How to test ignition coils?
 

I'm experiencing what I think is a misfire in my Buick that's killing my gas mileage (~20 MPG, mostly highway :eek:). I feel it most definitely when the car is at a stop -- uneven and rough pulsing through the steering wheel -- and also sometimes smell a twinge of unburnt gas after highway rides (but not on local rides, even when they last at least as long as the highway ones).

I guess my first question is to ask if you guys agree with my misfire diagnosis or not and if you think the unburnt gas smell is related to the misfire or not.

My second question, assuming that you would agree that I have a misfire, is: How should I test the coils? I've already replaced the spark plugs and am just going to replace the plug wires, since they are 20 years old and NAPA wires are $35 for a set, but I'd like to try testing the coils so that I don't spend $100 buying three new coils when I am assuming I don't have to.

How to test ignition coils?
 

Obd2 should throw a code for a bad coil, but check the spark at each plug. If one of the could went it will misfire every 3 ignitions, since each one has 2 plugs correct ?


Sent from my iPhone using Tapatalk

Also which iteration of the engine is it? I know at least on the 2.8s they had fuel pump/pressure problems (had it go on my celebrity too). I'm not sure about the 3.1/3.4 which are essentially the same


Sent from my iPhone using Tapatalk

Mine is a 1994 -- first year for the 3.1 L. It's OBD-I,and although there are ways to read OBD-I codes, I thought it would be more interesting to try to diagnose it myself.

Easy way to test the coils is to pull the plugs one by one and visually check the spark. You'll probably want to unplug the fuel pump or something so it doesn't start up on you, unless you're ok holding it while the engine misfires. Also if you do this make sure you are NOT the ground, those things kick. It's simple and crude but works.


Sent from my iPhone using Tapatalk

Don't allow the misfire to persist for too long, as you might be sending some unburned fuel down the exhaust system and overheating the cat.

A fuel leak would do those things for you as well.

Yeah you would smell it though. Also the car would more likely misfire at higher rpm than low. I wouldn't count. Out the alternator either, at low rpms it might now be giving enough electricity. Jooseppi try turning on and off some accessories when the car is doing it, see if there is any difference. Might not be enough to illuminate the battery ought.


Sent from my iPhone using Tapatalk

Pulling the wire off of each plug , in turn, of a running engine, :eek:is one way to check for spark

Hm, OK. How do I make sure I'm not the ground?
I can try that, but the alternator was replaced maybe 5,000 miles ago by the PO (since the car had been sitting for a good while), so I'd be surprised if it's that, since the battery/alt made it great through single-digit starts this past winter.
I did this many years ago when first screwing around with the engine on our lawnmower. YOW!

Ooh, good point.

Sure. Allow me to point you to the OP #1 to whit:

Don't be grounded to the vehicle and you are unshockable. As shocking as this may seem :D

I interpreted that as cat smell


Sent from my iPhone using Tapatalk

Duh, makes sense.

And that's prolly a good thing ...
 

I never met a cat that smelt like gasoline. :)

Be sure to wear rubber gloves and a condom just in case :D

First off, I would run the car in a dark garage at night. Spray a fine mist of water around and see if the plug wires are leaking.

If not, turn on the lights and pull out one wire at a time and plug it into a spark plug tester to see if the flame is steady and blue.

All of this is with the engine running.

If you're the ground, you'll know right away:smhair2:

I learned the same lesson in the same manner.
That is why I passed it along. Must keep traditions alive.:D

| Repair Guides | Distributorless Ignition System (dis) | Ignition Coil Pack | AutoZone.com

The DIS coils are all the same I am pretty sure. Something to start with.

Read the 2.2L stuff, the 2.3/2.4 is the Quad4 which did use a different coil.

What did the old plugs look like? Were they all the same?

Do you have the book?

MAP sensor, fuel pressure, injector resistance are all easy tests too.

If you haven't done so, take a close look at the distributor and rotor and use an Ohm meter to check continuity.

3.1 is distributorless.


You might check for leaking injectors, I did my fair share of 60* injectors when I messed with Fieros in high school.

I used to just pull the complete rail up and out but still connected to the feed and return with the upper intake manifold off. Key the car on and let it prime, if the tips get wet just sitting there, they are bad. 6 rebuilt injectors online are like $120.

That's all good stuff. I didn't even know such a thing as a spark plug tester existed, but Autozone has one for $8... I'm buying it. Thanks!
That should be a usergroup here on PP. "I got zapped when trying to pull a plug wire off of a running motor." :D
Oh cool, thanks... that looks exactly like what I need to test the coils.

Interesting question about the old plugs -- they did all look about the same, maybe like they'd been running a little rich but nothing horribly unusual.

What is this book you speak of? Does it hold the secrets to eternal life? Or at least to WVO?

Map sensor -- I don't have one, my car doesn't have satellite navigation. I'll check the rest, though.

(Just kidding about the map sensor. I'll check that too.)
I'll try that too.

