i have an 88 iroc z28 with the 5.7. Ive taken virginia emissions 3 times now and have failed all three times. to make matters worse the more i "tune up" my car the worse the emissions gets. can anyone shed some light.
Replaced the following:
- O2 sensor
- Plugs, wires & distributor
- oil
- adjusted timing
- corrected tps to .54
- have run seafoam & "guaranteed emissions" cleaners
- also took the car when the thermostat was 240 degrees.

test results:
---------15mph ----------25mph
----------limit --reading------ limit --reading
HC ppm --48 -----186 ---------88----- 210
CO% ----0.19 ---1.43-------- 0.28---- 1.52
NO ppm --632--- 1784-------- 614 ----1515

The air injection system, EGR, ventilation system, cat, fuel evap, and gas cap pressure test all passed.

 

Its Virginia right? Come down to Richmond and go to Jefferson Davis Highway and get your car inspected. I have never seen them do an emissions test. If fact, I have never seen anyone do an emissions test in Richmond. You must live up in N va. Anyway you get a Va inspection sticker and all is happy..

 

Put an ohm meter on the injectors when they're hot, and make sure they all measure at least 14 ohms. Anything less than 12 ohms and that one is bad.

 

Thanks ill check the injectors. I already have the car inspected but to register my vehicle in Northern VA gotta have the emissions too.

 

Looking at your numbers, either your timing is way off, except you say you've adjusted it, you're running rich, your cat is shot, or you've got a miss, OR you have something much more serious going on. ( leaking exhaust valves, stuck EGR, leaking injectors, plugged PVC, deposits on intake valves, worn and leaking rings )
Initially, if you're not getting error codes, and it seems to be running OK, I'd look at the cat.
About the only way to test a cat is a gas analyzer both before it, and after it. ( or just replace it and test again ) I don't think they did that. They just looked to see if one was present.
It's almost impossible to get high CO and high NOx at the same time with a functioning cat.
Something that makes it go rich, like leaking injectors, will burn out a cat in short order. ( as will a steady miss )
If you can, shake the cat, and the muffler. If you hear debris ratteling inside, the cat is definitely shot.

 

How old is the cat? Even with no smog pump, no AIR injection tube, I passed with /flying colors this year, here in Texas....with a 1 year old Magnaflow converter.

High Speed-2692rpm
HC 220-standard 4-my reading
CO% 1.20-standard 0-my reading

Idle
HC 220-standard 16-my reading
CO% 1.20-standard 0.01-my reading

 

Assuming things work there like they do everywhere else I've seen/heard, that means they can see them, not that they are working correctly (except the gas cap pressure test).

High HC = unburned or partially burned fuel (misfire, exhaust valve leak, low compression, etc.).
High CO = rich mixture (O2 sensor, leaking injector, etc.)
High NOx = high combustion temp or pressure, such as EGR not working properly, timing too advanced, lean mixture, etc.

I've seen a new cat lower all three.

 

the exhaust does smell rich and the converter is old. the pcv valve opens and closes fine. Ive run enough seafoam through it to be able to own 50% of the companies stock by now. Wouldnt the car have trouble starting if the injectors were leaking? It cranks right up everytime. since ive replaced all the plugs, wires, and distributor how could i fix a mis? Thanks everyone

 

Yeah, try replacing the cat. My last car, I put a high-flow on, and 1yr later it was already blown out. New cat, i passed (just barely).

Also, retard the timing a few degrees from what the emissions sticker says.

Finally, now I heard this from somebody else on here and it is known to cause fuel system problems, but run your gas tank as low as you are willing to go, then put in 2 gallons of denatured alcohol and 1 gallon of gas. Go take the test. Go straight back to the gas station and fill the tank with gas, to dilute the alcohol.

 

HC, CO, and NOx all high combined with the age of the vehicle usually points to the cat gone south. Replace the cat.