cylinder temperatures down so the pistons wouldn't cook off...

Now, your electrical problem (loss of spark)... As you said, only odd cylinders.. That CAN NOT be a trigger... Only a switchbox or a stator. Did you do the stator wire swap I suggest yet? If so, what result?

Chris..........

 

[Imjus4u2nv]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

ah, ok... That thread with all the video cameras down the plug holes was yours? I liked those pictures so much, I'm buying one of those cameras... So for that, thank you...

Your lean run may be the carb main jets. When I had my boat shop, one of my first customers had exactly the same problem as you appear to be having, running lean, cooking pistons. It's not actually a lean run condition. What it is, is that Merc had the inside of the last of the in-line six engine blocks EDP coated in the water jacket... Helps keep corrosion at bay, but slows the transfer of heat out of the cylinder walls and into the water around the cylinders.... The fix we came up with was to increase the size of the main jet in the carbs. I'm away from home at the moment (and will be for another couple of weeks), so don't have access to my manuals, but I think we increased the jets 2 sizes... That allowed enough fuel into the engine to keep the cylinder temperatures down so the pistons wouldn't cook off...

Now, your electrical problem (loss of spark)... As you said, only odd cylinders.. That CAN NOT be a trigger... Only a switchbox or a stator. Did you do the stator wire swap I suggest yet? If so, what result?

Chris..........

Yup that was me- pretty cool stuff (knew someone would appreciate the videos), with how many people you help didn't think you realized it was me. If you happen to remember, and get a chance would love to know about the bigger jets. Just had the carbs rebuilt, but can't tune until I get the cylinders sparking. I have actualy been in the water jacket when my first cylinder overheated (and dropped at the same time- not sure if this helps at all, but thought was odd t lose spark and overheat at same time). Not sure what the EDP looks like but will see if I can find a picture of the inside of the water jacket.
Still waiting on the stator wire swap as you suggested on the switchboxes, will do this week (swamped with work) and also waiting to get the DVA tester in case the switch doesn't reveal any answers. Still not sure how to use the DVA tester to test stator (high side/low side) guessing need to have engine running in some fashion to be checking these values.
I will be sure to update as soon as I conduct the wire swap you suggested. Thanks again!

 

[achris]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

Yup that was me- pretty cool stuff (knew someone would appreciate the videos), with how many people you help didn't think you realized it was me.

Yes, very cool.

If you happen to remember, and get a chance would love to know about the bigger jets. Just had the carbs rebuilt, but can't tune until I get the cylinders sparking.

That will be when I get back home (work away).

I have actually been in the water jacket when my first cylinder overheated (and dropped at the same time- not sure if this helps at all, but thought was odd t lose spark and overheat at same time). Not sure what the EDP looks like but will see if I can find a picture of the inside of the water jacket.

Looks a bit like black paint... Actually, quite a lot like black paint. As opposed to just bare aluminium casting.

Still waiting on the stator wire swap as you suggested on the switchboxes, will do this week (swamped with work) and also waiting to get the DVA tester in case the switch doesn't reveal any answers. Still not sure how to use the DVA tester to test stator (high side/low side) guessing need to have engine running in some fashion to be checking these values.
I will be sure to update as soon as I conduct the wire swap you suggested. Thanks again!

Use a DVA just as you would a multimeter. It just gives peak voltage rather than average...

Chris......

 

[Imjus4u2nv]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

OK, so I did the stator wire swap as instructed above. After the swap, I am still getting spark to the SAME three cylinders, which from the information provided looks like a bad switch box.
Agreed?
Now, I have two switch boxes, and from my research most people advise switching out both of them- any suggestions?
As far as the water jacket, I do remember it looking like black paint and not bare aluminum so may try to go for the bigger jets when you find the size. Are the jets difficult to replace. I actually took on of the carb's off this weekend to make sure the work was done properly and it was (new floats, nice and clean on the inside) although I did find that some of the fuel lines were very corroded and looked like they were narrow on the inside so going to replace those tubes also.
I also conducted the tests with the DVA meter and don't have the readings with me. I was having an issue with the AC volt setting (when you use 20k opposed to 2k do I have to multiply the readings- sorry amateur question). What I did learn, was that the stator AC was very high voltage (I think around 150v) on both sides, I also checked the voltage from the trigger, and while the readings did not seem to match the spec in the book, the readings from the 3 trigger wires going into the switch box 1 (not firing) and the three wires going into switch box 2 (firing) were all the same (I believe around 5v).

