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Connor280ZX

'82 ZXT Epic Smog FAIL! (1042 HC!)

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I've been trying to get my ZXT smoggsble for weeks now, but for whatever reason it just runs so damn dirty. Results at idle: HC 1042 Max 192.
Results at 2500 rpm: HC 238 max 168. This is the third test. First test I got 1459 HC which is insane. Replacing the following seemed to help, but the car is still a GP.

 

NO: 1PPM CO: 0.54% CO2: 13.5% O2 3.4%

I've replaced all Vacuum hoses, set timing to 22 BTDC, changed the oil, replaced spark plugs with proper NGK type, ran fuel system cleaner, checked resistance at AFM and CHTS and are within proper resistance, cap and rotor are new and plug wires look new too. New TPS, New o2 sensor, and cleaned electrical connections. Car runs pretty well besides a rough idle and hesitation when cold. Any suggestions? Car was also sitting for 6 years prior.

Edited by Connor280ZX

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It's got a visually good cat on it. No broken/melted cells, and can see right through it. I have not tested before and after exhaust temps yet since I haven't bought an infrared thermometer. 

I cannot retard the timing past 22 BTDC because the "Functional" test will fail if the timing is set further than 2 degrees beyond factory spec. My N/A failed smog once because timing was set at 11 BTDC over 8 BTDC factory. 

 

The spark plugs were all equally dark brownish. 

 

If it matters, the results at 2500 rpm were: 

 

HC = 285 ppm

 

NO = 131 ppm

 

CO = 0.36%

 

CO2 = 13.4%

 

O2 = 1.7%

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I have done resistance tests per FSM at the sensors themselves, and at the harnesses. Both yielded results in acceptable resistance range. There's a receipt in the glove compartment of a work order to replace the AFM and TPS with new units. This was from 2008. I can assume that the AFM is a rebuilt one. 

 

In that case, I will re adjust timing before next test. I also found that the inspection light from the ECU is not coming on. Not at they key ON position, or at 2000 RPM.

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The high O2 and HC indicate a misfiring cylinder.  Gasoilne (HC) and oxygen (O2) are passing through the misfire without catching fire and combining to form CO2 and H2O.  Focus on spark, check valve lash.

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Yes the shaft does wear, in my case the shaft looked ok but would not keep time. If the timing is correct you should be able to adjust it from 17-23. If you can't retard past 22 you may not have the spindle installed correctly

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Checked my valve clearances. .007-.009mm cold. Should be. 017mm cold according to the Haynes repair manual. Couldn't adjust them due to the lock it's being way too tight and starting to round off when I turned them. Will have to take it in to get them adjusted.

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Posted (edited)

Well, you got what I was going to suggest: valve lash.

If those mm numbers are right you were way tight making vacuum go to crap at idle and that will do it!

 

If you don't get the O2 light, you need to check the o2 sensor wiring as it should start switching after a few seconds at the higher rpm and continue till the sensor cools off.

Edited by Tony D

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Got the valves adjusted, and the car idled smoother for sure. There's hardly any fluctuation in the tech needle now. When I got the car, the o2 sensor wire was severed, and I attempted to reconnect it with a splice connector along with a new sensor. There seemed to be two layers of copper inside the wire, and they may be contacting each other with the way I spliced them together. Not sure if that matters though.

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Cali must be rough for emissions. Are are strict here but at least cars older than 1987 dont have to be emissions tested. They do have to have all original equipment and Ministry of transportation can pull your car off the road if it fails an inspection

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 got 202-206F in front of the cat, and 297-301F after the cat

Running rich.  The converter "burns" hydrocarbons that didn't get consumed during normal combustion.  Heat is produced.

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I mentioned that when holding the engine speed at 2000 RPM, that the ECU light does not blink, or come on at all for that matter.

 

I've been corresponding with a local shop that specializes is classic Datsun/Nissan cars, and the owner advised that I put a multimeter to the o2 sensor connector and read voltage at 2000 rpm. He told me that the voltage should fluctuate between 0.01-1.4v constantly at that rpm and should not remain steady. The lower the voltage, the more the ECU is trying to enrichen the mixture, and the higher the voltage, the more lean.

 

I'm getting a rock steady 0.021v throughout ALL rpm ranges including idle and 2000 Rpm, which means the ECU is trying to enrichen the mixture. HOWEVER, no matter what I do to change the mixture (pinching off return line, introducing vacuum leaks, unplugging CHTS etc) I cannot get a different voltage result. Tried 3 different o2 sensors and swapped ECU'S but the results stay the same! I'm at a total loss... May the Z gods have mercy on my soul.

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