L-jetronic.
02-11-2003, 11:53 PM
#1
Nordschleife Master
Thread Starter
L-jetronic.
I've been more and more impressed with the L-jetronic system. In my mind, it's growing to be wounderfuly designed. It addaps the mixture richer for higher throtal settings, for more power, and leaner at lower throtal settings for efficancy. It doesn't care in the slightest about the engines volumetric efficany, like a MAP system. Only thing it doesn't seem to take into acount is the change in pressure of the air intake. It's pretty clear from the paper that the Air Flow Sensor measures the volume of air supplyed to the engine. It tells the ECU the tempeture of the incomeing air, but not the pressure.
I've been going over a paper given to me by one of the board members about the L-jetronic system. I've also been looking up stuff in the wireing diagram.
I do have a question. What does the idle sensor do? On my car, it is not "clicked" at idle. I didn't worry too much about it, because it didn't seem to do anything when I clicked it.
Anyone know an easy way to adjust it? It's way down under the intake runners on my car. Any easy way to adjust it?
btw, are the runners for 80-82 US 83-83 US and 80-86 EuroS and Euro the same?
Thanks
I've been going over a paper given to me by one of the board members about the L-jetronic system. I've also been looking up stuff in the wireing diagram.
I do have a question. What does the idle sensor do? On my car, it is not "clicked" at idle. I didn't worry too much about it, because it didn't seem to do anything when I clicked it.
Anyone know an easy way to adjust it? It's way down under the intake runners on my car. Any easy way to adjust it?
btw, are the runners for 80-82 US 83-83 US and 80-86 EuroS and Euro the same?
Thanks
02-12-2003, 12:20 AM
#2
The only bad things I've ever heard about the L-jet is when it comes to modified engines; the air flow meter is restrictive and are easily maxed out.
The runners for the Euro S models are larger dia.
as well as the throttle body.
The runners for the Euro S models are larger dia.
as well as the throttle body.
02-12-2003, 04:28 PM
#3
VU,
Are you talking about the closed thottle position switch? There are a pair of switches attached to the throttle body. One is closed throttle and the other is full throttle.
The closed throttle switch tells the ECU to change injector pulses to a small duty cycle or idle setting. Thus, if you rev the car and step off the throttle quickly, the RPMs will drop very fast. Without the switch, the RPMs will drop slower.
One final thing, having the closed throttle switch working gives you a stable environment for setting idle and mixture.
HTH,
Scott
Are you talking about the closed thottle position switch? There are a pair of switches attached to the throttle body. One is closed throttle and the other is full throttle.
The closed throttle switch tells the ECU to change injector pulses to a small duty cycle or idle setting. Thus, if you rev the car and step off the throttle quickly, the RPMs will drop very fast. Without the switch, the RPMs will drop slower.
One final thing, having the closed throttle switch working gives you a stable environment for setting idle and mixture.
HTH,
Scott
02-13-2003, 03:17 PM
#6
Rennlist Member
The AFM works great at adjusting to different mass flow rates. Much of the published information, is incorrect. infact, in Pobst book about injection, they catagorically said that the AFM system (Ljet) could not adapt to changes in increase performance additions like headers, cams , throttle bodies, etc, and the engine would go lean. WELL, I can say , straight up, that that is Wrong wrong wrong. Ive gone from 175 rear wheel to 293 rear wheel HP with out changing anything to the AFM. It had the same fuel air ratios at stock, as it did with all the mods. How did this work???? becuause the AFM CAN meter air flow. LIke I said before in the lengthy discussion with John, Ive checked air fuel ratios at altitude with the the only input being the AFM, and the car didnt run richer. I even further verfied this test, by removign the 15% enrichement micro switch signal and the system went exactly the same leaness as it did at sea level, where the air density was 27% less dense.
so, in summary, keep in mind that the AFM is a crude mass flow sensor. the more mass pushed into the engine by atomospheric pressure, the more the fap is deflected and the more fuel is matched. the volume of the engine never changes at a given RPM. (ie 6000 rpm is 5000cfm for a 4.7 liter) Now, whether this 500cfm is close to atomospheric (full throttle) or is under high vacuum (closed throttle) , that is the question. but , its aways 500cfm at 600rpm. The AFM will move to the increase of mass flow. think of the AFM like a pivoted wing. the more mass flow around it, the more it is moved.
