12.1 MPG!! What's going on?

[Jesus A Rodriguez]

My 04 V8 sport is has been getting poor fuel economy lately. Today I was getting 12.1 on the highway. I just changed the fuel filter and air filter as both need to be changed but it still has not gotten better. Any ideas? Could it be the 02 sensors?

 

[joegr]

Yes, but it could be lots of things. Usually, it's marginal COPs. If you run long enough with marginal COPs, than add clogged catalytic converters to the suspect list.

 

[cubanocelso]

Sure the same thing happens to me .........right leg longer than the left :steering

 

[Jesus A Rodriguez]

Wow COP's cause so many issues with the LS. Its like every problem you have it could be the COP's. Im going to change the spark plugs and cop's.

 

[02pos]

do yourself a favor and order them from a wholesaler like rock auto, other wise you will end up paying $50-$60 a pop, and only find 2-3 at any one parts store

 

[wade0731]

Make sure to buy OEM COPs.

 

[LS4me]

Wow COP's cause so many issues with the LS. Its like every problem you have it could be the COP's. Im going to change the spark plugs and cop's.

Or any other computer controlled drivetrain....... The computer adjusts many, many other systems based on spark/explosion efficiency...

 

[FDR]

Or any other computer controlled drivetrain....... The computer adjusts many, many other systems based on spark/explosion efficiency...

Exactly. The reason why COPs cause so many LS issues isn't because the car is unusually dependent on them, but rather because the factory gaskets fail so often that COPs are the most common cause. I had the 40-50mph bucking issue and it would go into limp mode if I hit 6000rpm. New COPs, plugs, and unplugging the battery fixed it.

 

[joegr]

E...but rather because the factory gaskets fail so often that COPs are the most common cause. ...

I'll say it for the hundredth time.
All my COP failures have been dry. Neither of my LSes have had any valve cover gasket leaks so far. Ford first thought that the main cause of failure was oil leaking into the plug wells. They corrected that problem, but then still had a high COP failure rate. After further investigation, they tracked the cause down to being a breakdown of the epoxy they potted the coils with. Unfortunately, when this was discovered, it had already been determined that LS production was ending soon, so there wasn't much attention to solving the problem.

 

[FDR]

I'll say it for the hundredth time.
All my COP failures have been dry. Neither of my LSes have had any valve cover gasket leaks so far. Ford first thought that the main cause of failure was oil leaking into the plug wells. They corrected that problem, but then still had a high COP failure rate. After further investigation, they tracked the cause down to being a breakdown of the epoxy they potted the coils with. Unfortunately, when this was discovered, it had already been determined that LS production was ending soon, so there wasn't much attention to solving the problem.

Didn't know that. Back when I did my coils 4 months ago, all the threads said it was the oil. I had 7 oily coil boots and saw no reason to think otherwise. Granted, I questioned it since oil doesn't conduct electricity and people were stating that it was shorting the coil to the block, but I figure if I'm still going without a misfire, part of it must be right. Independent problems, I guess

 

[G-RELL]

Didn't know that. Back when I did my coils 4 months ago, all the threads said it was the oil. I had 7 oily coil boots and saw no reason to think otherwise. Granted, I questioned it since oil doesn't conduct electricity and people were stating that it was shorting the coil to the block, but I figure if I'm still going without a misfire, part of it must be right. Independent problems, I guess

Its not that it conducts electricity, the oil breaks down the rubber in the boot, providing less protection.

I would still suspect the epoxy as the main failure source, but weak boots aren't helping anything.

 

[joegr]

... but weak boots aren't helping anything.

Agreed...