what is open loop and closed loop
02-27-2009, 10:47 AM
#1
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Location: Maple Ridge
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what is open loop and closed loop
trying to get to the bottom of my motor issues without having to go the long way about it.
when a motor is running...
What is open loop?
What is closed loop?
are these only to do with fuel injection?
The motor I have was running fine in open loop when first started... as it warms up the motor goes into closed loop. If the closed loop does something to the injectors and creates ringwash could that be what caused all the smoke, misfires, hesitation etc...?
when a motor is running...
What is open loop?
What is closed loop?
are these only to do with fuel injection?
The motor I have was running fine in open loop when first started... as it warms up the motor goes into closed loop. If the closed loop does something to the injectors and creates ringwash could that be what caused all the smoke, misfires, hesitation etc...?
02-27-2009, 05:57 PM
#2
Open loop and Closed loop are YES fuel Injection only.
Open loop is when your car is cold as in the first fire of the day, or if the engine is not at it's full operating temp. It usually kicks over to closed loop when reaching 255 milliseconds.
So to break it down for you....
Operational Modes
The EEC operates in three distinct modes.
1) In closed loop mode the EEC uses the MAF sensor to determine the amount of air entering the engine to calculate a "guess" of how much fuel to inject. It uses facts about the engine (number of cylinders, injector size) to calculate the injector pulse width to deliver the right amount of fuel, and then at the appropriate instant when the cam position sensor says the engine is at the right point in the 4 stroke cycle, the EEC switches on +12V to the particular fuel injector and holds it there for just the right amount of time - the pulse width. Then it continuously uses the too-rich / too-lean signals from the O2 sensors to add a bit or subtract a bit of time to the injector PWs to achieve 14.64 A/F ratio. [14.64 A/F ratio is called stoichiometric mixture. It is the chemical mixture where gasoline burns with best emissions.
15.1 results in slightly better fuel economy, but creates more emissions. And you can't by an O2 sensor calibrated for 15.1 anyway.]
The EEC operates in closed loop mode almost all of the time.
2) In open loop mode the EEC completely ignores the O2 sensors and hopes to achieve some specific A/F ratio just by using the MAF sensor voltage, RPM, number of cylinders, and injector size to calculate fuel injector PW. I say hope because it is typical for your MAF transfer function and / or injector slope to be as much as 10% off. Without the O2 sensor feedback used in closed loop, open loop commanded A/F ratios are never very precise. Open loop mode is used whenever the EEC needs to achieve A/F other than 14.64.
Typically open loop is used at startup and at WOT when the engine needs an A/F ratio mixture richer than stoichiometric. Richer A/F is needed at engine startup, especially with a cold engine, just like a carbureted engine has a choke. Richer A/F is needed at WOT: Maximum HP at WOT typically occurs somewhere between 12 and 13. Also, this slightly richer mixture helps cool the combustion chamber and exhaust valves at the higher combustion temperatures of WOT.
3) Another mode the EEC may operate in is called limp mode. As the name implies, this mode is only invoked when the EEC thinks something is wrong. A typical reason for limp mode is failure of one or more sensors. Depending on what sensors failed, the EEC may refuse to operate or may operate in limp mode. [The Check Engine light always accompanies limp mode.] For example, if O2 sensors fail the EEC operates but cannot run in closed loop. The EEC can even run in limp mode with the MAF disconnected by using TPS and RPM to estimate PW - It just won't run very well.
Hope this helps you understand the three different operation modes.
Open loop is when your car is cold as in the first fire of the day, or if the engine is not at it's full operating temp. It usually kicks over to closed loop when reaching 255 milliseconds.
So to break it down for you....
Operational Modes
The EEC operates in three distinct modes.
1) In closed loop mode the EEC uses the MAF sensor to determine the amount of air entering the engine to calculate a "guess" of how much fuel to inject. It uses facts about the engine (number of cylinders, injector size) to calculate the injector pulse width to deliver the right amount of fuel, and then at the appropriate instant when the cam position sensor says the engine is at the right point in the 4 stroke cycle, the EEC switches on +12V to the particular fuel injector and holds it there for just the right amount of time - the pulse width. Then it continuously uses the too-rich / too-lean signals from the O2 sensors to add a bit or subtract a bit of time to the injector PWs to achieve 14.64 A/F ratio. [14.64 A/F ratio is called stoichiometric mixture. It is the chemical mixture where gasoline burns with best emissions.
15.1 results in slightly better fuel economy, but creates more emissions. And you can't by an O2 sensor calibrated for 15.1 anyway.]The EEC operates in closed loop mode almost all of the time.
2) In open loop mode the EEC completely ignores the O2 sensors and hopes to achieve some specific A/F ratio just by using the MAF sensor voltage, RPM, number of cylinders, and injector size to calculate fuel injector PW. I say hope because it is typical for your MAF transfer function and / or injector slope to be as much as 10% off. Without the O2 sensor feedback used in closed loop, open loop commanded A/F ratios are never very precise. Open loop mode is used whenever the EEC needs to achieve A/F other than 14.64.
