hotjava66

Have been having some issues, last year port engine would quit randomly, 1st time out this year(last weekend) it did not want to run at idle and was missing sometimes. Would just quit, then start ok, quit again, etc. Went ahead and changed out cap, rotor, sensor, and coil on both sides. Has new plugs and wires also. Now the problem motor will not start at all, other side that I did the same starts at the touch of the key. One thing to consider is last summer I had a coil wire on that engine burn off, was arcing inside the boot due to broken connection. I'm sure it probably arced for a bit before it burned off and stressed the ignition system. So now I'm thinking the ignition amplifier got hurt and is now giving up? Need some afirmation before swapping that out since its not cheap. Would bad amplifier cause a no run situation? The only other thing I can think of is maybe something in the wiring or harness got hurt somehow while the engines were out and I was working in the bilge but I don't see anything obvious. One more thing, when engine went back in it also did not want to fire and had no spark. The mechanic who was helping me jumped or arced something and got spark right away and then it fired right up. Need some help/input, trying to salvage what is left of the season.

Oh, it's a Merc thunderbolt VI with the ignition amlifier on the distributor

lakematdude

If the tachometer is shorted out you will not have spark.

Does the tach gauge move up to around 300 RPM while cranking?

Battery cranking amps are good at 550 CCA or more along with 12.6 volts ?

Disconnect the gray wire at the back of the tach gauge and see if you get spark.

There is a test in the Mercruiser service manual to test the ignition system. You may need to find and test it. It usually is available free online depending on what engine model you have.

What engine and year are you working on?