As a side note , my AFM also adapteed perfectly to the 5 liter engine displacement, with absolutely no other changes to anything!! why did the engine run the exact same fuel curve as before???? the AFM is very very good at metering flow!!
Mk
so, in summary, keep in mind that the AFM is a crude mass flow sensor. the more mass pushed into the engine by atomospheric pressure, the more the fap is deflected and the more fuel is matched. the volume of the engine never changes at a given RPM. (ie 6000 rpm is 5000cfm for a 4.7 liter) Now, whether this 500cfm is close to atomospheric (full throttle) or is under high vacuum (closed throttle) , that is the question. but , its aways 500cfm at 600rpm. The AFM will move to the increase of mass flow. think of the AFM like a pivoted wing. the more mass flow around it, the more it is moved.
As a side note , my AFM also adapteed perfectly to the 5 liter engine displacement, with absolutely no other changes to anything!! why did the engine run the exact same fuel curve as before???? the AFM is very very good at metering flow!!
Mk
02-13-2003, 06:00 PM
#7
Rennlist Member
The posts were correct regarding the idle switch. It is fuel cut of at off throttle. However, I leave it disconnected for racing, as it gives less of a compression decel, which can kick the backend around under decel. I dont like the way the idle drops down too far first, before it hunts back up to normal idle speed. with the switch disconnected it just falls right to the proper speed.
The runners off the euro are much larger diameter.
the AFM doesnt control leaness for fuel economy, thats the closed loop 02 sensor and ECU function.
generally, the AFM under full throttle is great. very little variation in mixuture at all rpms.
Like I said earlier, with our 4.7 to 5 liter conversion, the mixture was near identical for almost all performance upgrades.
MK
The runners off the euro are much larger diameter.
the AFM doesnt control leaness for fuel economy, thats the closed loop 02 sensor and ECU function.
generally, the AFM under full throttle is great. very little variation in mixuture at all rpms.
Like I said earlier, with our 4.7 to 5 liter conversion, the mixture was near identical for almost all performance upgrades.
MK
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02-14-2003, 01:36 AM
#8
Nordschleife Master
Thread Starter
The paper I'm reading by Bosch always calls the L-jet barn door sensor a :Air Flow Sensor" It also calls the barn doors input into the computer, "Volume of air".
Also, my math seems to indicate that it deals with volume very well, but not pressure.
Something to rember, atmospheric pressure changes what 1" Hg under extream conditons? Currently, it's 29.7" Hg in Denver, while it's 30.05 in Houston. 30.06" Hg in New York, and 29.94 in San Francisco. If atmospheric pressure changed 1" HG, that would be a diffrnece of about 1/2 a pis. The diffrence in the actual mass of air injested would be about 3% at most. And thats assumeing that it changes 1" Hg. The odds if it changeing that much are pretty low.
The current largest diffrece between the citys I named above is about .36" Hg, or about .18 pisa. Thats a mear 1.2% diffrence. I'd say thats not very sigificant. Mean while tempeture can be very diffrent. Anywhere along a 50 degree range from -20 `C to 30` C. Thats sigificant. Thus no pressure sensor, but temp sensor on the L-jet system.
What is cool on the L-jet system, a V-8 is a V-8 is a V-8. Heck, I'm not even sure if the ECU cares if it's hooked up to a V-8, or inline 4. Talk about a flexable system!
Also, my math seems to indicate that it deals with volume very well, but not pressure.
Something to rember, atmospheric pressure changes what 1" Hg under extream conditons? Currently, it's 29.7" Hg in Denver, while it's 30.05 in Houston. 30.06" Hg in New York, and 29.94 in San Francisco. If atmospheric pressure changed 1" HG, that would be a diffrnece of about 1/2 a pis. The diffrence in the actual mass of air injested would be about 3% at most. And thats assumeing that it changes 1" Hg. The odds if it changeing that much are pretty low.
The current largest diffrece between the citys I named above is about .36" Hg, or about .18 pisa. Thats a mear 1.2% diffrence. I'd say thats not very sigificant. Mean while tempeture can be very diffrent. Anywhere along a 50 degree range from -20 `C to 30` C. Thats sigificant. Thus no pressure sensor, but temp sensor on the L-jet system.
What is cool on the L-jet system, a V-8 is a V-8 is a V-8. Heck, I'm not even sure if the ECU cares if it's hooked up to a V-8, or inline 4. Talk about a flexable system!
02-14-2003, 04:21 PM
#9
Rennlist Member
your getting yourself in deep with that information.
