Hello All,
I have a Chevy Caprice 1988. In my state (IL) we must do emissions; we have three times to pass. I have failed two times so this is my last shot. Readings for both failures as follows:

SPEC 0.80(HC), 15.0(CO), n/a(CO2), n/a(NOX)
1st Try 0.93,18.8,493.7,2.80
2nd Try 0.84,11.5,500.7,2.40

Between the first and second try I had the car tuned up and changed the air filter,sparkplugs, rotor and wires. I also filled the tank with 93 octane and so called guaranteed to pass emission cleaner fluid. Ran the whole tank empty and then put some more 93 octane in and then went to test.
Why are my HC's still high and how do I fix this?

Thank-you

High hc's are usually caused by unburned fuel/rich mixture. Lots of issues with that, diluted oil, misfire, vapor cannister loaded with fuel, high fuel pressure, dirty injectors, bad coolant temp sensor, a weak cat can also cause this so lots of things to check out no singer answer will just pop on this, all these things need to be addressed/checked. If carbed, that can be a problem also with the carb running rich.

It won't be high fuel pressure or dirty injectors as this is a carbureted car.

My guess would be AIR system (smog pump) or catalytic converter - possibly a misfire on a cylinder.

My '84 was like that, just enough to be out of the money. I changed the cat and all was well. It has since been inspected twice, always passes with flying colors on the strict NY state test.

My mechanic was able to narrow it down for me to the cat being bad. I got one at NAPA for $115 plus $27 for some hose adapter kit. Took me an hour to change it, but I cheated and cut off all the nuts and bolts.

Bob

It won't be high fuel pressure or dirty injectors as this is a carbureted car.

My guess would be AIR system (smog pump) or catalytic converter - possibly a misfire on a cylinder.
Yeh, kinda remembered 88 was carbed still, eliminates the fp and dirty injectors issue, but the rest remain possibilities. The 4.3 6cyl was TBI, so we really don't know whats what here?

This is very true!

1. Higher HCs indicate unburned hydrocarbons. Higher CO indicate a lot of burned nydrocarbons which aren't converted to oxides. The higher octane fuel is not necessarily helping. You need something that burns fast and completely. 87 octane may provide better results, even with some detonation. Since the NOx doesn't apply, potentially higher chamber temperatures are not going to be a problem. The higher temperature exhaust may even help cat converter efficiency, as bobss396 indicated.

2. Make sure the engine is at full operating temperature. A thermostat opening at less than 195ºF is going to contribute to the problem. It's even worse with a carbureted engine, where intake heat is important to fully vaporize fuel.

3. If the oxygen sensor has more than 30,000 miles on it, change it. Yes, you should have one on your '88, and it will be important at idle and low throttle angles. As part of that, re-check the IAB settings (with a dwell meter) and make sure the choke is fully opened.

4. Save your repair parts and labor reciepts. If you can show that you've made attempts to repair the problem, you will still get certification. At least, it USED to be that way in Ill-noise. It used to be that if you spent $400 on repairs you would get the sticker even without blowing under the limits.

5. PLEASE - Tell us what engine is in the vehicle.

A poster wanted to know what engine is in this car: V8 350cc/5.7L.
I have been to three mechanics since original post . Two of them suggested that I bring my car so they could do diagnostics(what will diagnostics tell them about emissions???). I have no lights on my dash. Both of them talked of a bad PCV valve. The third advised me to change my cat conv and if I still failed, settle in for a long fight for a waiver.
Any comments,advice or thoughts welcome.

Thank-you

Don't think about the waiver - yet. In some states, such as here in AZ, a waiver is a one-time only affair for the life of the car, it doesn't matter if you sell the car - if a waiver has been used on it, you cannot get another one.

Does the MIL (service engine soon lamp) light up when you first start the car? It should flicker on, flicker off, then flicker on again, before going off.

