# 2005 LS2 GTO missing on 2,4,6 and possibly 8.



## Josh05ls2 (Sep 18, 2011)

I have a severe problem I need someone to help me with. The goat has been running very crappy and missing. I took it to o riellys and all it told me on the scanner was a random misfire detected. I took it to gm and they told me that the check engine light said there was a misfire in cylinder number 4. Scan test showed passenger side not firing and low compression on 3 cylinder; 2,4,6. Commpression was said to be between 125-150, I'm guessing that's running? 

Any help would be great, I want my car back on the road as soon as possible! 
It also has brand new plugs and wires.


----------



## svede1212 (Nov 1, 2005)

The 125-150# is probably compression measured turning the engine over. I believe you should be about 185# or so. If that's the case there is no quick or cheap fix. A scope in the cylinder or head removal will be necessary to find out what's going on. Valves, pistons or rings are the most likely cause.


----------



## Rukee (Feb 8, 2007)

if the cylinders are not firing, that could cause the low compression. 125 is enough to fire, so I'd be checking the spark and fuel supply to that bank. Possibly a restricted fuel rail or bad ground or power supply on the coil bank?


----------



## Josh05ls2 (Sep 18, 2011)

Thanks for the help guys, I ended up taking the passenger side doenpipe with catalytic converter off and guttin the cat to see if that made a difference. After puttin the doenpipe back on the GTO is running Like a dream again! I'll be ordering MagnaFlow Downpipes and new O2 sensors for it an installing them. I may also go a head and order the Kooks headers for a full exhaust setup. I currently have the Magnapak kit with X pipe and MagnaFlow mufflers. 

Thanks for the help guys!


----------



## svede1212 (Nov 1, 2005)

Cats and spark plugs don't cause low compression tests. I'd be worrying about why they're low. I also would never gut a cat. At the least they were worth money in one piece.


----------



## cmack111 (Feb 25, 2011)

svede1212 said:


> Cats and spark plugs don't cause low compression tests. I'd be worrying about why they're low. I also would never gut a cat. At the least they were worth money in one piece.


Svede is right...however. A plugged up cat will cause the gas not to be burnt and will wash down the cylinders causing the low compression. 

Get the compression checked again with the car running like it's supposed to and post those numbers


----------



## Rukee (Feb 8, 2007)

svede1212 said:


> Cats and spark plugs don't cause low compression tests. I'd be worrying about why they're low. I also would never gut a cat.* At the least they were worth money in one piece.*


Some are worth $200-300 to the scrapper guys.


----------



## HP11 (Apr 11, 2009)

cmack111 said:


> Svede is right...however. A plugged up cat will cause the gas not to be burnt and will wash down the cylinders causing the low compression.


I'm not sure if you've got that right. The cylinder wash down would precede the clogged cats. First, there have to be some type of condition that causes the engine to dump unburned fuel into the exhaust. That's what would cause the cats to get too hot and melt-down the ceramic substrate in it. That would cause clogging and create extra backpressure which would likely cause the engine to go into reduced power mode if not stall all together.


----------



## cmack111 (Feb 25, 2011)

HP11 said:


> I'm not sure if you've got that right. The cylinder wash down would precede the clogged cats. First, there have to be some type of condition that causes the engine to dump unburned fuel into the exhaust. That's what would cause the cats to get too hot and melt-down the ceramic substrate in it. That would cause clogging and create extra backpressure which would likely cause the engine to go into reduced power mode if not stall all together.


It could be that there was another problem causing the cats to fail or just the fact that they are old. Either way the cat's being partially plugged will cause the cylinder to wash down. Saw it two weeks ago on a customer' car. Another shop told them they needed a new engine...I replaced the cat's ran the motor and it has good compression.


----------



## HP11 (Apr 11, 2009)

That may be true but in your scenario, you simply replaced the cats. I'd want to know what caused them to fail......


----------

