Mercury 150- not running on all cylinders. Please help!

[chirojoe]

I have a 1992 Merc. 150 that is having a problem. The last 2 times that I had her out, she ran well for about 2 miles then suddenly lost power and sounded very bad. I hear a clanking when the motor is running bad as if it is not running on all cylinders. I brought it home to flush it and felt the cylinder heads after about 5 minutes. The port side top and bottom cylinder heads around the spark plug was cooler than the other cylinder heads. I replaced the inner switchbox 8 months ago after the oil injection alarm sounded and it only ran on the 3 starboard cylinders. Could this be the outer switchbox, or is there another viable culprit. Thanks for any replies, Joe.

 

[Laddies]

Re: Mercury 150- not running on all cylinders. Please help!

You need to establish if the engine is dropping 2 or 3 cyls. This can be establishsd with a spark gap testing is much easier with a DVA but can be done without one. spark missing on 1 cyl is a box or coil, spark missing on 2 cyls. ussally a trigger. On 3cyls or one bank could be stator or switch box to test stator swap red+ red white - blue and blue white wires on the boxes If the spark stays on the same cyls. its the box if it changes it's the stator

 

[chirojoe]

Re: Mercury 150- not running on all cylinders. Please help!

Laddies, thanks for the reply. What is spark gap testing? Can I take out the spark plug with boot attached and ground it to the engine then have someone turn the engine over to verify spark. I pulled a plug wire and turned the engine on to listen for any change, and repeated with each plug wire. The top port side plug made no difference. How do I test a coil. Thanks in advance, Joe.

 

[Laddies]

Re: Mercury 150- not running on all cylinders. Please help!

Many companies make spark testrrs but yes a regular plug with the ground electroid cut off will work. Exchange the coils from 2 cyls and see where the spark goes

 

[chirojoe]

Re: Mercury 150- not running on all cylinders. Please help!

I swapped the switch boxes and the port side top and bottom cylinders still have weak to no spark. I then swapped the leads coming from the stator to the switch boxes and still have weak or no spark on the port side top and bottom cylinders. What do I test next? I do not have a DVA multimeter but will get one if that's the only way to test ther rest of the ignition system. I will try to swap the coils around to see if that helps, but it sounds unlikely (but certainly not impossible) that two coils on the same bank would malfunction at exactly the same time. Thanks in advance for the replies, Joe.

 

[Laddies]

Re: Mercury 150- not running on all cylinders. Please help!

Normally a miss on 2 cyls. denotes a bad trigger winding but those 2 cyls. don't share a winding becuse if a windinding is bad it would efect 1+2 or 3+4 or 5+6 your is not like that I am afaid you may have to take it somewhere that has a DVA to test output voltages

 

[KCLOST]

Re: Mercury 150- not running on all cylinders. Please help!

Keep in mind that when you replace one switchbox of that vintage (mercury made) you should change both of them....<br /><br />However, your testing does not prove that the old one is bad...