Emissions Adjustment Question
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Mountain Pass
Joined: Nov 2018
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Emissions Adjustment Question
Here is Arizona they run my 81 F100 4.9l Automatic truck on the dyno for the emissions test. I had it running great with good power and no stumbling but when they tested it was high on Nitrates. This is due to the timing being advanced as I found out in reading. My initial timing was 11 to 12 degrees advanced. I reset the timing at 8 degrees and had it rested and the nitrates were down into the numbers they allowed but the CO2 readings were double before but luckily it was still acceptable. Now the question it runs like crap it doesn't have the pickup it has and it has some hesitation during normal driving. I understand the this is related to the temp inside the combustion chamber but even on a 120 degree day I? was not experiencing any overheating issues. Now that I have the blessing of the state for the next two years will it hurt the engine to go back to 12 degrees for the operation I am concerned because of the combustion temps. Thanks for your thoughts on this possible issue. Les
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Joined: Dec 2007
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From: Boise, Idaho
There's nothing wrong with running it how the engine likes for the 2 years between tests.
It's what I do here in Idaho. Every 2 years, I set the timing down to 6°, lean out the idle, etc. and get it to pass the test. Then, tweak it back to where the engine's happy.
However, it should run properly at stock configuration (considering your engine's stock).
You might have other issues that you're masking by raising the timing. Vacuum leaks, bad EGR valve, etc. Make sure all of that stuff is in good working order.
It's what I do here in Idaho. Every 2 years, I set the timing down to 6°, lean out the idle, etc. and get it to pass the test. Then, tweak it back to where the engine's happy.
However, it should run properly at stock configuration (considering your engine's stock).
You might have other issues that you're masking by raising the timing. Vacuum leaks, bad EGR valve, etc. Make sure all of that stuff is in good working order.
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Mountain Pass
Joined: Nov 2018
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I have a fresh Jasper Rebuilt engine with about 20,000 miles on it. All items repaired, new Chinese style Carter one barrel and engine vacuum of 19 when running at 12 degrees. I was just worried about that combustion temps being high causing the high nitrates reading. Some have told me that it can cause problems in the long life of the engine. I do think I will do as most seem to do set it to run good and just watch for issues. Thanks for the reply's and the reinforcement. Les
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Joined: Nov 2002
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High combustion temps inside the combustion chamber do indeed create harmful oxides of nitrogen. But they do not affect the reliability or durability of the engine. Retarding the timing, adding EGR reduce NOx. Running rich increases hydrocarbons and CO emissions but that will not affect the durability of the engine either..
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axman_F250
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
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Mar 16, 2011 04:47 PM
