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Followup To
Question -
Well the real issue is does a reading of 1.1 make the coil dead or better or worse? Your dont really seem to know. Buying another coil may just burn out if a reading of 1.1 makes it dead. then the question is what is burning out the coil? -------------------------
Followup To
Question -
My car starts sometimes. the coil is not sending a spark all the time. I got a new one but feel the old one is good. when I check the primary resistance terminals 1-15 I get 1.1 but the book says it should be between .4-.6 ohms. on the secondary resistance terminals 1-4 I get nothing but the book says it should be 5-7.2. is my coil good?
Answer -
Hi Gil,
I'm a firm believer that if the readings don't match up, the coil is dead. Take the coil, your reference manual and your tester back to the store and have them give you a new one, and test it there...don't bring home a coil that you aren't happy with.
As for the starting problems, it certainly could be the coil, but there are a number of other factors which could contribute to this bothersome problem. Write back to me, using the follow-up feature of All-experts, and let me know what you've tested. Thanks.
Dave
Answer -
Hello Gil,
As a matter of fact, I do know the difference between a good coil and a bad coil.
I'm sorry though, I must have misunderstood you. I thought you were trying to get your car started, and you were testing the newly installed coil, and since you were getting inconsistent readings, compared to your specs, you wanted to know if a newly bought coil could be the wrong one.
So my answer involved this logic: By getting a reading of 1.1 when the specs are .4-.6, it means that the new coil is not "dead", it has a typical primary resistance (most coils have a primary resistance in the 1-2 range), but that what Porsche wants is a coil with primary resistance of .4-.6, a much smaller resistance...and likely a special coil designed for this application.
I'm actually more concerned with the no-reading of the secondary resistance than the 1.1 reading of the primary resistance. But frankly, at this point, I don't know what you really want. I don't have any evidence the first coil was burned out, in fact, based on your description it makes me think the pick-up points in the distributor are dirty or worse.
If you'd like to follow-up again, please feel free.
Dave
What i want is to have my car start. The reason it does not start is my coil is not sending a spark to the system. Well then what causes this? a bad coil, a dme relay, etc. So I am starting with the coil. One thing you said is it could be a specialized coil. Coils are very expensive and i dont want to buy another if the solution is just a $20 relay. Having said that , i can assume the coil is good but may not be the correct one (the secondary on this coil is totally plugged making it un readable?). The weird thing is the car was running with this coil before. If you can think of anything that may be going on to prevent the coil sending a spark out, I would appreciate it.
AnswerGil, I curious about your comment that the "secondary being plugged so as to be unreadable". If it's dirty, the gunk may have infested the coil... actually making it bad. Do you feel it's cleanable? With carb cleaner, tiny brush, and/ or compressed air?
I also thought you had purchased a replacement coil already. So isn't it true that you know both coils are responding similarly...the 12vthey are receiving is not translating to any spark. If this is true, we have to move on to other suspects. Like the DME.
If you're still thinking the coil(s) is (are) good here's the test. Ican't take credit for this...but it's te clearest description I've seen, so give this a try:
1. Disconnect the ignition coil output wire at the distributor cap.
2. Connect a spark plug to the end of the ignition coil output wire which you just disconnected.
3. Ground one end of a new wire and its other end to the threaded portion of the spark plug.
4. Disconnect the ignition coil ground wire from your terminal #1.
5. Connect one end of a new ground wire to your terminal #1.
6. Turn the ignition switch to the ON position.
7. Tap the other end of the new ground wire jumper (from step #5) on a good grounding point (for example the battery negative terminal) and look for sparks at the spark plug that correspond to the frequency of your tapping of the ground wire.
If you have a good spark at the spark plug, the ignition coil is good.
If you don't get a good spark, re-check for approximately 12 VDC from the coil #15 terminal to ground with the ignition switch in the ON position. You should also get approximately 12 VDC from the coil #1 terminal to ground.
Finally, in your case, re-test the secondary resistance with th engine OFF: skip the #4 hole altogether and test the secondary resistance from the coil output terminal itself and the ignition coil #1 terminal. If you still don't get a resistance reading, the coil should be considered dead.
This will rule in or rule out the coil(s).
Looking forward to your results.
Dave
