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1988 Toyota Truck Won't Pass CA Smog

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New User

Nov 1, 2009, 3:15 PM

Post #1 of 4 (2449 views)
1988 Toyota Truck Won't Pass CA Smog Sign In

Hello I have a 1988 Toyota pick-up, its a 4 banger with 4wd (manual). I recently took it in to get it smogged in California and it passed everything (visual and functional) except the emission test because of the NO and CO. The truck had been sitting for a while besides the occasional start up and let it sit for a little bit and used to pass no problem, but now it wont. Below are the emission results. The person who tested it said that the reason the first CO was high was probably because the NO or it wasn't hot enough. Before we got the test we ran it for a while and made sure to have barely any gas in it and then filled it. Once we got there and sat for a while and probably cooled down. I was wondering if anyone has any ideas on what is wrong and/or what I should check out. ANY HELP WOULD BE GREATLY APPRECIATED.

TEST (15mph)

RPM: 1612

%CO2: 14.1

%O2: 0.8

HC (PPM)- MAX:135 MEAS:106

CO (%)- MAX:0.87 MEAS:0.91

NO (PPM)- MAX:1058 MEAS:2410

TEST (25mph)


%C02: 14.1

%O2: 0.8

HC (PPM)- MAX:115 MEAS: 42

CO (%)- MAX:1.08 MEAS:0.31

NO (PPM)- MAX:918 MEAS:1738

*MAX=Maximum Allowable Emissions MEAS=Amount measured

(This post was edited by Cm1lls on Nov 1, 2009, 3:47 PM)

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 1, 2009, 3:33 PM

Post #2 of 4 (2440 views)
Re: 1988 Toyota Truck Won't Pass CA Smog Sign In

You need to find a way to post that more clearly. It's unreadable this way.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

New User

Nov 1, 2009, 3:48 PM

Post #3 of 4 (2433 views)
Re: 1988 Toyota Truck Won't Pass CA Smog Sign In

Sorry I tried to copy/paste a table from Microsoft word in and didn't realize it didn't format correctly. I re-did it...Thanks for letting me know

Loren Champlain Sr
Veteran / Moderator
Loren Champlain Sr profile image

Nov 2, 2009, 8:19 PM

Post #4 of 4 (2415 views)
Re: 1988 Toyota Truck Won't Pass CA Smog Sign In

NOx is caused by heat (high combustion temps). The EGR valve was introduced to allow inert exhaust gasses to lower combustion temperatures.
There are many things that can contribute to high combustion temps. Engine operating temp, lean condition, inop. EGR, low octane, ect., ect., ect.... The fuel tank level will have nothing to do with the problem unless it is 'running out of fuel' and going lean. With the CO reading, I don't think this to be the case.
SW Washington

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