home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > maintenance & nonperformance

Reply
 
Thread Tools Display Modes
Old 11-12-2017, 07:45 PM   #1
maxitoman007
Board Member
 
Join Date: Feb 2017
Location: Calgary, Alberta, Canada
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?
maxitoman007 is offline   Reply With Quote
Old 11-13-2017, 11:09 AM   #2
brian smith
Board Member
 
Join Date: Nov 2010
Location: N.Y.
Default

Maybe watch O2 sensor voltage? If it swings across 0.5V at about 0.75hz or higher at idle - voila.
__________________
stuff:
one
two
brian smith is offline   Reply With Quote
Old 11-13-2017, 03:02 PM   #3
Ryan_R
Board Member
 
Join Date: May 2006
Location: Athens, OH
Default

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.

-Ryan
__________________
Athens, OH
1987 245
1989 245 GL
1989 745 GLE
1991 745 --Regina powered B234F!
1995 945T -- Mildly modded
http://www.ohio.edu/people/ridgely/Volvo_docs/
Ryan_R is offline   Reply With Quote
Old 11-13-2017, 05:22 PM   #4
lummert
Board Member
 
lummert's Avatar
 
Join Date: Jan 2008
Location: Portland IN
Default

Are you using any test equipment while making this adjustment?
__________________
Trying to understand stupid people is like trying to pick up a turd by the clean end.
lummert is offline   Reply With Quote
Old 11-13-2017, 07:51 PM   #5
maxitoman007
Board Member
 
Join Date: Feb 2017
Location: Calgary, Alberta, Canada
Default

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.
maxitoman007 is offline   Reply With Quote
Old 11-14-2017, 12:54 PM   #6
brian smith
Board Member
 
Join Date: Nov 2010
Location: N.Y.
Default

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.
brian smith is offline   Reply With Quote
Old 11-14-2017, 02:05 PM   #7
lummert
Board Member
 
lummert's Avatar
 
Join Date: Jan 2008
Location: Portland IN
Default

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.
lummert is offline   Reply With Quote
Old 11-14-2017, 02:06 PM   #8
lummert
Board Member
 
lummert's Avatar
 
Join Date: Jan 2008
Location: Portland IN
Default

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.
lummert is offline   Reply With Quote
Old 11-14-2017, 03:02 PM   #9
maxitoman007
Board Member
 
Join Date: Feb 2017
Location: Calgary, Alberta, Canada
Default

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?
maxitoman007 is offline   Reply With Quote
Old 11-14-2017, 07:44 PM   #10
lummert
Board Member
 
lummert's Avatar
 
Join Date: Jan 2008
Location: Portland IN
Default

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
lummert is offline   Reply With Quote
Old 11-14-2017, 09:56 PM   #11
ZVOLV
<Master Tech>
 
ZVOLV's Avatar
 
Join Date: Nov 2002
Location: California
Default

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.
__________________
No Start Thread
ZVOLV is offline   Reply With Quote
Old 11-14-2017, 10:18 PM   #12
ZVOLV
<Master Tech>
 
ZVOLV's Avatar
 
Join Date: Nov 2002
Location: California
Default

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.
ZVOLV is offline   Reply With Quote
Old 11-15-2017, 01:59 AM   #13
maxitoman007
Board Member
 
Join Date: Feb 2017
Location: Calgary, Alberta, Canada
Default

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?
maxitoman007 is offline   Reply With Quote
Old 11-15-2017, 11:16 AM   #14
ZVOLV
<Master Tech>
 
ZVOLV's Avatar
 
Join Date: Nov 2002
Location: California
Default

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.
ZVOLV is offline   Reply With Quote
Old 11-15-2017, 11:55 AM   #15
maxitoman007
Board Member
 
Join Date: Feb 2017
Location: Calgary, Alberta, Canada
Default

I've done lots of googling but I guess I'll do more research haha.
maxitoman007 is offline   Reply With Quote
Old 11-15-2017, 12:51 PM   #16
lummert
Board Member
 
lummert's Avatar
 
Join Date: Jan 2008
Location: Portland IN
Default

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.
lummert is offline   Reply With Quote
Old 11-15-2017, 06:22 PM   #17
maxitoman007
Board Member
 
Join Date: Feb 2017
Location: Calgary, Alberta, Canada
Default

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.
maxitoman007 is offline   Reply With Quote
Old 11-15-2017, 07:39 PM   #18
ZVOLV
<Master Tech>
 
ZVOLV's Avatar
 
Join Date: Nov 2002
Location: California
Default

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.
ZVOLV is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 02:26 AM.

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2017, vBulletin Solutions, Inc.