'89 240SX Emissions Problem Made Worse

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Outta nowhere - 22 Jan 2005 20:44 GMT

I was having trouble getting my '89 240SX through emissions testing.
I'd tried the usual suspects (PCV valve, air filter, even plugs and
wires) and it went from failing CO only to CO & hydrocarbons.

Despite the ECU not showing any errors, I tried to replace the O2
sensor with an old one I'd removed (that I think was ok). Now, it
won't even idle. If I try to let it idle or try to keep it at a
constant RPM with the throttle, it wants to die. Disconnecting the O2
sensor altogether seems to help a little. Putting the other O2 sensor
back in didn't change anything.

The ECU shows a code of 12 (air flow meter circuit) now. But, I don't
know if I should trust it. The O2 sensor connector seems frayed.

Could I have accidentally disconnected some hidden sensor, or should I
just buy a new O2 sensor now?

Thanks

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Mike - 31 Jan 2005 00:34 GMT

> I was having trouble getting my '89 240SX through emissions testing.
> I'd tried the usual suspects (PCV valve, air filter, even plugs and
> wires) and it went from failing CO only to CO & hydrocarbons.

How about the cat? The catalytic converter should be removing most of
the CO emissions. Excessive hydrocarbons and carbon monoxide tends to
mean that the engine is running rich (hence incomplete combustion).

> Despite the ECU not showing any errors, I tried to replace the O2
> sensor with an old one I'd removed (that I think was ok). Now, it
> won't even idle. If I try to let it idle or try to keep it at a
> constant RPM with the throttle, it wants to die. Disconnecting the O2
> sensor altogether seems to help a little. Putting the other O2 sensor
> back in didn't change anything.

Ok, you may need to try resetting the ECU by disconnecting the positive
terminal of the battery for around 10-20 minutes then reconnecting it. I
don't quite know what this actually does (no where in any manual says to
do it) but its helped me quite a bit in the past.

> The ECU shows a code of 12 (air flow meter circuit) now. But, I don't
> know if I should trust it. The O2 sensor connector seems frayed.

If the ECU gets a discontinuity from the O2 sensor, it will let you
know. Take the connector off the AFM and spray it with some electrical
contact cleaner (any electronics store should have this for around $10
USD I guess). I personally would tend to trust the ECU as it would be
quite hard for it to give a wrong error.

> Could I have accidentally disconnected some hidden sensor, or should I
> just buy a new O2 sensor now?

If all else fails, you can take it around to a nissan dealership and ask
them to check it out. Let them know in no uncertain terms that you know
what your talking about (but just don't have the resources to test
various parts) so they don't try and shaft you. Just ask them to find
out where the problem is, but not to fix it, as they charge an arm and a
leg for labour.

> Thanks

NP

-Mike

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Outta nowhere - 08 Feb 2005 03:56 GMT

After I replaced the O2 sensor with a new one, the engine would idle
again. I went ahead and replaced the plugs, and the idle smoothed out
to normal. Hopefully I'll have the chance to take it through
inspection tomorrow.

Tracy

>> I was having trouble getting my '89 240SX through emissions testing.
>> I'd tried the usual suspects (PCV valve, air filter, even plugs and
[quoted text clipped - 40 lines]
>
>-Mike

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Outta nowhere - 09 Feb 2005 00:00 GMT

Well, the hydrocarbons passed, but the CO is still failing...

>After I replaced the O2 sensor with a new one, the engine would idle
>again. I went ahead and replaced the plugs, and the idle smoothed out
[quoted text clipped - 47 lines]
>>
>>-Mike

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Outta nowhere - 10 Feb 2005 04:00 GMT

After driving it a couple of days, I decided to try and remove the
sensor harness from the air flow sensor. Now, it barely runs again
(but in a slightly different manner). So, I think the problem is
either a really screwed up air flow sensor or (more likely) a wiring
problem in the air flow sensor harness. Is there a documented process
for troubleshooting the air flow sensor? How about the harness? I'm
wondering if there's a break in one of the wires. Do they go to the
ECU?

Thanks,
Tracy

>Well, the hydrocarbons passed, but the CO is still failing...
>
[quoted text clipped - 49 lines]
>>>
>>>-Mike

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