I have a '00 SS M6, the engine is stock with a lid and a K&N filter.

Lately I have been noticing worsening gas mileage (~16mpg, used to get 19 with about the same driving conditions.

Last Friday on the way home from work I noticed a slight hesitation during acceleration (about 1/2 throttle) around 1400-1500 rpm. The engine was cold at that time. On Monday I felt the same thing. The engine feels different for a second or so, then is back to normal. In both cases it happened only once, upon acceleration after a 90 degree right turn.

The engine does not make unusual noises and appears to pull normal otherwise. It has not thrown any code except the EGR valve one twice, once about a year ago, the last time in late April.

I have been considering the following issues:

MAF dirty or damaged
O2 sensors
Fuel pump
Catalytic converters
Bad gas (though the last tank was at Chevron)
EGR valve?

I was planning on having the 60000 mile service done next week (have ~59100 right now), but im not sure whether to trust the dealer with this issue or go to some other mechanic.

What can I do myself to find out what's wrong?

I have a code reader and an Auterra DashDyno to record parameters with, but I am not sure what to look at for this problem.

Thanks

Christian

 

Start by cleaning the MAF.

 

Thanks. I'll start with that tonight.

Any advice on what to clean it with?

 

electrical contact cleaener. Spray the dirt off the tiny filaments without touching them. If you break one then you'll need a new MAF.

 

Go back to a paper filter too. You have to be a zen master of oiling to set up your K&N properly so that it doesn't mess up the MAF.

-Geoff

 

I pulled the MAF this morning and got MAF cleaner from Kragen. The screen was very dirty, so I sprayed the MAF from the back first and let it sit screen down on some paper towels. Then I tried to spray the front sides of the little wires through the holes in the screen but Im not really sure I got them.

Is there a way to take off the MAF screen without damaging it so I can spray the front of the wires properly? I don't want to run with the screen off as I found a dead fly on the screen. I havent oiled the K&N yet (it is still oiled the way it came from the factory) ,but I see your point about paper filters, so I am going to pick one up tomorrow.

 

Take the 4 bolts out and take the front and back off of the sensor part. wash everything up and put it back together. Be careful to watch/mark the orientation of the 3 parts so that you get it back together right.

 

Thanks, I got it apart and sprayed it thoroughly twice. Now im going to let it dry until tomorrow and see whether it makes a difference.

What else should I look at?

 

Have you changed gas stations? I seem to get better mileage with Shell, Mobil, or BP. I think it's the difference between 91 octane and 93 octane, 91 works... but you're better off getting 93.

Other than that I'd have the vacuum lines looked at. A vacuum leak give you some pretty awful mileage as well as lousy performance.

 

I tried 76, two different Chevrons and Shell. The hesitation could be caused by Chevron gas (was a few days after I filled up), the gas mileage was bad with all of them.

I'll go hunting for a vacuum leak, thanks.

 

Plugs and O2 sensors.

 

with the gas stations mixing ethonal you will get worse gas milage it burns faster.I have noticed this to .

 

I'm gonna say plugs.. A hesitating engine under a load is ignition related..



.............. Or a bad fuel filter.. And I'll agree with the possibilty of bad gas.. That happened to me once w/ my 2000 Z28 M6.. It was using about a gallon of gas every 5 miles or so! yes!! THAT BAD!!! IT was fine the next tank and also after I cleaned the air filter..

 

Can O2 sensors be part of the problem if they're not throwing any codes?

 

I had same hesitation changed plugs and wires all was good.

Also I would not go back to a paper filter the K&N filter is much better for air flow unless you dont care about performance than paper is fine. Oiling is not an issue just lightly spray it and let the oil soak into the filter before re-installing it, its not rocket science
I have been running K&N's in all my vehicles since the 80's never had an issue.