7000feet will be 27% less dense air moving through any car engine. (with exceptions for extreme changes in temp)
What math are you talking about.
the AFM works very very well as a mass flow sensor. as you said, v6, V8, etc, it adapts perfectly. like I mentioned, I increased HP by 100hp (thats more mass flow folks) and used the same Ljet system, without changing anything, and the fuel ratios stayed the same.
some of the books still use the "volume" term, but thats just semantics to differnciate from the true Mass flow device, the hot wire (MAF)
It regulates mass flow, check your math again!!
MK
7000feet will be 27% less dense air moving through any car engine. (with exceptions for extreme changes in temp)
What math are you talking about.
the AFM works very very well as a mass flow sensor. as you said, v6, V8, etc, it adapts perfectly. like I mentioned, I increased HP by 100hp (thats more mass flow folks) and used the same Ljet system, without changing anything, and the fuel ratios stayed the same.
some of the books still use the "volume" term, but thats just semantics to differnciate from the true Mass flow device, the hot wire (MAF)
It regulates mass flow, check your math again!!
MK
02-14-2003, 05:59 PM
#10
Rennlist Member
Here's a thought: If Viribus does math the way he spells . . . hoo boy. Sorry VU. You know we love your spelling. I've been wondering, what's a viribus unit? 
02-14-2003, 06:42 PM
#11
Nordschleife Master
Thread Starter
I'm not over my head, yet.
The K.u.K. Viribus Unitis was a very good looking, and powerful, battleship built for the Austrian-Hungaryian Empire, back before WWI. It was a so so design. Many good features, but some of the detail work sucked.
My math is MUCH better than my spelling. So much so that you wouldn't belive they were done by the same person. Thats why I'm trying to get an engineering major, NOT an english major!
I don't see how you get to that precentage. Atmospheric pressure doesn't change but maybe an inch Hg at most. Thats about .5 pis at most. Doesn't matter where you are. The air isn't very dense, so it doesn't varry much. The diffrence between say Denver, and the rest of the US is about .3" HG on most days. Thats about 0.15 pis. That works out to about a 1% diffrence. Do the math yourself.
Just to be sure, I'm going to run through the math on how the AFM reacts to density a few more times. I'm pretty sure, but not 100% sure of how it reacts when pressure is changed. About 98% sure.
Something to notice, unless your superchargeing, or turbochargeing the engine, and have the AFM after the turbo, density is NOT going to change. I don't care how much you increased the hp, as long as you don't change the pressure of the intake air, the density of it's not going to change. Thus unless density changes, volumetric flow is dirictly related to mass flow. It doesn't matter if the AFM measures mass, or volume, UNLESS you add positive intake pressure to it.
The K.u.K. Viribus Unitis was a very good looking, and powerful, battleship built for the Austrian-Hungaryian Empire, back before WWI. It was a so so design. Many good features, but some of the detail work sucked.
My math is MUCH better than my spelling. So much so that you wouldn't belive they were done by the same person. Thats why I'm trying to get an engineering major, NOT an english major!
I don't see how you get to that precentage. Atmospheric pressure doesn't change but maybe an inch Hg at most. Thats about .5 pis at most. Doesn't matter where you are. The air isn't very dense, so it doesn't varry much. The diffrence between say Denver, and the rest of the US is about .3" HG on most days. Thats about 0.15 pis. That works out to about a 1% diffrence. Do the math yourself.
Just to be sure, I'm going to run through the math on how the AFM reacts to density a few more times. I'm pretty sure, but not 100% sure of how it reacts when pressure is changed. About 98% sure.
Something to notice, unless your superchargeing, or turbochargeing the engine, and have the AFM after the turbo, density is NOT going to change. I don't care how much you increased the hp, as long as you don't change the pressure of the intake air, the density of it's not going to change. Thus unless density changes, volumetric flow is dirictly related to mass flow. It doesn't matter if the AFM measures mass, or volume, UNLESS you add positive intake pressure to it.
02-15-2003, 01:42 AM
#12
Inventor
Rennlist Member
Rennlist Member
Mark K. - thanks for the tip about disconnecting the idle switch. I disconnected mine and it made a nice difference in the feel of the car.
I hated that surge around 1800rpm after letting off the throttle (gone). Disconnecting also seems to have made an improvement in response to part-throttle acceleration after slowing.