Typically open loop is used at startup and at WOT when the engine needs an A/F ratio mixture richer than stoichiometric. Richer A/F is needed at engine startup, especially with a cold engine, just like a carbureted engine has a choke. Richer A/F is needed at WOT: Maximum HP at WOT typically occurs somewhere between 12 and 13. Also, this slightly richer mixture helps cool the combustion chamber and exhaust valves at the higher combustion temperatures of WOT.
3) Another mode the EEC may operate in is called limp mode. As the name implies, this mode is only invoked when the EEC thinks something is wrong. A typical reason for limp mode is failure of one or more sensors. Depending on what sensors failed, the EEC may refuse to operate or may operate in limp mode. [The Check Engine light always accompanies limp mode.] For example, if O2 sensors fail the EEC operates but cannot run in closed loop. The EEC can even run in limp mode with the MAF disconnected by using TPS and RPM to estimate PW - It just won't run very well.
Hope this helps you understand the three different operation modes.
02-27-2009, 10:07 PM
#3
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Join Date: Dec 2008
Location: Maple Ridge
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well thanks for that. The reason I'm asking is because of a motor I had some hack mechanic build.
The motor runs fine when first started. BLows no smoke and is just a dream... until it warms up. Then all hell breaks loose and she starts smokin like crazzy and coughs and sputters and hesitates until it hits around 3200 rpms at WOT and then it goes back to runnimg like a dream and screams to the point where I just dont want to keep my foot in it do to lack of experience with my 5oh and 340hp est.
I'm really hopin that throwing a carb unit on this motor will solve the issue.
The motor runs fine when first started. BLows no smoke and is just a dream... until it warms up. Then all hell breaks loose and she starts smokin like crazzy and coughs and sputters and hesitates until it hits around 3200 rpms at WOT and then it goes back to runnimg like a dream and screams to the point where I just dont want to keep my foot in it do to lack of experience with my 5oh and 340hp est.
I'm really hopin that throwing a carb unit on this motor will solve the issue.
02-28-2009, 04:29 AM
#5
Instead of giving up and putting a junk carb on it, lets try some trouble shooting.
There are many smart people on this forum that might be able to chime in and help.
First of all if the engine light on, and does the engine light even work...? When you first turn your key to the on position before starting does it come on?
This would be a great start
There are many smart people on this forum that might be able to chime in and help.
First of all if the engine light on, and does the engine light even work...? When you first turn your key to the on position before starting does it come on?
This would be a great start
02-28-2009, 10:21 AM
#6
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Join Date: Dec 2008
Location: Maple Ridge
Posts: 92
uh perhaps I should enlighten you as to where the motor is now.
on my engine stand... The mechanic dropped a stock motor in and gave me back mine complete.
and yes the check engine light comes on... randomly it comes on with this stock motor as well.
I have a spare car and was just going to drop a 750 carb on this beast and call it a day.
on my engine stand... The mechanic dropped a stock motor in and gave me back mine complete.
and yes the check engine light comes on... randomly it comes on with this stock motor as well.
I have a spare car and was just going to drop a 750 carb on this beast and call it a day.
03-02-2009, 01:45 AM
#7
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Join Date: Feb 2009
Location: sarnia
Posts: 47
The carb is not going to fix your issues if it smokes at higher rpm you might have a broken oil ring.Closed loop is when o2 sensor kick in if it is getting to much gas check pressure on fuel rail then check your injectors one mihgt be have a small piece of dirt causing a sticking ball floods out one cylinder smoke show.750 is way to big for 302 on street no throttle response 650 is big enough.Check firing order seen it happen runs good till you give it throttle ecu will keep it running at low rpm and sounds alright.
03-04-2009, 11:22 AM
#8
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Join Date: Sep 2008
Location: Newfoundland
Posts: 46
Don't throw that 750 on there. It will kill your cars performance. There was a 750 holley on my Mustang when I bought it. I guess the guy thought bigger was better. I put on a new holley 650 and the car is like night and day. All that said find someone with a scan tool and some knowledge before you give up on your EFI
03-04-2009, 11:43 AM
#9
Yep agreed, carb is old school!!!
750 is to big, I agree with a 650..but I don't agree with the Holley part I would put on a Edelbrock. Best bang for the buck and its bolt on and go no bs screwing with it.
Again don't give up on the EFI, you will regret it in the end.
Good luck man, and keep us updated.
750 is to big, I agree with a 650..but I don't agree with the Holley part I would put on a Edelbrock. Best bang for the buck and its bolt on and go no bs screwing with it.
Again don't give up on the EFI, you will regret it in the end.
Good luck man, and keep us updated.
