Re: high hydrocarbon in exhaust

["rendy_cheng" <rcheng@xxxx>]

Hi Everyone!
After adjusting air/fuel mixtures screw, the HC is a bit better, but 
not good enough to pass the smog check. During the smog 
check, we discover something interesting. HC readout from the 
smog analyzer is vary between 90 to 230 ppm (max allow is 
120ppm at idle). I don't understand why HC readout has such 
large variation. The technician believes the "guts" in catalytic 
converter may have damaged.

Before I did this smog check, I have find a few things about my 
car. (1) there is a vaccum leak (2) idle speed controller is dead 
(3) the idle speed screw is wide open (4) the air/fuel mixture 
screw has been change from previous owner (5) lamda sensor 
was dead. The only thing I have not done for 30k maintenace is 
valves adjustment. Based on all these info, I thik the system is 
dumping large amount of fuel in to engine for long time, the 
catalytic converter is saturated with unburn fuel. But this "theory" 
does not explain the variation in HC readout. Is there a way to 
check catalytic converter? Is there some type of fuel additive I 
can use to "clean" the catalytic converter?

Things I have done so far
(1) new spark plugs and wires
(2) new dis. cap and rotor
(3) new O2 sensor
(4) new idle speed controller (it idle much better now)
(5) fixed a vaccum leak (car accelerates much better now)
(6) adjust air/fuel mixture
(7) new oil, oil filter, air filter

Any more idea? Thanks!

rendy cheng #4220


> After following the advise on this forum, I have replace the O2 
> sensor, spark plugs, spark plug wires, Dis cap, dis rotor.
> Earlier today, I had my car smog check again.. Guess what? It 
> failed the test again. Result from the test are following :
> 
> HC (ppm) Max allow:150 My car: 111,
> CO (%) Max allow:1.50 My car: 0.54
> CO2 (%) Max allow:NA My car: 13.8
> O2 (%) Max allow:NA My car: 1.1
> RPM 2466
> 
> So... for high RPM, it is okay. The following values are from idle 
> case.
> 
> HC (ppm) Max allow:120 My car: 241 (too high)
> CO (%) Max allow:1.50 My car: 0.67
> CO2 (%) Max allow:NA My car: 13.4
> O2 (%) Max allow:NA My car: 1.5
> RPM 734
> 
> Other than catalytic converter, what else can be the cause of 
> this..
> 
> Thanks every one!
> 
> rendy #4220
>