Greetings

My 1989 740 GLE station wagon (clean clear coat paint) (364,500 MILES) with aw-70 A.T. NON-Turbo passed on emissions with exception to the NOx portion. It passed on H.C. grams 00.87, state limit= 02.00, on the CO grams per mile it read 008.73, state limit= 030.00 on the NOx it read 05.05, state limit= 03.00. The stated that it might be a timing,ignition, exhaust, 02 sensor, and or EGR issue. Well let me tell you the car is in excellent shape! I use nothing but premium fuels, change the oil regularly (Chevron Delo 400 15w-40) during the summer and Chevron supreme (winter)and synthetics! I keep a strict maintenance regimen, and the car has new exhaust, flame trap, plugs (NGK V-Power)etc. They also stated that it may be a cat issue! This car runs so smooth, and my gas mileage is roughly 27-30 mpg! My driving consist of 98% highway miles! Might it be a timing belt issue (loose and or in need of replacement) personally I think a bucket of you no what is being dumped my way. The said they had mechanics that could help resolve my issues etc. I am very mechanically inclined, however again, I believe the are full of hog wash! Oh and the car neither leaks nor burns any oil! The plugs are firing clean and normal. Might it be the higher sulfur content in the 15W-40 delo 400? Should I just swap back to the 10w-30 for the moment? What benefit would it be for me to drive the car for a good 45 minutes via highway and then bring it right back for another emissions test, would that shift the NOx readings in my favor? Again I passed everything else regarding emissions and safety,its just the silly NOx readings! My apologizes for such a long thesis, please help! Mr.Foster of Cape Cod are you available?

1988 740 GLE S.W. 425,700 MILES (same as above)
1989 740 GLE S.W. 285,000 miles (same as above)

VOLVOS ARE THE BEST!
Thanks in Advance!


Best Regards!

If the HC and CO are well below the limits then I would say that the cat is doing its job.

High NOx is caused by running hot and lean.

You need more fuel and/or less air and/or less advanced ignition timing.

I would suggest:

1. Set the base idle speed correctly with the IAC out of the circuit and car idling only on the throttle body bypass screw.

2. Check timing - retarding it will help.

3. Replace the fuel filter to help richen mix.

4. Replace O2 sensor to help richen mix.

5. Make sure cooling system is working well.

6. Make sure dist cap and rotor are in good shape and not corroded.

I don't see how driving the car for 20 minutes before testing to get everything good and hot would help the NOx, but maybe I am missing something.

Of course you can fool around but chances are it's the cat. They're only guaranteed for 50K (now up to 80) so 360K is a real good run.

There are tests you can do, like check the oxygen reserve before and after the cat, but now is probably the time to replace the cat.

A simple google search yields:
Catalytic converters can be checked in two ways. Temperature, the temperature of the outlet should be approximately one hundred degrees higher than at the inlet Emission levels; run the engine slowly up to 2500 rpm, hold steady while monitoring the 02 level, when the 02 level has bottomed out at it's lowest level (less than 1% with air management disabled) sharply tag the throttle. After the "snap throttle" bring the rpm slowly back to idle, the 02 level should rise and then come down.

(You can check the O2 level by reading the 02 sensor voltage).

Lastly, my experience with a 260K saab OEM converter was similar to yours...everything else was ok except high NOx. New cat fixed the NOx problem AND lowered the HC and CO levels to about 1/10 of what they were before (even though the car passed the HC and CO levels.
FWIW, the emissions test levels aren't going to get any higher...they keep lowering the pass levels at inspection every year even though the levels will probably never be as low as the car had to pass when it was new. The upshot is you'll probably fail your HC or CO emissions next time unless you replace the cat.

Oh and one other thing, none of my lights on my dash come on (not burned out)! Including my "CHECK ENGINE LIGHT" so code wise I am in the clear! All of my lights come on at first (test light feature as you know), however they immediately go out upon starting the engine. Again all of your experiences and or suggestions would be greatly appreciated!

Start with the 700/900 FAQ ("features" button above) for tips. High NOX is a result of high combustion temps due to:
-vacuum leak in the intake system (lean mixture)
-EGR faults
-timing off

Start with vacuum leaks: make absolutely certain you do not have a leaking air intake hose, vacuum hoses, or intake manifold gasket. Clean the EGR if so equipped. If you've got a B234 GLE, then you know that timing/balance belt changes are incredibly important.

thanks guys you have been very helpful! I have 60 days to clear up the matter. I was under the impression that my cat was for at least 100,000 plus! It is not even the original either. Where could one purchase a cat with the longest longevity, for a reasonable price (fcpgroton.com)?

Thanks again!!

As Steve indicates, the most likely culprit is O2 leakage into the intake. The more O2 present during combustion, the higher the temperature. NOx is formed when the nitrogen (about 80% of the air your engine breathes) combines with excess O2. Nox compounds can only be formed at high temperatures, and only when excessive amounts of O2 are available. Look for the simple stuff first before you start to throw money at it.