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2003 Deville
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9 Posts
Discussion Starter #1
I have a 2003 Cadillac Deville with a cylinder misfire on cylinder 4. Anyways, decided to open it up and throw a new NGK brand (I know, the Northstar Engine doesn't like these but it's all I had access to) spark plug in there. I have the coil pack that runs all 4 coils together, I put it back in and boom, perfect idling and no misfires. 2 days later, the problem comes back and the same exact cylinder is misfiring. Could it be the NGK spark plug? Could the coil pack be bad, and do I have to replace the entire thing?

Would love to know what to check next. Maybe fuel injected or throttle body problems?
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,587 Posts
Install the correct AC Delco 41-987 double platinum plugs before anything else. Pre-gapped to .050".

At least you're working on the easy coil cassette. Remove it, check all the plug boots for internal carbon tracking. Look closely at the cassette coil towers - absolutely clean gray, no cracks or black tracks?

Both coil cassettes and their removable ICMs are identical except for color. --- junkyard. yes, the entire cassette gets replaced.

Yes, you could check all the injector electrical connectors. Run a Top Tier 87 octane gasoline - Google it - and that's what the engine is calibrated for - it will NOT compensate for higher fuel octanes (2000 - 2004).

TB cleaning is good every couple of years or so - but it will not cause a single cylinder miss. If you're over 90,000 miles consider the complete AC Delco plug set with new boots. Have fun with the right (rear) coil cassette.

Click to enlarge, use the side < > to scroll. Click the little grid at the lower right to get the big picture.

coil-boot-plug 1.JPG DSCN0192.jpg Spark plug boot (single).jpg spark plug boots2.JPG 2011-07-09_100054_carbon_tracking.jpg
 

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2003 Deville
Joined
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9 Posts
Discussion Starter #3
Okay, so I installed the AC Delco spark plug you listed and idle speed is perfect and there is no cylinder misfiring at all now. I ordered the new coil pack just in case but I suppose I'll just drive it for a couple days to see if it comes back. As of now, I think my spark plug went bad and I installed a crappy one! The AC Delco one should've been installed from the beginning! Thank you though!
Install the correct AC Delco 41-987 double platinum plugs before anything else. Pre-gapped to .050".

At least you're working on the easy coil cassette. Remove it, check all the plug boots for internal carbon tracking. Look closely at the cassette coil towers - absolutely clean gray, no cracks or black tracks?

Both coil cassettes and their removable ICMs are identical except for color. --- junkyard. yes, the entire cassette gets replaced.

Yes, you could check all the injector electrical connectors. Run a Top Tier 87 octane gasoline - Google it - and that's what the engine is calibrated for - it will NOT compensate for higher fuel octanes (2000 - 2004).

TB cleaning is good every couple of years or so - but it will not cause a single cylinder miss. If you're over 90,000 miles consider the complete AC Delco plug set with new boots. Have fun with the right (rear) coil cassette.

Click to enlarge, use the side < > to scroll. Click the little grid at the lower right to get the big picture.

View attachment 573068 View attachment 573069 View attachment 573070 View attachment 573071 View attachment 573072
Okay, so I installed the AC Delco spark plug you listed and idle speed is perfect and there is no cylinder misfiring at all now. I ordered the new coil pack just in case but I suppose I'll just drive it for a couple days to see if it comes back. As of now, I think my spark plug went bad and I installed a crappy one! The AC Delco one should've been installed from the beginning! Thank you though!
 

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2003 Deville
Joined
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9 Posts
Discussion Starter #4
Install the correct AC Delco 41-987 double platinum plugs before anything else. Pre-gapped to .050".

At least you're working on the easy coil cassette. Remove it, check all the plug boots for internal carbon tracking. Look closely at the cassette coil towers - absolutely clean gray, no cracks or black tracks?

Both coil cassettes and their removable ICMs are identical except for color. --- junkyard. yes, the entire cassette gets replaced.

Yes, you could check all the injector electrical connectors. Run a Top Tier 87 octane gasoline - Google it - and that's what the engine is calibrated for - it will NOT compensate for higher fuel octanes (2000 - 2004).

TB cleaning is good every couple of years or so - but it will not cause a single cylinder miss. If you're over 90,000 miles consider the complete AC Delco plug set with new boots. Have fun with the right (rear) coil cassette.

Click to enlarge, use the side < > to scroll. Click the little grid at the lower right to get the big picture.

View attachment 573068 View attachment 573069 View attachment 573070 View attachment 573071 View attachment 573072
So here's where it gets weird. It was perfectly fixed until my check engine light and check gas cap light came back on. It ran perfectly and the gas cap light came on and it started shaking again if that makes sense. I'm on my way to pick up a gas cap, but how could that affect the way the engine runs??
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,587 Posts
I entered your car into your username banner. What trim level is it - base, DHS,or DTS - it makes a big difference in some advice offered.

The "Check gas cap" points to a leak or fault in the EVAP system, and it has set a trouble code. A bad EVAP solenoid or vacuum line will cause air leaks into the throttlebody/intake manifold.

The fuel tank and associated systems are monitored for vacuum/pressure leaks.

Learn how to pull diagnostic trouble codes from your car's built-in scanner/reader. Use the section by JimD in the sticky thread "How to pull codes". You use the 3 buttons just right of the DIC to enter and operate the code scanner.


2002 EVAP.gif
 

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2003 Deville
Joined
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9 Posts
Discussion Starter #6
I entered your car into your username banner. What trim level is it - base, DHS,or DTS - it makes a big difference in some advice offered.

