1994 Merc 225-HP 2-stroke misses, stalls

[Frank O]

After working through some recent issues, the 1994 Mercury 3.0L Offshore 225-HP carbureted 2-stroke on my 21-foot center console still has problems. At moderate to high speeds it sounds like it's missing. At harbor speed or idle, it stalls out frequently.

As a starting point, I'm planning on the following:

-- Run from portable gas tank to rule out fuel supply issues. A mechanic recently checked the fuel-water separator filter and said it's bone-dry.

-- Check each spark plug wire with timing light to look for any issues (either on a single plug or bank of 3).

I'd be interested in any thoughts on the following:

1) Do the symptoms (missing at higher speeds, stalling at low speed or idle) suggest any failure scenarios? For example, does this combination suggest, say, a timing issue?

2) Anything else you'd suggest I check to narrow down the diagnosis process?

Thanks much for any ideas.

 

[Faztbullet]

Re: 1994 Merc 225-HP 2-stroke misses, stalls

Good start to begin with along with compression check. Check the plug wires with ohm meter as these are prone to burn thru. Check cdm connections for corrosion and clean if needed. If you are getting as constant spitting , check reeds as these are known to chip and reed gasket blow outs. Also check the tpi setting on carbs as if its off it will run like crap.

 

[Frank O]

Re: 1994 Merc 225-HP 2-stroke misses, stalls

After a delay due to wet weather here, I got down to the boat today. Compression is good all around, spark plug wires are good. However, when I clipped a timing light to each plug wire in succession, I found intermittent dropouts in the spark on cylinder #5 (bottom starboard cylinder). This appeared to mesh with the sound of the engine missing. I unplugged the ignition module from the engine harness and sprayed contact cleaner, cleaned it carefully, applied dielectric grease and reassembled. This, however, didn't resolve the missing.

Would an intermittent problem like this point to the ignition module for that cylinder as the likely failure point? Or could it just as well be the stator or something else in the electrical system? I suppose I could swap a couple of the ignition modules to see if the problem followed the ignition module.

 

[hkeiner]

Re: 1994 Merc 225-HP 2-stroke misses, stalls

Swapping parts/wires around to see if the problem moves with the moved part/wire or if it stays with the plug is a common troubleshooting method. Also, using an inline spark tester sometimes provides a better indication of spark failure than using a timing light, especially when a single spark is just weak and not completely gone. It is sometimes hard to recognize a weak spark with a timing light. Another choice is using a DVA meter and ohmmeter to test the ignition system, but it requires more understanding of ignition specs.

It is often considered wiser to confirm that a particular ignition component is definately bad (using a troubleshooting method such as described above) before replacing an expensive part on a hunch or "educated guess" based upon how the motor runs.

 

[Frank O]

Re: 1994 Merc 225-HP 2-stroke misses, stalls

Thanks. I called a local Merc dealer and was told the ignition modules run $130 each, so swapping them around and retesting definitely sounds in order.