High NOx, can't pass CA smog

So I just failed my second smog test, here's the background...

1994 Cherokee Country 4.0, rebuilt engine .030 over, Ford 19# injectors, Borla header, Borla catback, new distributor, new rotor, new cap, new plugs, new wires, new 02 sensor, new Cat, checked fuel pressure at idle: 31psi with vacuum/39psi without vacuum, 29psi at 2500rpm.

I don't have the paper on me, but HC and CO numbers were super low, while NOx was mid 1100's at 15mph, mid 900's at 25mph. I have to get it down to close to 200.

I've heard of another individual that was able to pass by disconnecting the MAP to force it into limp mode, which made it run rich, which passed it. His assumption was that the injector pulse width was too short. Is there anyway to modify the width of the injector pulse? Should I move to 24# injectors? The fuel pump is stock, I believe, and the Jeep has over 220K....could the fuel pump just be too weak to provide necessary fuel under load?

Any input is greatly appreciated! TIA

So combustion temp is high from running lean so could you not just plug the vacume to the FPR to bump fuel pressere to make it run rich?

was another thought, but if it's a problem is with the pump not providing enough flow, then the increased fuel pressure wouldn't help because the pump still wouldn't be supplying enough.

Gonna try to chane the air charge and coolant temp sensors too since they supposedly affect the fuel injection as well according to the FSM.

I would change your fuel filter. It is nothing short of amazing how bad a plugged up fuel filter can make a jeep run. My wife's wj was suffering extended cranking, major hesitation, lean condition dtc's and I was positive it was the pump. Tried the fuel filter, and it runs better than ever.

Yeah but It might be enough, what kind of vacume do you think is applied at 25mph? maybe 10-12 and you were down to 900.. so what would it drop to with 0 vacume applied?

You could also do a fuel volume test and compare the PSI ratings to the FSM to verify pump operation.

Won't the smog shop diagnose it for you?

replace your convertor, it will clean up the nox rightaway!

I failed with high nox and got a new converter and passed with flying colors. When I failed I also had extremely low emissions in the other catagories. I also have Ford injectors and a 95 Jeep so that isn't your problem. Why did you rebuild? A blown headgasket will kill a converter so if that is why you rebuilt then you need a new converter.

Yes, save the headache, get a new converter.
When I could not pass NOX , I changed everything from the plugs, wires, cap and rotor, oil, coolant, air filter, fuel filter, and ccv. Seafoam twice, even tried that pass in a bottle stuff and unplugging coolant temp sensor. NOX still around 1900.
Tried about 6 times and finally had a cat put on. Passed no problem!!












Then it failed EVAP :banghead:

I thing the new cat in his original post was a new converter? Or he felt like randomly throwing out he got a new girlfriend as part of his smog diagnosis.

if you're running lean, why even mess around? no bueno for the engine, just fix the problem (pump, filter, etc)

Is your cat a three way or the less effective two way cat?

Vanimal, that's exactly what I'm trying to do....figure out why it's getting a lean condition. The engine was rebuilt by a local member who has quite a favorable reputation, and he too is baffled by the numbers.

As I mentioned, one other individual suffered from similar problems and had to short out the MAP....I'd prefer not to do that. His belief was that the injector pulse width was too short and hence causing the lean condition.

From the FSM, it seems pulse width is adjusted according to Load (MAP sensor) and temperature (air charge sensor and coolant temp sensor). So that's why I ordered those. The flow issues could be a bad filter....I hadn't really thought about it, but a few cans of sea foam have been run through with this filter, so maybe it just picked up all the crap and is a little clogged. Also, I think it may be a Fram filter, and if their fuel filters are like their oil filters, that could be the fuel restriction. And then of course, there is always the nearly 20 year old pump.

Regarding the catalytic converter, yes it is new. It was purchased from Kragen/O'Reilly's. It's a magnaflow converter that is stamped with CARB number. Although the CARB number dates back to 1985, but technically, they cant sell it if if isn't legit. I did notice however that NAPA sells two kinds of cat for my Jeep, one meets California and Federal emissions regulations, and one is a Cal Cat, for sale in California only. I'm guessing mine meets California and Federal regulations, but I'm curious if the Cal Cat has some significant difference so that it can only be sold in CA.

Thanx for all the input!

My current plan of attack is to pop on a new filter and install new RC9YC plugs for a 87-90 Jeep. They are supposed to be a colder range plug which should also help since the oversized cylinders will obviously also generate at least slightly more compression.

I would think pump and filter as well, you can have good pressure with low volume, resulting in a lean condition and high nox.

Well I hope you can solve this NOx thing mine always just squeaks by in the 700's iirc.ive also tried all the home remedies.

Hah! You haven't seen the new test then....700's I could pull with fuel regulator or colder plugs....new limit is in the 200's! =(

SanDiegoXJ said:

Hah! You haven't seen the new test then....700's I could pull with fuel regulator or colder plugs....new limit is in the 200's! =(

Click to expand...

