460 NOx Emission failure
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460 NOx Emission failure
Looking for suggestions on how to reduce my NOx emissions on my 1997 F259 HD 4x4, 460 truck. I failed the CA smog test twice. All pass except NOx about 10% over max spec. Dealer replaced EGR & sensor. Dealer now recommends chemical treating for carbon removal ($120). Since the dealer did not fix it the first time ($500), I have my doubts about their advice. I am thinking the O2 sensor(s) may be contaminated/faulty. Plus, this vechicle is difficult to inspect in CA due to the first generation OBDI plug. Any recommendations or known fixes appreciated.
Regards,
John
Regards,
John
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From: Las Vegas, Nevada
Oxide of Nitrogen (NOx) are a funny thing. The things that you would normally do to decrease the HC and CO in an engine such as retarding the timing, leaning out the mixture, etc, increase the NOx! This is because NOx levels are dependent to a degree on engine or more exactly, combustion temperatue. This is why they use EGR systems, which dilute the fresh charge with exhaust thereby reducing the effecency and combustion temperature of the engine. If this has been replaced and is working, you could try advancing the initial timing some or richening up the mixture a bit. Both of these actions will bring down your combustion temp a little, maybe just enough to pass. Remember though, most of the things you do to reduce your NOx will then increase the CO and HC. Also, there is Spearco water injection.....
Good luck!
Good luck!
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My HC and CO are are the low side so I have some room to adjust. I thought the timing was controled in the engine computer module. (Is there an easy way to retard the timing or enrich the fuel mixture?) I fail NOx by 10% at 15 & 25 MPH on the dyno. I have read some posts on NOx failures on the 4.0 L engines. Some success was to remove carbon build up using chemical cleaners. Since the EGR and sensor has been changed, I am thinking on trying the chemical cleaners and trying to put my foot into it on the steep grades. I have not looked into the water injection. If it lowers the combustion temp. it should work too. I will need to check if it is CA smog legal. Thanks for the suggestions.
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Originally Posted by JHD
Looking for suggestions .... Dealer replaced EGR & sensor.
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I do not know if the EGR passages were cleaned. After the EGR was replaced, the NOx dropped from 1950 to 1748 at 25 MPH. The 15 MPH only dropped by 50. Since there was not an extra charge for cleaning the passages, I doubt it was done. Do I need to pull the intake or heads to do it? That is a good thing to check. After I failed the NOx text at the local smog referee station, I went back. The tech. did some additional testing and said the compression was a little high. He recomended the chem cleaning for top end carbon reduction. I may need to pull the EGR and look. It is frustrating that to test the NOx per CA, I need a dyno and 5 way gas tester. CA smog has given me a, one time, 2 year extension since I have spent over $450. Thanks for the advice.
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Yeah, you are computer controlled, what was I thinking! Not a whole lot you can do as far as the richening up or timing changes. I would have to go the cleaning route too. Make sure the passeges are cleaned out to the EGR valve. They, and the exhaust crossover in the manifold can get pretty carboned up and not flow very much exhaust. The reason why they are recommending the carbon clean out is that the carbon raises your compression, therefore raising the combustion temps. I can't really see why you would have that much carbon build up though. But....every little bit helps.
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I bought my truck 2 years ago with 100K miles on it and only put about 3K miles on it in those 2 years. I am not sure how the previous owner drove it. It runs really good and I want to keep it. I will try chem cleaning and clean out the cross over if I still fail. The other thing I read was that in the winter months in Calif. the gas is oxygen enriched. This lowers HC & CO but heard it may raise NOx by about 10%. All I need is a little lowering of the NOx and I will pass. Thanks for the advice.
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JHD, something else that came to me was have you checked the cooling system? Something like a stuck thermostat, a broken fan shroud or a bad fan clutch could also be causing the engine to orun just hot enough to not pass the NOx. Just another avenue......
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My truck tends to run on a little on the cool side. The temp. gauge stays in the lower middle section as has never went into the red even on the hottest days going up grades. The fan, belts and shroud look OK. I think the thermostat and fan clutch are working OK, but have not tested them. Thanks for the tech. tips.
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