My 1990 5.8 w/ 195k miles (65k on motor) just failed a smog test for NOx output too high.
It measured:
1022 ppm (vs. 970ppm Max @ 15mph)
956 ppm (vs. 830 ppm Max @25mph)
The tech said that the NOx max limits were reduced 500ppm's just two-weeks ago and that he thought it was unfair of CA to do that.

The HC and CO both passed with low numbers.

HC was measured at 0.0 ppm's for both the 15 and 25mph test. The max allowed is 110/90 ppm's.

Seems suspicious that the tech got 0.0 readings!!

The CO measured 0.14% (0.58% max / 15mph) & 0.05% (0.77% max /25mph).

Engine was just tuned up with new plugs, wires, rotor, TP Sensor, EGR sensor, etc. It performs well on hills and gets good gas mpg (12+ for 6000# GVW 4x4 FS EB Bronco is good)

A friend said that he took his jeep truck to a smog test only facility and failed the same NOx test and then 1/2 hour later took it to a garage that does both repairs and smog test, and it passed.

I wonder if all the smog only test stations are honest or have thoroughly calibrated test equipment?

My Questions:

What controls the NOx? (O2 sensor, Catalytic Xverter, Air pump, thermostat)

Does a OEM two chamber (with pre-heat) CAT last forever? A muffler shop and mechanic said that was true and tested it by putting a hole in the pipe before and after the CAT and measured the after flow to be the same as the entry or before flow. This was done about six months ago.

Even though a O2 sensor test OK, can it react slow and cause the NOx to be higher? (something another mechanic said)

How do you test a CAT and the Air pump?

If the engine runs on the cold side of the temp gauge is that a cause for the NOx being off?

Where can I get the original specifications for the NOx emission of my '90 vehicle? I think they may have moved it lower than when it was originally manufactured.

Thanks for any help you experts can provide!!

Ron

 

[updated:LAST EDITED ON 22-Dec-02 AT 11:12 PM (EST)]>A friend said that he took his jeep truck to a smog test
>only facility and failed the same NOx test and then 1/2 hour
>later took it to a garage that does both repairs and smog
>test, and it passed.
>
>I wonder if all the smog only test stations are honest or
>have thoroughly calibrated test equipment?

Even well-calbrated equipment has a tolerance for error, and can fail and go beyond that tolerance. Take it to another place & have it tested again.

>What controls the NOx? (O2 sensor, Catalytic Xverter, Air
>pump, thermostat)

NOx is produced by high combustion-chamber temperatures brought on by the programmed lean burn at high RPM, which improves economy. The EGR system reduces the temperature (and therefore the production of NOx) by introducing inerts into the combustion chamber. The system is totally blind in that there is no sensor to detect NOx and regulate the EGR's activity. It's all programmed into the computer, which merely executes the program regardless of the actual results.

>Does a OEM two chamber (with pre-heat) CAT last forever? A
>muffler shop and mechanic said that was true and tested it
>by putting a hole in the pipe before and after the CAT and
>measured the after flow to be the same as the entry or
>before flow. This was done about six months ago.

Theoretically, the cat should last forever, but so should the whole vehicle! The cat is a ceramic honecomb of tubes held in the exhaust stream within the steel housing. The ceramic is made with powdered platinum metal, which catalyzes the reaction of excess hydrocarbons with oxygen, pumped into the exhaust by the air pump (smog pump/pollution pump/etc). When a cat is "clogged", it means the platinum has been permanently coated with lead, which used to be added to gasoline to reduce preignition/knocking/pinging/dieseling/run-on. It doesn't mean that the exhaust flow is actually restricted. However, impact can shatter the ceramic, causing it to block the exhaust, and that's the only possibility your mechanic's test eliminated. The emissions' HC score of 0 says that the cats are fine & the smog pump system (thermactor air) is working perfectly.

>Even though a O2 sensor test OK, can it react slow and cause
>the NOx to be higher? (something another mechanic said)

It will never react "slowly", but it could be coated or blocked causing it to react incorrectly. It doesn't hurt to replace it, but whenever you replace an electronic part, you should unplug the battery for a few minutes to clear the computer's Keep-Alive Memory (KAM) and force it to forget the old sensor's malfunction and learn the new one's behavior. This could be the problem with your new EVP sensor.

>How do you test a CAT and the Air pump?

As above, the emissions test checks their overall condition, but you can check the flow from the air pump by disconnecting the outlet and seeing how much air it can pump. Don't expect high-pressure; it's a high-flow low-pressure pump.

>If the engine runs on the cold side of the temp gauge is
>that a cause for the NOx being off?

The temp gauge is notoriously unprecise, which is part of the reason there are no temperatures on its scale. But a low temperature would only improve your NOx score.

>Where can I get the original specifications for the NOx
>emission of my '90 vehicle? I think they may have moved it
>lower than when it was originally manufactured.

Isn't that what the tester said? You might be able to find it in some EPA archives, but it's probably moot - you have to pass the current test.

 

A BIG 6 Thanks Steve to your quick reply!!

However, with your comments and suggestions, you've triggered a few more questions.

Does the O2 sensor affect NOx emissions at all? I was told it affects fuel-air mixture and thus MPG. I tested the 4-wire O2 unit with a test unit that test the sensor cold and heated with a propane torch. It does NOT check the heater portion (gray wires) and that makes me wonder if it affects the accuracy of the O2 output voltage. I'll be replacing it since its been in there about ~150k miles! (and I still get 12 mpg!) It is a NTK brand that Ford sells. I don't see that brand in the aftermarket?

I think the O2 sensor is a system Feedback device and its data controls the EGR system and more, right?

