Check Engine Light and Fuel Mixture
 

I have a high mileage 95 Explorer which I now only use for
biking and camping trips. These trips usually take me through
the mountains of Colorado. Lately and consistently the check
engine light has been going on and off as I drive through the
mountains making significant elevation changes. However, once
I'm at my destination or at home the light stays solid off and
the engine runs smoothly. During the times the light is turning
on and off the engine runs slightly rough. From what I understand
the computer is making adjustments to the fuel mixture during
elevation changes based on the sensor imput from the MAF in the
upper intake manifold and the Hot O2 in the exhaust pipes. I think
there are three Hot O2 sensors in the exhaust system. All of these
sensors are the original. I'm thinking one or more of these
sensors is now marginal.
My question to the group is can I eliminate the on/off of
the check engine light during elevation changes by changing one
or more of these sensors? When the vehicle was newer the check
engine light never came on. However, I can now reliably predict
when the check engine light will start coming on based on where
I am driving in the mountains. I know there are voltage measurements
that can be made to the sensor outputs. However, when I am at home
the light never comes on so I am assuming the sensor outputs are
all in a normal range.

Thanks in advance for any input on this subject.
Mark

In article >,
Mark Barrett > wrote:
> My question to the group is can I eliminate the on/off of
>the check engine light during elevation changes by changing one
>or more of these sensors? When the vehicle was newer the check
>engine light never came on. However, I can now reliably predict
>when the check engine light will start coming on based on where
>I am driving in the mountains. I know there are voltage measurements
>that can be made to the sensor outputs. However, when I am at home
>the light never comes on so I am assuming the sensor outputs are
>all in a normal range.

The best way to deal with this is to get the codes pulled from the
computer to see why it's turning on the check engine light. I think
places like Kragen or AutoZone will do this for you. Once you know
what is causing the check engine light to come on, check back here
and someone can probably tell you what you need to look at next.


--
Mike Iglesias Email:
University of California, Irvine phone: 949-824-6926
Network & Academic Computing Services FAX: 949-824-2069

You might have trouble finding a place that will read the codes for a 1995.
I think it wasn't until 1997 models that the interface to read the codes
conformed to the industry standard.
At any rate, I took my 1995 to an autoparts store and they told me they
couldn't read codes off of pre 1997 Explorers.

"Mike Iglesias" > wrote in message
...
> In article >,
> Mark Barrett > wrote:
> > My question to the group is can I eliminate the on/off of
> >the check engine light during elevation changes by changing one
> >or more of these sensors? When the vehicle was newer the check
> >engine light never came on. However, I can now reliably predict
> >when the check engine light will start coming on based on where
> >I am driving in the mountains. I know there are voltage measurements
> >that can be made to the sensor outputs. However, when I am at home
> >the light never comes on so I am assuming the sensor outputs are
> >all in a normal range.
>
> The best way to deal with this is to get the codes pulled from the
> computer to see why it's turning on the check engine light. I think
> places like Kragen or AutoZone will do this for you. Once you know
> what is causing the check engine light to come on, check back here
> and someone can probably tell you what you need to look at next.
>
>
> --
> Mike Iglesias Email:

> University of California, Irvine phone: 949-824-6926
> Network & Academic Computing Services FAX: 949-824-2069