Re: 1998 Buick Skylark Code P0420

Thanks very much for your input. I have been told
about a reputable garage in my area & I am taking
the car to them today.
Thanks again,
Robert

Bobby12333 wrote:
>
> Hey Guy's
> I took my 98 Buick Skylark to a reputable mechanic
> & they kept it for two days checked everything with their sosfiscated
> equipment & everything is
> within specs & ECM tests were good.

Post back with voltages for all the O2 sensors.

Post back with voltages for all the O2 sensors.

I just wanted to post back & tell you guy's that
The MIL has come back on again after driving 223 miles since I last took
it to a garage that performed all tests & turned off the MIL since they
could not find a problem. One person had mentioned to post back with 02
sensor voltage readings. The Mechanic did not remember the exact voltages
from my first visit but did tell me they were all within specs. Anyway I
have taken it back to the same garage & told them to keep it as long as
needed to see if they can pinpoint the problem since I have another
vehicle I can drive. May sound a little crazy but after they turn light
off I can fill the car & it will always get to between 3/4 & 1/2 tank of
gas & then the light will come back on. By the way I have also replaced
gas tank cap. I have relayed all this info to the garage owner.
The owner of the garage is going to test drive as long as needed with
scanner attached to see if he can come up with any answers. He has
graciously agreed not to charge me anything at all unless he can fix the
problem. This garage is highly recommended in my area as being fair &
honest in these type of situations. I know this is a long letter but I
figured you guy's would be interested. I will post back & let you know
what
the mechanic comes up with as soon as I get the car back. Man this has
been one mind boggling problem.
Robert Joyner

Bobby12333 wrote:

> I just wanted to post back & tell you guy's that
> The MIL has come back on again after driving 223 miles since I last took
> it to a garage that performed all tests & turned off the MIL since they
> could not find a problem. One person had mentioned to post back with 02
> sensor voltage readings. The Mechanic did not remember the exact voltages
> from my first visit but did tell me they were all within specs. Anyway I
> have taken it back to the same garage & told them to keep it as long as
> needed to see if they can pinpoint the problem since I have another
> vehicle I can drive. May sound a little crazy but after they turn light
> off I can fill the car & it will always get to between 3/4 & 1/2 tank of
> gas & then the light will come back on. By the way I have also replaced
> gas tank cap. I have relayed all this info to the garage owner.
> The owner of the garage is going to test drive as long as needed with
> scanner attached to see if he can come up with any answers. He has
> graciously agreed not to charge me anything at all unless he can fix the
> problem. This garage is highly recommended in my area as being fair &
> honest in these type of situations. I know this is a long letter but I
> figured you guy's would be interested. I will post back & let you know
> what
> the mechanic comes up with as soon as I get the car back. Man this has
> been one mind boggling problem.
> Robert Joyner


Hi Robert...

Not a mechanic, just an old retired electrical guy who loves
cars... so take my thoughts for what they're worth

Anyone considered the possibility that there may be a crack
or pinhole in the fuel tank dip tube? Perhaps at 3/4 of a
tank the fuel sloshing could expose an air leak intermittently,
and at a half tank do it even more often.

Yeah, I know, this should set a lean fuel code if anything,
but.... suppose the pump sucks air for a tiny time. Computer
says gee that's real lean. Richens it up. Then the fuel sloshes,
sucks pure fuel again, and it's waaaay over rich. Possible?

Just thinking...

Ken

Ken,
Thanks for the info. I did relay the situation to
the mechanic about the problem happening after filling up then the light
coming back on between
3/4 & 1/2 tank. With the situation with my car
I guess anything is possible. The mechanic will
keep & test drive the car as long as necessary to see if he can come up
with a solution. I have read & read on OBDII Forums & have not seen where
anyone else has encountered this exact problem. This is an interesting
problem & I intend to post back & let everyone know if the mechanic comes
up with a solution so it might help someone else in the future. Thanks to
everyone for your replys.
Robert Joyner