Fuel Economy issues,,

[TSmiley98]

There used to be alot of threads on why the cars got poor fuel mileage, I dont remember what the main cause was but does anyone remember the remedy for this? We have a car that is getting under 200 per tank and no CEL's it is a 5spd and isnt getting beat on either

[Buster]

Things to check/suggestions:

Replace air filter or clean/oil if K&N.

New fuel filter.

Run some Chevron Techron through tank.

Clean MAF.

Clean TB.

Clean out intake tube.

Check/change spark plugs.

Tire pressure = 35 psi (check often to maintain).




These are just a few initial and very easy things to do to see if it improves things. I did all of these at once last year when I was getting bad MPGs and it not only boosted the fuel economy, but the car ran a lot smoother and seemed to accelerate better.

[mechtech]

O2 sensor or MAF may be puked on your car. Fuel pressure sensor and TPS should be checked, also.
Is the exhaust plugged?

[Buster]

He said no CELs.

O2 or MAF failure would likely trigger one.

[J_Mob]

Things I found that affect gas mileage on my ZX2 (which is still non-op) was the tranny not shifting out of second (atx) and the MAF/IAT sensors covered in trans fluid and oil from previously overheating the trans. That did log IAT codes in the turd's brainbox though.

In general, I have found that different fuel suppliers gas burns up at different speeds (in the same octane rating, under the same dri ving conditions. I think it's the ethanol and water contents).
Also, does the car have a stock or aftermarket fuel pump, and is there a return line for unused fuel to return to the tank. Maybe something in that area.....

[crazy34]

when was the last time it had a good tune-up too.....i wonder if an aluminum flywheel would help mpg.....was thinkin about puttin one on a buddies car to see if it would help

[mechtech]

A total failure should throw a code.
A lazy O2 or slightly out of spec one will not. Ditto for the MAF.

[Buster]

Actually it will. It will have a "Slow response" code. This could happen randomly to O2 sensors for several months before failure.

[krux]

02 sensor is bad. Get a scope on it and watch out slow it will responded. For a obd-2 car it has to fail 1.5 times vs a obd-1 is like 3 times out of its curve before it give a code.

[mechtech]

It may or it may not give a code, in real life.
Slow or inaccurate o2 sensors are common, and there are often no codes. Plus a lot of other sensors!
I wish there were - it would make diagnosis easier on customer's cars!