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When I built my car I installed switchable ignition coil +12 volt leads like in an old time race car.
When I started the new engine for the first time, it fired right up and after things settled down I decided to test the ignition circuits and viola - one circuit didn't work!
Upshot was my 993 had blown "ignition module" - the current amplifier that handles the coil's current for the ECU.
The engine ran fine on only one circuit and I wonder how many 993 are out there with a blown transistor in their module shutting down one distributor like I experienced.
In my case, I feel, the idle runs incrementally smoother with both plugs firing. At least once a year I unplug the primary distributor to tests the distributor belt and at that time I would become aware of the secondary having a problem. You make a good point though, that I never test specifically for the primary and so testing the primary at the same time in the future would be a good addition to the procedure.
Thank you for your thoughts here.
When I built my car I installed switchable ignition coil +12 volt leads like in an old time race car.
When I started the new engine for the first time, it fired right up and after things settled down I decided to test the ignition circuits and viola - one circuit didn't work!
Upshot was my 993 had blown "ignition module" - the current amplifier that handles the coil's current for the ECU.
The engine ran fine on only one circuit and I wonder how many 993 are out there with a blown transistor in their module shutting down one distributor like I experienced.
That's interesting, during an engine swap a few years ago we managed to fry one of the ignition modules for no apparent reason
In my case, I feel, the idle runs incrementally smoother with both plugs firing. At least once a year I unplug the primary distributor to tests the distributor belt and at that time I would become aware of the secondary having a problem. You make a good point though, that I never test specifically for the primary and so testing the primary at the same time in the future would be a good addition to the procedure.
Thank you for your thoughts here.
Andy
Short of an oscilloscope, disconnecting each coil's high tension secondary or 12 volt primary lead one at a time and then starting engine is only way I can think of to test for a blown module.
Short of an oscilloscope, disconnecting each coil's high tension secondary or 12 volt primary lead one at a time and then starting engine is only way I can think of to test for a blown module.
When I speak of primary I am speaking of the mechanical distributor directly driven from the engine and the secondary being the distributor rotated by the internal belt. I may be using the wrong terminology for this.
Seems you could just unplug the coils one at a time. If the car dies, you have a problem? That's how we first found my (first) ignition module problem.
That's interesting, during an engine swap a few years ago we managed to fry one of the ignition modules for no apparent reason
Fry being the operative word. These modules need adequate heatsinking. If there isn't a good metal-to-metal contact for the modules, they will overheat
a pea sized blob of heat sink compound wouldn't hurt either
Just had this on my 993. I did the usual routine belt failure check by pulling each coil and seeing if it starts. It was only firing on the driven/secondary distributor. Swapped the wires on each coil positive and negative and the issue moved to the secondary coil and the primary was working which prove the coils were ok. It seems that only one channel on the ignition module was working. Took a punt and ordered a new module and now have two working distributors. I also found that just putting a timing light on each coil lead and checking for operation of each distributor is a better was of checking operation also. Really happy it wasn’t a wiring issue or ECU.
Thanks for the above information as it helped my diagnosis immensely.
Long time ago I purchased a tool called OK SPARK. It's a little pricey but it will reveal all of your ignition issues without wrenching on anything.
I discovered a failing spark plug boot which otherwise would have never found.
Just had an issue with mine.
The PO has relocated it from under the seat to an aluminum block to mount seat down lower I believe.
So, I remove it from the aluminum block and just had it hanging in front of the seat.
Not thinking about the module, Took the car for a shake down drive nearby and it was running fine and then all of of sudden just dies.
Cranks but won't start. Smells like fuel. Tried DME, no luck. Then think maybe the module needs to be grounded. Try holding it to metal, no luck. Then I see it's split open. Unbelievablly, the PO not only had a spare DME, but also a spare module in the trunk. Swap it out and it fires right up.
Now, my questions is, when I look it up on the parts sites, there is also an insulator? Is that needed? I've got it mounted back where it should be but want to make sure I'm good.
04-03-2015, 12:38 AM
Ignition module failure discovery
