Emissions failure - Volvo

NJC

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1989 Volvo 740 turbo. Just failed emissions today and now have 3 days to fix. So it's dumping gas on the idle circuit but not running rough at idle. From 0% to 4.49% at idle, so something significant has changed. I'll check idle vacuum, and snoop around tomorrow. But any clue as to which would cause such a dramatic change?
 
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Hi NJC: In case no one here can give you the answer I would check out the following forum and see what you can find: http://www.brickboard.com They have a comprehensive FAQ on the Volvo 740/940 and may have some suggestions listed. If not, I would join the forum and post your question there on the 740 forum. The Volvo-specific knowledge available there is amazing. Andrew S.
 

NJC

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Thanks dnastrau - I did check their faq but it's generic info. I'll try to google and see what turns up.
 
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You have a misfire. Simple as that. Nothing else can explain high HC(unburned fuel) and CO(paritally unburned fuel). Since it isn't running rough, it's probably a rich misfire.
 
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Checked with my dad the Mechanic and he says the car seems to be running too rich. Check for leaky injectors not standing up to idle pressure, Bad O2 sensor, Bad plugs and/or wires. Is this a CIS injection system? If so it could be that the idle mixture screw is a tad rich and needs to be turned back counter-clockwise.
 

NJC

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It's LH 2.2 (Jetronic). Vacuum seems to jump between 18-19 in/Hg at idle. No obvious leaks. The plugs haven't been done in awhile, so I'll replace. Maybe check wire resistance tomorrow.
 
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Change the plugs first and make sure the new ones are in the right gap specifiction as outlined by the sticker on your hood. This ignition system can be very fussy! I would also back off the idle mixture screw underneath the tamper proof plug, just a bit counter-clockwise to lean out the mixture a tad. This is located on the top of the air box. These can move over time from vibration. Once it passes the test you can turn it the other way again if you want to. It uses a 3mm allen key.
 

NJC

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Changed the plugs this AM - NGK - BPR6EGP. Gap was >.028" as required by my car but box said not to gap (damage to platinum electrode). Vacuum came up to 21 in/hg. Thanks - will have a look at the air mass meter too.
 
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The gap has to do with the resistance and voltage required to produce the spark. If it varies from the factory spec it's because they have taken this into account and it will not effect the ignition pattern. ;\)
 
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Not on this fuel injection system IMO... It's most likely the idle mixture screw is set too rich. Any other injection system I would agree with you, but I had this very same problem with my VW Cabriolet which is equipped with a similar injection system as this Volvo.
 

NJC

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Max allowable HC is 110 and I tested 177ppm. But the CO is waaay over the limit - max allowable .84% and tested @ 4.5%. Average reading .02% I don't think it's the cat, considering the immediate jump in readings vs last year's test.
 
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Just a few additional thoughts on this: I would check the cap and rotor if that hasn't been changed lately. They can definitely cause a misfire condition if the contacts are burned. They really should be changed about every 30K based on my experience with other Bosch distributors on my VWs and Volvos in the past. If your oxygen sensor is old, you might want to change that as well - perhaps the duty cycle isn't refreshing as quickly as it should anymore thereby causing higher emissions. As mentioned earlier, is your catalytic converter in good shape? On the LH 2.2 Jetronic injection: This system is TOTALLY different from the CIS system and does not have an idle mixture screw (as far as I know - unless it is part of the MAF.) LH 2.2 uses an electronic mass airflow meter (MAF) like most other cars these days, and the computer adjusts the idle mixture based on feedback from the oxygen sensor, etc. I have also heard that filling up the tank with Super Unleaded (higher alcohol content as mentioned earlier in this thread) and taking a hard run down the highway right before an emissions test can help with the numbers as well. I hope you find a solution soon! Andrew S.
 

NJC

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 Originally Posted By: dnastrau
If your oxygen sensor is old, you might want to change that as well - perhaps the duty cycle isn't refreshing as quickly as it should anymore thereby causing higher emissions.
The O2 sensor failed in 1999 but both driving and idle CO was excessive, not just idle.
 Originally Posted By: dnastrau
As mentioned earlier, is your catalytic converter in good shape?
I had assumed, looking at low numbers, that it had been replaced. Hard to imagine a 20yr old Volvo with ~150K on the clock putting out such low numbers the last 4yrs. But I'm only speculating.
 
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