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emissions test on a 1991 Chevrolet pick up (4WD i think)?
i have a co worker that is having a problem getting his car to pass smog. the original sheet passed every thing. his fort time through the test it had elevated co% on the low speed test but every thing else was on range to pass. on the high speed test every thing fell in line and passed that part of the test. he says that he did a tune up and went for a follow up test. this time the low speed test passed but the high speed test had elevated hydrocarbons but nothing else was out of range. i am trying to make sense of it but i am at a loss. if you need actual results i will continue with those on the next installation. i should mention that he stated that he adjusted timing to 2 degrees btdc before the second test but that is still within guide lines.
if it was a vacuum leak, nox would be a second reason to fail and it would be at all ranges, more at higher speeds but still obvious.
now i will give the test results that i have access to. the initial results before change of ownership
ll visual inspections passed, low speed results were as fallows; rpm 1403, co2 14.2 o2% .6 hc ppm max115 measured was 71.
high speed 1088,co2%14.2, o2% .8 hc ppm max 95, measured 78
first test results; all visual tests passed again, low speed: 1423rpm,co213.7,o2 1.38, co .63,measured .85.
(falied)
high speed; RPM 1089, co2 13.7,o2 1.38 hc max 95, measured 94, co%max 82, measured .31. (passed)
low 1423rpm, 13.7, 1.38, 115 max, 106 measured, .63 max, .85 measured,
high, 1089 rpm, 14.00% co2, 1.34 o2, max hc 95, measured 94, co max .82 measured .31.
nox it passed on all three tests.
any vacuum leak would create a lean condition and a hot combustion chamber temperature, this hotter cylinder temperature would increase NOX, because that is not what it failed, i really do not think that t hat is the issue but i will mention that to him. keep the ideas coming.
3 Answers
- 1 decade ago
It's either a vacuum leak, leaky injectors, or a bad plug or wire.
Have him replace the grommets on the valve covers for the PCV valve and the breather on the other side, if they're loose at all, or if there is goo in the hoses or the back of the throttle body.
The throttle body base gasket is also a source of vacuum leak with age.
Check the resistance of the wires, especially if he changed them during the tune up. Even if he didn't, he may have broken one.
Watch the spray from the injectors, it should not drip, it should spray a cone of fine mist.
Maybe also check the coolant temp sensor with a multimeter.
edit: have him re-set the timing to "0"
- braatenLv 45 years ago
relies on why it's failing if the emission manipulate instruments were tampered with, no! if the cat converter is gift however now not running, there are matters you'll be able to purchase so as to add to the fuel that can reactivate it you deliver no clues as to why it failed, well success!
