Am I in open or closed loop?
Thread Starter
Drifting
Joined: Jul 2001
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From: Largo Florida
Am I in open or closed loop?
I have been t-shooting a problem for 2 months now and am making progress I think. My bad idle and cutout problem is nearly gone when I disconnect the engine coolant sensor from the front of the water pump. Am I running in open loop all the time and therefore the O2s are not being used? Autotap shows -40 F when I am testing it this way and of course the fuel trims are at -100%.
Just trying to figure out the next step.
Just trying to figure out the next step.
Le Mans Master
Joined: Jun 2002
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From: High Plains Drifter Fayetteville, AR
Re: Am I in open or closed loop? (ericcer)
65ZO1 has a procedure where you jump the diagnostic terminal like you are going to pull codes. Then you watch the SES light, if I remember correctly, a 1Hz (one flash/second) flash is closed loop. I can't remember wether open is slower or faster, contact 65, and he'll be able to tell you
Edit: DOH! not paying attention, this is for an OBDI car, not an OBDII car such as yours. Sorry :(
[Modified by JCAIRE2, 8:05 PM 12/8/2002]
Edit: DOH! not paying attention, this is for an OBDI car, not an OBDII car such as yours. Sorry :(
[Modified by JCAIRE2, 8:05 PM 12/8/2002]
Race Director
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Re: Am I in open or closed loop? (ericcer)
Diacom shows it very plainly weather you are in closed loop or open loop. I would think autotap should show you the same. If it doesn't then I would look up a way to make it display that, or find some other software.
DOH! I should have said Datamaster! It shows it very clearly and that's what I use. I'm pretty sure Diacom does also though. Of course neither of these is OBDII, but you would think it wouldn't be hard to make it say open or closed loop somewhere
[Modified by Nathan Plemons, 8:46 PM 12/8/2002]
DOH! I should have said Datamaster! It shows it very clearly and that's what I use. I'm pretty sure Diacom does also though. Of course neither of these is OBDII, but you would think it wouldn't be hard to make it say open or closed loop somewhere
[Modified by Nathan Plemons, 8:46 PM 12/8/2002]
Burning Brakes
Joined: Oct 2002
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From: Wichita KS
Re: Am I in open or closed loop? (Nathan Plemons)
I had to dig out the factory service manual for my 95' on this one. I have OBD-1 but your OBD-2 should be the same for this circut.
The PCM applies a 5 Volt reference signal to the coolant sensor, when the sensor is cold it receives/reads most all of the 5 volts back, when the engine hot or is at 203 Deg F, it should only receive/read 1.5-2.0 volts back to the PCM from the sensor.
If I interpret page 6E3-A-49 step #2 of the testing procedure correctly, when you remove the coolant temp sensor connector the Tech-1 (equivalent for the most part to autotap/diacom) will display -22 Deg F. The service manual does not specifically say you will be in open or closed loop, but IMHO if the PCM is looking at -22 Deg F you would most definitely be in open loop.
:seeya
The PCM applies a 5 Volt reference signal to the coolant sensor, when the sensor is cold it receives/reads most all of the 5 volts back, when the engine hot or is at 203 Deg F, it should only receive/read 1.5-2.0 volts back to the PCM from the sensor.
If I interpret page 6E3-A-49 step #2 of the testing procedure correctly, when you remove the coolant temp sensor connector the Tech-1 (equivalent for the most part to autotap/diacom) will display -22 Deg F. The service manual does not specifically say you will be in open or closed loop, but IMHO if the PCM is looking at -22 Deg F you would most definitely be in open loop.
:seeya
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Re: Am I in open or closed loop? (superlund)
Let me see if I'm getting what you're saying here.
It's basically a variable resistor which changes the voltage based on temperature. Ok, I'm cool with that. Am I understanding you correctly to say that the voltage gets lower when the temperature goes up and the voltage goes up as the temps go down. As such with full 5 volts it should read very low temp, and the closer you get to 0 the higher the temp would be right?
If this is the case then how can it read low temp if you unplug the sensor? That would mean that there would be 0 voltage because it is an incomplete circuit, shouldn't this make it read really hot? Obviously it doesn't, I'm just trying to understand how that works.
Somebody please explain it to me :crazy:
It's basically a variable resistor which changes the voltage based on temperature. Ok, I'm cool with that. Am I understanding you correctly to say that the voltage gets lower when the temperature goes up and the voltage goes up as the temps go down. As such with full 5 volts it should read very low temp, and the closer you get to 0 the higher the temp would be right?
