Emissions Question

[Guest Anonymous]

I have a question for anyone that has had to pass emissions. I have a 77 V8Z with a mild cam and a new Carter AFB carb. I failed emissions this year terribly.

First pass I failed for High Carbon Monoxide at Idle and Load. I put the largest metering rod in the carb that I could and severely retarded the timing, the car barely runs but my Carbon Monoxide went down to nothing. Now I'm failing for High Hydrocarbons on both Idle and Load.

Does anyone have any ideas or tricks that they use to get thru emissions testing? Thanks for you help.

[Modern Motorsports Ltd]

You may have retarded your timing too far and dropped temps too much ....6 mos. ago when I had to pass I paid $20 to a shop to use their 'sniffer' and had my carb setup in 30 minutes as I tweaked and a tech told me what the meter was saying (ie. rich on load etc) and it barely ran but passed.....quite a variety in the archives. Make sure your timing is not negative at idle. Just disconnecting vaccum (or a ball bearing inserted if they have a visual) can help;^)

http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=8&t=000233

http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=8&t=000319

 

and a number of others I haven't listed

 

good luck

[Guest Anonymous]

After looking through the archives,it seems that the racing fuel has helped alot of people. I have a friend that runs a local track and I could get the fuel.

My concern is can't the emission tester pick this up in the reading? Also do I go back to my original timing adjustments and put the stock metering rod back in the Carter AFB carb? Thanks Again.

[Sumo]

If you have it in Arizona try a bottle of RXP, it is a little orange 2.5 ounce bottle and costs around $6.95. It's available here in Texas at HiLo and Autozone.it should help lower your HC and CO. Plus it makes sure your gas completely burns and gets your engine decarboned. Good luck.

[Tim240z]

Slip the tester an extra $50..

[Guest Anonymous]

Thanks for the info Ross, Tim I like your idea too. I will look through the archives.

 

The Carter AFB carb. that I have doesn't have an EGR valve unless it is in the carb. The new carb came with a block off plate for the intake. Maybe that is for the heat riser or are these the same thing? Probably a stupid question.

Thanks

[Guest Anonymous]

[ October 14, 2001: Message edited by: 280z8 ]

[Guest Anonymous]

280Z8,

In a nutshell, CO readings come from the carb, and HC readings come from the engine.

CO equates to air/fuel mixture, and HC readings are merely a measurement of UNBURNED gasoline which made it all the way through the combustion process WITHOUT being burned. (For what ever mechanical reason, not carb mixture reason)

Here is the sequence by which you cure errant emission readings.

First of all, set your timing with a vacuum gauge attached to the intake manifold. Advance and retard until the highest reading is achieved. Note the actual stroboscopic timing amount in degrees. With a mild cam this reading should be somewhere around 12 to 17 degrees BTDC at 1000 rpm.

Next:

A. High CO at idle: Screw in the idle adjustment screws in one at a time until the engine stumbles, then back them out just enough to smooth out the idle. Stop.

B. High CO on cruise (no load) With a Carter or Edelbrock carb, change metering rods until you get a 1.0% to 1.5% CO reading. Remember that metering rods are the fine tune adjustment between jet sizes. If you are still too high on CO, drop your primary main jet size one step at a time.

C. High HC at idle: Don't mess with the carb, it is does not cause high HC readings if the CO is anywhere over 1% or under 5%. (a wide range) A healthy engine will burn all the fuel offered to it to burn, up to approximately 6% CO.

Check for vacuum leaks, bad plugs, wires and any other ignition related areas. Don't overlook excessive backpressure in the exhaust. Verify back pressure, DO NOT EVER ASSUME THAT YOUR EXHAUST IS FLOWING ADEQUATELY.

4. High HC at cruise: Check for fuel saturation in the oil. Quick way to check is to disconnect the PCV valve and plug it. The same checks for high HC at idle apply here also.

Notes:

A.Too lean (under 1% CO) will cause high HC even if all else in the engine is mechanically and electrically sound. Rich the idle mix up to 2%, if leaness was the cause of the high HC at idle, the HC count will come down.

B. If your camshaft has a lobe center of less than 110 degrees, vacuum production will be reduced. It is virtually impossible to eliminate HC waste at idle with such cams.

I don't know what parameters your state is setting for either CO or HC. Post them and your cam specs (and compression ratio) and I will try to give you a realistic set of numbers you might be able to attain with tuning.

I run a 234 degree at .050 cam, on a 114 degree lobe center with 11.3-1 compression. HP output is rated at 490+. Emission after tuning were as follows:

Idle: 2.5% and 800 PPM HC

Cruise: no load: 1.0% and 150 PPM HC at 3000 RPM.

Timing specs: 20 degrees BTDC at idle, 36 total. No vacuum advance.

This HC reading is normal for such a cam. Increases in richness (CO) will not drop this figure any lower. Mileage on the highway has topped 22 MPG with OD trans at 75 MPH cruise.

Only an air injection pump can reduce idle HC assuming all other factors of the motor are working to the best of their capacity.

Emissions tuning is one of thw areas of mechanics which can be kibbutzed at long distance. Post your actual readings, and engine specs and I will give it a go.

Kim