Back again... this time I took my 1986 Z-28 camaro in to get inspected and it failed emissions. It has a 305 fuel injected engine (automatic). The harmonic balance ?end? has shifted so I have to time the car by sound. I was hoping someone could look at these numbers and explain what I should do to help my camaro pass...

Pollutant High speed (25mph) Low Speed(15mph)
Standard current standard current
HC(PPM) 148 241 152 286
CO% .94 .94 .86 1.39
CO2% 13.4 13.0
O2% 1.4 1.7
NOx(ppm) 1047 147 1146 178

I failed on the HC on both high and low speeds, and the CO% on the high speed. At the low speed I just barely passed. The NOx seems to be okay though... any suggestions?

Chris

 

Chris,

Strictly by analysis of the numbers, it appears that you're running rich and possible too cold.

The most obvious thing to check is the oxygen sensor. If it hasn't been replaced in the last 30,000 miles, it's time to do so.

It would also be a good idea to find the TDC and mark your balancer. If you don't have teh facilities to do that, you can remove and replace the balancer for about $50, or install a degreed balancer cover for about $19. They bolt to the three center holes on the back side of the balancer hub, so they don't depend on the integrity of the elastomer ring on the balancer.

 

So how do I check the oxygen sensor? And if my A.I.R. system isn't working properly, could it account for the difference in the numbers? And should my air pump be pushing air to the outside... It tends to shunt a little air no matter what, but not like before, when it felt like another fan was under the hood...

Finally, I cleaned all my spark plugs. How much difference could that make, if any?
Thanx,
Chris

 

You can perform a basic GO/NO-GO test on the O² sensor with a digital voltmeter and a propane torch. About all it will reveal is whether the sensor is functional or completely dead. The sensor has to be removed either way.

Remove the sensor and connect the voltmeter on a 2.0VDC scale. Hold the sensing element end in the flame of a propane torch while measuring voltage. The sensor should produce a signal of at least 0.75VDC within 60 seconds. A fresh sensor will create 800 mV in only 5-10 seconds. Removing the flame should drop the sensor output to less than 0.10VDC. Again, this does not test the quality of the sensor, but will tell you if it is completely "dead" or not. A propane torch flame is nearly devoid of all oxygen and should produce a fairly high signal as a result, just like a very rich mixture. If you don't get the voltage, your sensor may be toast, or contaminated with coolant, carbon, incompatible RTV curing agents, or oil.

For the price of most oxygen sensors (about $22.00) it's good insurance to replace it every 30K miles or so. Heated sensors are supposed to last longer (why, I'm not sure), but the jury is still out on that opinion.

 

I agree to check mixture control things (oxygen sensor). High hydrocarbons do result from running rich. Things I always make sure to do before an emissions test are:
Air filter
PCV filter
new plugs
oil change

Despite being designed as an emissions control device, I wouldn't expect a problem with the AIR system to cause you to fail. At least, a problem with the AIR system alone won't cause you to fail. That said, I don't fix AIR problems, I remove them (and continue to pass).

MikeS

 

Ok guys, I adjusted the Idle throttle plates by the screw the way Chilton's says to, put in a new Air Injection Divertor Valve, Ajdusted the timing (mainly guesswork, not yet marked properly) and took it back in. It failed worse than before. Here are the numbers.

High speed 25mph
--------------standard--------current reading
HC(PPM)-----148------------------423
CO%---------.94-------------------1.11
Nox(PPM)---1047----------------1276

Low Speed 15mph
--------------Standard------current reading
HC(PPM)----152----------------422
CO%---------.86-----------------.97
NOx(PPM)---1146-------------1458

As you can see, the only thing that is better is the CO% on the low speed. However, the car runs much smoother now and smells cleaner. Is my problem now just timing? Or should I be closing the throttle plate more. Yes, I have been adjusting the Throttle Position Sensor every time I touch the screw... I just thought of that. And is there any instrument I can get to measure HC(PPM)? What else should I be looking for?

Please help me,
CJ

 

How did you go about setting the base timing? Did you disconnect the electronic spark control and use a timing light?

 

To set the base timing I had my dad turn the engine until the piston was at top dead center. Then we placed the distributer in with what would be the number one spark plug right on the rotor. At first it was 180 degrees off. (I never said we were smart!) But then we got it. The timing light wouldn't work unless I got back under there and reset the number one piston to TDC. If you think that would help, I could then mark the harmonic balance with a "new" top dead center. Unfortunately I have to wait until Sunday to do it, since my dad's out of town and I don't trust anyone else to put a socket on the driveshaft bolt and turn it. The guy that had it before smeared it, and it's a delicate job. Is that worth doing?

 

I would definately set it using a timing light. I'm not sure why you say a light wouldn't help right now without resetting. Do you have access to a light? If not, it's one of those things that is worth buying I think. If you've got a light, you should be able to set the timing by youself. There isn't any real reason to have to remove the distributor or reset the engine to TDC. Just unplug the wire to the electronic spark control and start the car. Hook up the light, and see where the timing is set. Going with an "eyeball" approach like you did before isn't really accurate enough. It only takes a small rotation of the distributor once you've got the clamp loose to affect the timing. If you're only off a little bit with the distributor placement, the base timing can still be signifficantly off. Too bad you're not in GA. I'd loan you a timing light and get things straightened out.