Is this normal? Mix adjust question
09-13-2004, 11:40 PM
#1
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Is this normal? Mix adjust question
I am in the process of adjusting my mixture. I have a meter attached to the O2 sensor and have been using my new homemade special tool. I am driving the car to work and after it warms up I hit WOT a few times and see where the meter is reading. If it is still too high, I back off the mix screw 1/2 turn when I reah work/home.
The problem is that I have now been doing this for over a week and it doesn't seem to be changing the mix.
I have a couple of theories:
1) The PO had many vacuum leaks and had the mix on full rich so it would suck enough gas to run
2) The screw is stripped and I could do this for years without making a change
3) This is completely normal and it takes many turns to have an effect
Any opinions? I am now at around 6 full turns (yes counterclockwise
) and really no noticable difference.
If nothing changes soon, I am going to order a CO meter.
TIA
The problem is that I have now been doing this for over a week and it doesn't seem to be changing the mix.
I have a couple of theories:
1) The PO had many vacuum leaks and had the mix on full rich so it would suck enough gas to run
2) The screw is stripped and I could do this for years without making a change
3) This is completely normal and it takes many turns to have an effect
Any opinions? I am now at around 6 full turns (yes counterclockwise
) and really no noticable difference. If nothing changes soon, I am going to order a CO meter.
TIA
09-13-2004, 11:48 PM
#2
Nordschleife Master
When your in the high sensitivitiy zone for the O2 sensor, it has an effect fairly quickly.
However, outside of the high sensitiveity zone, it has basicly no effect.
If the meter is reading between say .3 and .6 volts, you int he high sensitivitiy region. Outside that, you can turn the screw, and notice no diffrence on the O2's voltage.
May I assume you in the .7 v region? In that case, crank down on the screw a whole lotta times. Say 8 times. If the O2 sensor drops to below .5 volts, turn it back out the correct number of turns and you should be set. Keep landing on the other side of .5 volts untill your at the half turn stage, and call it good.
However, outside of the high sensitiveity zone, it has basicly no effect.
If the meter is reading between say .3 and .6 volts, you int he high sensitivitiy region. Outside that, you can turn the screw, and notice no diffrence on the O2's voltage.
May I assume you in the .7 v region? In that case, crank down on the screw a whole lotta times. Say 8 times. If the O2 sensor drops to below .5 volts, turn it back out the correct number of turns and you should be set. Keep landing on the other side of .5 volts untill your at the half turn stage, and call it good.
09-14-2004, 12:27 AM
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What V is saying is that within a certain small region, a tiny movement of the allen wrench equals a large change in mixture.
The Lambda or O2 sense system can control mixture a small amount. It varies fuel pressure via a thing known as a "frequency valve" or valve that vibrates and reduces fuel pressure to fine tune the mixture. Fine tune it is...
However, he's actually wrong. There is no "fine range" or "wide range"- the allen wrench controls mixture with absolute linearity.
It's just that the O2 loop might conspire against your fine settings is all! A second mind, per se.
-Now you know what those of us with LH Jetronic are up against every day!
N!
The Lambda or O2 sense system can control mixture a small amount. It varies fuel pressure via a thing known as a "frequency valve" or valve that vibrates and reduces fuel pressure to fine tune the mixture. Fine tune it is...
However, he's actually wrong. There is no "fine range" or "wide range"- the allen wrench controls mixture with absolute linearity.
It's just that the O2 loop might conspire against your fine settings is all! A second mind, per se.
-Now you know what those of us with LH Jetronic are up against every day!
N!
09-14-2004, 01:04 AM
#4
Nordschleife Master
There is no fine range or wide range on the adjustment screw for the L-jet cars.
However, the O2 sensor has a range in which the voltage changes dramaticaly with the changeing CO concentration. Outside that range, the O2 sensor is just not sensitive to changes in the CO level of the mixture. This range is aproximently .3-.6v.
If the CO level is outside of the range that would normaly return a .3-.6v on the O2 sensor, the O2 sensor is just not sensitive enough to notice the diffrence in the CO level that a single turn on the adjustment screw produces.
However, the O2 sensor has a range in which the voltage changes dramaticaly with the changeing CO concentration. Outside that range, the O2 sensor is just not sensitive to changes in the CO level of the mixture. This range is aproximently .3-.6v.
If the CO level is outside of the range that would normaly return a .3-.6v on the O2 sensor, the O2 sensor is just not sensitive enough to notice the diffrence in the CO level that a single turn on the adjustment screw produces.
09-14-2004, 01:54 AM
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Thanks for the comments. So just to be clear what I am measuring is the voltage at WOT so the O2 sensor is out of the loop and just acting as a sensor (which makes for a fun commute!!). According to the meter mfg I am currently running between 12.5:1 and 13.2:1 which is pretty rich so in the area of 0.9V on the o2 sensor.
I guess I just need to keep cranking it back until I get off the shoulder of the curve.
VU - Sorry to see that you are punting. Let us know if you need help keeping the pickup running :-)
I guess I just need to keep cranking it back until I get off the shoulder of the curve.
VU - Sorry to see that you are punting. Let us know if you need help keeping the pickup running :-)
09-14-2004, 02:13 AM
#6
Nordschleife Master
You'll never get it to work if you keep hitting the WOT switch!
Dude, you need to unplug the O2 sensor, but DON'T ground it. This makes the ECU think the sensor is bad, and innore it. If you ground it it just thinks the mixture is lean, and will try to enrich it. When the ECU thinks the sensor is gone, it falls back on limp home mode, and goes open loop, but trys to stay as close to stochic as it possibly can be.