I hated that surge around 1800rpm after letting off the throttle (gone). Disconnecting also seems to have made an improvement in response to part-throttle acceleration after slowing.
02-17-2003, 04:44 PM
#13
Rennlist Member
Viribus, where do I start?????
Ok, first, dont become a weather man or an engineer unless you start to understand about barometric pressure changes at altitudes.
(ie at 7000feet, you will see a 27% change in density or pressure. (the terms are synonomus)
standard atmospheric is 29.92 / 68degrees.)
running your car in Dever would be a 20% lower density. The AFM would be able to adjust to this changing mass flow. speed traveling over the afm plate is the same, less molecules ,less deflection, less fuel metered, the world is at peace.
volumetric flow is realted to engine size and RPM, not mass flow. the more you have reduced the pressure drops along the intake path, the more mass flow. the pressure on the outside of the AFM is still the same, but the density of the air going through it is different. just if you lifted your foot from 6000rpm. the CFM would still be 500cfm, but the density would be in high vacuum, thus not alwing many molecules of air (density, per unit volume, or mass flow) thru the AFM. it would be closed, and only the air traveling through the idle hole would allow the car to continue to run at idle.
The AFM reacts to mass flow in the following way:
PV/NRT.
MK
</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by ViribusUnits:
<strong>I'm not over my head, yet.
Thats why I'm trying to get an engineering major, NOT an english major!
I don't see how you get to that precentage. Atmospheric pressure doesn't change but maybe an inch Hg at most. Thats about .5 pis at most. Doesn't matter where you are. The air isn't very dense, so it doesn't varry much. The diffrence between say Denver, and the rest of the US is about .3" HG on most days. Thats about 0.15 pis. That works out to about a 1% diffrence. Do the math yourself.
Just to be sure, I'm going to run through the math on how the AFM reacts to density a few more times. I'm pretty sure, but not 100% sure of how it reacts when pressure is changed. About 98% sure.
Something to notice, unless your superchargeing, or turbochargeing the engine, and have the AFM after the turbo, density is NOT going to change. I don't care how much you increased the hp, as long as you don't change the pressure of the intake air, the density of it's not going to change. Thus unless density changes, volumetric flow is dirictly related to mass flow. It doesn't matter if the AFM measures mass, or volume, UNLESS you add positive intake pressure to it.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">
Ok, first, dont become a weather man or an engineer unless you start to understand about barometric pressure changes at altitudes.
(ie at 7000feet, you will see a 27% change in density or pressure. (the terms are synonomus)
standard atmospheric is 29.92 / 68degrees.)
running your car in Dever would be a 20% lower density. The AFM would be able to adjust to this changing mass flow. speed traveling over the afm plate is the same, less molecules ,less deflection, less fuel metered, the world is at peace.
volumetric flow is realted to engine size and RPM, not mass flow. the more you have reduced the pressure drops along the intake path, the more mass flow. the pressure on the outside of the AFM is still the same, but the density of the air going through it is different. just if you lifted your foot from 6000rpm. the CFM would still be 500cfm, but the density would be in high vacuum, thus not alwing many molecules of air (density, per unit volume, or mass flow) thru the AFM. it would be closed, and only the air traveling through the idle hole would allow the car to continue to run at idle.
The AFM reacts to mass flow in the following way:
PV/NRT.
MK
</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by ViribusUnits:
<strong>I'm not over my head, yet.
Thats why I'm trying to get an engineering major, NOT an english major!
I don't see how you get to that precentage. Atmospheric pressure doesn't change but maybe an inch Hg at most. Thats about .5 pis at most. Doesn't matter where you are. The air isn't very dense, so it doesn't varry much. The diffrence between say Denver, and the rest of the US is about .3" HG on most days. Thats about 0.15 pis. That works out to about a 1% diffrence. Do the math yourself.
Just to be sure, I'm going to run through the math on how the AFM reacts to density a few more times. I'm pretty sure, but not 100% sure of how it reacts when pressure is changed. About 98% sure.
Something to notice, unless your superchargeing, or turbochargeing the engine, and have the AFM after the turbo, density is NOT going to change. I don't care how much you increased the hp, as long as you don't change the pressure of the intake air, the density of it's not going to change. Thus unless density changes, volumetric flow is dirictly related to mass flow. It doesn't matter if the AFM measures mass, or volume, UNLESS you add positive intake pressure to it.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">
02-17-2003, 07:04 PM
#14
Nordschleife Master
Thread Starter
I understand that atmophereic pressure reduces with altitude.
btw, density and pressure are NOT the same thing. Density is related to both tempetrue AND pressure. Not just pressure.
