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04 Disco Cylinder 8 misfire

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Old 12-19-2018, 07:02 AM
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Default 04 Disco Cylinder 8 misfire

Hi guys and girls,

I recently got my discovery back from the shop where they put new plugs and wires in and all lights were off the dash (miracle!).

I drove it for a couple of miles then the SES light came back on and got P0308 code again and could tell there was a misfire when going up hill and the rough idle.

After reading other related threads, it sounds like it could be head gasket or fuel injector replacement? I checked this morning and didn’t see any leaks on the ground either.

I’m going to call the shop again today but wanted to have somewhat of a diagnosis before taking it back. Any help would be greatly appreciated.

Thanks everyone!
 
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Old 12-19-2018, 07:32 AM
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Get a little mirror on a stick and look at the rear of the engine where the head and block meet on the passenger side. If you see a black area then you got problems.
 
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Old 12-19-2018, 08:26 AM
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It could be a more serious issue but I'd go for the simple stuff first... Is the boot all the way seated? Spark plugs and cracked?
 
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Old 12-19-2018, 09:08 AM
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Thanks for the responses. Spark plugs don’t look cracked, what do you mean by boot?
 
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Old 12-19-2018, 10:18 AM
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Originally Posted by Deespin
Thanks for the responses. Spark plugs don’t look cracked, what do you mean by boot?
If they just did the plugs and wires, the boot at the coil pack and the boot at the spark plug. All it takes is a small hairline crack to cause misfires. Pull the spark plug out. Also look inside cylinder when the plug is out. If it's perfectly clean in there, suspect head gaskets.
 
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Old 12-19-2018, 10:20 AM
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"boot" = the part that sleeves over the top of the plug or the coil pack connector.
 
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Old 12-19-2018, 11:43 AM
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I know I’ve said it 1,000,000,000 times, but anytime you’re going to the trouble of new spark plugs & wires I highly recommend replacing the coil packs at the same time (especially if you are still on the OEM coils). Then you know without a shadow of a doubt all your hardware is new. Before jumping to HG’s you can double check the plug (some times they get dropped at the auto parts store), the wire, and you can examine the plug itself to see if it’s wet or getting discolored.
 
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Old 12-19-2018, 06:18 PM
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When diagnosing a problem always first ask what's been done or what has changed that might explain the problem.

Since the misfire appeared within a couple of miles of having the plugs and wires changed that's the obvious starting point. It's very possible the shop did not get the cylinder 8 boot seated fully on either the coil pack or the spark plug, or, as others have said, it's possible the spark plug is defective.

Start there and eliminate those possibilities before even thinking about head gaskets or something else.
 

Last edited by mln01; 12-19-2018 at 07:38 PM.
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Old 12-19-2018, 10:13 PM
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Thank you everyone for the responses, I’m learning a lot about this truck with the more problems I have I spoke to a rep at Atlantic British and he said the same thing, start by replacing the coil packs and go from there. They are new plugs and wires but not new coils packs, which makes sense now to have just replaced all of it. Not saying this may be the solution butlikeyou guys said, start small and go from there. Any recommendations on coil packs?

Also, to preface this I was getting cylinder 8 misfire prior to the shop which is what made me put new plugs and wires on in the first place.

@mln01 are you in NC?
 
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