When you hit the WOT switch, the ECU not only goes to open loop, but also goes to WOT enrichment. The end goal of the WOT enrichment is a 12:1 a/f ration. That is WAY to rich for the O2 sensor to give you an accurate reading. The O2 sensor is only sensitive near the 14.7:1 a/f ratio. Instead of returning you a .5v, the O2 sensor is going to return more like .7 or .8 volts.
So, what you do is unplug the sensor, resulting in open loop, but near stoch. opperation, and then measure the voltage returned. Do this whole NOT engageing the WOT switch.
Also, you only need to adjust it at idle. Thats why it's called the idle mixture adjustment. If the idle is good, but your off at speed, that means something else is wrong.
Dude, you need to unplug the O2 sensor, but DON'T ground it. This makes the ECU think the sensor is bad, and innore it. If you ground it it just thinks the mixture is lean, and will try to enrich it. When the ECU thinks the sensor is gone, it falls back on limp home mode, and goes open loop, but trys to stay as close to stochic as it possibly can be.
When you hit the WOT switch, the ECU not only goes to open loop, but also goes to WOT enrichment. The end goal of the WOT enrichment is a 12:1 a/f ration. That is WAY to rich for the O2 sensor to give you an accurate reading. The O2 sensor is only sensitive near the 14.7:1 a/f ratio. Instead of returning you a .5v, the O2 sensor is going to return more like .7 or .8 volts.
So, what you do is unplug the sensor, resulting in open loop, but near stoch. opperation, and then measure the voltage returned. Do this whole NOT engageing the WOT switch.
Also, you only need to adjust it at idle. Thats why it's called the idle mixture adjustment. If the idle is good, but your off at speed, that means something else is wrong.
09-14-2004, 02:44 AM
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Hmmmm. The reason I was going for WOT was at the suggestion of the A/F meter manufacturer. They claimed at WOT the mixture should be slightly on the rich side - around 14.2:1.
If the end goal of the WOT is 12:1 then I am right on the money there. As for the adjusting at idle, Garth had suggested this method in a previous post. Damn. I was having a lot of fun with the WOT method!
I didn't realize that the L-Jetronic had a limp-home mode, I assumed that was reserved for the fancier (digital) models. I guess I need to head back into the bosch books again.
If the end goal of the WOT is 12:1 then I am right on the money there. As for the adjusting at idle, Garth had suggested this method in a previous post. Damn. I was having a lot of fun with the WOT method!
I didn't realize that the L-Jetronic had a limp-home mode, I assumed that was reserved for the fancier (digital) models. I guess I need to head back into the bosch books again.
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09-14-2004, 07:10 AM
#8
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Ahhhh crap! - hate to spoil your WOT fun 
The ~12.5 would be correct with the right foot firmly planted; however, I'm surprised that with a large number of turns in the direction to lean the mixture (CCW) that the car does not 'surge' heavily: it's quite easy to lean the mixture to the point where the car will not start. Enrichen past that point, and at steady speed, the engine will 'hunt'/ surge, etc. Then, as Normy says, things happen quickly with small adjustments as you get to "stoichiometric".
Look at the shape of the lambda curve vs O2 sensor output - it is nearly vertical in the 0.3-0.7v range.
Some of the AFMs were reputed to have a spring loaded adjustment screw - I do not know if that is factual; however, I do know that it is tricky to get the tool correctly engaged in the impossible to see screw - perhaps that is a problem ( that could be corrected in version II of your tool design with a micro light at the tip).
L-jetronic is unlikely to have the sophistication of a 'limp' program: it does have the predetermined 'open loop' settings
The ~12.5 would be correct with the right foot firmly planted; however, I'm surprised that with a large number of turns in the direction to lean the mixture (CCW) that the car does not 'surge' heavily: it's quite easy to lean the mixture to the point where the car will not start. Enrichen past that point, and at steady speed, the engine will 'hunt'/ surge, etc. Then, as Normy says, things happen quickly with small adjustments as you get to "stoichiometric".
Look at the shape of the lambda curve vs O2 sensor output - it is nearly vertical in the 0.3-0.7v range.
Some of the AFMs were reputed to have a spring loaded adjustment screw - I do not know if that is factual; however, I do know that it is tricky to get the tool correctly engaged in the impossible to see screw - perhaps that is a problem ( that could be corrected in version II of your tool design with a micro light at the tip).
L-jetronic is unlikely to have the sophistication of a 'limp' program: it does have the predetermined 'open loop' settings
09-14-2004, 11:22 AM
#9
Nordschleife Master
When I mean limp hom mode, I mean a way to keep running even when the O2 sensor is shot. And the reason I'd callit limp home, is that it would let you get home, but will not help your cat or emissions.
This is not the same as the limp home that the later cars have when the MAF goes out.
This is not the same as the limp home that the later cars have when the MAF goes out.
09-14-2004, 02:04 PM
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I do know the screw is turning as I can see it with special accessory #7994 - the 500,000 candlepower spotlight :-)
I have been looking at the curve, and I am likely still on the shoulder. I may just break down and buy the Gunson Gastester which is on ebay for $164. It seems like a good excuse to buy a fun tool.
I have been looking at the curve, and I am likely still on the shoulder. I may just break down and buy the Gunson Gastester which is on ebay for $164. It seems like a good excuse to buy a fun tool.
