I have a question for those familiar with ignition modules: I have been trying to get a small gas engine running but have had no luck. Checked for spark and one was there so I have been chasing carb issues as the likely culprit. After about 4 trips to the field with no success, I finally swapped out the module and it started on the first flip. So, my question is this; How can the module throw a spark but not allow the engine to start? During the process, I even tried an electric starter to check it with a fast spin rather than a hand-flip. No luck. Bye the way, the module has been used sucessfully for the first 3 hours of operation prior to this issue.

What could occur internally that would allow for a spark but not allow it to run?

For those who can offer an explanation, thank you in advance!

Different timing of the module.

There are many reasons possible for what you have described . A weak coil may give you enough spark to jump a dry plug exposed to atmospheree, but with the increase in resistence from a compressed fuel/air environment may require more current than the coil can provide .

A torn silicon plug boot inside the cap is a more common senario. This is similar in result but different in cause, as current will flow to the path of least resistence . The spark may jump inside the cap rather than through the higher resistence spark plug in a compressed fuel /air environment.

If your ignition uses a metal cap, the cap can be replaced for less than $20.00 . One caveat is that the failed or damaged cap (if this is the problem)may have stressed the ignition module and it may fail soon after the cap is replaced .

You know the problem is the ignition , you've proven that. I would buy a new RCEXL ignition and put your worries behind you. Or if the engine is still under warranty contact the seller and see what they say.

+1 on the RcExcel. They are wonderful. I went thru several seasons of head scratching with my Chinese Engines. Turned out that a swap to RcExcel cured my troubles! Look at rcextremepower.net. He is great to deal with. Good service and a great source for knowledge.

+1 on both the RC exl ignition and Milton at RC Extreme Power

Karol

If you want to test an ignition, this info is in post 24 of the gas engine sticky
Below is a cut and paste of Jedijodi's instructions

It was requested that I post this troubleshooting guide for Rcexl and many C&H ignitions here in this thread. If you have no spark or think you are having an ignition problem, carefully following this guide will test the ignition module, hall sensor, and spark plug cap components. This guide can be used for single or twin cylinder ignitions, it does not test the manual or any optical ignition switches that may be in the system. You will need a good fully charged 4 cell Nicad or Nimh battery, an old servo extension, and your trusty volt meter. So,......


<span style="LINE-HEIGHT: 115%; FONT-FAMILY: 'Verdana','sans-serif'; FONT-SIZE: 10pt">Take an old expendable servo extension and cut off the male plug end, separate the wires, strip a bit of insulation from each of the 3 leads and plug the other end into the sensor lead on the ignition module.

Put a good spark plug in the cap, doesn't need to be all the way seated but far enough for the hex of the plug to make good contact with the metal shell of the plug cap, plug a fully charged 4 cell battery directly into the ignition.

Test for battery voltage at the red and black wires of the test extension you made and plugged into the sensor lead of the module, if there is no voltage replace the module, if there is battery voltage-&gt;

Short the white and black wires together, every time you break this connection there should be a spark, no or intermittent spark=bad module, has good spark-&gt;

Remove the test lead and plug the sensor on the engine into the module and turn the engine over, no spark, replace the sensor, good spark-&gt;

Remove the spark plug, look down into the plug cap and turn the engine over, if you see spark arcing through the silicone boot to the metal shell, replace the spark plug cap, no visible spark but you hear a snap-&gt;

Put a small <font color="#000000">screw</font> driver into the bottom of the cap, turn the engine over and you should observe spark jumping from the screw driver to the plug cap shell outside of the silicone boot, an arc of about 1/4"-3/8", if it does this there is nothing wrong with the ignition, if you hear an arc but it's not in the cap with the screw driver, it could be a problem with the </span><span style="LINE-HEIGHT: 115%; FONT-FAMILY: 'Calibri','sans-serif'; FONT-SIZE: 11pt"><span style="LINE-HEIGHT: 115%; FONT-FAMILY: 'Verdana','sans-serif'; COLOR: black; FONT-SIZE: 10pt; TEXT-DECORATION: none">resistor</span></span><span style="LINE-HEIGHT: 115%; FONT-FAMILY: 'Verdana','sans-serif'; FONT-SIZE: 10pt"> in the cap or the high tension lead where it goes into the cap, replace the plug cap.

All of this can be done on a bench, the plug does not need to be grounded to the engine.

Good luck!


</span>

Thanks for the replies, but I still have the same question: How can it produce a spark but not allow the engine to fire? I replaced the old unit with a new one and it fired right up. Again, does anyone know how the old one can spark, but not support the engine to run?

It all depends on how you tested the spark. Out of the engine, the spark should at least bridge a 6mm ( 1/4" ) gap. If not, the coil is too weak.

If the ignition has a choice of firing across the gap in a plug, as well as something requiring slightly more power (say a leak within the spark plug boot, or a coil that's starting to break down internally?), the extra power required to fire the plug at the top of the compression stroke can make the difference between which path offers the least resistance for the spark to get to ground? It is not THAT unusual to have a plug fire when outside of the cylinder, but not while under compression.

Other symptoms might include an infrequent pop or 2, exhaust smoke, back firing, etc. This has happened to me twice now, and replacing the spark plug boot has fixed the problem both times. -Al

Thanks to all that replied. As I said, the old unit was replaced and the new one works fine. I think that for most modelers the check for an ignition unit is limited to verifying a spark. Once that is evident, I don't know where else one could go. I spent a 3 trips to the field with no flying because of this issue and it seems that the old module was slowly dying. Very frustrating.

Again, thanks to all.

Ok I had the same problem last year. Fitted a new module and was fine... After a lot of head scratching I found the coil firing after TDC. I checked the magnet for shifting, all ok.

The new module I fitted still used the old pick up... I bench tested to whole unit, when I used the new pick up as in normal opperation the spark was retarded, turned it the other way (Hall effect) It was now firing BTDC..I refitted the system and did a few flights untill I had a dead stick..Same problem, rotated the hall effect and was now BTDC..I tried the old hall effect and the problem was gone..... I couldnt work out what was going on and had no trust on the module. It went to the bin and the RCEXL stayed... God knows what goes on with cheap Ignition modules....

So For your answer..It happens..

If the coil is weak it will fire the plug when not under pressure but will not fire when the plug has pressure from being installed in the cylinder.

Also the spark will go to the point of less resistant, If there is a bad place in the silicone plug cap it will fire the plug when plug is not under pressure but will fire inside the cap when the plug is under pressure.

Milton

The cap is okay so I think it was the coil. In any case, the old module has found a new home in the circular filing cabinet. Thanks to all!

They just told you in the last two posts.Read again.
BCCHI

I did read them. That's why I pitched it.

All above makes good sense. Another question I have asked and never got a answer is....I have 2 or 3RCEXL ignitions. From brand new I noticed only one had a real crisp blue spark with same sparkplug...all tested with same battery and pickup sensor. Why is the spark better on some RCEXL units than others? Could it be a sign ofhow long they may last???? Just curious. Capt,n