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Discussion Starter · #1 ·
Hello All,

I have a 2001 SLS with 207,000 miles on the car. 3000 miles ago I replaced all the sparkplug with AC Delco and boots. The old plugs were all worn, but all showed as running fine (Light Tan)
Today at an idle it throws a P0301 code ( misfire on cylinder #1) I can feel the engine running rough in idle and in drive.And the Check Engine light comes on
Once a go from idle to highway speeds the the engine runs good and has plenty of power..Also the P0103 goes from CURRENT to HISTORY at highways speeds. As soon as I come to a stop light the engine is running rough and the Check Engine light comes back on and P0301 goes back to CURRENT.

Any Idea's?
Plug?
Coil Cassette?

Thanks for all your help
 

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Discussion Starter · #3 ·
Hello All,

Thank for a response Ranger!
I guess I answered my own question. Took a compression test of cylinder #1 and it is 60 psi compared to cylinder #3 at 165 psi. Must be the famous blown head gasket?

Thanks again
 

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2010 DTS
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88,297 Posts
A bad HG rarely shows up on a compression test. You need to do a leak down test. Low compression on a leak down test usually means a burnt valve or worn rings (not common at all on these engines. If the HG was bad enough to show that kind of compression difference on a compression test you'd be using a LOT of coolant and be billowing steam from the pipes.
 

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Discussion Starter · #5 ·
I agree!
Reading a lot of posts I don't see a lot of bad valves or rings!
I must say in the last few weeks I noticed antifreeze on the ground around the water pump location, the pump has over 120K on it and I thought it was time to change it again.
The HG thought was I have also noticed that when the engine is cold after sitting all night when I remove the radiator overflow cap the system has a LOT of pressure.
I don't have a lot of blow-by so maybe a combination of stuck rings and a bad HG

Thoughts?

Thanks
 

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2010 DTS
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Reading a lot of posts I don't see a lot of bad valves or rings!
Almost unheard of.

Pressure in the surge tank after cool down is not a good sign though, but still not a condemnation.
 

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Discussion Starter · #7 ·
Hello All,

Here is the update...Removed the engine and did the headbolt inserts, changed the main bearing, changed the oil pressure switch and both Crankshaft Sensors and then did a complete re-gasket.

There was for sure a problem with the valves in cylinder #1, when the head was removed cylinder #1 the valves and the top of the piston were very clean, not black carbonized like the other cylinders, this I believe was either due to the anti-freeze getting into the cylinder or the fuel washing it clean. Visual inspection on the valves all looked good, saw no cracks or missing valve. Looking at the seats they look good also.I replaced the head with a known good one for a recycler.

Did nothing with the pistons and left them in the bores.

The engine runs perfect, so what caused cylinder #1 to go bad? As I stated before I was sitting at a stop light waiting for the light to turn and the engine started to run bad the check engine light came on and it was a Cylinder #1 misfire...I had just come off the expressway and maybe the hot valve got a shot of anti-freeze and cracked something???

The head-gasket on the head looked good, but after the inserts and the new head gasket there in no more pressure in the system after the engine has cooled down, so the head-gasket WAS BAD

So everyone...Your thoughts
 
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