Situation is the following:

LS1 2001 Z28 M6
52.000 kilometers
all stock
air filter changed @ 50k (stock one used)
no SES light
Castrol 0w30 oil
Gas used - Sunoco 94
normal idle and power
sometimes smelly exhaust fumes
city consumption was 18MPG now is 13 MPG

normal driving style, short shifting before 2200rpm (no stunts, rush hour to work and back 10 km each way)

Plus I went to the dealer and they said no light = no code and refused to scan for the codes???

Any suggestions?

 

change the plugs to the Delco 41-985 plugs cause factory plugs do not last 100k miles like they say they do, make sure they are all gapped at .040, run a can of Seafoam fuel injector cleaner through it (available at Advance auto or where i work at Westwood auto in Alabama if you live there and NAPA to i think), run amaco or chevron gas only i know its expensive but its the best and it will keep the fuel system clean, use 10w30 oil, and last but not least, get a new floor board or repair the dent i know your foot put in it

 

wow...that's some strange advise...

brand of gas has very little to do with anything. just make sure to run proper octain, you can get away with lower than 94...bone stock 89 would be fine. just make sure the gas station is a well used one...so it's not old gas.

0w30 oil seems a bit thin, not sure where you live (assume canadia from the Km) but maybe step up to 5w or 10w.

spark plugs are a good idea, don't need anything special. and for sure don't need expensive platnums like the factory. invest the $2 per plug for some good NGK tr55s...and stock gap is 0.60"

can't hurt to run the seafoam, half can into the engine, half can into the oil and a full can into a full tank of gas. do a search on how to properly do all this.

try changing out the o2 sensors (fronts). those are the most common cause of bad milage. they are a bit $$ so you may not want to bother.

 

I agree. Also, check to see when the last time your fuel filter was changed. It's a cheap replacement and should be done at least once a year IMO (depending on how often you drive the car).

 

oh yeah....

check your tire pressure....i've noticed it takes almost -10 psi from proper pressure to be visibly noticed.

it doesn't affect alot...but it could add up

 

Tire pressure
Oxygen Sensor
Run a bottle of fuel system/injector cleaner

 

Remember accelerate slowly from a stop sign or red light. Even if honda is speeding past you.

 

Are you the dude from England?? I remember a post from someone like you.....anyway.....I'd say the O2 sensors...DON"T GET BOSCH!! Get genuine AC Delco..they last longer. make sure you're running the proper octane..check the air filter, just for shats...

 

Canada, Ontario here..

What are the chances to have some engine codes without ses light coming out?

If i need to change the O2 sensors i would like to have that confirmed by the engine code reading.

Other than that, i have checked tire pressure, yes, it was little bit lower but not of any drama.

In about two weeks I am planning some highway trip which will be some sort of "Italian tune up" deal, because car was chocked for the whole winter.

At the same time i will run injector cleaner just to see if that will help.

If there is no success after this kind of "tune up" I will move on with other advices.
Definitely will post the outcome of each step.

 

you won't have a code stored without the SES light on.

and if the o2 sensors are slightly bad, they won't really show up on any scanner.

you could take them out and try clean them, not sure what to use. maybe some electircal cleaner?