Running RICH....options?

[LannyL81]

So I tapped into the O2 sensor output so I could monitor the O2 output with a DMM and adjust the idle mixture, dwell, etc....so I could try to get near the 14.7 A/F ratio which would be 0.5Vdc.
Did not matter what I did, adjust the idle air mixture screws or idle air bleed valve screw...I could not get an average voltage reading of less than say...about 0.8 volts....which means running rich.
I have the dwell varying between 30 and 40, idle RPM at about 700-800.

I do have the HyperTek PROM as the stock one was dead when I got the car....do not know if that makes much diference at idle..doubt it.

Any suggestions??

 

[Peer81]

Did you also measure it when driving?

Most of the time mine is or was running lean. With the carb I have now it is running rich at idle, almost on the spot (15:1 to 16:1) under normal road driving and at 12.5:1 under WOT. And I think it isn't going to get any better then this.
I think you also know a narrow O2 sensor doesn't have a liniear mixture graph. When 0.5Vdc is on the spot you can't derive what 0.8Vdc could be.

On the subject. Running rich, is the engine fully hot, are the air flaps in the aircleaner opening when hot? Is the ECM in closed loop? Can you acces the lean and rich stops and are they set correctly?

When I have my dwell on 30 degrees the air fuel meter is reading between 16:1 till 17:1 (way lean!) So I don't even know if the ECM is looking for the ideal 14.7:1 mixture.

Greetings Peter

 

[LannyL81]

Engine was hot when I was doing all of this. Did not take it driving...all of this is at idle. And you are correct the curve is very steep at 14.7 A/F ratio...almost a vertical line. I had the air filter housing off. And the CCC was in closed loop as the dwell was varying as I made adjustments. Mixture solenoid is set correctly. Sure wish I could bring that Oscilloscope home from work so I could "see" what the dwell and O2 outputs look like.

I have the parts now to build my LED bar graph A/F ratio meter so I can watch it while driving. It is quick to build, but will take some time to get wired into the car the way I want to.

 

[Hib Halverson]

Know that a narrow-band sensor is NOT a good choice for an in-dash air-fuel ratio meter because the only area of the fuel curve at which they will be accurate is a narrow-band of AFRs 0.5 or perhaps 0.75 either side of stochiometric. Narrow band sensors are good for tuning at part throttle but nothing else.

Do not attempt to use narrow-band sensor data to tune at AFRs more lean that 15.5 or more rich than 13.7.

 

[LannyL81]

Agree........what I did was more of just an experiment to see what would happen, if the carb adjustments would make any difference, etc. I am not gong to spend the money to get a wide band sensor....just having some fun on a Sunday morning.

 

[Peer81]

About the running rich problem. I think the difference is minimal but it should be easy to alter. Most of the time getting more fuel out of the carb is a bigger problem then less. I see you already changed the idle air screws and air bleed screw. Do you know if the air inlet about the fuel channels are open. If not you'll have a bad fuel/air mixture (minimal atominized or something like that) and the big fuel drops will show as to much fuel. I hope you know what I mean because half the words I want to use have slipped my mind... :ugh

Greetings Peter

 

[VetteV8]

You should be here more often Peter, seems like you are now loosing your language abilities: practise makes perfect

Cor

 

[geekinavette]

The response of a narrowband O2 sensor is not linear...a stoichiometric reading can cover from about 0.25 to 0.75 volts. 0.8V is nothing to worry about. The loading of your meter alone can cause a small increase in the voltage reading.

 

[LannyL81]

Last time I had the carb apart I cleaned all the air ports with a wire, carb cleaner and air pressure. So I am pretty sure that all is good there.

And yes I know the narrow band O2 sensor output is not linear...almost a vertical line between .3 and .8 volts. I doubt the DMM loaded the output as it is at least a 1M input impedance.

It would have been nice to have a O'scope on the mixture control solenoid instead of just a dwell meter. I think I would have seen the CCC adjust the pulse width as the adjustments were made.

May be another day.