I don't know about California emissions but there are two different emissions systems for the 7200 gvwr and the 8600 gvwr on non California vehicles. The higher one is lest stringent. Make sure they are testing at the correct one if that is the case.
How to lower hydrocarbons
- Thread starter Bbonez
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How were the other pollutants? Also close to the limit? High HC but NO and CO low usually means the engine is misfiring. The plugs may have been the whole problem.
You may want to pull the thermostat and make sure it is stock temperature. If the computer doesn't see the engine fully warmed up, it will run it rich, which means high HC and also CO.
You may want to pull the thermostat and make sure it is stock temperature. If the computer doesn't see the engine fully warmed up, it will run it rich, which means high HC and also CO.
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Originally Posted By: Lubener
Originally Posted By: CT8
HC = unburned gasoline . Misfire? Does the engine smoke?
HC is basically a lean miss. No smoke.
In that instance the mixture is too lean to ignite so it passes through without combustion?
Originally Posted By: CT8
HC = unburned gasoline . Misfire? Does the engine smoke?
HC is basically a lean miss. No smoke.
In that instance the mixture is too lean to ignite so it passes through without combustion?
It could be a normal mixture but if the spark plug doesn't fire, all the HC goes out unburned. The differentiation is in the CO. if too rich you will read high CO, and if really too rich you will see black smoke. If the testing station also measures and reports the tailpipe O2, that is useful in telling if rich/lean.
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Here is the other info provided by the failed smog test:
At Idle
%CO2 12.5
%O2 3.1
CO % 0.13
At 2500 RPMs
%CO2 14.4
%O2 0.4
CO % 0.25
It passed all of the requirements besides the HC. They used 8600 as the GVWR.
At Idle
%CO2 12.5
%O2 3.1
CO % 0.13
At 2500 RPMs
%CO2 14.4
%O2 0.4
CO % 0.25
It passed all of the requirements besides the HC. They used 8600 as the GVWR.
Just went to the shop and had the truck sniffed, the HCs were fluctuating between 160-300 PPM. I need to get them under 150, the HCs came down from the 409 they were at on the fist test but not good enough yet.
The CPI/CSFI spiders are a sore point on those trucks - but the newer MPFI retrofit won't work on the pre-1996 trucks, GM did a switch from CPI to CSFI in 1996-1997.
IIRC these were TBI. The TBI injectors are only $50 ea new X2.
Originally Posted By: Trav
IIRC these were TBI. The TBI injectors are only $50 ea new X2.
Looks like you're right, I did see TBI units on the older GM trucks when I was at the junkyard hunting down a hard line for a friend's 1998 Tahoe.
http://www.chevythunder.com/gm_cpi_and_cspi_19922004.htm
IIRC these were TBI. The TBI injectors are only $50 ea new X2.
Looks like you're right, I did see TBI units on the older GM trucks when I was at the junkyard hunting down a hard line for a friend's 1998 Tahoe.
http://www.chevythunder.com/gm_cpi_and_cspi_19922004.htm
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Could faulty injectors be contributing to a high HC reading? I would like the truck to pass smog but the value of the truck is not much so I cant see dumping a ton of $ into it......
Originally Posted By: Bbonez
Could faulty injectors be contributing to a high HC reading? I would like the truck to pass smog but the value of the truck is not much so I cant see dumping a ton of $ into it......
On this one it could, this has a single cat with one O2 for both banks I believe this one doesn't even use a rear O2/monitor. This means if one injector was lean the ECM would add fuel to both injectors making the other bank run a little rich.
A dirty/tired O2 can also cause issues, a dirty bulb can make the ECM believe its lean and signal it to fatten things up. An OBD I scanner would be helpful, you don't want to start throwing parts at it but unfortunately OBD 1 isn't very helpful with onboard diagnostics like OBD II.
Could faulty injectors be contributing to a high HC reading? I would like the truck to pass smog but the value of the truck is not much so I cant see dumping a ton of $ into it......
On this one it could, this has a single cat with one O2 for both banks I believe this one doesn't even use a rear O2/monitor. This means if one injector was lean the ECM would add fuel to both injectors making the other bank run a little rich.
A dirty/tired O2 can also cause issues, a dirty bulb can make the ECM believe its lean and signal it to fatten things up. An OBD I scanner would be helpful, you don't want to start throwing parts at it but unfortunately OBD 1 isn't very helpful with onboard diagnostics like OBD II.
Originally Posted By: Bbonez
I put E85 today and plan to do a seafoam treatment and slightly retard the timing tomorrow. D
Retarding would make HC worse. Advancing takes away from HC but adds to NOx if you go to far and cross in to pinging territory. .
Faulty or wrong thermostat will make your HC higher.
Bad O2
Bad ignition system parts.
I put E85 today and plan to do a seafoam treatment and slightly retard the timing tomorrow. D
Retarding would make HC worse. Advancing takes away from HC but adds to NOx if you go to far and cross in to pinging territory. .
