Hey guys, I had to run a gas analysis for my lab in AET class. I knew I was running rich because I was getting black crap on my exhaust tip and getting pretty poor gas mileage. I ran the test this afternoon and im alittle confused by the readings.
Idle:
HC-309 CO-3.68 O2-.43 CO2-12.4 NOx-113

2500prm:
HC-126 CO-.66 O2-.73 CO2-13.9 NOx-325

Why am I running so rich at idle? Why does my NOx go so high at 2500 RPM?

 

If you run leaner (like at 2500 rpm)you tend to get a more complete reaction. Hence the more NOx

Whats the units of those readings? mols/min or cf/min..?

 

after checking my specs again I forgot I wasn't running a cat, which would explain the higher CO.

HC's and NOX are PPM. CO, O2, and CO2 are %.

It looks like im running just a touch rich.

 

I think cat converters don't convert HC's, just CO and NOx to N2 and 02 and CO2, and some sulfurs to safer sulfurs.

HC-309 CO-3.68 O2-.43 CO2-12.4 NOx-113

2500prm:
HC-126 CO-.66 O2-.73 CO2-13.9 NOx-325

From your numbers, you're running quite a bit leaner at idle than at 2500 dont you think? CO is produced mostly in incomplete reactions. Its pretty hard to deduce any real information from just this data without injector pulse and duty cycle as well as throttle position and load.

 

Isn't CO the rich detector? rich is greater then 2% and lean is less then 1%? Im "fairly" new at reading these numbers. I have my pulse and duty cylce somewhere...

 

did you take these measurements on a cold engine? The engien has to be loaded for a few minutes before you can get accurate results from any gas analysis an engine.

 

yes it is, qualitatively, but not quantitatively

 

High nox is usually the result of no/damaged cats or egr valve not working properly. Always warm up your car to normal operating temps before doing any kind of exhaust readings.

 

NOx is always there without a cat, and is dependant on the amount of fuel burned, since NOx are not in the vapor state in gasoline (not in large amounts).

 

Interesting thread, subscribing.

 

I have no cat so that explains the NOx, I had the car warmed up prior to running the tests.

 

just to show what we were doing...

Here's if you fogged your intake with unburnt propane
Idle:
HC-919 CO-12.35 CO2-5.8 NOx-2

2500 RPM:
HC-572 CO-10.31 O2-.79 CO2-7.6 NOx-97

Here's if you create a BIG vaccum leak.
Idle:
HC-418 CO-1.10 O2-9.59 CO2-7.2 NOx-268

2500 RPM:
HC-523 CO-.70 O2-7.54 CO2-8.6 NOx-488

Here's if you unplug a spark plug wire
Idle:
HC-2763 CO-.35 O2-6.58 CO2-9.9 NOx-381

2500 RPM:
HC-3380 CO-2.51 O2-5.77 CO2-9.3 NOx-439

 

HC is hydrocarbons (unburnt fuel) right?

 

correct