I have a 92 940 sedan, not the original motor, failed emissions for high NOx. HC 1.1 CO 11.2 NOX 8.2 OVER three times the limit. My motor has no EGR VALVE, If it was the CAT WOULDN'T ALL THE LEVELS BE HIGH? The engine light is off, I poured some guaranteed to pass on the tank, now I have to drive it until empty again. Help!!

 

usually high NOx is the cat. the other readings are fine because the oxygen sensor and pcv system are working. my 89 240 was showing almost non-passing NOx 4 years ago , and 2 years later i had to replace leaking exhaust anyhow and replaced the cat. NOx went all the way down .

 

emissions are a balancing act between HCs and NOs. Generally high NOx reading suggest a lean burn condition which creates enough heat to create the NOx. Different things can create this condition ie engine timing (spark too advanced etc), intake air leaks (unmetered air), exhaust leaks (the O2 sensor won't be accurate). When you say your car has no EGR valve, do you mean your model's design doesn't use an EGR valve or somebody removed the one that's supposed to be there? The idea of an EGR system is to blend some inert exhaust gas back into the intake to cool the combustion temperatures. Essentially the whole point of the EGR system is to LOWER NOx amounts!

 

The original motor had an EGR VALVE, someone has replaced that motor, and it has no EGR VALVE. I even took it to a Volvo dealership to see if they could find the EGR VALVE. The car runs and idles good. I just hate to replace the cat if not needed. If the egnition timing was advanced wouldn't you be able to tell by the way it runs ?

 

Not sure of the ignition set up on the 92 but I'd doubt if the timing is adjustable - probably is triggered by a crank position sensor. I think you may have some luck searching a local yard with a 940 to see if you can scavange its EGR system. You can try searching car-parts.com to see what yards near you may have a 940 engine for sale and go from there. I don't know if running without the EGR will ruin the cat or not, but it will keep you from passing emissions. BTW, a replacement cat for a base 940 non turbo is only about $125 for an aftermarket brand... Sheesh, an OEM fuel pressure regulator for my s40 cost me $200... :-)

 

thanks for the information, will be very useful I hope, I know from reading that the EGR VALVE is for eliminating the nox fumes. So you think it will never pass emissions with no EGR VALVE on the engine?

 

that's a good question... I think it depends on how far off the measurements are but I'd have a to think about anything you could try to do as a temporary fix... Maybe run cooler plugs or widen the gap a bit, Also try running premium gas - particularly look for a brand without Ethanol prior to testing. Last thing is to retard the timing. There's actually a way to do this! Advance/retard timing on EZ116K - Turbobricks Forums

Good luck. BTW in the long run you probably want to install the EGR set up - not sure if running with a failed (missing) EGR will cook a turbo or cat but at least this will give you time to sort it out.

PS - Cliff, I moved this thread to the 740/940 board, to get some views and comments by our resident red block experts!

 

if the car didn't come with EGR, don't even think of retrofitting it.

*ALL* the EGR does on these motors is let he engine use a little less fuel at higher RPMs when coasting along with hardly any throttle, it does this by inserting some already burned exhaust into the air intake so it can then inject less gas without creating a 'too lean' condition. if the car came with EGR then a smog inspection will verify the EGR system is present and still operational, otherwise, if your locale didn't require it new, there's no point in installing it.

yes to post #5, the ignition timing on 1990+ turbos and 1989+ nonturbos is fixed by the crank position sensor and computer, there's no adjusting it. the spark advance is purely electronic.

and yeah, high NOx is almost certainly a worn out catalytic converter. the OEM cats last maybe 300K miles give or take. do NOT use a cheap replacement or it won't last a year.

 

Thanks for the feedback, I replaced the cat and oxygen sensor, brought the nox and all emissions levels way down, relieved to report my car finally passed inspection on Saturday. Thanks again!

 

I replaced my Catalytic Converter after failing 2 prior smog tests on a volvo 940 for excessive NOx, and immediately failed again with the exact same NOx readings
as the prior tests with a 28 year old CAT. So it is not always true that high NOx can be cured with a new Catalytic converter, based on my experience. I did notice
a reduction in HC after installing the new Catalytic converter but the NOx readings were unchanged at the high speed test. I saw a slight reduction in NOx at the low
speed test.

My thoughts on Exhaust leaks causing O2 sensor offset/false readings,... well, an exhaust leak would allow extra O2 into the exhaust is what I have been told, and this
would cause the O2 sensor to read leaner. The end result would be the ECU adds more fuel trim to create a richer fuel mixture. What I have been told is a rich fuel
mixture will actually reduce NOx... so this contradicts the idea that an exhaust leak would increase NOx emissions.

However I might not fully understand the catalytic converters behavior. I think the ECU switches between lean and rich as part of the catalytic converters function of
storing oxygen and then releasing oxygen.

However walker exhaust website says the following

• SLIGHTLY LEAN CONDITIONS ARE THE MAIN REASON FOR HIGH NOX READINGS
• EXHAUST LEAK PREVENTS CONVERTER FROM REDUCING NOX EFFICIENTLY
• NOX IS NORMALLY TESTED ON A DYNO WITH ENGINE AT PARTIAL LOAD
• 02 READING SHOULD BE CLOSE TO BUT OFTEN SLIGHTLY LOWER THAN CO READING (WELL WITHIN .1% OF CO)
• HIGH READINGS INDICATE A LEAN CONDITION THAT CAN RESULT IN A FALSE P0420 CODE

so I guess you are probably right about this. I hear some slight exhaust leak near the front of the car so perhaps I need to replace some gaskets or look for holes in the pipes.