Scratch that, I looked at the numbers wrong.
Readings are as followed
15mph 1693 rpm
HC
Max 63
Ave 26
Meas 9

CO
Max 0.66
Ave 0.04
Meas 0.02

NO
Max 517
Ave 203
Meas 1163 FAIL

25mph 1641rpm
HC
Max 38
Ave 16
Meas 6

CO
Max 0.80
Ave 0.05
Meas 0.01

NO
Max 539
Ave 233
Meas 986 FAIL

OK, so here's a recap...
Existing items:
Borla header
Borla catback
19# mustang injectors from Precision Auto Injectors
K&N Air Filter

New items before first smog test:
Rebuilt engine 0.030 over with new cam
Magnaflow California catalytic converter
Distributor and cam sensor
Champion spark plugs gapped 0.035
Spark plug wires
CPS
TPS
IAC
O2 sensor

system failed high no....don't have numbers because DMV took them to give me an extension.

New items before second test:
MAP sensor
Seafoam in the fuel (to clean injectors)
New Fram Toughguard air filter (to try to restrict some air flow)

Next test was free retest.
Second test results:


Numbers were basically identical as first test.

New items before 3rd test:
Lucas fuel injector cleaner
Coolant Temp Sensor
Air Charge Temp Sensor
Fuel filter (but even the old one seemed to have nice flow)
RC9YC spark plugs
Changed out NGK O2 for Bosch 02

Don't have those yet, but will post when I do...basically same numbers as second test yet again....so essentially all new sensors, new cat, fuel treatment, tested fuel pressure regulator, and it's fine...haven't tested fuel flow from pump, but beginning to think that isn't a contributing factor either.

Now, I believe I got really lucky in that I wanted to the 3rd test on a sunday and could only find one place open locally, so I went.

After he tested, I told him everything I did to it, he said (you have an exhaust leak before the cat.) So I pointed to a pinhole leak I knew I had, and he said that's your problem! So a fellow member, sdspearo, invited me to come up and weld my hole closed...I trot back down to test a 4th time.

By now I'm also realizing the Jeep is running hot...on the freeway, the temp is cool as can be, but as soon as I hit traffic, it gets warm mighty quick...in fact, haven't heard the aux fan turn on in some time, and suddenly it's coming on everytime I come to a standstill.

he runs a 4th test and the results are as follows:



So, I say I got lucky because I noticed the guy also pulled the hose off the pressure regulator to try to increase pressure plugging up the vaccuum line. He also said that before the final test, he sniffed it and it ran super clean at 15mph, but at 25, no would start around 250, and every 10 seconds climb another hundred so by the end of the test it was upwards of 800. He still hasn't charged me a dime for two tests, putting my Jeep on a rack so I could mess with my exhaust using his tools, and finally told me to bring the Jeep back Tuesday night, so he can run a "cold" test wednesday morning. He says a new cat will heat up quicker than the engine and it gives him a couple minutes to run the test while the cat is hot enough to catch the HC and CO, but the engine isn't hot enough to start producing NO.

My quandry now is, I now notice that I have 02 in my exhaust...that wasn't happening before. Could that be because the colder plugs just aren't burning all the O2 at lower RPM? And could that ultimately be a cause of the higher NO readings at 25, since it's actually running at lower RPM, leaving a higher concentration of O2 in the exhaust.

I would really love to actually find out why it's running lean. Could it be possible that the 0.030 is enough to require a 24# injector?

According to a Lambda calculator your car isn't running lean. It is actually just about perfict.

There was another thread a few months ago where the guy was having problems passing NOX with a Magnaflow converter, he was the one who ended up pulling the plug on the coolant temp sensor to richen it up to pass. Maybe Magnaflow's don't scrub the NOX as well as the non high flow converters out there. His was doing the same thing, the NOX was jumping up every few seconds.

Ecomike posted some links to sites explaning how cats work and troubloeshooting tips for them. Might want to search back to Jan some time.

I know we all love working on our own vehicles but sometime it is worth it to take it to a smog shop that will give you a diagnosis for a hundred bucks. It saves money in the long run.

I figured my cat was bad but wanted someone to properly test it before I spent 200 bucks on one. It was money saved in the long run because I didn't just throw sensors at it.


http://www.smogsite.com/calculators.html#lambda

Are they new/reconditioned fuel injectors?

There are 2 ways dirty fuel injectors can affect NOx without causing increased levels of HC and CO. First, the dirt in the injector can affect the injector spray pattern, this change in the spray pattern can cause hotspots in the cylinder's which can cause elevated NOx levels.

A second way in which an injector can affect NOx levels is when only one injector is clogged. The rest of the injectors can keep the HC and CO level within specs, but the lean cylinder's temperature increases, causing NOx to form.

When they rebuilt the engine, did new freeze plugs get installed? One or many could have gotten in the water passage way and blocking/restricting water flow.