Spark color

"I have a 1987 5.7 mercruiser.

"I have a 1987 5.7 mercruiser. What color should the spark be, Yellow? Orange? Blue? Etc?
Also should the spark plug gap be increased when converted to electronic ignition? Thanks

Lee M"

Blue
Depends on the output of

Blue
Depends on the output of the coil.

What does it mean if my spark

What does it mean if my spark is orange? What should I check? Whats failing. Thanks

Lee M

Plug gap remains the same. Ch

Plug gap remains the same. Check the plugs and wires and dist. rotor and cap. Coil HV lead to the cap.; check the spark there first. Coil may be breaking down.

"it should be blue/white/yello

"it should be blue/white/yellowish. If you've got spark and the boat runs, i wouldn't worry about it. What makes you think you've got a problem?

The spark often looks very different under a compression load situation."

"Boat doesn't run well. H

"Boat doesn't run well. Hard to start, low power, and won't get up to top speed. I have checked just about everything else and this was the only item that didn't check out. Should I chec the coil?


Lee M."

known good fuel? (my first

known good fuel? (my first suspect)
Timing too far retarded?
Plugs getting loaded up with black crud?

"Lee...
As MistaHays mentione

"Lee...
As MistaHays mentioned, the appearance of spark looks much different under the pressure of compression. If you are just pulling a plug out and grounding it to look at the spark while cranking, it won't be accurate. It should however have a good loud snap to listen to. Increasing the gap of the plugs will make the coil work harder as it has to develope more voltage pressure to jump the increased air gap. Automotive coils of the 1980's used to build about 45,000 volts to jump .032 plug gap, but as plug gap has increased up to .080, HEI coils have to build up to 85,000 volts. This does increase working temp. of the coil and may speed up break down of an older coil not meant to jump these larger gaps. There should be resistence values available for you to check your coil (and wires per foot length) with an ohm meter. If you have an old coil, I wouldn't be increasing plug too much. It may be just as easy to put on a new set of wires and find a known good coil and try it out.

Just thinking out loud
Wrench"

If you have Thunderbolt Igniti

If you have Thunderbolt Ignition look under the rotor and see if the optic sensor is rusted. I replaced mine for $50 and it made a world of difference. This optic sensor replaces the points. You'll need to check the timing when done. Just an idea.

"Fuel is known to be good.
T

"Fuel is known to be good.
Timing at 10 BTDC.
Plugs a little dark but not bad.

I have electronic ignition, new cap, rotor, wires, and coil about 1 year ago.
Boat ran well until one day I started having problems, not much power. Fuel pressure is normal. Wondering if I got a bad coil or if electronic ignition has gone bad."

"Lee:

You may have some cor

"Lee:

You may have some corroded connections on the ignition amplifier attached to the port side of the engine. Remove the + battery cable from the battery and starter and clean all 4 connections first. Next remove and clean the main engine ground from the battery; clean both ends of the cable and block area. Then remove the ground on the amplifier and clean it. Do the same on the coil, both connectors. Inspect the amplifier quick connects and clean as needed. If it does not improve, Perform the test below. I would buy a new coil before I spend $450 on an amplifier unless the amp. fails the tests.

Tests for Thunderbolt Ignition:

W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!

#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts is present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced."

Lee
It wouldn't hurt to c

Lee
It wouldn't hurt to check your voltage at various points on the ignition system.
Bert

good consistent compression re

good consistent compression readings??

yes

yes

"At normal atmospheric pressur

"At normal atmospheric pressure, you should get a hot, blue-white spark that will jump at least 1/4" to a good engine ground. If the spark won't jump that far, either the coil is going bad or the coil + voltage is low, or the wires are toast. Carbon string spark plug wires are usually only real good for a couple of years before they start to exhibit too much resistance due to breakdown. I advise using spiral wrapped cores like good ngk wires."

"Spark should ALWAYS be blue.

"Spark should ALWAYS be blue. An orange spark--as I found out the hard way years ago--is a weak spark that causes bad starting, idle and running problems.

Sound familiar?

Jeff"

"Fast Jeff,
What did you do t

"Fast Jeff,
What did you do to eliminate your weak orange spark?

Thanks."