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California98Civic · 07-26-2012, 03:48 PM

This thread convinced me to do mostly engine-on pulse and glide on the freeway, instead of engine off, in order to keep the CAT lit and control emissions better. And I just did my smog test, and here are the results and my thoughts about the results.

"Black and Green" passed on the first go. But at the 15mph 1793 rpm test hydrocarbons were 7x the ave for this model car and only 2ppm below the allowable limit. The CO and NO were close to the averages for this model, with the exception of CO at 1793 rpms, which was four times average (though still only 20% of the allowable limit). The was evidence of "unburnt fuel" the tech said.

The car has been running a WAI, 14* ignition timing advance, and non-stock specified spark plugs. And most importantly I do a lot of engine off P&G on surface roads. I have noticed that the long term fuel trim turns slightly rich under lots of engine-off P&G, which is maybe the reason for the unburnt fuel.

To get ready for the test, I reset timing to stock (12*), installed stock spark plugs, and reinstalled the stock air box apparatus. Then I drove forty miles on the freeway without engine off coasting at all. The first 20 miles I did engine-on pulse and glide, accelerating with 80% load and then coasting in neutral. Fuel trim moved from 0.00 to -1.6%. On the way back to the smog check, I held a steady 60 mph on the speedo for 20 miles. Long term fuel trim returned to 0.00% then to -0.78% before I pulled into the check station.

I don't think these results confirm or refute Sentra-SER's findings in this thread. But my gut tells me P&G, especially combined with engine off coasting using an injector kill switch plays a big role. That's because I know the ECU on my Civic responds to rapid throttling changes by slightly enriching the AFR. When I bump start and press the throttle to get to 80% load ASAP, I think the AFR gets a little rich. Then I suddenly cut the engine with the injector switch. My +0.78% to +1.6% long term fuel trim readings under engine off P&G driving would seem to confirm that P&G produces "unburnt fuel," as the tech put it. Conversely, I have observed -2% and even -3% long term trim on the freeway, doing engine on P&G, which I think gets the ECU to lean-out AFR because of the tumbling rpms each time I drop into neutral and let the engine decelerate from 2700 to 700 rpms. I imagine the ECU thinks of the rpm change as a DFCO type situation, and so it goes leaner for a second.

BTW, The tech suggested I might want to change the O2 sensor on the exhaust manifold (it has never been changed). He thinks that might return my car to better average emissions. I'm thinking a Denso (stock O2 sensor brand). And I will experiment with modifying my surface street techniques with more engine-on P&G. But considering the production and distribution of the gasoline, I still believe that on balance I am saving gas money and reducing my car's total pollution (see: 1, 2, 3).

07-26-2012, 03:48 PM	#162 (permalink)
California98Civic Cyborg ECU Join Date: Mar 2011 Location: Coastal Southern California Posts: 6,299 Black and Green - '98 Honda Civic DX Coupe Team Honda 90 day: 66.42 mpg (US) Black and Red - '00 Nashbar Custom built eBike 90 day: 3671.43 mpg (US) Thanks: 2,373 Thanked 2,172 Times in 1,469 Posts	My CA emissions test results This thread convinced me to do mostly engine-on pulse and glide on the freeway, instead of engine off, in order to keep the CAT lit and control emissions better. And I just did my smog test, and here are the results and my thoughts about the results. "Black and Green" passed on the first go. But at the 15mph 1793 rpm test hydrocarbons were 7x the ave for this model car and only 2ppm below the allowable limit. The CO and NO were close to the averages for this model, with the exception of CO at 1793 rpms, which was four times average (though still only 20% of the allowable limit). The was evidence of "unburnt fuel" the tech said. The car has been running a WAI, 14* ignition timing advance, and non-stock specified spark plugs. And most importantly I do a lot of engine off P&G on surface roads. I have noticed that the long term fuel trim turns slightly rich under lots of engine-off P&G, which is maybe the reason for the unburnt fuel. To get ready for the test, I reset timing to stock (12), installed stock spark plugs, and reinstalled the stock air box apparatus. Then I drove forty miles on the freeway without engine off coasting at all. The first 20 miles I did engine-on pulse and glide, accelerating with 80% load and then coasting in neutral. Fuel trim moved from 0.00 to -1.6%. On the way back to the smog check, I held a steady 60 mph on the speedo for 20 miles. Long term fuel trim returned to 0.00% then to -0.78% before I pulled into the check station. I don't think these results confirm or refute Sentra-SER's findings in this thread. But my gut tells me P&G, especially combined with engine off coasting using an injector kill switch plays a big role. That's because I know the ECU on my Civic responds to rapid throttling changes by slightly enriching the AFR. When I bump start and press the throttle to get to 80% load ASAP, I think the AFR gets a little rich. Then I suddenly cut the engine with the injector switch. My +0.78% to +1.6% long term fuel trim readings under engine off P&G driving would seem to confirm that P&G produces "unburnt fuel," as the tech put it. Conversely, I have observed -2% and even -3% long term trim on the freeway, doing engine on P&G, which I think gets the ECU to lean-out AFR because of the tumbling rpms each time I drop into neutral and let the engine decelerate from 2700 to 700 rpms. I imagine the ECU thinks of the rpm change as a DFCO type situation, and so it goes leaner for a second. BTW, The tech suggested I might want to change the O2 sensor on the exhaust manifold (it has never been changed). He thinks that might return my car to better average emissions. I'm thinking a Denso (stock O2 sensor brand). And I will experiment with modifying my surface street techniques with more engine-on P&G. But considering the production and distribution of the gasoline, I still believe that on balance I am saving gas money and reducing my car's total pollution (see: 1, 2, 3). __________________ See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green* over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.