I took my ride in for inspection on Saturday and it failed the NOx portion of the emissions test.

High Speed Emission Results (25 MPH)
NOx Standard: 956 ppm
Current Reading: 2064

Low Speed Emission Results (15 MPH)
NOx Standard: 1046 ppm
Current Reading: 2082

This is off a brand new engine in my truck. I had it rebuilt in April and it only has ~4500 miles on it. How would a brand new engine be putting out excessive NOx? I've read the AirCheckTexas website and looked at the details regarding excessive NOx. From the website:

"High NOx can occur when there is excessive temperature in the combustion chamber or a damaged catalytic converter. Check the following:
-Air injection system
-Exhaust gas recirculation system (EGR)
-Combustion Chamber Deposits
-Oxygen Sensor
-Catalytic Converter"

The CEL is not on so I don't have any indication there. I talked to my mechanic who does minor work for me and he said he couldn't pull any codes from the ECU because it's a 1995 model. He can only do the OBDII models. He said in 90% of cases like this the catalytic converter is bad and I should just go ahead a replace it. It would be cheaper than paying someone to pull the codes, tell me it's the catalytic converter, and then paying to have it replaced.

Is there any way I can pull the codes myself or do I need to take it somewhere to have it done? And what does it mean by " excessive temperature in the combustion chamber"? Do they mean in the catalytic converter?

I only have until the 27th to get my ride fixed and re-tested. One of my friends told me to drive around for 30 minutes and then go have the test done again. Some of the threads I've read here indicate this won't do anything for high NOx levels. Is this the case?

Basically, I'm stuck and don't know where to proceed from here. Any suggestions on what to do next?

 

If you do confirm this to be a bad cat, be sure to get a new one on ebay. Go for a Magnaflow Car Sound cat (high flow). They are about $57 shipped. Best deal going IMO.

 

I would check the EGR, could be a clogged passage or stuck valve.

 

High NOx = EGR, test and clean all parts of the EGR system, make sure it is fully working.
If you can, retard the timing a few degrees and run high octane gas.

FYI: My 22RE went from ~2200 NOx to 880 NOx by doing the above steps.

 

you can pull the codes yourself. You mechanic doesn't know what he is talking about. All you need to do is connect the two jumpers under the hood. Sticker is on the underside og the hood to show you how, then look at the check engine light on the dash. It will blink the codes to you (short & long) it will keep repeating them. If there are no codes the rythum will be slow and steady. To clear the codes you will want to pull your EFI fuse for 30 seconds.

Good Luck

 

NOx is formed by "burning" nitrogen in the air sucked into the engine. Only happens when it is really hot. NOx = Oxides of Nitrogen. So the key to reducing NOx is reducing the temperature of the fuel/air burning inside the engine. How to do that? EGR, which works by Recirculating Exhaust Gas from the exhaust back into the intake. Exhaust gas has no O2, it is essentially inert, so it dilutes the fuel/air mix, less fuel and air = cooler combustion, ergo less NOx.

Pull and read the codes yourself:
http://www.4crawler.com/4x4/CheapTri...CheckConnector

 

Are there any codes to pull since I don't have the CEL on?

 

Yes, often there are codes in the computer when the check engine light has never come on. I get them all the time due to the mods I made the how low the rpm go when I was plowing snow. So go ahead and check them, you might be suprised what is in there.

 

OK. I can't get around to pulling the codes until Thursday, but I will post them here for more troubleshooting help. Thanks.

 

Finally had a chance to pull the codes. They were 24, 41, and 52. Not what I was expecting.
________________________________________
24: INTAKE AIR TEMPERATURE SENSOR SIGNAL--OPEN OR SHORT IN INTAKE AIR TEMP. SIGNAL
--INTAKE AIR TEMPERATURE CIRCUIT

--INTAKE AIR TEMPERATURE SENSOR

--ECU

41: THROTTLE POSITION SENSOR SIGNAL--OPEN OR SHORT IN TPS SIGNAL
--TPS SENSOR

--TPS SIGNAL/CIRCUIT

--ECU

52: KNOCK SENSOR SIGNAL--OPEN OR SHORT IN KNOCK SENSOR SIGNAL
--KNOCK SENSOR/CIRCUIT

ECU
_______________________________________


So what do these mean in relation to the high NOx and what do I do next?

 

If all those things are really out, surprised the engine is even running. Test out the components and see if indeed they are bad (now) or these are old, old codes stored in the ECU:

AFM: http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml
TPS: http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

The KS is supposed to retard the ignition timing under knock/ping conditions, the detonation that occurs under pinging = high combustion temps = high NOx. Make sure the wire to the KS is intack, both the signal and the ground shield around it. Not uncommon for the ground shield to break, leaking the KS basically unconnected.

 

Unfortuantely, testing each component is above my technical skills. I do know this much: when I got my truck out of the shop after having the engine rebuilt, the CEL was on and the code at that time was 52. The guy at the shop said I had a bad knock sensor. Well, I removed the plenum and checked the knock sensor wire only to find that it had not been put back on properly. One of the two wires had been pulled out of the connector. I fixed that, and got both wires back into the connector the way they should be. Then I hooked the knock sensor wire back up, got the plenum back on, and fired up the engine. No more CEL.

But, in hooking the knock sensor wire back up, I broke the plastic housing around the end of the wire. I'm assuming this is what you're referring to as the "ground shield". Are you saying this could be causing my problem?

 

There is typically a coaxial wire to the knock sensor, just like your TV antenna/cable uses (not the exact same type of connector). There is a wire in the center, surrounded by insulation and that is covered with a braided shield and then further insulation. The KS puts out a very low voltage, high frequency signal that would be swamped by noise from the engine if not for the shield (it keeps noise out of the inner wire). If that connection is broken (search here for threads on repairing the knock sensor ground connection), then either noise can get into the wire or worse yet, the ground connection is lost all together.

If you are unable to test the components (you'll need an inexpensive volt/ohm meter, mine cost all of $2.99 and some feeler gauges), then take it to a shop and have those things checked and repaired.

 

Since you mentioned "old codes" I'm wondering if I should clear my ECU and try to pull codes again. Would this do me any good?

 

The ECU stores codes in order received. They mine be years old (or whenever the ECU was last reset). One idea is to clear the codes and see if they return in normal operation. For example the old Knock Sensor code may have been left over from when the sensor was disconnected.

 

OK, then I'm going to clear them and see what comes back.

 

I cleared the ECU by disconnecting the negative battery cable and pullilng the ECU fuse. I let it sit 15 minutes and then went and hooked everything back up. When I try to pull the codes now, the CEL just blinks steadily at a rate of about 2 blinks per second.

 

So I've driven about 12 miles since resetting the ECU. I pulled the codes again and I got nuthin'. The CEL blinks steadily at about 2 flashes per second.

But one thing I noticed when I had the hood up this last time. I was inspecting the throttle body and noticed two of the tiny hoses coming off it were disconnected. I don't know how that would have happened since I didn't do it myself. Both of these hoses run into metal tubes that then run into the EGR valve. I don't know where the Intake Air Temperature Sensor is located on the throttle body, but is it possible that these were the cause of my problem?

 

The two hoses likely run to the EGR modulator, without them the EGR gets no vacuum and as a result may not operate. No EGR = high NOx. The air temperature sensor is inside the air flow meter, see the specifics on it in the AFM page I posted earlier.

 

Thanks, 4Crawler.

I'll post a pic tomorrow of the two hoses I'm talking about to give you a better idea. I'm betting this is the cause of my problem.