O.k. This car is giving me fits now. I changed the oil, air filter, plugs and plug wires. It is STILL getting crappy mileage. This tanks was 230 miles when the low fuel light came on. I guess the only thing left is the PCV valve and the O2 sensor ( although it is not throwing a check engine light)

It is throwing the codes P0582 and P0586 and that is because the cruise control doesn't work, at least that is what the book says.

Does anyone have any ideas???? someone posted in the other post about this that his Neon was getting 400 miles per tank !! Will a faulty O2 sensor or PCV valve really make that much of a difference??

 

Don't know if this will help you specifically or not. But on my Saturn, the O2 sensor would impact mileage significantly. As a matter of fact it would be the first thing I would replace when mileage dropped and it almost always cured the problem. Hopefully it's not too expensive a part on the Neon.
mishkaya

 

O2 sensors can be out of spec & not trigger a check engine light on many cars . .just makes the car run funny/get bad mileage.

 

Thecar runs fine, Just bad mileage. I guess I will be buying the O2 sensor tomorrow and see if that does the trick...

 

Yep the O2 sensor is one of the thigns that tells the engine how to program the fuel curves and therefore how much fuel to deliver.. If it's buggered up it could tell the engine to run much richer than it needs to be.

 

X3 on the o2 sensor advise.

 

I'm the one that posted and the light has been on in mine for about eight years now and I am still getting 36 to 44. The code says EGR flow. I really should look at it but as long as it is doing like it is, I ain't touching it. I did replace both o2 sensors and it made no difference at all.

 

I just got as code today and it wasn't anything close to what i was thinking. It is a P0441 which is the EVAP system and usually means the gas cap is off or loose. Nope, gas cap is fine and now i am really confused.

 

I know this may seem far fetched, but I once had a Chevy truck with a 305 that used to average 20-21 mpg. All of a sudden it dropped off to 12-13. I noticed that the truck seemed sluggish and not as responsive as it once was. I had a friend suggest taking it to a muffler shop and having catalytic converter changed out for a high flow one. When they removed the old converter the shop guy brought it to me and showed how plugged up it had become. More than 70% of the honeycomb structure had plugged up.

Might be worth a look.

Gary

 

Try going old school. Go buy a vacuum gauge and hook it up. Doesn't matter that an engine is computer controlled or not. A vacuum guage will help diagnose engine problems that a computer either can't sense or wasn't designed to do.

Once I had helped pinpoint why a 98 Jeep wrangler (with the 4.0 straight six) had dismal performace and poor mileage. I put on the vacuum guage and it helped us quickly pinpoint a plugged exhaust system. Replaced the catalytic convertor and all was well again.

Another time was with a 92 Chevy Blazer (the big one, not the S10). Engine ran cold, and had poor mileage. After trying a couple different sensors that didn't fix the problem, we hooked the vacuum gauge to it and found that it had a massive vacuum leak. After digging around the intake, we found a broken EGR valve that was stuck wide open, causing the computer to overfuel and cause the engine to run cold and have terrible mileage.

In both of those problems, the ECM did not think anything was wrong and there were no codes or a check engine light.

 

Naw, that makes too much sense. Just throw more parts at it.


Smart remarks aside, this is a good suggestion.