 

[achris]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

OK, so I did the stator wire swap as instructed above. After the swap, I am still getting spark to the SAME three cylinders, which from the information provided looks like a bad switch box.
Agreed?
Now, I have two switch boxes, and from my research most people advise switching out both of them- any suggestions?

Yes, that sounds very much like the switchbox. Yes also on replacing both. It's very common for a 'good' switchbox to be a serial killer. Every time you replace the 'bad' box, the 'good' box will kill it... Hence replace both... And throw them in the trash-can!

As far as the water jacket, I do remember it looking like black paint and not bare aluminum so may try to go for the bigger jets when you find the size. Are the jets difficult to replace?

No, you can do it with the carbs in place on the engine. The main jet is behind the plug that is directly below the throttle opening. Just remove the plug , unscrew the main jet and put the new one in. One in each carb...

I actually took on of the carb's off this weekend to make sure the work was done properly and it was (new floats, nice and clean on the inside) although I did find that some of the fuel lines were very corroded and looked like they were narrow on the inside so going to replace those tubes also.
I also conducted the tests with the DVA meter and don't have the readings with me. I was having an issue with the AC volt setting (when you use 20k opposed to 2k do I have to multiply the readings- sorry amateur question).

No, just read the number off the scale.

What I did learn, was that the stator AC was very high voltage (I think around 150v) on both sides, I also checked the voltage from the trigger, and while the readings did not seem to match the spec in the book, the readings from the 3 trigger wires going into the switch box 1 (not firing) and the three wires going into switch box 2 (firing) were all the same (I believe around 5v).

Those readings sound right... I think the book reads minimum 2v....

Jet sizes... I have a listing that says the standard jet for those engines was 0.074. I would go with either 0.076 (part #1399-3796) or 0.785 (part #1399-3520)... Pull the jets out and have a look and see what size you have in...

Chris.......

 

[Imjus4u2nv]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

thanks Chris, I am going to try that if I get it back up and running!
I am going to order the switch boxes and want to make sure im getting the right ones. The number on my switch boxes, is 332-7778a1. I was going to order Sierra 18-5775, as Sierra seems much cheaper then CDI and Mallory. I can find the Sierra one brand new on ebay for $100 a piece.

Most sites for the Sierra 18-5775 boxes say SWITCH BOX
392-806529A1, 898253T24
SWITCH BOX
Replaces: 332-7778A6,
(Uses External Resistor)
332-7778A9,A12

The CDI website says its part, # 114-7778 Replaces:
18-5775, 332-5524, 332-5524A 1, 332-7778, 332-7778A 1, 332-7778A 3, 332-7778A 5, 332-7778A 6, 332-7778A 9, 332-7778A12, 9-25100, 114-7778

 

[achris]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

Sounds good. I wait with baited breath...

Chris.........

 

[Imjus4u2nv]

Re: No Spark on Odd Cylinders, Switch box Help - 90hp inline 6

VICTORY (for now)!
Replaced the switch boxes and I have strong spark on all 6 cylinders. Was not able to start it up as I am waiting on bleeder hose for my carbs (they were all gunked up and when I went to remove one it ripped in half).
Now, I will take it one step at a time, but trying to decide whether to let it run on all 6 cylinders (recall #3 overheated at one point and was never fired after that), or just 5. Think I will finally take the transfer plate off and have a look inside- stay posted. (Once I look under the transfer plates, and make ad ecision to move forward, then I will need to tackle the lower unit which was full 98% with water at the end of the season.
THANK YOU CHRIS, I OWE YOU!