motronic questions
10-23-2006, 01:41 PM
#1
Burning Brakes
Thread Starter
motronic questions
what does the DME do when the O2 sensor is disconnected.....is there a separate map for this mode?
how can the part throttle fuel be altered (mapped) as long as the O2 sensor is working.....seems like the feedback will always limit the fuel to a 14:1 AFR?
you can see what i'm getting at....i'm thinking my car would run better (part throttle) a little richer but the feedback will always prevent this
how can the part throttle fuel be altered (mapped) as long as the O2 sensor is working.....seems like the feedback will always limit the fuel to a 14:1 AFR?
you can see what i'm getting at....i'm thinking my car would run better (part throttle) a little richer but the feedback will always prevent this
10-23-2006, 10:36 PM
#2
Three Wheelin'
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Dougn,
14.7:1 is a pretty rich mixture for part load.
You could recode the DME for non lamda operation so you could set the fuelling any where you like.Dont forget to remove the cat !
I would suspect re mapping ignition timing would bring more benifit .
Does this motor have uprated cams ?
All the best
Geoff
14.7:1 is a pretty rich mixture for part load.
You could recode the DME for non lamda operation so you could set the fuelling any where you like.Dont forget to remove the cat !
I would suspect re mapping ignition timing would bring more benifit .
Does this motor have uprated cams ?
All the best
Geoff
10-24-2006, 05:54 AM
#3
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Sorry for butting in (don't mean to hijack), but my car is an option 150 car with no O2 sensor nor cat. My understanding is that a jumper plug on the DME can be set to ignore the O2 sensor, which is probably what dougn is looking for. If I am not mistaken, this procedure is described in Adrian's book, or a search on the forum will turn up something.
10-24-2006, 11:13 AM
#4
Three Wheelin'
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Thats what I meant by recoding the DME . With coding links you can set the DME for cat/non cat , manual/auto transmission.
The 964 was designed as a cat/unleaded gas motor so the leaded-non cat option was for countries where unleaded gas is not available.
A few goes at setting idle fuel on the AFM will demonstrate that Porsche were not too interested in that mode of operation !
All the best
Geoff
The 964 was designed as a cat/unleaded gas motor so the leaded-non cat option was for countries where unleaded gas is not available.
A few goes at setting idle fuel on the AFM will demonstrate that Porsche were not too interested in that mode of operation !
All the best
Geoff
10-24-2006, 11:22 AM
#5
Burning Brakes
Thread Starter
"A few goes at setting idle fuel on the AFM will demonstrate that Porsche were not too interested in that mode of operation !"
what happens?
what happens?
10-24-2006, 01:01 PM
#6
Burning Brakes
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Geoff,
Are you saying the system doesnt keep the co setting very well without the ox sensor or that the screw itself adjusts the system too crudely or sensitively?
Would you mind elaborating?
Are you saying the system doesnt keep the co setting very well without the ox sensor or that the screw itself adjusts the system too crudely or sensitively?
Would you mind elaborating?
10-24-2006, 02:31 PM
#7
Three Wheelin'
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OK,
Because the system is running " open-loop" the fuelling setting will wander to a degree .The big turn off is that access to the flap adjuster is a PIA !!Maybe you disagree are are happy to get in there ?
I guess what I was getting at is that if running with lamda/ closed loop gives a good fuelling level with no adjustments ever required why bother with open loop unless the lack of suitable unleaded gas forces you down that route .
If it helps labda=1 is a good fuel target for carb motors at part load !!
All the best
Geoff
Because the system is running " open-loop" the fuelling setting will wander to a degree .The big turn off is that access to the flap adjuster is a PIA !!Maybe you disagree are are happy to get in there ?
I guess what I was getting at is that if running with lamda/ closed loop gives a good fuelling level with no adjustments ever required why bother with open loop unless the lack of suitable unleaded gas forces you down that route .
If it helps labda=1 is a good fuel target for carb motors at part load !!
All the best
Geoff
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10-24-2006, 03:19 PM
#8
Burning Brakes
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Hey Geoff,
Funnily I hadn't even thought about that part of it. You are absolutely correct though. Its a huge p.i.a.
I played with mine a bit to see if it changed the running issue I have so I played with it over a period of time. On hot days you can burn yourself sticking your arm up in there to turn an allen.
Funnily I hadn't even thought about that part of it. You are absolutely correct though. Its a huge p.i.a.
I played with mine a bit to see if it changed the running issue I have so I played with it over a period of time. On hot days you can burn yourself sticking your arm up in there to turn an allen.
10-24-2006, 05:29 PM
#9
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Originally Posted by Red rooster
Because the system is running " open-loop" the fuelling setting will wander to a degree ... why bother with open loop unless the lack of suitable unleaded gas forces you down that route.
Mine's an M150 car, running on premium 97 RON unleaded, which is the best I can get in NZ.
10-24-2006, 08:21 PM
#10
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adwriter,
New Zealand- beautiful country . Been once , never forgotten !
Dont take this too seriously. The 964 systems were basically designed for cat operation in its largest markets, Germany, USA, UK.
An operating lamda probe holds the part load /idle fuelling more closely than the M150 option. Having said that your 964 should have no real fuelling stability issues so you shouldnt loose any sleep over this !!
Its just the PIA factor in AFM adjustment that made me query converting from lamda to open loop operation.
97 RON is very good stuff for a 964 . Bit of DME tweaking on the horizon ??
All the best
Geoff
New Zealand- beautiful country . Been once , never forgotten !
