bushcat Posted January 14, 2017 Report Share Posted January 14, 2017 I just took my Datsun 720 to get smogged. It measured 1.67 CO2 @ 15MPH when the max allowed is 1.58 CO2. It measured 1.48 CO2 @ 25MPH when the max allowed is 1.38 CO2. It also failed the fuel cap test, so I ordered a new one. I warmed it up for about fifteen minutes and drove it an additional ten minutes on the freeway before bringing it in. Am I failing by a lot? What can I do to get it to pass? Quote Link to comment
datsunaholic Posted January 15, 2017 Report Share Posted January 15, 2017 That's not CO2. CO2 should be OVER 15% That's CO numbers, and they should be under 0.5% How old is your catalytic converter?. Quote Link to comment
MikeRL411 Posted January 15, 2017 Report Share Posted January 15, 2017 Get a new gas filler cap. Quote Link to comment
KoHeartsGPA Posted January 29, 2017 Report Share Posted January 29, 2017 Air filter too old maybe?, every little thing helps. Quote Link to comment
240zness Posted January 29, 2017 Report Share Posted January 29, 2017 My 86 didn't have a working O2 sensor, right there on the ex manifold? Quote Link to comment
datzenmike Posted January 29, 2017 Report Share Posted January 29, 2017 CO is caused by over rich fuel/air (carb) or incomplete combustion. (ignition) Either way, gas isn't being burned and is sent out the exhaust. Carb too rich 1/ choke on or part on (maybe air filter, but never seen one so dirty it would do this) 2/ float set too high, inlet needle stuck, fuel pressure too high and flooding 3/ jet size too large (off idle only) 4/ idle mixture set too rich (idle only) Ignition 1/ Make sure both sides of plugs are firing, gaped and NGK BPR6ES and BPR5ES (exhaust side) 2/ Check ignition timing Other 1/ Check valve lash.... tight exhaust would leak compression 2/ Check compression.... could be a badly sealing valve. Quote Link to comment
MikeRL411 Posted January 31, 2017 Report Share Posted January 31, 2017 If it "measured passed" max limit,no sweat! If it "Measured past" limit,you have a physical/mechanical problem. I will pass on the spelling problem. Quote Link to comment
oakrun Posted February 19, 2017 Report Share Posted February 19, 2017 how long did you drive it to the smog inspection station? if it's close by, your engine needs more time to warm up + everything said above Quote Link to comment
Daryl Posted February 19, 2017 Report Share Posted February 19, 2017 The following is not only good for smog but also for a reliable daily driver. Full tune up (plugs, cables, cap, rotor, vacuum hoses, filters), change motor oil before test, carb in tune, compression would be good to know, fresh gas fill up before test is good. Catalytic works best when heated up so drive it for a good 1hr and keep er hot before test. If it fails again, better keep your pockets full of cash. Quote Link to comment
datzenmike Posted February 19, 2017 Report Share Posted February 19, 2017 CO is unburned gas. So either it wasn't lit properly (ignition) or there was too much for the amount of oxygen in the air. (carb) The catalytic converter simply cleans up what isn't burned in the engine but it can't work miracles if you are dumping fuel in from a bad carb or poor ignition. In addition the cat needs an oxygen supply to combine the excess fuel with, in order to work. This extra 'air' is provided by the AIS (air injection system) using negative exhaust pulses to suck in air from the air filter through a one way valve. You should have a single pipe from the exhaust manifold to a small box on the side of the air filter where the one way valve is. Quote Link to comment
datsunaholic Posted February 20, 2017 Report Share Posted February 20, 2017 High CO is "underburned" fuel. Unburned fuel is high HC. High CO can be too rich (carb leak, closed choke, plugged air filter, sunken float), or burning oil vapor from an open PCV. High HC can be too lean (lean misfire), cracked/leaking vacuum hoses, or ignition failures (no spark in a cylinder, wrong timing, weak spark from bad wires/cap/rotor, etc), or a very worn out engine (oil fouling and blowby). That's what the books say, at least. Quote Link to comment
datzenmike Posted February 20, 2017 Report Share Posted February 20, 2017 You're right. HC is unburnt fuel. CO isn't just unburned fuel but fuel burned without enough oxygen present. I'm only partly right. Properly burned, carbon bonds with two oxygen atoms (dioxide) Carbon monoxide (one) is carbon bonded to only one oxygen atom and is extremely toxic.. Quote Link to comment
distributorguy Posted March 16, 2017 Report Share Posted March 16, 2017 Run non-resistor plugs such as the BP6ES not BPR6ES. = hotter spark. Run a GOOD set of plug wires that Ohm less than 5000 Ohms per wire. = hotter spark. Retard the ignition timing so it runs poorly = hotter combustion chamber & converter = less CO at the tailpipe.. That should get you to pass smog. Quote Link to comment
G-Duax Posted March 16, 2017 Report Share Posted March 16, 2017 Quick fix........Move to a non-gestapo state. Quote Link to comment
willz Posted March 16, 2017 Report Share Posted March 16, 2017 Dafuq is a smog test Quote Link to comment
Doctor510 Posted March 16, 2017 Report Share Posted March 16, 2017 Get some CRC GTP additive. GTP is Guaranteed to Pass, worked for me. Quote Link to comment
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