Faulty or wrong thermostat will make your HC higher.
Bad O2
Bad ignition system parts.
Originally Posted By: Ramblejam
Have an IR temp gun?
That's how a smog tech tracked down bad cats - usually a good cat will ramp up quickly in temperature compared to a bad one that's been poisoned or coated with soot. In new cars, cat light-off is within seconds of the engine starting.
Get an IR temp gun, start the truck and aim the gun at the cat but don't lock the reading. It should be hotter than the exhaust manifold or the exit pipe.
Have an IR temp gun?
That's how a smog tech tracked down bad cats - usually a good cat will ramp up quickly in temperature compared to a bad one that's been poisoned or coated with soot. In new cars, cat light-off is within seconds of the engine starting.
Get an IR temp gun, start the truck and aim the gun at the cat but don't lock the reading. It should be hotter than the exhaust manifold or the exit pipe.
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Originally Posted By: Trav
A dirty/tired O2 can also cause issues, a dirty bulb can make the ECM believe its lean and signal it to fatten things up. An OBD I scanner would be helpful, you don't want to start throwing parts at it but unfortunately OBD 1 isn't very helpful with onboard diagnostics like OBD II.
Is this something that would benefit from a 4-wire heated o2 retrofit? Get a new generic o2 and just wire the two white wires to power and ground. That'll keep it "awake" during idle.
A dirty/tired O2 can also cause issues, a dirty bulb can make the ECM believe its lean and signal it to fatten things up. An OBD I scanner would be helpful, you don't want to start throwing parts at it but unfortunately OBD 1 isn't very helpful with onboard diagnostics like OBD II.
Is this something that would benefit from a 4-wire heated o2 retrofit? Get a new generic o2 and just wire the two white wires to power and ground. That'll keep it "awake" during idle.
before you start replacing parts (and maybe find out it doesn't solve the problem)
see my post at
https://bobistheoilguy.com/forums/ubbthreads.php/topics/2936296/Re:_Smog_Test_Coming_Up_in_Nov#Post2936296
after a lot of miles everything needs a bath.
if you have time then try both the gas and the oil treatments.
if not then CRC but use the minimum tank fill (I think its 10 gallons) per bottle
and run it at least 2 times. maybe even a long trip to somewhere on a highway where
you can even add an Italian tune-up
this should drop the HCs down enough to pass.
Bob
see my post at
https://bobistheoilguy.com/forums/ubbthreads.php/topics/2936296/Re:_Smog_Test_Coming_Up_in_Nov#Post2936296
after a lot of miles everything needs a bath.
if you have time then try both the gas and the oil treatments.
if not then CRC but use the minimum tank fill (I think its 10 gallons) per bottle
and run it at least 2 times. maybe even a long trip to somewhere on a highway where
you can even add an Italian tune-up
this should drop the HCs down enough to pass.
Bob
Originally Posted By: eljefino
Originally Posted By: Trav
A dirty/tired O2 can also cause issues, a dirty bulb can make the ECM believe its lean and signal it to fatten things up. An OBD I scanner would be helpful, you don't want to start throwing parts at it but unfortunately OBD 1 isn't very helpful with onboard diagnostics like OBD II.
Is this something that would benefit from a 4-wire heated o2 retrofit? Get a new generic o2 and just wire the two white wires to power and ground. That'll keep it "awake" during idle.
Heated O2 provides benefits over non heated, it gets into closed loop faster and stays in closed loop during long idle times, stays cleaner so yes if it can be converted easily enough there are no negatives.
This is a good article on O2 sensors, it also explains the post O2 operation on some vehicles can be the cause of fuel trim issues and possibly P420/430 codes.
https://www.linkedin.com/pulse/how-test-oxygen-sensor-mandy-concepcion
Originally Posted By: Trav
A dirty/tired O2 can also cause issues, a dirty bulb can make the ECM believe its lean and signal it to fatten things up. An OBD I scanner would be helpful, you don't want to start throwing parts at it but unfortunately OBD 1 isn't very helpful with onboard diagnostics like OBD II.
Is this something that would benefit from a 4-wire heated o2 retrofit? Get a new generic o2 and just wire the two white wires to power and ground. That'll keep it "awake" during idle.
Heated O2 provides benefits over non heated, it gets into closed loop faster and stays in closed loop during long idle times, stays cleaner so yes if it can be converted easily enough there are no negatives.
This is a good article on O2 sensors, it also explains the post O2 operation on some vehicles can be the cause of fuel trim issues and possibly P420/430 codes.
https://www.linkedin.com/pulse/how-test-oxygen-sensor-mandy-concepcion
JTK
$100 Site Donor 2025
You could try throwing parts at it, but at it's age and mileage, the catalytic converter is probably not doing anything. A fully functioning CC should process that excess hydrobarbon to CO2 and water vapor. Being pre OBDII you don't have a "catalyst inefficiency" warning to tell you it's not working.
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