Help - Smog Test Results Analysis

I had my '88 4Runner (V6 Engine) tested at a California "test only" station. The carbon dioxide and nitrous oxide levels were normal, but it barely passed the hydrocarbon limit at 15mph, but easily passed hydrocarbon at 25mph.

Any ideas of what could have caused such a result? Are there any tricks or repairs that I can use next time to reduce the hydrocarbon at the slower speeds? CO2 % O2 % HC(PPM) HC HC Test RPM MEAS MEAS MAX AVE MEAS RESULT

15 mph 2824 14.33 0.29 121 35 118 Pass 25 mph 2466 14.52 0.04 101 24 27 Pass

Thanks, Paul

Reply to
Krystonia5
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Air-injected? If so, check the plumbing that controls when the air injection is active. Mine was vacuum-operated, and with a crack in the vacuum line, was failing miserably on hydrocarbons at all speeds, no matter what I did to the beast. Finding and replacing that length of vacuum line completely cured the problem. Also look at the air pump (if any) and plumbing between that and the point where the air gets injected.

Reply to
Don Bruder

A bit on the lean side when slower. Lots of places to check. Air leaks in air path, EGR leak-by (carboned pintle), or just the catalytic converter wearing out.

- Bill

Reply to
Bill Hodgson

Bill - Can you explain how a worn out catalytic converter would explain the high HC level at 15mph while the 25mph reading is fine?? Also how did you determine that the 15mph reading shows the truck is running leaner than at

25mph?

thanks, Paul

Reply to
Krystonia5

Your results:

118 Pass
27 Pass

Lower speed (15 mph) shows higher RPM (lower gear) than higher speed (higher gear). Lower speed shows HC MEAS(ured) 118 just under the MAX 121. New catalytic converter can bring this down because it will have fresh chems. Higher RPM means more gases through the pipe at higher velocity. This means those gases will not have the same time-exposure to the catalytic so more HC get out the pipe. On the other hand, the EGR process of recycling exhaust gases has an effect on combustion temperatures and it also causes a leaner mixture which creates higher HC's. So if it's malfunctioning, it could create the same result.

- Bill

Reply to
Bill Hodgson

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