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'89 240SX Emissions Problem Made Worse

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

Reply to
Outta nowhere
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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).

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.

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.

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.

NP

-Mike

Reply to
Mike

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

Mike wrote:

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Outta nowhere

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Outta nowhere

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

Outta nowhere wrote:

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Outta nowhere

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