failed nox emission testing
 

Hey ...does anyone know why my 92 Ranger would fail the low speed emission testing in the Nox (ppm) with a reading of 2794?? the hi speed reading passed @1116?? Just last June 2004 my truck failed and I had the catylitic converter replaced and asstd. other fuel cleaning stuff for around $500.00!! I hardly drive this truck only once a week for a couple of hours!! HELP???

For a start, welcome to FTE :-X25

Oh, and I moved your thread :)

Hey...thanks for the welcome

[QUOTE=BigF350]For a start, welcome to FTE :-X25

Oh, and I moved your thread :)[/QUOTE

Hey thanks for the welcome...any ideas??]

Ok..hello I finally figured out where to answer ...lol Any ideas ??

http://www.txdps.state.tx.us/vi/

Hey, this may not apply to your state, but the point is the same. Find your symptons, you'll get the causes.

In my case of failure, a cat converter matched in both of the categories I failed, so that did fix things for me.

If the problem is a high NOx level, then the reason for that is the combustion temperatures are getting too high.

Aside from the obvious things such as a deficient cooling system, an engine that is running lean (that is, too much air and/or not enough fuel) will cause higher combustion chamber temps. Hence, look for air and/or vacuum leaks which could allow air too be drawn into the engine. A new fuel filter couldn't hurt if it's more than a few years old. Also, a dirty Mass Airflow Sensor (MAF) can cause an engine to run lean, you might try cleaning yours:

https://www.ford-trucks.com/forums/s...hreadid=126093

Hi, welcome

Agreed, NOX increases when the combustion chamber temp rises above approx 2500F. It is at it's highest at part throttle with a light load which is exactly what the higher speed test is.

Typically it means that the EGR, or the hose connecting to the EGR is plugged. THat is both the most likely cause and the cheapest to fix. The EGR's primary function is to cool combustion temp's by feeding spent gases back into the chamber.

Advanced timing will raise combustion temps but most vehicles from mid 90's on won't allow you to alter the timing much if at all so it's not usually the cause for them.

Next likely is the Cat convertor but it is very unlikely in your case as you just changed it a bit ago.

good luck

Steve

What engine? If 3.0L V6, did the 92' come with EGR? I know my 93' 3.0L V6 Ranger does not - which is quite frustrating since as previously mentioned this is usually the cause of high NOx. Mine has a dist so timing is settable.

I just went through this in So Cal. My NOx was around 1200-1300 at 15MPH and 25MPH dyno. Allowable limit was ~560 and 760.

After doing a good tuneup AND replacing the O2 sensors and cat converter, my NOx readings dropped to 40 and 0 !!!

Did you fully warm up your ranger before taking the test? Just idling before the test doesn't count - idling too long can actually cool the catalytic down.

[QUOTE=probedude]What engine? If 3.0L V6, did the 92' come with EGR? I know my 93' 3.0L V6 Ranger does not - which is quite frustrating since as previously mentioned this is usually the cause of high NOx. Mine has a dist so timing is settable.[/QUOTE

Computer controlled variable timing is one of the ways they were able to do away with the EGR.

If you have no EGR I think you'll find that you can't adjust your timing by tuning the distributor. Don't get me wrong, you can physically do it and the timing will change, but the computer will kick in and change it back. If you turn it far enough to over ride the computers ability to adjust it back then , on most cars, the computer will kick back to the factory programmed saftey defaults and the vehicle will run very rich.

Steve

FWIW, there's no EGR on a '92 4.0L either.

Computer can't change it back if the only source of the timing signal is from the dist. itself, as it is on my 1993 3.0L V6 ranger.

Computer controlled timing has been around for a long time. I remember I had a early 80's dodge that adjusted the timing on a per cylinder basis. In my Ranger's case I'm guessing the reason for low NOx is also due to low compression, combustion chamber shape, and the dual 3-way catalytic converters (one right after the other).

Here in calif, your base timing has to be within +/- 3 degrees from factory setting. Retarding the timing 2 degrees would still pass the visual/timing test.

Another related emissions trick is to pull the SPOUT connector which defaults the ignition to base timing (10* BTDC). This essentially takes the computer out of the equation.

Any update? Did you get your ranger to pass smog?

Base timing is still adjustable and needs to be checked from time to time. The computer just adds timing to the initial static advance. If the vehicle has no knock sensors then the computer can't retard timing unless its in the lookup tables somewhere. The computer ASSUMES that the base timing has been set to 10 degrees BTDC but the computer has no way of checking the position of the distributor rotor relative to the terminals in the cap. Creative folks have even found ways to adjust the base timing on many vehicles that use distributorless ignitions without using a chip.

Many smaller engines don't use EGR because their tune (spark and fuel) allows operation without it. Very few engines use smog pumps these days for the same reason. Many engines only have a catalytic converter, fuel vapor return and PCV system as their only emission control devices these days. That's in stark contrast to the cars of the 70s and early 80s that had so much pollution control junk on them that they'd hardly run in certain conditions.

If the motor has no EGR valve, there are a couple of reasons why NOx could be high. First off, check the cooling system for proper operation. The thermostat may be sticking closed or isn't fully opening or perhaps the fan clutch isn't operating as it should. Second, it could be the result of a lean mixture. Check O2 sensors and clean the MAF. Also you should always change the oil before going in for an emissions test if its been over 2-3k miles since your last oil change.

Wish me luck guys, I'm about to take my Ranger to get tested right now!!