1994 3vze Smog fail. High HC at idle
Sep 27, 2017 | 05:12 PM
#1
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Joined: Sep 2017
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1994 3vze Smog fail. High HC at idle
I've done a bunch of digging and trying to figure out what could be causing my truck to not pass smog at idle but pass with flying colors at 2500rpm
Symptoms:
No CEL
Rough idle when warm
What I've done:
New plugs, wires, cap and rotor
New oil and filter
In lots of the old threads they have dead links to many of the procedures that members have suggested like checking the O2 sensor circuit, tps, etc. Also the online FSM seems to be down. Also, some people have mentioned the Cold Start Injector and I'm going to unplug it to see if the rough idle goes away but I'm not thinking that it is the problem. Others have mentioned retarding the timing and messing with the VAFM. I guess my question is, does anyone have a link to a working site to test the O2 sensor and what else should I be looking at to try and get this smog issue figured out?
Smog numbers:
Idle
HC:
220ppm (legal limit)
351ppm (reading) FAIL
CO2: 10.6%
CO: 0.00%
2500RPM
HC: 47ppm
CO2: 13.6%
CO: 0.01%
Symptoms:
No CEL
Rough idle when warm
What I've done:
New plugs, wires, cap and rotor
New oil and filter
In lots of the old threads they have dead links to many of the procedures that members have suggested like checking the O2 sensor circuit, tps, etc. Also the online FSM seems to be down. Also, some people have mentioned the Cold Start Injector and I'm going to unplug it to see if the rough idle goes away but I'm not thinking that it is the problem. Others have mentioned retarding the timing and messing with the VAFM. I guess my question is, does anyone have a link to a working site to test the O2 sensor and what else should I be looking at to try and get this smog issue figured out?
Smog numbers:
Idle
HC:
220ppm (legal limit)
351ppm (reading) FAIL
CO2: 10.6%
CO: 0.00%
2500RPM
HC: 47ppm
CO2: 13.6%
CO: 0.01%
Sep 27, 2017 | 06:15 PM
#3
Registered User
Joined: Sep 2007
Posts: 8,379
Likes: 871
From: San Francisco East Bay
1. Where is your smog test? You've given enough information, but the tests are different in different jurisdictions, and you may have more information someone from your neighborhood may be familiar with.
2. Rough idle is almost synonymous with misfire, particularly when you pass at 2500rpm. (misfire means you're dumping unburned fuel into the exhaust, which raises HC). So it's not likely to be the O2 sensor (could be the TPS, though). So try the spark test; pull the plug leads one at a time, to see if you have one that doesn't change the idle. That cylinder isn't firing. Also, put your timing light pickup on each plug wire. If you have one that doesn't flash the light, that PLUG isn't firing.
3. Since you've got the idea to check the TPS, remember that the 340H transmission will do it for you! http://web.archive.org/web/201408160...34electron.pdf (page AT-128). Checking the TPS with a voltmeter is hard enough on a 22re, but on the 3VZE the connector points away from you and it is very difficult to probe. Use the built-in tools you have!
2. Rough idle is almost synonymous with misfire, particularly when you pass at 2500rpm. (misfire means you're dumping unburned fuel into the exhaust, which raises HC). So it's not likely to be the O2 sensor (could be the TPS, though). So try the spark test; pull the plug leads one at a time, to see if you have one that doesn't change the idle. That cylinder isn't firing. Also, put your timing light pickup on each plug wire. If you have one that doesn't flash the light, that PLUG isn't firing.
3. Since you've got the idea to check the TPS, remember that the 340H transmission will do it for you! http://web.archive.org/web/201408160...34electron.pdf (page AT-128). Checking the TPS with a voltmeter is hard enough on a 22re, but on the 3VZE the connector points away from you and it is very difficult to probe. Use the built-in tools you have!
