coil testing on audi a4
 

Ok so i have an 2002 audi a4 that has 100000 miles on it with 50000 on the motor. The spark plugs were changed last year. This winter a vibration has developed that is much worse when it is cold outside and hardly noticeable when its very warm outside. Several people in my other forum have suggested that i have a coil starting to go bad (the audi dealer also said this was the case). I do not have a vag com and have NOT gotten a single check engine light. I'm heard of testing them with an ohm meter? Help me out please.

You will need an Ohmmeter or a digital multimeter set to measure resistance (ohms)

To ohm out your ignition coils:

1) remove ignition coil

2) Set meter to measure resistance(ohms)

3) Place either lead on pin one and hold it there (you'll see the pins labeled when you look into the coils receptacle). I have alligator clips on my leads which does make it easier to do but it can be done without them obviously.

From pin 1 to pin 2 you should read around 70k-80kohms much higher or lower indicates bad/failing coil.
From pin 1 to pin 3 you should read around 70k-80k ohms much higher or lower indicates bad/failing coil.
From pin 1 to pin 4 you should read OL (open circuit)

From pin 2 to pin 3 you should read a range from 350-500ohms much higher or lower indicates bad/failing coil.
From pin 2 to pin 4 you should read OL (open circuit)

From pin 3 to pin 4 you should read OL (open circuit)

Place a lead on pin 4 and place other lead on the metal surface of the coil and you should read very low resistance only about 10-15ohms. Pin 4 is your grounded (neutral) pin.

If meter is displaying any measurements between pin 4 and anyother pin then coil is bad or failing as that would indicate a short to ground.

I conducted these measurements for you a couple hours after I last ran my car. I performed test on 3 good coils to compare my measurements they all read exactly the same as what I have listed. I also tested on 1 failed coil that I had laying around every pin to pin was OL. Coils were bathwater warm not hot. Heat increases resistance so my measurements can be reflecting that but it's not off by much. If you were to do this test on your coils while they are still hot I would expect measurements to be higher possibly even considerably higher. If you were perform this test on cold (car wasn't run 5 or more hours ago) coils the test may not reflect that the coil is failing. I'd do 'em warm. Literally no hotter than what you'd comfortably hold in your hand. Stress the comfortably.

Post what your getting for measurements and I'll be glad to give you my interpretations. Good luck.

I forgot to mention ^ that this alone would not really indicate to me that an ignition coil is failing it'd almost eliminate them as suspect. I'd still ohm them out to be sure though. The coils, being a solid-state device, are more prone to fail due to exposure to heat. Usually solid-state devices perform better in cold ambient temperatures because heat is dissipated more quickly, reducing fatigue. Although I would suspect, that once the engine's running at temp and the coils are saturated with heat they absorb from the spark-plugs and cylinder head, cool ambient air has minimal if any benefit.

My next guess would actually be your spark-plugs. Definitely check the gap on them. Hell I'd just go get some new NGK BK7RE's if your chipped, if your not chipped run the NGK BK6RE's and gap them to .28. The NGK BK_RE's are a copper plug which despite some misconceptions, are actually better for performance because (platinums and iridiums are good for going 50k miles but actually suck performance-wise) copper dissipates heat more efficiently than platinum or iridium. They need changing about every 6k but it's easy and they're about $1.99 apiece.

wow very impressive post to say the least.
Ok some quick quesitons....
1) Do i pull the entire coil out or just the wiring plug to the coil? In other words, do i just pry the wiring plug off and test the coil with it still in the cylinder or just test the coil while it is out of the cylinder and unplugged from the wiring plug.

2) Also do i test the plug or the actual coil itself?

3) In your second post you talked about ohming them out? Whats the difference in what you told me to do and ohming them out? Could you tell me how to ohm them out as well.

I've never done a whole lot of coil testing. I have the haynes manual for this audi and it has instructions for getting the coil out.

Thanks a ton for the very informative post.

Yes, remove the coil, that is Step 1 in my first post.

The Coil.

What I explained in my first post is ohming them out.

I was unaware Haynes made a manual for B6 A4's. The coil(s) literally takes <5 seconds to remove once you open the hood.

Honestly man, I'm more than happy to help. Hope that it does. Good luck.

Ok so i tested them just a few minutes ago. I got some weird results but they were pretty consistent. I did as you said and took one lead and put it on pin 1 and took the other lead and then put it on pin 2. I did this for the other three. (I told you this all again to make sure I did everything right).
*On coil 1 and 2 the resistence from pin 4 to something metal on the coil was alot higher

Coil 1 (numbered from the nearest me to furthest away)
pin 1 to pin 2 = 50.3 (for this I turned my ohm meter to 200k
pin 2 to pin 3 = 400 ohms (I turned the meter to 2000)
pin 1 to pin 3 = 50.6 (same as pin 1 to 2)
pin 4 to something metal = 80* (I turned the meter to 200)


Coil 2
pin 1 to pin 2 = 49.9 (for this I turned my ohm meter to 200k
pin 2 to pin 3 = 400 ohms (I turned the meter to 2000)
pin 1 to pin 3 = 49.6 (same as pin 1 to 2)
pin 4 to something metal = 1.8* (I turned the meter to 200)


Coil 3
pin 1 to pin 2 = 49.6 (for this I turned my ohm meter to 200k
pin 2 to pin 3 = 400 ohms (I turned the meter to 2000)
pin 1 to pin 3 = 49.3 (same as pin 1 to 2)
pin 4 to something metal = 8 (I turned the meter to 200)

Coil 4
pin 1 to pin 2 = 49.3 (for this I turned my ohm meter to 200k
pin 2 to pin 3 = 400 ohms (I turned the meter to 2000)
pin 1 to pin 3 = 49.6 (same as pin 1 to 2)
pin 4 to something metal = 11 (I turned the meter to 200)

Ok so tell me if I did something wrong because these readings are different from yours.

On coil #2 the 1.8ohms is curious to me but I'd be more suspect of the 80ohms your getting pin 4 to ground on coil #1. I would bet that 80ohm reading would increase exponentially as the car got to temperature and definitely would affect how that coil performs. It's worth a shot to throw a new coil in there. There about $26 at any VW/Audi dealer.

The rest of your readings appear within what I'd say is an acceptable range. My coils are only about 3 months used and that may account for the slightly different readings it also could be the different meters, or leads or temperature of coils or age of coils but they were consistant with the 50k between pins 1+2 and 1+3 as well the 400ohms between pins 2+3. So I'd say they tested well with the exception of coil #1's 80ohms to ground. Run the car for 5 minutes or a little more and retest coil #1 see if that 80ohms increases.

I'd still replace or at the least gap the spark-plugs (check my 2nd post, I added to it). $8.00 to do new plugs and then they would be eliminated as a suspect. Keep me posted, I'm curious.

thanks again for the information. Yea i'm either gonna order a coil from rock auto or from the audi/ vw dealer. The spark plugs in the car are less then 8 months old granted that doesn't mean that one is bad. I will def. restest coil #1 tomorrow after the car has been running for a lil bit.

Also the Haynes manual I was talking about I got off ebay actually. I payed a little more then normal (granted it is hardback) but its from Europe or London I believe. I does have all the English increments and of course its in English. It covers the 1.8T, 2.0, and the TDI A4's. Its def. come in handy but then other times its also a haynes. Thanks again

Will these specs work on an ignition coil for a 2003 A6 Quattro? It has 4 terminals, so I figured it would get me close.