The question is how much? Basicly how did you come to the 7,000 feet up equals 27% less air density.
From a short look on the internet, Denver is at about 29.93" Hg, while Houston is at about 30.14" Hg. A while back, Denver was at 29.7"Hg, while Houston was at about 30.06" Hg. I'm not seeing a 20% drop.
Assumeing that the ideal gas law is even close, 1 " Hg works out to no where near 27% of the density. Maybe 2.7% and the diffrence between Denver and Houston is about .4" Hg at most.
Denver is a little over 5,000 feet up, while Houston is basicly at sea level.
For a little extra info, go here:
<a href="http://www.conservatory.com/vw/manuals_nyx/L-Jetronic.html" target="_blank">http://www.conservatory.com/vw/manuals_nyx/L-Jetronic.html</a>
Your going to want page 24 and page 27. You'll probably have to enlarge the photo. Notice the optional altitude compensater. Why? An L-jet is a L-jet.
Finaly, if the AFM measures mass, why did Bosch chose to include a air intake temp sensor?
btw, density and pressure are NOT the same thing. Density is related to both tempetrue AND pressure. Not just pressure.
The question is how much? Basicly how did you come to the 7,000 feet up equals 27% less air density.
From a short look on the internet, Denver is at about 29.93" Hg, while Houston is at about 30.14" Hg. A while back, Denver was at 29.7"Hg, while Houston was at about 30.06" Hg. I'm not seeing a 20% drop.
Assumeing that the ideal gas law is even close, 1 " Hg works out to no where near 27% of the density. Maybe 2.7% and the diffrence between Denver and Houston is about .4" Hg at most.
Denver is a little over 5,000 feet up, while Houston is basicly at sea level.
For a little extra info, go here:
<a href="http://www.conservatory.com/vw/manuals_nyx/L-Jetronic.html" target="_blank">http://www.conservatory.com/vw/manuals_nyx/L-Jetronic.html</a>
Your going to want page 24 and page 27. You'll probably have to enlarge the photo. Notice the optional altitude compensater. Why? An L-jet is a L-jet.
Finaly, if the AFM measures mass, why did Bosch chose to include a air intake temp sensor?
02-17-2003, 07:46 PM
#15
Rennlist Member
Yes, youre right, but are getting confused on the details. pressure is not density, but for our discussion, it can be. they are related, as density is pressure with temp and humidity factored in.
Denver is 5000feet, and thats a 17% change in pressure and density. at 6000feet its about 20% and at 10,000feet its about 27%. I used this example in another discussion along with the answer for your question about temp sensor. it is there to further refine inputs for best effiency. From the bosch book, the temp sensor as well as barometric sensors in a MAF were there to refine the inputs to the ecu, even though at 7000feet the AFM was more than able to regulate changes in Mass air flow.
pull out any physics book or aero eng book an look under charts for stardard atmosphere. you will see what Im talking about. your presumption of a 1-2% change in density at 5000feet is wrong. its in the 17% range. this is a known value. better do some double checking of your work.
if you see the small changes on weather reports for denver vs other cities, they have more than likely been adjusted already for standard atmosphere . Meaning, that they are already adjusted 17% up or down.
you have made comments on what you think you know rather than what you do know. better to ask the question , than to make presumptions with the folks that know this stuff cold.
MK
Denver is 5000feet, and thats a 17% change in pressure and density. at 6000feet its about 20% and at 10,000feet its about 27%. I used this example in another discussion along with the answer for your question about temp sensor. it is there to further refine inputs for best effiency. From the bosch book, the temp sensor as well as barometric sensors in a MAF were there to refine the inputs to the ecu, even though at 7000feet the AFM was more than able to regulate changes in Mass air flow.
pull out any physics book or aero eng book an look under charts for stardard atmosphere. you will see what Im talking about. your presumption of a 1-2% change in density at 5000feet is wrong. its in the 17% range. this is a known value. better do some double checking of your work.
if you see the small changes on weather reports for denver vs other cities, they have more than likely been adjusted already for standard atmosphere . Meaning, that they are already adjusted 17% up or down.
you have made comments on what you think you know rather than what you do know. better to ask the question , than to make presumptions with the folks that know this stuff cold.
MK