OK, this is driving me nuts. '91 camaro, l03, edelbrock performer tbi, smog removed, a/c removed, mild timing advance (4-6). Engine runs great but i've been getting ses light showing code 43 (esc failure). Happens when i'm stopped at a corner, turn the wheel and gas it. Also happened today after a hard break then gassed. Don't know if this will have any effect on test results. The first test earlier this month had results like this: hc ppm | limit 57, reading 56 @ cruise | limit 200, reading 253 @ idle co % | limite .32, reading .04 @ cruise | limit 1, reading 1.13 @ idle no ppm | limit 0632 reading 613 @ cruise | blacked out @ idle I did realize that the timing was set about 6ATDC (set timing last year after having plug wire crossed, late night hehe). So yesterday I reset the timing to about 6BTDC hoping that would stop the ses and maybe help with the e-test. Well here are the results: hc ppm | limit 57, reading 62 @ cruise | limit 200, reading 356 @ idle co % | limite .32, reading .01 @ cruise | limit 1, reading 1.74 @ idle no ppm | limit 0632 reading 1455 @ cruise | blacked out @ idle Any info would be appreciated. I don't know where to start but I don't want to modify things I don't need to otherwise i'll never diagnose the problem. Can I test the o2 sensor? Could the knock sensor be causing drive clean issues seeing as how it may be causing my code 43? Thanks.

Reset the timing to zero and put a new knock sensor in it. Also you may want to reinstall the smog stuff just for the test.

Unfortunately the smog stuff is long gone... it's passed before I don't know what's up now.

I agree retard the timing and replace the air filter. The high co and hc indicate it's running rich. Also don't get it too hot before the test it may increase the NO. You want it hot enough that it burns off the hc and co but not so hot that it boosts no.

I've got a K&N air cleaner and I just put on an xtreme lid. What about o2 sensor? Possibly bad?

If you do not remember when you replaced it, you probably should. I found this a while back and thought it maybe useful The Warning Signs of Failed O2 Sensors, Brian Manley, Underhood Service, August 2001

I've never replaced the o2, i'll try that thanks.

set your timing to the factory spec, if your O2 sens. is old replace it.

Your hc is telling you, there's an ignition problem, the CO is telling you, the mixture is off, and the nox is telling you the egr isn't working.

An O2 sensor will help the CO, if it's bad, and may even help the hc a bit, for that part check your ignition system.

As far as the nox your gonna need an egr valve, or an extremely efficient cat. if you just want it to pass emmisions hook your egr up to it and T- it into ported manifold vacuum, which is where they generally come from, when the car's on the dyno under load it will crank the vavle open bring the nox down, and usually bring the CO down some too.


Run some heavy duty injector cleaner through it. our "silver bullet" is a machine called a "motor vac". cleans the injectors, the valves the chambers, and the cat.

I replaced the egr about 3 years ago, would it be gone again already?? I guess I can check the vacuum and make sure it's still operating properly. What part of the ignition system would control the hc? I'm running stock distributor, msd6 ignition box and msd coil. The cat is a high flow and when I removed the smog I welded a bung into the line that tied into the A.I.R. system.

Thanks again

a current knock sensor code will affect emissions readings.

you too rich at idle, & it looks like you may be too lean at cruise.
a new O2 sensor would be a good place to start.
make sure you don't have any exhaust leaks before or within about 2 feet after the O2 sensor.
as Pony said, check your ignition system, any misfire can fool the O2 sensor.


do they give you the O2 & CO2 readings? if so, post them also. O2 can give indications of a misfire, CO2 can give indications of how good the cat is working.

in addition to checking the vacuum, with the motor idling open the EGR with your hand, it should cause the motor to start running rough or maybe make it stall, if there is no change check the EGR ports.

OK, i changed the the 02 sensor and reset the timing to 0btdc. Still failed for a 3rd time. NOx was normal now but hc still too high. They figure that the high nox may have destroyed my cat... oh well. Must be a sign, new exhaust next week, heddman hedders & y-pipe, magnaflow 3" high flow cat a 3" magnaflow cat back ss dual 3" tips. Should sound nice and run clean.

Ya, that's what I'd do, toss a bunch of dollars at go-fast parts instead of putting the car back like it's supposed to be.

Maybe you'll get lucky, hope so.

Hey GT, go to the hardware store and pick up some acetone.. this will NOT hurt any parts and it will boost octain and drastically reduce emissions. It is cheaper than using that expensive stuff from Auto Zone and it will boost mileage as well. If you use about 4 ounces per tankfull it will help but if you are going to try to pass emissions I would use a lot more.
Also, I knew a Mustang owner that put a couple of 3/4" holes on the top of the exhaust pipe where it curves over the differential, this will allow enough air in to pass it.
HTH's