No spark on middle cylinder

[Plumber87]

I have a tohatsu m70c 1998 3 cylinder motor. I'm not getting spark on the middle cylinder. I have replaced the coil, the powerpark and have new plugs. I have done an ohms reading on the stator plug for each wire to earth. They were 200, 201, 205. I have changed the working could to the middle cylinder and they won't spark there. I'm stumped and so is my mechanic. Is there anything else that would cause this. Compression is 120 on all cylinders.

 

[pvanv]

That motor has a single exciter, 3 pulsers, a CD, and 3 ignition coils. There isn't any stator. Ohm readings must be taken with a meter that runs on a battery of 3v or less.

When cranking, but not running:

The exciter should deliver at least 130 DVA, and resistance should be between 220 and 330 ohms, +/- 25%. , Each pulser resistance should be 160 - 220 ohms +/- 25%, at at least 3.0 DVA. CD output needs to be 130 DVA minimum. Each ignition coil should have a primary side resistance of 0.16 - 0.24 ohms +/- 25%, secondary windings should each be 3.3 - 5 K ohms +/- 25%. See section 7 of the Tohatsu 3- and 4-cylinder Factory service manual for full details.

 

[Plumber87]

I have only just started to get into boat motors so don't know that much. The plug which comes from the 3 pulsars and has ground in it. They had all around 200ohms. What is the exciter? The cd unit is brand new. I don't have a tohatsu manual yet.

 

[Plumber87]

I also noticed with the plastic flywheel cover off that when running the flywheel seems a bit warped or not straight.

 

[pvanv]

I have only just started to get into boat motors so don't know that much. The plug which comes from the 3 pulsars and has ground in it. They had all around 200ohms. What is the exciter? The cd unit is brand new. I don't have a tohatsu manual yet.

The exciter charges the CD. The pulsers discharge it. The ign coils each step the voltage up for spark.

 

[pvanv]

I also noticed with the plastic flywheel cover off that when running the flywheel seems a bit warped or not straight.

I would expect the flywheel to be flat within say 0.20". If not, maybe it is not installed correctly.

 

[pvanv]

You really want a meter with DVA capability. But... assuming the exciter is OK (2 cylinders are firing), then you either have a faulty pulser, a faulty cd, a faulty ign coil, or a bad plug. You can always swap out components to see where the problem follows. What is the "running" plug condition of cyl. 2? If wet, no spark. If dry, no gas.

 

[Plumber87]

Running condition of plug is wet and clean. The coil is new, the spark plug is new, the cd is new. All brand new. What's the pulser?

 

[pvanv]

There are 3 pulser coils; one for each cylinder.

 

[km1125]

I also noticed with the plastic flywheel cover off that when running the flywheel seems a bit warped or not straight.

That would concern me. Double check and see if that is true. If so, then definitely take off the flywheel and find out why. Is the key perhaps in wrong, which would throw off timing but also if the flywheel is crooked then some of the magnets (perhaps the one for the middle cylinder) is too far from the pulser for that cylinder and won't fire it. When you remove it, see if there was any damage to the magnets inside.