Ca smog issues any tech insight

[tonyt2293]

so I recently rebuilt my jeep 4.0 engine and stroked it to a 4.6 new sensors and injectors
Took it to smog and it failed nox by alot
Engine only has about 150 miles on it

Going over everything I noticed 2 exhaust manifold bolt were loose and one of the flange bolts to the down pipe was missing and the donut gasket was falling apart both leaks before the cat and o2 sensor how much affect would this have on the nox readings ?.

 

[Wrenchturner44]

If you have 02 sensors downstream of the leaks in the exhaust system, then they are not getting an accurate sampling due to those leaks and thus cannot provide the ECM with good data for making adjustments.

 

[Trav]

Anything like that can effect all the readings, is the EGR still functional?

 

[tonyt2293]

Anything like that can effect all the readings, is the EGR still functional?

Didn't come with a egr from the factory
Did a temp reading on the cat after driving at 55 for a few minutes and had 630 Inlet and 710 outlet the cat itself was around 270

 

[tonyt2293]

If you have 02 sensors downstream of the leaks in the exhaust system, then they are not getting an accurate sampling due to those leaks and thus cannot provide the ECM with good data for making adjustments.

Wouldn't that also effect hc and co as well ?

 

[Wrenchturner44]

Yes, most likely any smog reading that is running in closed loop mode.

 

[eljefino]

Was it hot? Try and get it less hot, down to thermostat temp. Wire the AC fan to run all the time, weaken the antifreeze mixture. Obviously fix the exhaust too.

Cars without EGR valves sometimes get the same effect with intake/ exhaust valve overlap, I am wondering if you did something to the volumetric efficiency that changes this "calibrated leak."

 

[tonyt2293]

Was it hot? Try and get it less hot, down to thermostat temp. Wire the AC fan to run all the time, weaken the antifreeze mixture. Obviously fix the exhaust too.

Cars without EGR valves sometimes get the same effect with intake/ exhaust valve overlap, I am wondering if you did something to the volumetric efficiency that changes this "calibrated leak."

I thinking so had a coolant overflow today and tested the rad cap and it was bad just replaced it as well I have a 3 fan set up were 2 fans kick on at 180 and the 3rd kicks on if it hits 210

Valves were kept stock and timing isn't adjustable at least mechanically it isnt just whatever the ecu adjust

 

[wpod]

Been a long time but isn't now a lean condition.

 

[Cujet]

NOX is caused by high combustion temperatures. Early Attempts to lower NOX included low compression ratios. If you increased the stroke and did not change the combustion chamber volume, the CR would be higher.
Did the new pistons have the changes necessary to maintain the stock CR?

of course a modern 3 way cat should knock down NOX a lot

 

[tonyt2293]

NOX is caused by high combustion temperatures. Early Attempts to lower NOX included low compression ratios. If you increased the stroke and did not change the combustion chamber volume, the CR would be higher.
Did the new pistons have the changes necessary to maintain the stock CR?

of course a modern 3 way cat should knock down NOX a lot

Yes the pistons were dished
According to the numbers stock the 4.0 was at 8.8:1 and with the pistons ,deck work , and cam I'm at 9.3:1 static and 7.43:1 dynamic adjusted for elevation

 

[KrisZ]

Since there is no EGR, I would focus on finding all leaks on the exhaust and intake. A leak will cause a lean running condition and therefore high NOX.

You already found leak in the exhaust, there could be some on the intake side as well. These need to be fixed.

 

[paulo57509]

I'm wondering if the increased stroke has an effect on NOx levels?

There's no external EGR; isn't this taken care of through valve timing? Running a different cam to compensate for more stroke?

 

[clinebarger]

Yes the pistons were dished
According to the numbers stock the 4.0 was at 8.8:1 and with the pistons ,deck work , and cam I'm at 9.3:1 static and 7.43:1 dynamic adjusted for elevation

You have a custom ground Cam? Just curious how the Cam (Valve Timing) is playing into the high NOx.....Coupled with the higher static CR.

Was the cam ground with emissions compliance in mind?

 

[Cujet]

Have you chosen a direction here? A tune to retard timing and possibly change the mixture a touch?

It is possible a failed cat can result in high Nox, but my money is on high combustion chamber temps.

 

[tonyt2293]

Hi sorry for the late reply it was a combo of bad cat and bad afr. Stock fuel pressure regulator couldn't supply enough fuel making the jeep run lean and the cat was clogged up she passed smog today but nox is still borderline allowable is 517 and 530 at 15 mph and 25 mph respectively and jeep was high 400s for both wondering if I may be off a tooth on the distributor as the obd1 ecm is not tune able and according to dyno my afr was 14.6 and 14.8 so **** near perfect

 

[tonyt2293]

You have a custom ground Cam? Just curious how the Cam (Valve Timing) is playing into the high NOx.....Coupled with the higher static CR.

Was the cam ground with emissions compliance in mind?

It is a stage one cam from cleggs according to them designed to play nice with the computer and not require a tune with a slight bump it power and response over stock . I know a few guys on the stroker fourm who run it and have passed

 

[spasm3]

I'd run a cooler thermostat for emission checks. A 160 or 170f thermostat should make the computer richen the mix, which should lower nox.

 

[tonyt2293]

I'd run a cooler thermostat for emission checks. A 160 or 170f thermostat should make the computer richen the mix, which should lower nox.

May just do that as the stock is 195 jeep runs anywhere from 200 to 230 depending on load and if the ac is running

 

[PandaBear]

So typically for NOX: running lean (leak), ignition too far advanced, MAF / MAP sensor, plugs, thermostat, timing belt jump a tooth, fuel pump / injector problem, etc.