Spark plug voltage?

[scout-j-m]

I just got a spark tester that has the adjustable gap for helping determine the spark strength. I was thinking that the voltage the coil delivers to each plug is around 20,000 Volts. Does this sound correct for a 1994 70HP Force with Thunderbolt ignition or is it even higher?

 

[Frank Acampora]

Higher! The spark should be able to jump a 1/2 inch gap.

Personally, I never use a spark tester. If there is a bright blue spark at the plug, then the voltage is adequate. If the spark is reddish or red-yellow, then it is too weak to fire the plug under compression.

 

[scout-j-m]

Higher! The spark should be able to jump a 1/2 inch gap.

Personally, I never use a spark tester. If there is a bright blue spark at the plug, then the voltage is adequate. If the spark is reddish or red-yellow, then it is too weak to fire the plug under compression.

I am wanting to use the spark tester because I believe my ignition system is sporadically missing on one cylinder. I figured if I set the gap to the correct distance and turned the engine over several times I may notice something I would miss by just grounding the plug to the head.

How much higher would you say it is? 40k V?

 

[Outsider]

Use a timing light ...

 

[scout-j-m]

Use a timing light ...

Will the timing light work if it is constantly creating spark but sporadically firing off a weak one? I'm unfamiliar with timing lights but I assumed the inductive type will show any fire, even if it is weak from inadequate voltage.

 

[Frank Acampora]

The old Motorola CD ignition with a distributor was around 20,000 volts. The Prestolite system is higher by a significant amount. I don't remember the exact voltage though. Maybe Nordin will jump in He usually knows such things.

 

[Jiggz]

I have the Prestolite system which has a voltage output of 15K~40K volts at the ignition coil. The Thunderbolt ignition system is basically the same with 15K~40K volts going to the spark plugs. Misfires are one of the hardest electrical problems to troubleshoot especially if it is intermittent. Personally, I use a timing light for preliminary t-shooting as it requires very little effort to do so. Use the timing light bounced against a dark surface or paper and watch the consistency of the sparks (strobe of the timing light) on each plug in relation to the engine running tone. If you do not have a timing light you can also use the proper tool which is the in-line spark tester. If you come up with a suspect the only proper way to diagnose is to replace the suspected faulty parts with known working parts. Remember, if the strobe from the timing light misses (which should be the same for the in-line spark tester) THE PROBLEM IS NOT THE SPARK PLUG BUT RATHER UPSTREAM OF THE SPARK PLUG, i.e. ignition coil, CD modules, switchbox, trigger wires, etc.

 

[Nordin]

Well a regular battery ign.system will generat 10-15000 volt, a battery CD ign.system such as first generation Motorola/Delta system which Chrysler used and the system Merc and OMC used, produce 15-25000 volt.

The selfgenerating CDI system with magnets in the flywheel such as Prestolite produce 20-30000 volt.

The problem is that it is very hard to measure it.
1. You need a voltmeter that can handle 10-50kVolts. A regular Fluke with true RMS can not.
2. The evolution of the voltage is a peak and very fast, you can not see it using a digital meter, maybe with a analog.

The only easy way to measure is using a oscilloscoop with probes that has attenuation 100 times or more.

A good rule is as Frank mention, if the spark can jump 10 millimeter gap (I am in Sweden and use metric system) or 1/2 inch in air. It is enough for jumping under compression.

 

[GA_Boater]

I have the Prestolite system which has a voltage output of 15K~40K volts at the ignition coil. The Thunderbolt ignition system is basically the same with 15K~40K volts going to the spark plugs. Misfires are one of the hardest electrical problems to troubleshoot especially if it is intermittent. Personally, I use a timing light for preliminary t-shooting as it requires very little effort to do so. Use the timing light bounced against a dark surface or paper and watch the consistency of the sparks (strobe of the timing light) on each plug in relation to the engine running tone. If you do not have a timing light you can also use the proper tool which is the in-line spark tester. If you come up with a suspect the only proper way to diagnose is to replace the suspected faulty parts with known working parts. Remember, if the strobe from the timing light misses (which should be the same for the in-line spark tester) THE PROBLEM IS NOT THE SPARK PLUG BUT RATHER UPSTREAM OF THE SPARK PLUG, i.e. ignition coil, CD modules, switchbox, trigger wires, etc.

I would have agreed until I found a bad plug using an inductive timing light. Erratic flashes that stayed with the plug. I was surprised.

 

[scout-j-m]

I have the Prestolite system which has a voltage output of 15K~40K volts at the ignition coil. The Thunderbolt ignition system is basically the same with 15K~40K volts going to the spark plugs. Misfires are one of the hardest electrical problems to troubleshoot especially if it is intermittent. Personally, I use a timing light for preliminary t-shooting as it requires very little effort to do so. Use the timing light bounced against a dark surface or paper and watch the consistency of the sparks (strobe of the timing light) on each plug in relation to the engine running tone. If you do not have a timing light you can also use the proper tool which is the in-line spark tester. If you come up with a suspect the only proper way to diagnose is to replace the suspected faulty parts with known working parts. Remember, if the strobe from the timing light misses (which should be the same for the in-line spark tester) THE PROBLEM IS NOT THE SPARK PLUG BUT RATHER UPSTREAM OF THE SPARK PLUG, i.e. ignition coil, CD modules, switchbox, trigger wires, etc.

I am almost certain there is a problem with either the trigger or the stator. In fact, it likely is not either actual component but rather the wiring. I noticed last week that the wiring bundle from both the stator and trigger were stripped where the flywheel had rubbed them. There was also electrical tape indicating someone had already tried to do a quick fix on it before. I am going to take a closer look at it this weekend and I'll start a new thread specifically regarding my ignition troubles.

 

[Jiggz]

Stripped wires should be corrected properly or even replaced if need to. Use shrink tubes on top of electrical tape to make sure it stays sealed. Bundle wires using tie wraps to prevent them from vibrating or even better place them in spiral cable wraps.

 

[scout-j-m]

If it turns out the cause is purely from those wires, I will definitely fix them the right way.

Look for a new thread on it tomorrow or Saturday. I will make sure and include some pictures.

 

[gm280]

If you have one particular cylinder that is firing erratically, swap the coil from the good cylinder to the suspect cylinder and see if your problem follows the swap. If it still has erratic firing, change the next part that feeds the coil and see what happens. Usually you can isolate the problem part and buy a new one. However, it can get expensive if there is a CDI unit that can't be swapped. If you can find a high voltage probe that will handle spark voltages you can use such a probe with an analog meter to see what the voltage is from any coil. But really, knowing the voltage really doesn't solve much that can't be done with a very cheap spark tester sold at most auto part stores for a few bucks. Another great way to see what is happening is to run the engine at dark and see if you can see any jumping from any of the coils, wires or even boots to ground. That will cause erratic firing indeed and it cost zero to test. JMHO!