Smog fail on 91 Comanche

[pigneguy]

Having trouble passing Smog.
Replaced rotor, cap, wires, plug, o2 sensor, cleaned injectors , new cat etc, figures are way down but mechanic says probably need EGR to get it to pass, except this is a federal car so never had an EGR.

only fail is :
NO (PPM)
25 mph MAX 609 AVE 265 MEAS 893
 

[jdog]

Location?

4 or 6 cyl

Nox?

2 more posts and the classifieds will open up for you. You can always put your Vin in the registry

[pigneguy]

Los Angeles, and its a '91 4l straight 6. HO.

[jdog]

I didn’t think the ho had a egr any ho guys wanna correct me?

[fiatslug87]

jdog is corrrct, no EGRs in 91 & 92 MJs.

 

Why are you asking for a 90 EGR valve for a 91 HO?

[jdog]

Can you post a picture of the smog report?

[87MJTIM]

If the vehicle didn’t come from the factory with an EGR, how can DMV require one be installed?

 

Just asking.

[gogmorgo]

What did the old spark plugs look like when you pulled them? Badly carbonned up, evidence of running lean maybe?

[pigneguy]

youre right ,no egr on a '91

here's smog reports:
initial gross polluter and last one with new cat. wires, plugs, rotor, cap etc
swapped out O2 sensor but purchased a bosch ny mistake, will swap in an NTK this week



 

IMG_1554.HEIC

[Eagle]

NOX is related to temperature, isn't it? What thermostat are you running -- and does it work? What spark plugs are you using?

 

[pigneguy]

champion plugs RC12LYC

[Eagle]

https://janaktech.wordpress.com/2016/02/19/particulate-matter-and-nox-emissions-phenomena-in-engines/

 

https://www.alentecinc.com/papers/NOx/The formation of NOx_files/The formation of NOx.htm

 

[zomeizter]

change the oil and take it in again...

[oldmanche]

Any luck getting it to pass?  I'm having the same problem with my '91 - high NO.  We had a bad vacuum leak (bent injector rail) but that is fixed along with a bunch of other clean up to vacuum lines and grounds.  I can't even remember what we have done at this point.  With everything we have done to it to try and pass it runs amazing, especially after we  just installed 4 hole injectors these week and taking in in.

[Inadaze]

Switch to a 185 thermostat 

With a spray nozzle on your garden hose clean out the fins on your radiator

Make sure your mechanical fan clutch is working fine or just replace it

Run 91 octane (can be debated if 91 creates a cooler combustion chamber temperature) 

Smog it with a 1/4 tank keep the weight down

Sea foam your engine and do an oil change

Run some fuel injector cleaner through your fuel system

Change out your fuel filter

Check or change out your fuel injector pressure regulator on the injector rail

By your numbers look like you could afford to create a richer A/F ratio

Trying to get your computer to create a richer burn, same air, more fuel, lower combustion temps, lower NOx

Also

Check for a cracked exhaust manifold down at the collector 

Check the exhaust manifold gasket especially around the #5 and #6 cylinders

Any pre cat leak could cause a High NOx situation

To check for leaks just pressurize your exhaust system and with a spray bottle with some soapy water spray the gasket and collector areas and look for bubbles (small shop vac works well)

 

 

 

[oldmanche]

Well except for the vacuum we have done all of that.  We've checked for leaks but not as thorough as that method - will need to give it a try.

[pigneguy]

On 10/23/2021 at 3:02 PM, oldmanche said:

Any luck getting it to pass?  I'm having the same problem with my '91 - high NO.  We had a bad vacuum leak (bent injector rail) but that is fixed along with a bunch of other clean up to vacuum lines and grounds.  I can't even remember what we have done at this point.  With everything we have done to it to try and pass it runs amazing, especially after we  just installed 4 hole injectors these week and taking in in.

no luck, no vacuum leaks, swapped out the bosch O2 sensor for an NTK.....figures barely changed it's frustrating.

[pigneguy]

On 10/24/2021 at 8:53 AM, Inadaze said:

 

Trying to get your computer to create a richer burn, same air, more fuel, lower combustion temps, lower NOx

Mechanic says he can't adjust the timing etc as the computer justs re-adjusts..... how does one "hget the computer to create a richer burn..." under these circumstances ?

 

 

 

 

[jdog]

Does the mechanic have a scan tool to see live data?

[Inadaze]

Yes, you are correct, it has no adjustment, that's were the --

Cleaning out your radiator 

Going to a colder thermostat

Cleaning out your injectors or maybe bigger injectors

Maybe A colder spark plug

91 octane

Make sure the clutch on your fan is working

--Comes into play. 

High combustion temperatures leads to High NOx

Ask me how I know. 

The cooler it runs the richer the computer will try and make it run, like starting it up on a cold morning.

Also, check for an exhaust leak! 

 

[Inadaze]

pigneguy

Did pressurize or did you pull a vacuum on you exhaust system? 

[pigneguy]

PASSED!!

[fiatslug87]

Congrats!!!

So, what did you do???

[Inadaze]

Awesome, every 2nd year I always sweat bullets.  I forgot to to ask if it was Auto or Manual, RPMs on the 25mph 2305 rpm on the Fail vs 1478 on the pass the lower RPM also could of played a roll in the Pass also. I Love to see these on the road, I have a goal to have as many or more as Fiatslug !!! Hopefully we get one in over at Fairfield PnP, meetup, and tag team it and save a little bit of history  

[pigneguy]

16 hours ago, fiatslug87 said:

Congrats!!!

So, what did you do???

Smogged cold and kept shop fans on the front. Lower rpms seem to have helped also.