The "Check gas cap" points to a leak or fault in the EVAP system, and it has set a trouble code. A bad EVAP solenoid or vacuum line will cause air leaks into the throttlebody/intake manifold.

The fuel tank and associated systems are monitored for vacuum/pressure leaks.

Learn how to pull diagnostic trouble codes from your car's built-in scanner/reader. Use the section by JimD in the sticky thread "How to pull codes". You use the 3 buttons just right of the DIC to enter and operate the code scanner.


View attachment 573087
So I pulled the codes for my car, which by the way is a 2003 DeVille Base trim. The only code it gives me is a P0440 error though, nothing more. What's really weird is that every time I put a new spark plug in it fixes the issue for a day and then it comes back. It's so weird to me.
 

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2003 Deville
Joined
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9 Posts
Discussion Starter #8
New boot ? (carbon tracked).

Coil cassette high voltage towers perfect ?
Hmm I didn't replace the boot but it looked okay when I pulled it out. I'm not 100% sure how to check for carbon tracking though to be honest. After looking it up on the website it looks like very similar symptoms. Stumbles on acceleration and a misfire that keeps coming back.
 

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2004 Deville base
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284 Posts
Might be time for some new boots. Even a small pin hole or a small hard to see crack will allow the spark to shoot right through.
This problem is really easy to see on an overhead valve exposed boots engine. Check it in the dark, spray a little water mist oh, you got a light show.
Can't see it on these dual overhead cam setups.
 

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2003 Deville
Joined
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9 Posts
Discussion Starter #10
Might be time for some new boots. Even a small pin hole or a small hard to see crack will allow the spark to shoot right through.
This problem is really easy to see on an overhead valve exposed boots engine. Check it in the dark, spray a little water mist oh, you got a light show.
Can't see it on these dual overhead cam setups.
I think you may be right. So here's another thing I didn't know was a big deal until now, but when I changed the spark plug the first time it was drowned in oil. Oil up to the top to where I couldn't even see it. I thought that was normal but after reading I know it isn't. If I go and buy a new boot, will I need to change the spark plug again from yesterday? Also, should I clean out the spark plug ports to make sure there isn't any more oil?
 

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Super Moderator
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86,145 Posts
Some oil in the spark plug well is normal due to O ring seepage, but yours is excessive. Suck it out with a turkey baster or such. Don't worry about the left over residual oil. May as well do them all while you are at it.

Yes, change the plug as well as the boot. If you don't change both, the carbon track can simply transfer itself back and forth and you end up chasing your tail.
 

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2003 Deville
Joined
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9 Posts
Discussion Starter #12
Some oil in the spark plug well is normal due to O ring seepage, but yours is excessive. Suck it out with a turkey baster or such. Don't worry about the left over residual oil. May as well do them all while you are at it.

Yes, change the plug as well as the boot. If you don't change both, the carbon track can simply transfer itself back and forth and you end up chasing your tail.
Found out the oil lube place filled up the oil and got some into the coil pack. It drained from the top, and it leaked into that cylinder. Changed the boot, but not the spark plug (I just wiped it off) and it is still misfiring so I'm wondering if the old boot ruined the spark plug within a day?
 

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2003 Deville
Joined
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9 Posts
Discussion Starter #13
Some oil in the spark plug well is normal due to O ring seepage, but yours is excessive. Suck it out with a turkey baster or such. Don't worry about the left over residual oil. May as well do them all while you are at it.

Yes, change the plug as well as the boot. If you don't change both, the carbon track can simply transfer itself back and forth and you end up chasing your tail.
Okay, here's where I'm at. Changed the boot, cleaned the well of all the oil seeped in. With a new boot and new plug it STILL has a misfire in the 4th cylinder. I pulled the plug with some oil still in the well stupidly, it ended up going down into the engine. Would that be affecting it?

Also, could it be the 4th cylinder coil? Is there any way to swap it and figure out or should I just replace the coil pack altogether?
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,587 Posts
The coil cassettes are changed as a whole unit. As posted earlier, junkyard. 2000 - 2003 Northstar cars. Identical except for color. As posted earlier, inspect the coil towers for carbon tracking or cracks - guaranteed miss.

Some oil in plug well(s) is normal.
 

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Super Moderator
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86,145 Posts
Okay, here's where I'm at. Changed the boot, cleaned the well of all the oil seeped in. With a new boot and new plug it STILL has a misfire in the 4th cylinder.
That leads me to believe the problem is in the coil.

Also, could it be the 4th cylinder coil? Is there any way to swap it and figure out or should I just replace the coil pack altogether?
Swap the coils (ignition cassettes). If the misfire follows the coil, then replace the cassette.[/QUOTE]
 

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2003 Deville
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9 Posts
Discussion Starter #16
That leads me to believe the problem is in the coil.


Swap the coils (ignition cassettes). If the misfire follows the coil, then replace the cassette.
[/QUOTE]
Okay, I didn't actually know you could swap the coils within the cassette? Or I'm assuming you mean swap with the right side cassette?
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,587 Posts
Post #14.

Swap the cassettes - side to side. No way to replace/swap individual coils in the 2000 - 2003 cassette system. 2004 and + went to individual C-O-P ignition. No, you can't "update" our systems.

If the miss follows the cassette swap then you have found the problem. BUT, because the right (rear) cassette is such a bitch to replace, I'd swap in a junkyard gray cassette first.
 
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