high nox readings on emissions

Hey, my NOX reading on the chassis dyno at the emission place here in phoenix says I'm just a hair too high. I've failed three times:

acceptble is 4.50 g/mile
I've run 4.53, 4.63, 4.85....these were taken in order of the runs.

The last one was running premium gas.

So, the truck has failed worse each time, even after correcting and "uncorrecting" the same vaccum leaks. What's the deal? The dude at the testing center says EGR, and I'm not inclined to believe him since as he puts it so well "I'm not a mechanic." I figured I would get the opinions of actual jeep owners. What sayeth the readers of forums? What do I need to fix to get this thing to pass?

I ran into the same problem last year in MD. I replaced the EGR, O2 sensor, and replaced the cat/exhaust system (needed it anyway). Than I passed. The guy up here said the same thing to me, EGR for NOX. They aren't that much money and worth replacing if you think it's suspect. Juice

what year? only the 87-90 have an egr valve.

NOX passing emissions

Did you try stock or equivalent spark plugs? If you are running premium plugs, they often cause the mixture to run lean.

sjx40250 said:

Did you try stock or equivalent spark plugs? If you are running premium plugs, they often cause the mixture to run lean.

Click to expand...

just curious, why would plugs make it run lean?

It's got brand new splitfires in it, came with the truck as my cheapa$$ would not put the money into something like that. It's also on new wires, new cap an rotor, new oil, new airfilter, new fuel filter...what else... The cat is new, but I don't know about the O2 sensor, can I test the resistance to see if it's alright? How about testing the EGR valve, I know it can be done, but how should I do it?

I'd focus on the egr. It's purpose in life is to control NOX.

I'm at work and cant' help you on the test method other than recomend checking the vacuum lines.

Same on my 89 replaced the EGR and O2 sensor then passed

Good Luck

If you have 87-90, check for vacuum leaks at the EGR (I'd expect that, since it's getting worse) or see if the valve is non-functional. Also give the solenoid a check.

If you have 91+, you don't have an EGR valve. Focus on cleaning the injectors, and make sure you don't have a lean mix by checking your spark plugs against a colour chart in a Chilton's manual.

Either way, take some time to check your cooling system as well. NOx is caused by elevated combustion temperatures, which is caused either by a lean mix or inefficient cooling. The O2 sensor is a minor culprit here - its failure usually results in a rich mix, driving up HC and CO at the expense of NOx.

For those reporting emissions failures for diagnosis, please report ALL gas measurements, Dyno or Static test, and MY of your XJ/MJ. This is all important information, and if you don't mention it you are likely to be asked...

5-90

Thanks for the help, I'll check the lines and look into an egr replacement. The test was done on a chassis dyno, they take it up to 60 mph....it's a whole lotta fun hearing those swampers and xterrains (I changed tires last week) scream on the rollers

EGR DEFINATELY...It has the most control over NOx.

Blaine --

Unless I skimmed over it too fast, you still have not said what year XJ you have. Therefore, it is important to repeat that ONLY THE 87-90 XJ HAS AN EGR.

The purpose of the EGR is to recirculate a small quantity of exhaust into the incoming fuel charge to cool the combustion, which reduces NOx. From 91 and on, Chrysler eliminated the EGR valve and used a different camshaft grind to cause some exhaust to remain in the cylinders as the new fuel charge is drawn in, theoretically achieveing the same result.

High NOx is caused by too hot a burn. That's usually caused by a lean condition.

What about hitting the auto parts stores for a can of that magic elixer that's guaranteed to get you through emissions? You're SOOO close that the stuff might actually work for you. Or try just dumping in a few cans of DriGas (alcohol) and see if that'll cool things down a bit.

It says in his profile that its an 87.

When my 89 failed I traced it to a bad egr solenoid that was preventing the egr from working. Do the test procedure in the fsm or chiltons on the solenoid. Mine was sticking half open and a bank of the wrench on the solenoid got it to open and allow the full vacum to past through. Also check the power to the solenoid during wide open throttle. A new solenoid and cat fixed my emission problem. Greg

Hi NOx is usually the EGR sticking, leading to a lean mixure and excessive combustion temps. The valve opens and introduces inert (previously burned) exhaust gas into the intake, to mix an intake charge that cannot burn as hot (one that has less O2 than normal). This lowers the chamber temp and produces less NOx emissions. When it sticks closed (or it's opening is partially blocked by soot) it fails to mix the proper volume of inert gas, and it fails to lower the high temps that promote NOx.

If you have ever experienced a bucking sensation at a light throttle cruise speed, it is an indicator of intermittant EGR sticking (leading to an eventual failed EGR).

On the 87 to 90 XJ's the EGR valve is located under the TB, on the side of the intake manifold. Pull the air filter box and you will see it easy.

The actual EGR is the metal capped valve bolted to the manifold, and the solenoid is the plastic piece with the hose piped into it.

Make sure the hose connections are intact (pull them and inspect the hose). These XJ's are known to burn the hose piped to the exhaust gas side of the manifold.

Before you replace the EGR itself throttle the engine and watch to see if the stem moves as the rpm changes (it should). A static test is to move the EGR stem with a screwdriver and see if it springs closed (it should). You can also pull a vacuum on the actuator as a test (use a jumper hose directly on the valve's hose port and watch the stem move). Movement will usually clean the seat and port of the EGR valve and restore it's operation (if the actuator is good).

The other option (if you are real cheap) is to pull the EGR (IIRC two bolts) and clean the valve seat and port with brake cleaner.

You are so close, that the EGR valve and port are probably just partially blocked with soot, and need some exercise and cleaning.

BTW, it you read hi CO2 change the O2 sensor as well (otherwise leave it and focus only on the EGR).

dry gas and low octane fuel almost always work. but clean and check the egr

yeah, the co2 and hydrocarbons(?) are less than half the limits...I'll check the egr and assorted plumbing and let you guys know what happens....

Great explanation by Ed Stevens. I have one minor comment however. The electric solenoid that controls the vacum supply to the egr is on the drivers side inner fender. The little plastic thing near the egr valve w. vacum lines in and out of it is not the electric solenoid but rather a control valve (perhaps solenoid in effect) controlling the vacum flow on deceleration IIRC per my fsm. Greg

Greg Smith said:

Great explanation by Ed Stevens. I have one minor comment however. The electric solenoid that controls the vacum supply to the egr is on the drivers side inner fender. The little plastic thing near the egr valve w. vacum lines in and out of it is not the electric solenoid but rather a control valve (perhaps solenoid in effect) controlling the vacum flow on deceleration IIRC per my fsm. Greg

Click to expand...

Thank you, I neglected to mention the electric solenoid that is next to the ballist resistor. The hoses to this solenoid should be checked as well as the plastic lines can get stiff and will sometimes crack if the filter changer gets heavy handed with the filter box clips.

It's good to have others helping to check and clear up the total picture ( helps again).

yeah....I was trying to get that filter box out of there and was pretty rough on it.....perhaps that's the problem. We'll see.