High NOx level - Volvo Forums - Volvo Enthusiasts Forum


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Old 04-20-2017, 05:28 PM
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Default High NOx level

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!!
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Old 04-20-2017, 06:22 PM
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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 .
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Old 04-21-2017, 11:46 AM
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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!
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Old 04-21-2017, 10:46 PM
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Originally Posted by mt6127 View Post
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 ?
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Old 04-23-2017, 12:16 PM
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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... :-)
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Old 04-23-2017, 01:21 PM
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Originally Posted by mt6127 View Post
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?
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Old 04-24-2017, 10:32 AM
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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!
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Old 04-24-2017, 03:57 PM
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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.
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Old 05-15-2017, 04:38 AM
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Originally Posted by pierce View Post
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!
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