how to find out what coil is bad?

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marco93L

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Well, I think that I have a coil gone bad. I was driving to the house yesterday and it is starting to shudder and miss at an idle. It didnt hit all at once. I really think that if it is a coil, it is working some of the time. Is this normal?

If it isnt, what would be other options to look into?

Also, if I am going to be changing a coil, I would like to change the plugs in it. I dont think that they have ever been replaced, so can I go with something alittle cheaper than the Irodium plugs that they call for? At the parts store, they said that they can give me a cheaper plug (like $3 each vs $10 for the Irodiums.) I know that they are good plugs and such, but I dont use these plugs for the race car. So what are the benifits of using such a pricey plug for a stock and going to stay stock car?

Thanks
Marco
 
marco93L said:
Well, I think that I have a coil gone bad. I was driving to the house yesterday and it is starting to shudder and miss at an idle. It didnt hit all at once. I really think that if it is a coil, it is working some of the time. Is this normal?

If it isnt, what would be other options to look into?

Also, if I am going to be changing a coil, I would like to change the plugs in it. I dont think that they have ever been replaced, so can I go with something alittle cheaper than the Irodium plugs that they call for? At the parts store, they said that they can give me a cheaper plug (like $3 each vs $10 for the Irodiums.) I know that they are good plugs and such, but I dont use these plugs for the race car. So what are the benifits of using such a pricey plug for a stock and going to stay stock car?

Thanks
Marco
Click to expand...

1. Yes, this is the normal failure mode of the V8 LS COP (Coil On Plug).
The only way to test the coils is to scope them during a stress test. Few people have the equipment for this. Most have also found that once one coil fails, the rest will follow. The best thing to do is to replace them all.
2. Use the correct OEM plug that is called for. The LS does not like all plugs, so why take the chance. Also, it is a pain to change the plugs. Do you really want to do it every 30K miles instead of every 100K miles? Also, be aware that a failing plug can kill a coil.
3. Benefits of using the correct plug - It works, and it works for a long time.
 
Do you think that I can unplug a coil one at a time and see if it changes the way that the car is idleing?

Or maybe just buy a new one and replace one at a time till the miss goes away?

I would like to buy all new ones, but I cant right now. This last Monday was my last day for work and I am going to grad school. So, I need to keep everything that I can unless I have no choice.
 
marco93L said:
Do you think that I can unplug a coil one at a time and see if it changes the way that the car is idleing?

Or maybe just buy a new one and replace one at a time till the miss goes away?

I would like to buy all new ones, but I cant right now. This last Monday was my last day for work and I am going to grad school. So, I need to keep everything that I can unless I have no choice.
Click to expand...

You can try moving one new coil around.

Don't try disconnecting one at a time. That is a good way to ruin a catalytic converter or two and maybe fry the PCM. You wouldn't be able to detect a marginal coil that way anyhow.
 
Thanks.

If the car has 110K on it , do you think that it would be better ( I mean really necessary) to replace the plugs

Are they that big of a pain in the arse to change?
 
marco93L said:
Thanks.

If the car has 110K on it , do you think that it would be better ( I mean really necessary) to replace the plugs

Are they that big of a pain in the arse to change?
Click to expand...

Yes, I would replace the plugs. They were due at 100K. As the gaps in the plugs wear bigger, it will put more stress on the coils and kill them. By the time you have opened up the covers and starting swapping coils around, you have done 90% of the work of changing the plugs anyway.
If you are really lucky, you may find that all you need to do is to replace the plugs and that the coils are all okay (rare, but you can hope).

Having 110K on the plugs, I would definitely change them, and I would do that before I assumed I had a bad coil and went looking for it.
 
Do you have a v6 or v8? I believe it's harder on the v6 because you have to remove the upper intake while on the v8 you don't. There are guides on how to remove intakes, coils, and plugs in the Tech Articles which can be found up by the search function.

If it were me and I had a miss at idle then I'd disconnect each coil to see if it changes the idle. I've done things like this plenty of times before and never had any adverse effects.
 
Well, I will grab 8 plugs tomorrow and go from there.

I usually always go with the NGK's.

What would you recommend for the LS, can I get by with something cheaper or just spend it.

I am just guessing, but I just need to pull the covers that are hiding the coils and the plugs are under them? This is all new for me, I like the old pushrod motors, I like the Modulars, but I am just uneducated in them. So this is all new for me.
 
Oh and when/if you changes your plugs do it when the engine is cold. Aluminum is soft and carbon buildup can damage the heads especially when hot. I personally like to use anti-seize on the threads when reinstalling plugs in aluminum heads.
 
I went with NKG G-power platinum plugs. IMO if you don't go with a good NKG plug then go with ford plugs.
 
