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Discussion Starter #1
I just pulled the coil from my '87 Veloce to test. The accepted values for primary resistance are 0.6-1.0 ohms and secondary are 3.0-5.0k ohms.

I am getting 1.2 ohms for primary and 3.8k ohms secondary. My primary is 20% over the maximal value.

Would you consider this to be a good coil or should I replace? I currently can't start my spider and I am trying to diagnose potential issues.

Thanks,
 

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But Mad North-Northwest
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Touch the probes of your voltmeter together and measure the resistance. It probably won't be zero. You need to subtract that from what you measure, so probably the coil is in spec.
 

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It seems that the coil is the most misunderstood component of an automobile ignition system and as such they always seem to be suspected as the culprit when something isn't working right.

The fact is they hardly ever fail. They are, after all, just a couple of coils of unbroken wire around an iron core so unless you've dropped it or somehow inadvertently hooked it up to your arc welder there's virtually no chance there is anything wrong with it. Yes there are specs for the primary and secondary resistances but really you're just looking for an open or short and you certainly can't put any merit on the very low resistance measurement of the primary using a thirty dollar ohmmeter from Home Depot.

For a non-start issue there is a specific procedure for troubleshooting and locating the problem. It is far more likely to be the crank position sensor or a fuel injection problem. Your coil is good.
 

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Coils fail when the insulation breaks down and a standard test meter will not tell you that. You would need a high voltage insulation tester. Measuring the resistance of the windings tells you what type of coil you have but very little about it's condition. I agree with Gubi that the higher primary resistance that you see may be due to contact resistance in the measuring circuit. In my experience, failing coils first cause problems at higher rpm or large throttle openings - misfires or serious drop in power.
 

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Discussion Starter #6
Thank you all for all the great information and suggestions. Perhaps I should back up a little. I recently purchased this spider about 4 weeks ago. I actually drove it home about 300 miles and used it a few times and it started right up every time.

However it had a progressively worsening problem where it ran rough and bucked when I would press on the throttle. I asked this question a few weeks ago and was advised to look at the air inlet tube for leaks. Before I did this I also went to pressure wash the engine compartment taking care not to hit electrical components. The car started right up and I drove home. I then disassembled the air tube and cleaned it inside and out and looked for holes that would give vacuum leaks. None were found and I reassembled the tube and also cleaned and re-oiled the K&N air filter. One other problem that I noticed was the last time I used the car the speedo and tach stopped working. So I checked the fuses and noticed that it had several fuses that were over the recommended size and changed them out. However the fuse for the speedo was OK (I will check this out further once I get the car to started again.

Okay tried to start the engine a few days ago and it will not go...it didn't even try to catch at all. Very disappointing. So I decided to look at the ignition system. First looked at the spark plugs. First plug I pulled was the #4 and it was horrible! It had gunk built up that it bridged the electrodes (wish I had taken a photo). I tried to clean it and then noticed that half the insulator on the electrode was broken off. This probably explains the rough running/bucking that I was getting due to misfiring from that plug. The other plugs looked good except they were wet from the gas from trying to start the engine. Put in 4 new NGK's; the old ones were Bosch plugs.

So now I have to complete the diagnosis of my current problem of the car not starting. The the consensus I have here is the coil is probably okay. I will clean up all the wire terminals that attached to the coil and re-install. I will then look at the distributor cap and rotor and make sure water did not get into there.

Any other ideas would be most welcome. Thanks.
 

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I will post the comment that I am sure everyone else is thinking. After you had tried to start the car and found the dud spark plug did you re-charge the battery?
Even if there is enough charge left to turn the engine over, the voltage might not be high enough to get the electronics going.
 

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Discussion Starter #8
Anglospider...thanks for the tip. I had not recharged the battery and will do so this evening. Hope this does the trick :001_unsure:
 
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