First, let's determine that the engine is in fair running condition. Does it run smoothly and on all 8 cylinders? High HC, as Blue Bowtie pointed out, indicate an incomplete fuel burn. Leaky exhaust valves (as in burned valves) can lead to this - Over-advanced ignition can also cause this, where the engine knocks. Your car should have ESC on it - check that the knock sensor is working. If the static timing is set properly (8 degrees BTC - I have the same car with the same engine), you should be good in this regard. Verify the installation of:

*The ignition rotor.
*The distributor cap.
*The plug wires - kept away from the exhaust manifolds - no light or "white" spots on the cables near the manifolds
*The spark plugs - AC/Delco R43TS or R44TS - properly torqued.
*All vacuum hoses - a small vacuum leak can lean out one or more cylinders, leading to a lean misfire and consequent high HC
*Carb, although a carb usually results in high CO as well as HC
*The M/C solenoid and idle air bleed, as Blue Bowtie noted above, will require an ignition dwell meter
*Plugged air filter
*Exhaust gas oxygen sensor - often a failed EGO sensor can fake being good. It's less than $20 for your car for a Bosch, throw a new one on that puppy.

If you're adept at computers and electronics and want to play around with it, you can download WinALDL and install this on a laptop, and make an interface cable following the directions on the WinALDL site - use pins 1 and 4 on the ALDL connector, with a 3.9kohm resistor between pins 1 and 2, and use the 1984 car/85/86 truck setting in the software. This will give you a live-data scanner in which you can see what your sensors are doing at any given time. This data can be used to help diagnose the car. That's right, you don't need EFI or OBDII in order to see in real time what your computer sees. Do note though, that if you do use this software and go this route, that you lock your computer's RS232 port (COM port, usually COM1) to 2400 baud and not 1200 as stated in the software, or it won't work right and will do weird things. winaldl.joby.se

Also, follow Blue Bowtie's advice on the octane level - 87 is what you want, not 93. Also, make certain that your engine is at proper operating temp (with a 195 degree tstat installed) before you attempt the emission test. A cold engine is a test failure waiting to happen.

If all of the above checks out, and it fails again, you can get a replacement CATCO catalytic converter at Autozone, specifically made to fit the car (vs. a 'universal' model), for around $70 or so, and it takes about ten minutes to replace.

A poster wanted to know what engine is in this car: V8 350cc/5.7L.
I have been to three mechanics since original post . Two of them suggested that I bring my car so they could do diagnostics(what will diagnostics tell them about emissions???).

The diagnostic scan will help reveal whether the oxygen sensor is active, whether the engine is reaching correct temperature, whether the ESC and detonation sensor are active, if the base timing is correct, and if they also use a gas analyzer, whether the oxygen sensor is weak, if the MC solenoid is active and IAB is adjusted properly.

These are all things you can do yourself with a multimeter, timing light, and dwell meter or duty cycle function on your multimeter.

I have no lights on my dash. Both of them talked of a bad PCV valve. The third advised me to change my cat conv and if I still failed, settle in for a long fight for a waiver.

Any comments,advice or thoughts welcome.

If the oxygen sensor is weak and failing in the normal failure mode, the signal will get weaker. This indicated to the ECM that the mixture is lean, and it will try to "correct" by enriching the mixture. Until the sensor gets so weak that it will produce almost no signal, there will be no "Check Engine" warning lamp. However, the E4ME carburetor really only controls mixture at low throttle angles such as idle and very light load cruise. If that is how the teat is being done, the O² may solve your problems.

Also, there is no post-cat sensor to check converter efficiency, so the cat may be bad and no "Check Engine" light will ever turn on.

If there is a general rich condition AND hard starting (you never said how the engine is actually running) there might be other carburetor problems.

I'd agree with silicon212 about the cat converter, EXCEPT that it might take a little more than ten minutes to replace. Seated on the Arizona desert floor, he doesn't get to "enjoy" all the winter slush, salt, and brine spray that we get, and all its ravages, such as rotting out and molecularly fusing every piece of metal under the vehicle that isn't 302 Stainless Steel. It might take ten minutes just to break the first flange nut free, if you're lucky.