I was also told that flushing out the coolant and making sure the cooling systems components are tip top keeps the NOx number down. Is there any truth to that? Something about cooling efficiency has to do with it. You know the stuff that coats the water passage walls and prevent the heat from being carried away as compared to when the walls were new and heat conducted effortlessly. I reworked a Mitsubishi 2.6 turbo engine cooling system that had hi miles and it came back with low NOx number from the last smog test. That's why I put in one of those back-flush kits on the heater hose, so I don't have to use anything but a water hose to flush it till it turns clear?

About KAM, I put in a Ford Motorsports Lightning MAF conversion Kit back in 1998. (Kit involves a new Computer, harness, 30# Injectors, 80mm MAF sensor, Airbox w/ hoses.) When I replace the EVP, TBS, etc. I tried to clear the codes by disconnection the battery cable overnight and with the headlight switch on. The Hd light sw on was by another Ford enthusiast suggestion and said it works but doesn't know why. I guess it is because it puts a resistive shunt on the system? Well, neither worked, most of all the old codes are still in there. These were the codes that alerted me to replace the parts that I did to get it in tune.

Is there any other way to clear memory or codes? Do I have a defective computer memory chip?

The Air Pump Vanes can wear out, right? 195k miles on it, how long do they last? I am getting '0' ppm HC, doesn't that say the vanes are still good? I'm shocked that Ford made a part that last that long, if that is true.

You said that a low temp would improve NOx emissions, what if I put in a lower temp thermostat? Say go from 195 to 190 degrees.

Regarding EPA specs, I just hate to buy a new vehicle for the reason that the CA government manipulates the numbers to the 'impossible range' and thus manipulates ME in spending $$$!

BTW, does TN give you grief with your '83 EPA requirements? Yours is carbureted?



Thanks again,



Ron

 

>Does the O2 sensor affect NOx emissions at all? I was told
>it affects fuel-air mixture and thus MPG. I tested the
>4-wire O2 unit with a test unit that test the sensor cold
>and heated with a propane torch. It does NOT check the
>heater portion (gray wires) and that makes me wonder if it
>affects the accuracy of the O2 output voltage. I'll be
>replacing it since its been in there about ~150k miles! (and
>I still get 12 mpg!) It is a NTK brand that Ford sells. I
>don't see that brand in the aftermarket?
>
>I think the O2 sensor is a system Feedback device and its
>data controls the EGR system and more, right?

You can find EEC-IV gurus on the net, but my understanding is that the HEGO only detects oxygen - not NOx - so it has no effect on the EGR. You can do a simple continuity test or hook it up to 12V power to test the heater circuit. I run a Bosch HEGO from O'Reilly.

>I was also told that flushing out the coolant and making
>sure the cooling systems components are tip top keeps the
>NOx number down. Is there any truth to that? Something
>about cooling efficiency has to do with it. You know the

I doubt it - the instantaneous hi-temps in the combustion chamber occur to rapidly for a few degrees of difference in the coolant to affect.

>Is there any other way to clear memory or codes? Do I have
>a defective computer memory chip?

I doubt there's anything wrong with your computer, but Haynes tells how to clear the codes - unplugging the battery clears the "adaptive strategy".
http://www.broncodata.com/tech/codes.htm

>The Air Pump Vanes can wear out, right? 195k miles on it,

More often, they seize, but it sounds like yours is OK.

>You said that a low temp would improve NOx emissions, what
>if I put in a lower temp thermostat? Say go from 195 to 190
>degrees.

Not enough difference to make a difference, and no, I wouldn't recommend it anyway.

>BTW, does TN give you grief with your '83 EPA requirements?
>Yours is carbureted?

I live outside the city, which is the only place around here that gets smog tested, but my '95 EFI engine would probably pass anyway!
http://www.webphotos.com/list_photos.asp?mi=3&smi=1&a=13217

 

I had the exact same problem a few weeks ago...turned out that the vacume line that controled the EGR valve was burnt to a crisp behind the intake manifold (almost impossible to see. Turned out that all five lines were broken. Replaced the lines and passed the NOx with flying colors! Just my 2 cents.

 

Just checked out your pictures >>>WOW<<< only one question.....DEWD where do you get the time to do all that???? looks great

 

I've had this truck since '90, so that's 12 years of playing around, wrecking it, and changing crap just for the fun of it.

 

I started to fix the NOx problem again.

So I checked the vacuum at the EGR valve while stepping on the throttle and it only got a reading of 5 in. Hg and at the vacuum tree it gets almost 20 in. Is this insufficient vacuum? What controls the vacuum? Could that be defective too?

When I observe the EGR valve rod move upon stepping on the throttle it only moves about 1/8 to 3/16" max travel. Do I need to replace the EGR valve?

TIA,

Ron

 

There's a solenoid valve that only applies vacuum to the EGR diaphragm under certain conditions, so it's not surprising you didn't get any vacuum. If you e-mail me, I'll send you a copy of the MityVac manual that tells how to test all the vacuum-operated systems on your truck (and SEVERAL other systems, too!).

 

 

I replaced the O2 sensor and the EGR valve, checked the EVP sensor and the EGR solenoid. The best price for the EGR was from NAPA for ~$75.00 (with AAA card discount).
Also changed the ignition rotor which was a little dirty or carboned up and re-timed it to 10 degrees.

Went to the smog station today and it PASSED!!

Results for NOx:
647 ppm/970max @15mph & 715ppm/830max @ 25mph

With the new O2 (Bosch) sensor it resulted in higher HC's
72ppm/110max @15mph & 47/90 @ 25mph
Both higher than average, I wonder why?

I may change it back to the old O2 sensor, if the mpg is less than before.

I hope it will pass the next test in 2 years.


Thanks for the help!

Ron