Hi Yall ....New and not very mechanical....but trying. [sm=gears.gif] I have 95 Neon that has just had full tune up and fuel pump changed $550.00 Ughhhhh! She still acts like fuel pump.......I will b driving and then no gas showing codes, 12,21, 43. was wondering if cat could b problem. My friend tells me it's the way I drive...lol. garage tells me to put a piece of black tape over the light ....soooo here i am.......what do u think????

 

12 - Is battery disconnected within the last 50 key on cycles (Nothing to worry about)
21 - Is O2 sensor, either upstream or downstream (More than likely upstream)
43 - Is multiple cylinder misfire (Change your spark plugs with stock champion plugs)

You probably didn't need the new fuel pump.

 

Hey thanks for the fast reply........plugs have been changed (unsure of what kind ...definitely will check tomorrow).......when i changed the air filter it was extremely dirty....would like to know about something called a mass air flow sensor (where it is and how to check). also my cat is bad , could this cause me problems? Sorry if these r lame[sm=hail.gif], but i appreciate your help . Many thanks!

 

chances are, if the cat is bad then there is your problem.....and neons dont have a mass air flow sensor

 

Isn't there a connection between the downstream O2 sensor and the cat?

 

Yes there is a connection to the downstream sensor and the cat. The DS (secondary) sensor is what measures the converters performance. Everyone jumps to the upstream (primary) as being bad. Alot of the time this is not the case.
A bad converter will act very much like a bad fuel pump.
You are lucky however. People will tell you that the downstream sensor does not affect fuel curves. On the 95 or earlier it does not, however, 96 and newer Chrysler products it does. DMx holds the patent on that technology. You will still throw the CE light on a 95 but it will not affect fuel curves. Most people think that Howell automotive and Modern sell the secondary o2 bypass to keep the CE light from staying on, but that is not the case. It is to fool the PCM into thinking the converter is still in place and doing its job so the PCM won't try to counter the read.
You can gut the converter and still fool the PCM on a 95 so it will not through a code resulting in a CE light. Go to your local Napa and buy a spark plug non-fouler. Drill out the center of the non-fouler so that the o2 sensor will thread into it and the end sticks out the other side. Thread the non-fouler into the the converter. This only allows 1/8" of the sensor to be into the exhaust path which makes the PCM think the temperature variance is within spec. which would mean the converter is doing its job.
The only problem with gutting the converter on a neon is that you may experience a power loss. Not only a low end loss of torque, but through out the power range. It is called expansion chamber syndrome. This is caused by the exhaust gases freely expanding inside the empy converter chamber and having to be recompressed to continue through the rest of the exhaust system. It does not affect all engines the same. Porches tend to run better with an expansion chamber in the exhaust system.
I would highly advise you to invest in a high flow cat, or since it is a 95, delete the converter all together using a test pipe or race pipe. Just ignore the CE light, you will get used to it. Don't believe me? The clock on my VCR has been blinking for 7 years now and I don't even notice it anymore. As a matter of fact, it is kind of like a night light / strobe light in the dark. Best of luck to you.

 

Hi guys......I have eliminated the cat .......still same problem ......guess O2 sensor would b next ........what r the symptoms of a bad O2 sensor anyway. Feels like she is starving for air or gas.....seems random but is ocurring more frequently now. Also what r the syptoms of a bad EGR....wouldn't i b getting a reading of EGR if it was bad? Also am i doing damage by driving her this way? On the up side ......I look at my CEL in a whole new way[sm=yeahsmile.gif]....lol, and 5.0LTREATER, thanks for the the wonderfully clear CAT explanation.

 

Changed the fuel filter within the last 30k miles?

 

Yep....air and fuel.......a week ago.

 

check you fuel pressure regulator and your injectors.. if you misfiring and you changed plugs and wires you have to get your coils checked out. i had that problem but new plugs solved it for me. if cat was bad you would smell a good awful smell while driving.