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Old 11-12-2017, 07:45 PM   #1
maxitoman007
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Default Way to tell if you enter closed loop?

I am trying to set the idle AFR on my 87 740 Turbo but I would like to make sure I have entered closed loop before I make any adjustments. Is there any way to tell?
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Old 11-13-2017, 11:09 AM   #2
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Maybe watch O2 sensor voltage? If it swings across 0.5V at about 0.75hz or higher at idle - voila.
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Old 11-13-2017, 03:02 PM   #3
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Really, when the engine is warm. Closed loop is more of the ECU starting to "listen" than an outward trigger from the sensor itself. When I had the AMM unplugged for diagnostics MANY years ago, you could hear and feel when the car went closed loop when idling. Kinda cool.

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Old 11-13-2017, 05:22 PM   #4
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Are you using any test equipment while making this adjustment?
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Old 11-13-2017, 07:51 PM   #5
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Well I know my base mixture is way out of wack because not only did I have the proper rotation of the amm screw mixed up in order to lean out the mixture (installed browntops). I was also tuning using a wideband with a broken sensor (realized this when it read even richer than stoich in open air). So idk if the car will even enter closed loop when the mixture is this far off, still irked though Allbeit s little rough... I've tried checking o2 sensor voltage but if I remember correctly it was just staying around .45v although attaching my dmm also changed the idle so it might not be high enough resistance(?) to make an accurate measurement, I'm not sure. Maybe I have fouled the regular o2 sensor from idling very rich while trying to tune? Hence the weird voltage and no voltage fluctuation, I'm not sure.
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Old 11-14-2017, 12:54 PM   #6
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As long as your mixture is close enough to allow the engine to run, warm up, and heat the O2 sensor up to working temperatures, it's close enough to go into closed loop.
How about warming up the engine, then holding it at 2k+ rpm. If your O2 sensor isn't working and the output voltage not fluctuating then, you've got a sensor worth replacing to get your car running correctly, and a possibly fouled sensor that you could rehab on it's own later...
Can you use your gauge read narrowband O2 sensor output rather than the DMM? Mine does, and I never wonder if I'm in closed loop yet or not.
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Old 11-14-2017, 02:05 PM   #7
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If you've gotten the AMM adjustment way out of whack try setting it using a VOM across AMM pins 3 and 6 to 380 ohms. This would be a good starting point.
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Old 11-14-2017, 02:06 PM   #8
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If you've gotten the AMM adjustment way out of whack try setting it using a VOM connected to pins 3 and 6 of the AMM to 380 ohms. This would be a good starting point.
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Old 11-14-2017, 03:02 PM   #9
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I don't think I can use my wideband gauge on my narrowband sensor. I'm worried that reading it with my dmm is inaccurate due to the idle changing when I back probe the signal wire to read voltage. I will set my amm back to 380 ohms before I start tuning again, does more resistance lean out the mixture? Lastly won't my o2 sensor not fluctuate if it's too rich/ lean? Just hold a high voltage for rich and low voltage for lean? I think my o2 sensor is reading too close to 0.5 to be reading rich/lean. How can you revive a foiled sensor? Propane torch?
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Old 11-14-2017, 07:44 PM   #10
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Quote:
Originally Posted by maxitoman007 View Post
I don't think I can use my wideband gauge on my narrowband sensor. I'm worried that reading it with my dmm is inaccurate due to the idle changing when I back probe the signal wire to read voltage. I will set my amm back to 380 ohms before I start tuning again, does more resistance lean out the mixture? Lastly won't my o2 sensor not fluctuate if it's too rich/ lean? Just hold a high voltage for rich and low voltage for lean? I think my o2 sensor is reading too close to 0.5 to be reading rich/lean. How can you revive a foiled sensor? Propane torch?
Less resistance = leaner mixture
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Old 11-14-2017, 09:56 PM   #11
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It would have to be VERY rich or lean to be pegged at .1 or .9v.

On modern cars scan tool data shows long and short fuel trim data. I see o2 sensors still oscillate when the fuel trim is maxed out at 30% or -30% at times. The computer can still bring it back in usually enough to idle ok, but throw a mixture code.

Back to old brick: Your dvom is good enough. Do a snap throttle and it see if it drops down to .1v for a sec. Maybe try adding brake cleaner and watch it go to .9v.

The computer measures cross counts (where it passes .45v) to determine if the mixture is off. On LH 2.2 there is a test wire that blinks cross counts at you, No? And you change idle mixture until it blinks steady, but that doesn't fix other issues! On some MAFs you can pop the cover off and mess with even larger adjustments.
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Old 11-14-2017, 10:18 PM   #12
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It would have to be VERY rich or lean to be pegged at .1 or .9v.

