New LS1 Owners - Newbie Tech - Bad mpg

I have a 98 trans am completely stock but a lid... It seems recently I have been getting pretty bad gas mileage.. Just wondering what some causes might be?? The car is also running pretty rich. I can smell strong fumes when I am idling. Any thoughts are welcomed. No misfiring though. And the car is running strong.

What are your bad mpgs? My 99z m6 can get 16-18 city driving and up to 30 on the highway

whens the last time you did a tune up? or have you tried fuel system cleaner?

I have a 98 trans am completely stock but a lid... It seems recently I have been getting pretty bad gas mileage.. Just wondering what some causes might be?? The car is also running pretty rich. I can smell strong fumes when I am idling. Any thoughts are welcomed. No misfiring though. And the car is running strong.

This can be bad o2,dirty fuel filter,plugs,dirty maf,bad gas,or a heavier foot. What you can do is buy some of this stuff and follow these instructions...http://ls1tech.com/forums/general-maintenance-repairs/534376-how-seafoam-your-car.html

Ya I am starting to believe it is a combination of O2 sensors and plugs/wires. I just seafoamed the car about a month ago and changed the fuel filter. I always use 91 octane. Best I can get in Cali.

my MPG highway right now is around 20.. I know my car gets better than that.

city MPG is around 16.

Ill do everything listed above and hopefully she is back to normal

OP there is definitely something wrong with your car. Do all the simple stuff first plugs,wires,clean maf, and your 02 sensors. Also you might have a vacuum leak somewhere. My DD truck was having a mpg issue and I did all the above mentioned things. It didn't help then I looked and found a vacuum line that was cracked. I fixed the vacuum leak and my mpg went from 21 to 26. Also to let you know my car in sig. got 19mpg 100% city driving last week.

if you're running rich, your o2's may be stuck on the lean side. could be a dirty mass airflow meter, or a bad air charge temp sensor....which i think is part of the maf? poss. bad coolant temp sensor, if there's a map sensor in there, it could be bad too.........plugged air filter?

If the plugs haven't been changed in a long time, change them. I'd also pick up some MAFS cleaner and clean it, and have it checked for any codes.

OP there is definitely something wrong with your car. Do all the simple stuff first plugs,wires,clean maf, and your 02 sensors. Also you might have a vacuum leak somewhere. My DD truck was having a mpg issue and I did all the above mentioned things. It didn't help then I looked and found a vacuum line that was cracked. I fixed the vacuum leak and my mpg went from 21 to 26. Also to let you know my car in sig. got 19mpg 100% city driving last week.

WHere was the vacuum leak??

Thanks guys I am going to check all this stuff out!

Just to add guys... I have been noticing lately that when I run my air conditioner I get a fume like smell coming through the vents. Kinda gives me a headache. Any ideas what could be causing this?

WHere was the vacuum leak??

The vacuum leak was on my DD truck not the F-body. I was just using it as an illustration that a vacuum leak could be the issue is all.

Same as above, plugs if they haven't been done in a while or if you aren't sure of the age/gap. Clean maf anyone because a can of cleaner is $5. Do fuel filter regardless since they are $10-$15. If u know someone with a scanner, have them check how the 02s are switching and replace as needed

Seafoam is awesome and only $15ish iirc. Do the intake as well as adding it to the fuel tank

you can hook up a scanner and check the O2 sensor.

did plugs and wires MSD/Ngktr55.. damn #8 is a pain in the ass.. Then I took the MAF off and found a piece of foil/trash in there. Whoever had the car before me wrapped the MAF with a foil insulator and then connected it to the lid.. well over time I guess it came lose and went into the MAF, so I removed it and then cleaned the MAF with some autozone cleaner. Must of just happened recently b/c i just checked it like a month ago when I was seafoaming/ cleaning the TB. Hope that was my problem... well see... thanks guys

How is it doing now?

Are you a4 or m6? My 01 gets mid-high 14s all city. Run 91 and no codes. Smells a little rich but could be cuz I have no cats. I make it to 180 every time "check gages" pops up then it's 12gal from empty to full.

Just to add guys... I have been noticing lately that when I run my air conditioner I get a fume like smell coming through the vents. Kinda gives me a headache. Any ideas what could be causing this?


Probably since the A/C isnt used that often could be building up mold in the evap core. They make a cleaning kit for HVAC systems but I've never used one. Also keep in mind A/C will reduce your MPGs by a little mostly city MPGS, its more efficient to use A/C at highway speeds and have the windows up.

I get 17 drivin city and a few miles hwy with long tubes no cats 3.42 gears lid and 18's and that's givin it hell a few times and I have stock tune burning rich

If the car drives fine and feels fast, but is running rich, it might not be going into closed loop. Your 02 sensors might not be working correctly.

are you sure there isn't any leaks in your exhaust manifolds? you may not even be able to hear a leak or a cracked manifold. I had it happen on my stock 2000 Z28 years ago. never threw a code or anything just ran rich and bad mpg only reason I found the leak is i had it on a lift changing oil and when we lifted it back up to make sure it wasn't leaking etc the exhaust was blowing in my hair by my oil filter. I know its a long shot but might wanna take a look.