Touching and feeling is great for working with women. For injectors, the only complete test is on an injection bench. It will tell you if they are spraying at the correct volume and pattern. Anything else is a SWAG.

MAP sensor was one of the first things I had to change on my 89 grand prix, oh so many years ago. Injectors were first. Eventually changed the fuel pressure regulator, crank position sensor and a bunch of other stuff. Don't think I changed any coils but I wouldn't swear to it. It was a good car but I changed a lot of parts. Alternators are fragile too. Charge it, don't jump it and let it charge itself.

If you had a bad coil pack I would expect that the plugs would show a difference. Check it anyway.

Joe is explaining how he tests for spark....

That's a "surefire" way of determining spark.

I can just visualize it.... Ouch! Hot. Ouch! Hot. Nothing. Dead......



One attribute of a failing coil is that they will tend to fail more when hot, and tend to fail more when at higher RPMs. At speed, you get a feeling like the the engine was not getting enough gas, back down on the speed, and the engine would begin running well. Drive long enough, and the degradation would begin at lower and lower speeds. But it would get better as you slowed down, I didn't drive the car far enough to have a rough idle, though.

These were my symptoms that were fixed by a new coil.

With three coils on your engine, if one has hard failed, you'd surely notice the extremely rough idle... Right? Vice an intermittent miss?

Jim

Hey Jooseppi Luna, just replace those worn out old plug wire and your problem will be solved. You undoubtedly aggravated the problem putting in the new plugs. Just touching with those 20 year old wires, (and there is no wire in them) will easily mess them up. Replace them and be happy!

there are a mess of tests you can do. is this the 4 cyl or v6? the v6 has a mass air flow sensor on it. if you have the v6, clean this sensor and see if things improve.

really though, without looking at live data, you are just shooting in the dark. if you are smelling raw fuel, it may also be time for new o2 sensors.

I found the problem on my son's Omni ( yes, MANY years ago!). Cold start, fine, but as it warmed up, it would miss. He drove from Cinnci OH to Richmond, VA for a gig, all in short spurts. Every shop would replace something different, and send him on his way.
I reached down to the distributor while it was running, and got shocked. Found that the module on the side of the distributor was bad. Sometimes mechanics don't take the time to find the underlying problem.

Check prices at rock auto.

That car might have a MAF. I was assuming it was the older speed density system. Some cars have a MAF and a MAP.

Need a book. I bet you can buy the original factory shop manual for small money on eBay.

High voltage parts mentioned in a couple posts are routine replacements. Test parts, don't guess or throw money at it.

You are correct, however whatever injectors GM used are notorious for just pouring fuel out of worn tips. My test would identify horribly bad injectors. If if can't hold fuel in it with the car off its bad. It will not reveal the poor patterns but if you're running pig rich and pissing away fuel that can sometimes find it.

3.1s are speed density. They didn't get MAFs on 60*s until obd2 I don't think, on like the 3400, 3500, and 3900.

I'm noticing a theme in your spark-ignition adventures. How are you still alive :D?

Low amperage

And very quick reflexes....
Its probably a good thing I don't have a heart monitor implant. The docs might be puzzled by all the spikes.

Some people like high voltage. They say the psych ward really comes alive during lightning storms.

OK, so I tested the three front plugs with a spark plug tester, and they check out. I still need to test the rears, but first need to dig the wires out... you need to remove the coils and the ICM and the coil mount etc. to get at them, which is a pain.

I would have done it today, but I ran into another interesting test in which you slip a short length of vacuum hose over each of the coil towers and connect the wires to those, leaving a sliver of the coil tower showing under the vacuum hose. Then, you use a test light to short out one coil tower at a time. If a shorted coil tower does not produce a change in RPMs, that cylinder is misfiring.

First time I did the test, It seemed crystal-clear: all cylinders resulted in a drop in RPMs except cylinder #6, which created no change in idle. Ah-ha! I found the problem cylinder!

...no, wait, I had just forgotten to plug that plug wire back in after running the spark plug tester on it. Brilliant.

I tried the test again after plugging in #6, and all cylinders gave a more-a-less equal drop in revs. Then I realized that the engine wasn't misfiring at that point, and that of course all the cylinders would check out... the misfire then kicked up, so I quickly did the test again, and would say the cylinder fed by the coil tower furthest to right seemed (perhaps) a little suspect, but the misfire abated as I was still testing cylinders, so I can't say for sure whether it was that cylinder or another cylinder.

Today, I'm going to drive around the block, then chock the rear wheels and have my sister sit in the car and put it in reverse in an attempt to force the misfire -- the misfire is generally the worst ~2 minutes after startup when the car is in gear.

I test ignition coils the same way I test temp sensors... :uhoh:

Moooon Riiiiver...

I don't think the neighbors would appreciate me walking around in the driveway with no pants on, sticking live ignition wires into my butt...

Pics or it didn't happen :)

It ain't happenin', so no worries about pics! :silly:

EDIT: Was that directed to me or Swamp?

Ewwwwwwwwwwwww ... either !!!