On modern cars scan tool data shows long and short fuel trim data. I see o2 sensors still oscillate when the fuel trim is maxed out at 30% or -30% at times. The computer can still bring it back in usually enough to idle ok, but throw a mixture code.

Back to old brick: Your dvom is good enough. Do a snap throttle and it see if it drops down to .1v for a sec. Maybe try adding brake cleaner and watch it go to .9v.

The computer measures cross counts (where it passes .45v) to determine if the mixture is off. On LH 2.2 there is a test wire that blinks cross counts at you, No? And you change idle mixture until it blinks steady, but that doesn't fix other issues! On some MAFs you can pop the cover off and mess with even larger adjustments.

Interpreting o2 voltage isn't as straightforward as you may think. Mess around with introducing air leaks as a test to see what happens.
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Old 11-15-2017, 01:59 AM   #13
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Quote:
Originally Posted by lummert View Post
Less resistance = leaner mixture
Now I'm confused haha because I always read about people adding resistors to amm wires to compensate for bigger injectors.

Yes there is a test light tool you can get that'll blink like you say if the mixture is correct but I don't have that tool and don't have money to spend on one. I'll try to do some tests with my o2 sensor to see if it's working properly. If not can I just pull any 3 wire sensor cut the leads, connect to Volvo leads and be good to go? Or are there Volvo specific o2 sensors that must be used?

Oh, and what's a snap throttle? Just a blip of the gas pedal?
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Old 11-15-2017, 11:16 AM   #14
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These sensors make their own voltage with crystals.

If it's dead dead dead, it may make no voltage. If its lazy it may stick only sometimes. I see that sometimes on scan tool data.

They can also be lazy and not move fast enough.

I strongly recommend you Google this ****! The bench test with burning propane is particularly interesting.
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Old 11-15-2017, 11:55 AM   #15
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I've done lots of googling but I guess I'll do more research haha.
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Old 11-15-2017, 12:51 PM   #16
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I have used a DOM connected between the CO test point (DOM ground lead) and battery positive (DOM positive lead) to test oxygen sensor output. Adjust the AMM pot screw to get even sweeps of voltage. No voltage sweep = too lean, steady 12 volts no sweep = too rich. After getting the voltage sweep, the mixture will be slightly lean. Turn the AMM pot screw 2 to 3 turns clockwise.
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Old 11-15-2017, 06:22 PM   #17
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Thanks, I've heard you can do that but that the mixture has to be close first. And isn't CCW rich in Lh 2.2? Still confused about people Adding resistors to compensate for bigger injectors. I think the resistance on my amm goes up when turning clockwise.
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Old 11-15-2017, 07:39 PM   #18
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I don't have a pic hosted of 02 sensor voltage graphed at idle, but here is a pic of the voltage graphed on a scope at a 2000rpm steady rev:





Snap throttle may show some sign of life as the mixture goes way lean, then rich, the back to steady. Watch YouTube vids.
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Old 12-01-2017, 06:22 PM   #19
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A vehicle has entered closed loop when the o2 sensor starts to oscillate between 0.1v and 0.9v!
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Old 12-01-2017, 06:42 PM   #20
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Perfect thanks.
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Old 12-01-2017, 07:50 PM   #21
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I was working on a modern car, one that has the 450mv reference voltage sent to it, and scan tool data showed it stuck at 450mv; there was a bad connection. I fixed the poor connection and monitored the data. After a minute or so of running it started to oscillate again and the data, concurrently, indicated that the vehicle had entered closed loop.

Driving the car, when you got on it hard, it stops listening to the o2 sensor and goes off preset maps again=open loop. The oxygen sensor was reading 800-900mv during hard accel as it should since it's running richer during load. Cruising, back to closed loop and computer constantly adjusts the mixture and the o2 sensor swings as the computer tunes the mixture.

Old Volvos do NOT have the 450mv reference like modern cars . On modern car if it's pegged at 450mv it means it not connected. Saw it recently on one with a break in the wire.

So you replaced the O2 sensor and now it oscillates at idle? Seems like that was another thread of yours....
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Old 12-01-2017, 09:06 PM   #22
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Quote:
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So you replaced the O2 sensor and now it oscillates at idle? Seems like that was another thread of yours....
Yes indeed it was, conclusion was that it was a bad o2 sensor. I ended up replacing it with the Bosch o2 sensor for I believe a 92 mustang V8 (?) I found the part # on a turbobricks o2 sensor compatibility thread. Costed $41 CAD vs around $75 for the universal Bosch most people use. Cut and spliced the wires and voila, worked great.
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