California smog.. about to set my truck on fire

[s r g]

Advice needed..

My truck is an 84 720 4x4, it always smogged well till this time.. here are the numbers

HC MAX 134 mine was 106 ----- CO MAX .90 mine was 7.98!!!!!!! everything else was normal and the fail on the CO was during the 15mph test... any ideas? the smog tech was of no help.

I am not sure if its related but it was tested at 1588 rpms at 15 mph... seems a tad low... advice?
Thanks

[dpdatsunman]

they are supposed to do two tests, one at 2500rpm for 30 seconds and one at idle for 30 seconds, idle can be 600-1000 rpm or so.

idk what u mean by 15mph so explain that. HC (hydrocarbons) are unburnt fuel, ur reading was good. CO(carbondioxide) is burn fuel byproduct, this can be caused by and exhaust leak, even a small one. I would check the exhaust and cat to make sure their good. And make sure ur vacuum system is not leaking, and ur gas cap isnt leaking either.

good luck, smog sucks...

[s r g]

the part of california i live in does 2 tests.. one at 15mph and the other at 25mph.... no idle test... the 15 mph test caused the CO to go nuts.....

[dpdatsunman]

wait, so they do a driving test? where in california?

[s r g]

its done on a dyno....... 95% of california does it this way

[sjracer]

Originally Posted by dpdatsunman

they are supposed to do two tests, one at 2500rpm for 30 seconds and one at idle for 30 seconds, idle can be 600-1000 rpm or so.

idk what u mean by 15mph so explain that. HC (hydrocarbons) are unburnt fuel, ur reading was good. CO(carbondioxide) is burn fuel byproduct, this can be caused by and exhaust leak, even a small one. I would check the exhaust and cat to make sure their good. And make sure ur vacuum system is not leaking, and ur gas cap isnt leaking either.

good luck, smog sucks...

if you don't know what your talking about please don't try and help.
15mph is 15 Miles Per Hour. 25mph is 25 Miles per hour.
our tests are ran on a dyno.
CO is carbon MONOXIDE. it along with Co2 is an indicator of fuel mixture. it CANNOT be caused by an exhaust leak.
exhaust leaks show up as high O2 readings. they can affect the readings of a O2 sensor and cause it to have problems. but, when you look at the overall picture of how everything is coming out the tailpipe you can usually pick that out.

to the OP:
post your readings as follows:
15 mph,
co=
hc=
O2=
CO2=
Nox=

25 mph
co=
hc=
O2=
Co2=
Nox=


just reply to this message, put your answers in red. also the year/make/model/trans type/engine size would help.

[s r g]

15 mph, tested at 1588 rpm
co= 7.98 FAIL
hc= 106
O2= 1.6
CO2= 9.4
Nox= 72

25 mph tested at 1592 rpm
co= 1.03
hc=1.03
O2=1.8
Co2=12.7
Nox=133
Sorry it wont come up with red text...
the truck is a 1984 nissan 720 5 speed 2.4 .. its a california legal federal emissions truck (hard to explain) look it up on ca.gov if you dont believe me.
33 inch tires 4.10 gears.
Thanks for your time.

[s r g]

s

[sjracer]

your engine is running super rich.
what i noticed is the rpms at the speeds isn't much of a change indicating the smog guy had to switch gears, your tires may be at fault. if theyre larger than stock it can cause the truck to bog at the lower mph and the fuel system to switch to an enrichment mode. during the test the truck is supposed to be in second gear only the whole time.
if you can, borrow some stock sized tires and run it again. that might help.
you may have to pay someone to diagnose this one.
last, in california they have a assistance program for those who's vehicles fail smog, check the "california bureau of automotive repair" website. the cost of repairs may be covered.

[s r g]

cool thanks.... it just boggles my mind only one part of the test is so far off,,, usually the HC's follow... at least from what i have seen...
the truck has no "modes" to speak of.. it is similar to a car you see in the 70s... very little emission parts.
it is supposed to have 215x75x15 tires... far smaller than what i run now..
The smog guy will have a good laugh if i pull up with stock tires and a 7" lift.. haha

[westracing01]

CA doesn't have a 25+ year old exemption?

[sjracer]

Originally Posted by westracing01

CA doesn't have a 25+ year old exemption?

nope. were hoping they move the exempt vehicle year up to at least 1980, but no word yet.

[broncobowsher]

As stated, running real rich. large tires could cause it, sticky choke as well. Did you have it good and warmed when tested?

Last I heard about California emissions exemptions is post '75 needs testing. Basicly if it came from the factory with a cat it needs testing. The 25 year exemption stopped in 2000 and went to a '75 and newer need testing. My friends over there always debate the value in getting a pre-smog check car. That late 60's/early 70's is such a fuzzy window. Technically not legal to de-smog a car (or truck), but it isn't checked anymore. But what happens if they decide to start checking again, or you get caught in some random check?

I have a hard time keeping up with the neighboring California laws. The AZ laws are a big enough pain. Funny when you see a vehicle for sale that is clearly from out of state or freshly modified. They then find they can't pass emissions and not a realistic chance of going back to stock. Then they ask a couple hundred less then what a passing vehicle goes for. They never get that then half a year later you can get it for nothing just so they can get rid of it. When shopping for a car in a smog area the first thing you do when you open the hood is check if all the smog stuff is there, if not then you don't even bother to check the oil.