Mercruiser 3.0L LX - EST Ignition - how to check for proper spark?

[Bilesks]

Hi there,

We have a 1997 Searay 175 with the Mercruiser 3.0 LX. Engine is running really rough with black smoke. Did extensive troubleshooting, but all things point to being really rich.

-CHOKE is open
- Spark plugs are all black with soot
- I pulled the wires off when running 1 at a time, #3 and #4 made no change, but I do hear some clicking when getting close to putting wire back onto the plug.
- Compression is good, timing is good, double checked the carb settings, fuel pressure is good, choke is fully open.

How can I check that the ignition system is putting the proper signal strength to the plugs? I did the resistance checks on the coil and seemed within spec. Is there a certain voltage I should see at the spark plug wires? Is there any checks I can do right at the distributor? I just want a way to eliminate the ignition system all together from the troubleshooting list.

Thank you!

 

[alldodge]

Right now I don't see where you have an ignition problem, it might be incorrect firing order but my guess is it's low compression or a carb issue

Have you done a compression test, if so what are the numbers?
Your firing order should be 1-3-4-2 and the distributor turns clockwise

 

[JustJason]

The easiest way to check for spark is to clip a timing light to each plug wire, one at a time, and see if the timing light flashes evenly and consistently with engine RPM. If it doesn't there is a spark issue; if it does, there isn't a spark issue. Just make sure your plugs are new and the plug wires are seated because the timing light can flash if the spark is arcing around the plug, instead of through it.

 

[nola mike]

The easiest way to check for spark is to clip a timing light to each plug wire, one at a time, and see if the timing light flashes evenly and consistently with engine RPM. If it doesn't there is a spark issue; if it does, there isn't a spark issue. Just make sure your plugs are new and the plug wires are seated because the timing light can flash if the spark is arcing around the plug, instead of through it.

This will tell you if there's the impulse for the spark, but not the quality. Good first step but not definitive. That said, if this is all 4 cylinders then probably fuel. 2 cylinders OP could be dropping cylinders from ignition/compression/fuel. Best way to check is with a dedicated spark tester. You can get some idea by pulling a plug, grounding it, and seeing if a bright blue spark is jumping the gap.

 

[Bondo]

How can I check that the ignition system is putting the proper signal strength to the plugs?

Ayuh,...... Welcome Aboard,........ Here's one way to do it,.....