I have an 88 that failed smog yesterday with too much NO and no CO.

I don't think the oxygen sensors have ever been replaced. So, I am thinking that may be the cause.

It is a base model, 5.7L. Is there one on each side or just the one I see on the drivers side?

Do you think I am on the right track?

You have only one. I know nothing about Kali emissions - I'd think it wise maybe to get it evaluated by someone that's very familiar with Kali emissions. I'd think it very wise to get it on a proper scanner and be prepared for maybe a considerable effort!

Has it done emmisions prior or is this '88 new to you?

I've had it for about 5 years now and this is the first time it failed. I don't drive it that much, and hadn't driven it for a couple of months prior to getting it smogged for reg renewal. Seems to run fine.

One sensor in the left header pipe on the L98.


Get the FSM and there are a variety of tests you can do by jumping the diagnostic terminals, such as watching O2 sensor switch rate.




Jonathan.....

If your EGR is working you have a good known 02 sensor and a fresh cat (make sure it has a CA approved stamping on it they look) you should be Ok. Usually the latter 2 does the trick.

If you can find a Delco sensor on ebay. They read better
I have a brand new one for a 90 1 ton I just sold. Bet money they are the same one...if so let me know. Im off the 126 and 5. Dealer only had 1 left it was only $30 didnt need it but grabbed it in case
Had bad luck with off brand stuff.

CA SMOG SUCKS.

1 and if it s original I would change it give it a good run and bring it in hot for testing.

Some suggestions from the AZ emissions test.

BE SURE YOUR VEHICLE WILL PASS
These preparations can help your vehicle pass the test the first time!

Fresh fuel, make sure your tank is at least ½ full
Oil Change (dirty or deteriorated oil can cause higher emissions)
Tune-up (fresh spark plugs, proper timing, proper RPM) and if applicable, plug wires and vacuum leaks

I'm not in CA but....

NOx is controlled with your EGR and 1 (of the two) stages of converter. One part lowers/removes NOx while the other converts carbon to CO2. (IIRC).

Point being, I'd be more suspicious of a bad (or clogged) EGR and/or converter before thinking the O2 had taken a dive.

Because NOx is the high reading, I'd start with EGR function.

This too!

Unless it is totally out of spec, it will run "just fine" according to the SOTP dyno which, IMO is useless. Often they get slow and the ECM uses it for adjusting fuel trim so.....

Thank you all our replies.

I replaced the oxygen sensor since it was so cheap of a repair, ran it, and it passed smog today.

I don't know for sure if that was the problem, or just running it a little more before the test did it, but it passed.