Dont take this too seriously. The 964 systems were basically designed for cat operation in its largest markets, Germany, USA, UK.
An operating lamda probe holds the part load /idle fuelling more closely than the M150 option. Having said that your 964 should have no real fuelling stability issues so you shouldnt loose any sleep over this !!
Its just the PIA factor in AFM adjustment that made me query converting from lamda to open loop operation.
97 RON is very good stuff for a 964 . Bit of DME tweaking on the horizon ??
All the best
Geoff
10-24-2006, 08:40 PM
#11
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Hi Geoff
I'm glad you liked NZ. It's a great place to drive a 911, for sure!
Yes, have been thinking about tweaking the DME. But there seem to be so many conflicting opinions about what can and can't be done. And as far as I can make out, it means fitting a new chip that can be remapped, and is best done on a dyno that can take 4wd vehicles. Over here, that is easier said than done.
Best,
Chris
I'm glad you liked NZ. It's a great place to drive a 911, for sure!
Yes, have been thinking about tweaking the DME. But there seem to be so many conflicting opinions about what can and can't be done. And as far as I can make out, it means fitting a new chip that can be remapped, and is best done on a dyno that can take 4wd vehicles. Over here, that is easier said than done.
Best,
Chris
10-25-2006, 01:05 PM
#13
"what does the DME do when the O2 sensor is disconnected.....is there a separate map for this mode?"
Some much mis-information!
There isn't a separate map for when the O2 sensor is disconnected. The DME basically goes to
a neutral injector pulse width based on the internal 500mv O2 reference point. When the O2 sensor
is connected the O2 input will change causing the fuel map to be offset to correct the pulse
width thus correcting the mixture to where the O2 sensor "sees" an AFR = 14.7.
Bottom line: The DME doesn't know whether the O2 sensor is connected or not, e.g. it could
be stuck at 500mv and be connected, it only "looks" for a change at the O2 input.
"When mapping the ECU you can set a DEBUG code and the ECU will ignore the O2 sensor"
True, the O2 sensor DME code can be "patched" such that the O2 is ignored in which case
no map OFFSET occurs, but NOT another map is used. If there were different maps,
it would require an INFINITE number of maps (REAL BIG EPROM) as the O2 sensor
voltage has basically an infinite (analog) number of values.
"how can the part throttle fuel be altered (mapped) as long as the O2 sensor is working.....seems like the feedback will always limit the fuel to a 14:1 AFR?"
You're absolutely correct! That's why performance chips that modify the fuel maps
have NO effect other than at WOT, i.e. the O2 feedback is ALWAYS correcting the mixture
back to an AFR = 14.7.
Some much mis-information!
There isn't a separate map for when the O2 sensor is disconnected. The DME basically goes to
a neutral injector pulse width based on the internal 500mv O2 reference point. When the O2 sensor
is connected the O2 input will change causing the fuel map to be offset to correct the pulse
width thus correcting the mixture to where the O2 sensor "sees" an AFR = 14.7.
Bottom line: The DME doesn't know whether the O2 sensor is connected or not, e.g. it could
be stuck at 500mv and be connected, it only "looks" for a change at the O2 input.
"When mapping the ECU you can set a DEBUG code and the ECU will ignore the O2 sensor"
True, the O2 sensor DME code can be "patched" such that the O2 is ignored in which case
no map OFFSET occurs, but NOT another map is used. If there were different maps,
it would require an INFINITE number of maps (REAL BIG EPROM) as the O2 sensor
voltage has basically an infinite (analog) number of values.
"how can the part throttle fuel be altered (mapped) as long as the O2 sensor is working.....seems like the feedback will always limit the fuel to a 14:1 AFR?"
You're absolutely correct! That's why performance chips that modify the fuel maps
have NO effect other than at WOT, i.e. the O2 feedback is ALWAYS correcting the mixture
back to an AFR = 14.7.
Last edited by Lorenfb; 10-25-2006 at 01:25 PM.
10-25-2006, 05:19 PM
#14
Burning Brakes
Thread Starter
so i wonder typically how much the O2 sensor input can effect the AFR......+/- 1 or 2 or......
10-25-2006, 05:39 PM
#15
Nordschleife Master
The O2 feedback only works within a small range, about 14.3 - 15.0:1 and is designed to keep the engine operating at 14.7:1. It works as a short term and long term trim value that are added or subtracted from the base fuel table which in the case of the 964 is a 3d table where AFM voltage and ROM are the axis as well as the idle map which is a 2d map.
If you have a situation where the base fuel table is controlling the engine to 13.0:1, the O2 sensor is not going to be able to correct the base fuel pulsewidth to obtain a 14.7:1 AFR. There are limits to the amount of fuel it can add or subtract to the base pulsewidth.
A narrowband sensor does something called protobation which keeps the AFR about 14.7:1 but not quite. This alteration between rich and lean about the 14.7:1 target is called protobation and is what keeps the catalytic convert performing correctly.
If you have a situation where the base fuel table is controlling the engine to 13.0:1, the O2 sensor is not going to be able to correct the base fuel pulsewidth to obtain a 14.7:1 AFR. There are limits to the amount of fuel it can add or subtract to the base pulsewidth.
A narrowband sensor does something called protobation which keeps the AFR about 14.7:1 but not quite. This alteration between rich and lean about the 14.7:1 target is called protobation and is what keeps the catalytic convert performing correctly.