Coil Replacement and Hot spark Plugs

[LemonShark2]

Hi Guys,

Starting a new thread regarding what was narrowed down to a spent coil. Just had one more question - Although I got the coil today, and will be installing it today to be tested tomorrow, wanted to know if that had a co-relation with the two hot plugs issue I also noticed during the engine failures.

Just a reminder of the original issue, that my engine would start to stall after 1 hr of use. Engine cooling was not an issue.

One user thought it could also be related to switched spark plugs wires, or a bad alternator.

[ndutton]

I would treat the different plug temps separately from coil concerns. A funky coil will affect all four plugs equally.

[JOHN COOKSON]

After you install the new coil start the engine and rev it up a bit, so the alternator kicks in, then take a voltage measurement at coil +. Let's be sure the alternator is not kicking out more volts than it should which will lead to shortened coil life.

TRUE GRIT

I think the magic number is less than four amps. (Not sure) To find amps divide voltage at coil + by coil resistance. (Ohm's law)

[ndutton]

I think the magic number is less than four amps. (Not sure) To find amps divide voltage at coil + by coil resistance. (Ohm's law)

We've been recommending 3.4 amps for a 15% margin of safety. 4 amps is the edge of the cliff maximum.

Be sure to take the voltage measurement between the small coil + post and the engine block. The small coil "-" post is NOT a ground.

[LemonShark2]

Hot Spark Plugs

So I've been doing a bit more digging on the site regarding the hot plugs, and started thinking about what John C said "why are you running on two plugs" I didn't think it was literal, until I unplugged the 2 spark plug wires from the plugs closest to the flywheel, and the engine ran exactly how I'm used to it. Its running off just those two hot plugs I mentioned.

In addition, now that I've fixed my RPM gauge, I've only been getting about 1400 under power, and am not achieving hull speed on a Catalina 27.

Thinking back, this odd issue regarding gradual shutdowns after an hour started after this time I over-revved the engine after stepping on the accelerator, to the point where I got a large backfire. Could be the originating incident, or could be dated as far back as PO.

From these two threads, I've started to suspect I have a head gasket failure.

http://www.moyermarine.com/forums/showthread.php?t=2528

http://www.moyermarine.com/forums/showthread.php?t=2359

This is my list of things for tomorrow:
-Treat two cylinders not firing with MMO (or all 4?)
-Order new head gasket in case
-Buy voltage meter to test coil voltage (installed tonight)

Any thoughts that prolonged running on 2 plugs could have done any lasting damage to the engine?

Thanks!

[BunnyPlanet169]

A compression test would be pretty interesting before you started pulling things apart.

Edit: See also this recent thread... http://www.moyermarine.com/forums/showthread.php?t=9731

[LemonShark2]

compression test

Going to go pick up a tester today and give it a shot. I've got some MMO on stand buy, and found a "Compression test for newbs" thread that should help out.

Quick question - I pulled off one of the spark plug wires on the non running plug, and started the engine, wanted to see if it could throw a spark to the engine. Didn't see any spark. Should it be powerful enough to jump out?

Thanks!

[ArtJ]

Re Coil issues

Hi Guys,

Starting a new thread regarding what was narrowed down to a spent coil. Just had one more question - Although I got the coil today, and will be installing it today to be tested tomorrow, wanted to know if that had a co-relation with the two hot plugs issue I also noticed during the engine failures.

Just a reminder of the original issue, that my engine would start to stall after 1 hr of use. Engine cooling was not an issue.

One user thought it could also be related to switched spark plugs wires, or a bad alternator.

The guys on this site isolated coil failures to a larger than expected
dwell time. This was aggravated by some electronic ignitions.One
symptom was a recovery after a 30 to 60 min cooling time.
They determined that the addition of a resistor to reduce voltage
to the coil solved the problem. See posts elsewhere on this issue
Regards
Art

[ndutton]

They determined that the addition of a resistor to reduce voltage to the coil solved the problem.

Basically true but to be technically accurate we controlled the amperage by manipulating voltage following Ohm's Law as True Grit John pointed out.

[LemonShark2]

Compression Results

I did the compression test after bringing the engine up to temp, then letting it cool a bit. Results were better than expected. From the flywheel back to the transmission:

110
110
110
113

I also purchased a little plug wire tester, basically a light that connects between the wires and the plug, and all wires checked out...

Starting to feel like a bit of a hypochondriac false diagnosing myself with every new thread I read.

Next question, and not the last I'm sure... Now that I know I have water flow through the head (after blocking the bypass)... Is it possible there is a water blockage within the head that isn't allowing water to reach the end of the block closer to the transmission? Thus the two hotter plugs? I plan on doing a vinegar soak within the next couple of days.

[JOHN COOKSON]

So I've been doing a bit more digging on the site regarding the hot plugs, and started thinking about what John C said "why are you running on two plugs" I didn't think it was literal, until I unplugged the 2 spark plug wires from the plugs closest to the flywheel, and the engine ran exactly how I'm used to it. Its running off just those two hot plugs I mentioned.
Thanks!

I'm running out of ideas.
Did you put the two possibly bad plugs where the working plugs are working plugs where the two (possibly) bad plugs are? Instead of a tester you can pull a wire off a spark plug, put a screw driver in the boot, and while turning the engine with the starter see if you can jump an arc to the plug.

TRUE GRIT

Edit: The spark plugs are cold because combustion is not happening inside the cylinders they are in. It has nothing to do with engine coolant temperature.