Mechanicboy said:
Oh and when/if you changes your plugs do it when the engine is cold. Aluminum is soft and carbon buildup can damage the heads especially when hot. I personally like to use anti-seize on the threads when reinstalling plugs in aluminum heads.
Click to expand...

Yes, I will never again forget to use anit-sieze Did that once and that isnt something that I will forget, ended up costing me quite a bit to fix:D
 
Mechanicboy said:
...
If it were me and I had a miss at idle then I'd disconnect each coil to see if it changes the idle. I've done things like this plenty of times before and never had any adverse effects.
Click to expand...

Putting raw gas into the cats will shorten their life. There's nothing to debate about that.

It's rare, but if you unplug a coil on a running engine at just the right moment, you can damage the PCM.

I assume the OP can send you a bill if such happens?
 
joegr said:
Putting raw gas into the cats will shorten their life. There's nothing to debate about that.

It's rare, but if you unplug a coil on a running engine at just the right moment, you can damage the PCM.

I assume the OP can send you a bill if such happens?
Click to expand...

5 seconds won't kill a cat. I also said "If it were me" so read my quote below.
 
Mechanicboy said:
5 seconds won't kill a cat. I also said "If it were me" so read my quote below.
Click to expand...

So, it will take you less than one second per cylinder to find the marginal coil? (Remember, we aren't talking about a coil that isn't firing at all, we're talking about one that misfires maybe once every hundred times. At least that's the way the LS coils have failed on me...)

I suppose that we will have to agree to disagree on this.


BTW, marco93L if no one has ever changed the valve cover gaskets on your gen I LS, then expect to find oil in the plug wells. If you do, you will need to change the valve cover gaskets, and should change the oil soaked coils.
 
joegr said:
BTW, marco93L if no one has ever changed the valve cover gaskets on your gen I LS, then expect to find oil in the plug wells. If you do, you will need to change the valve cover gaskets, and should change the oil soaked coils.
Click to expand...

Man, this is getting better and better!

Anyone want an Ls?
Ran great, just has a slight miss occassionaly one maybe one coil.

All it will need is some coils, new plugs, maybe more coils if there is oil on the covers, and some hundred dollar apiece gaskets for the covers. Oh, and a full day with lots of beer to fix.:D

But seriously, thanks for the information. I am going to buy the new plugs for the car and start there. I will look for oil in the wells, then just order the gaskets. I just hope that there isnt so that I can start driving the car again. I like the truck, but I started to get spoiled with the quite car (no moddified exhaust and lowered suspension) Getting the truck out kinda sucked
 
The way I see it is that the longer he has a miss the longer he will have raw fuel being dumped into his engine and cats. When I was saying 5 seconds I was refering to 5 seconds per plug. Pull connector and listen 1....2....3....4....5.... reconnect. That's how I found that it was a bad plug on my town car i had. once I found the wire(it wasn't COP) I followed the wire and OHM tested it. It tested good so I pulled the plug and the insulator had broke. I replaced all the plugs at the point for good measure.
 
I picked up a set of 8 coils on ebay for $139.95
From what I looked up on this forum (before I bought them) they seem to be good coils for the money. And a lot cheaper than spending $50 a piece through Autozone.
The ebay seller was "per4mance_part$" They have 100% feedback. They shipped me the coils priority for free. Got them within 3 days. And after working all night tonight I'll be putting them in this morning. :)
 
marco93L said:
I am going to buy the new plugs for the car and start there. I will look for oil in the wells, then just order the gaskets. I just hope that there isnt so that I can start driving the car again.
Click to expand...

Sounds like a good plan. If you were near me I help out. I'd love to get out of the house as the old lady of mine is pregnant and shes getting emotional this time around. Don't get me wrong I love her and my kid/kids to be but it sucked today at dinner.
 
One more thing, if there's a lot of oil in the spark plug wells then you are going to get that in your cylinders when you pull the plug. If too much gets in there and you start your engine before it all leaks back down into the crankcase it can cause engine damage so be careful.
 
Mechanicboy said:
One more thing, if there's a lot of oil in the spark plug wells then you are going to get that in your cylinders when you pull the plug. If too much gets in there and you start your engine before it all leaks back down into the crankcase it can cause engine damage so be careful.
Click to expand...

That will be good to re seat the rings incase they are stuck!

I will keep an eye on that though.
Thanks
 
If you have a masochistic streak, are a cheap guy, and oil in the plug tunnels is the problem, try re-using the coils after cleaning, replacing the boots, and installing new plugs and gaskets. Worked for my '02 LS V-8. Be aware that according to other members, there is a Ford bulletin that some coils had manufacturing defects and should not be re-used.
 
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