I recently installed one of Matt's high performance heads on my 85 Bertone. When I posted this, Matt asked if I'd done any AFM re-mapping. According to him, many of his modded X's run lean, and need to have the AFM re-mapped.
Reviewing the archives, I decided to try Matt's AFM air flap test. Sure enough, about 5-6 clicks richer seemed optimal, although the idle appeared way too rich. Road testing showed a noticeable power improvement, no doubt about it.
I remembered a thread comment about how it's neat to put a voltmeter on the O2 sensor lead & watch it dance. Being an electrical engineer, I couldn't resist this one... My voltmeter only showed about 200 millivolts, and no variation when the throttle was blipped. The normal output is roughly between 0 and 1 volt (1,000 millivolts). High readings indicate rich/ low readings indicate lean. I varied the AFM settings, but no meter variations. The sensor was definitely bad.
After two frustrating days, the old sensor was finally out & replaced. Trying the air flap test now revealed best 2,500 rpm operation at 10-11 clicks richer! At that setting, the new O2 sensor stayed pegged at 900 millivolts; way too rich for the computer to handle. I reduced the AFM enrichment by one click at a time. At 7 clicks, the O2 sensor voltmeter came alive, dancing merrily about mid-range. Dropping down to idle, the O2 sensor reading continued dancing about mid-range. Success!
After fine tuning the idle, which required adjusting both the CO adjustment & the plenum idle speed, and re-checking to make sure that the O2 voltage was fluctuating properly, I buttoned it up.
To sum things up, if I was only running at the races, I would probably run at 11 clicks rich. But, for street use, where fuel mileage & emissions are real concerns, I want to see the computer actively controlling the mixture, based upon the O2 sensor. I'm seriously considering adding a small voltmeter to the dash or console, just to make sure things are still working. I strongly advise an analog meter (the "old fashioned" kind with the moving needle), rather than a digital, as the trends are much easier to follow. (Can you imagine driving with a digital number readout tach?)
Brian, "in da UP"
Reviewing the archives, I decided to try Matt's AFM air flap test. Sure enough, about 5-6 clicks richer seemed optimal, although the idle appeared way too rich. Road testing showed a noticeable power improvement, no doubt about it.
I remembered a thread comment about how it's neat to put a voltmeter on the O2 sensor lead & watch it dance. Being an electrical engineer, I couldn't resist this one... My voltmeter only showed about 200 millivolts, and no variation when the throttle was blipped. The normal output is roughly between 0 and 1 volt (1,000 millivolts). High readings indicate rich/ low readings indicate lean. I varied the AFM settings, but no meter variations. The sensor was definitely bad.
After two frustrating days, the old sensor was finally out & replaced. Trying the air flap test now revealed best 2,500 rpm operation at 10-11 clicks richer! At that setting, the new O2 sensor stayed pegged at 900 millivolts; way too rich for the computer to handle. I reduced the AFM enrichment by one click at a time. At 7 clicks, the O2 sensor voltmeter came alive, dancing merrily about mid-range. Dropping down to idle, the O2 sensor reading continued dancing about mid-range. Success!
After fine tuning the idle, which required adjusting both the CO adjustment & the plenum idle speed, and re-checking to make sure that the O2 voltage was fluctuating properly, I buttoned it up.
To sum things up, if I was only running at the races, I would probably run at 11 clicks rich. But, for street use, where fuel mileage & emissions are real concerns, I want to see the computer actively controlling the mixture, based upon the O2 sensor. I'm seriously considering adding a small voltmeter to the dash or console, just to make sure things are still working. I strongly advise an analog meter (the "old fashioned" kind with the moving needle), rather than a digital, as the trends are much easier to follow. (Can you imagine driving with a digital number readout tach?)
Brian, "in da UP"
