please help w/ check engine light

[erik671]

I have a '96 XLT with the check engine light on. The OBD code says that catalyst system is below threshhold.

The check engine light was on before for the same reason, and I was told that the engine was running cold which may be causing that error since the catalytic converter has to be hot enough to be effective. Anyway, they replaced the thermostat and reset the code and the light stayed off for a while.

But now the light is on again with the same code. What could I check? Which sensors could be the culprit for that code? I thought it might be the MAF sensor malfunctioning and causing the engine to run fuel rich (and cool).

Please help.

Thanks,
Erik

 

[Alec]

No matter how bad the thermostat, MAS, or other related sensors are, the engine will not run cool enough for a significant amount of time to not be in the operating range of the catalytic converters.

My guess is that either the O2 sensor behind the cats is bad or the cat itself is bad. How many miles does your truck have? If it has over 60000, I'd guess its a bad O2, and you might as well replace all of them (3 or 4, I forget).

How is the truck running otherwise? Any performace problems or strange odors? Again, my guess is the O2, but if you have other problems it could be the cat itself.

 

[erik671]

It has about 86k on it. There aren't a lot of other symptoms except it doesn't seem to have as much power as it used to, and I think the gas mileage has gotten worse.

Is it worth checking the O2 sensors? Or should I just replace them?

Thanks,
Erik

 

[erik671]

I replaced the sensor that is after the cat. converter, reset the engine light, and the engine light came on again.

Does that mean that the cat. converter is bad? Could a 0420 code be caused by the upstream sensors? (they have never been changed..)

-Erik

 

[oahrens]

COuld BE....

Just a thought.

I had bad gas mileage...poor power....chk eng lght on my 91 xlt with 75000. I don't know what the code was.

I cleaned the MAF to no avail.
Next was the fuel pressure regulator and resetting the computer.

SO far so good.

If sympoms are the same...screw the codes and try the FPR.
BTW...you can test the fuel pressure yourself to verify before installing.