If this is the case then how can it read low temp if you unplug the sensor? That would mean that there would be 0 voltage because it is an incomplete circuit, shouldn't this make it read really hot? Obviously it doesn't, I'm just trying to understand how that works.
Somebody please explain it to me :crazy:
Burning Brakes
Joined: Oct 2002
Posts: 1,152
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From: Wichita KS
Re: Am I in open or closed loop? (Nathan Plemons)
Kinda tough for me as electronics’ never were my strongest point in school, but here goes.
Yes it is a variable resistor circut, essentially a (2) wire circuit.
(1) wire into the sensor/resistor is the 5v reference signal from the PCM.
(1) wire comes out of the sensor/resistor and routes to ground.
When the PCM applies the 5v signal to the cold sensor/resistor the resistance is "high" within the sensor/resistor, thus very little of the 5v flows thru the sensor/resistor & the PCM senses most all of the original 5v it applied.
When the PCM applies the 5v reference signal to a hot sensor/resistor the resistance is "low" within the sensor/resistor, thus most of the 5v signal applied flows thru the sensor & directly to ground.
So to sum up the above when you actually unplug the connector the 5v reference signal is never flowing thru the sensor/resistor and the PCM still senses the full 5v setting there, which the PCM interprets as a” cold" engine condition, you see if you never route any of that 5v signal thru that resistor to ground you still have 5v.
:)
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Re: Am I in open or closed loop? (superlund)
Ok that makes sense, effectively it routes the current elsewhere. I was picturing a 2 wire system, essentially making a circuit with the variable resistor in the middle.
You essentially describe a system in which the resistor is connected between the two wires, in fact it would be safe to say that the two wires just make a loop inside the sensor and are directly connected, the resistor is just tapped into it and connects from the one wire to ground, in a T shaped fashion, the horizontal being the 5v reference and the vertical connecting to ground. At full resistance, IE cold all of the current flows across the horizontal section and thus the PCM sees all 5 volts and sees this as cold. As the resistance goes down more power goes straight to ground and essentially less of it gets back to the PCM.
Makes sense but I'm still a little fuzzy on where everything is connected. If one of the wires is the 5v output and the other is the 5v return, it should still read hot if you unplug it because it would see 0 voltage on this. Unless, of course there is a crossover somewhere else......
Hmm, I just thought of how that could work but it would be far easier to draw then to explain. Oh well, I see how it works now :cheers:
You essentially describe a system in which the resistor is connected between the two wires, in fact it would be safe to say that the two wires just make a loop inside the sensor and are directly connected, the resistor is just tapped into it and connects from the one wire to ground, in a T shaped fashion, the horizontal being the 5v reference and the vertical connecting to ground. At full resistance, IE cold all of the current flows across the horizontal section and thus the PCM sees all 5 volts and sees this as cold. As the resistance goes down more power goes straight to ground and essentially less of it gets back to the PCM.
Makes sense but I'm still a little fuzzy on where everything is connected. If one of the wires is the 5v output and the other is the 5v return, it should still read hot if you unplug it because it would see 0 voltage on this. Unless, of course there is a crossover somewhere else......
Hmm, I just thought of how that could work but it would be far easier to draw then to explain. Oh well, I see how it works now :cheers:
Burning Brakes
Joined: Oct 2002
Posts: 1,152
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From: Wichita KS
Re: Am I in open or closed loop? (Nathan Plemons)
I believe you are possibly looking at it as a "loop" where as the power actually goes out loops thru & comes back (5v return) there really is no return, PCM applies 5v & that 5v is reduced by the resistor.
Think of it as a water pipe with a valve at the house that has 5 PSI of water pressure, by closing the valve (high resistance sensor) none of the water at 5 PSI gets thru (stays at PCM or house)
When you open the valve on the house (low resistance sensor) the water begins to flow thru the valve thus reducing the 5 PSI at the source. (PCM).
When you completely unhook the water hose (Elec connector) lets assume for this discussion the valve on the house is closed. The water just sets there at 5 PSI.(PCM still senses this 5v)
Best analogy I could muster at this hour, and yes it’s much easier to draw.
Off to another great day of work :rolleyes:
Think of it as a water pipe with a valve at the house that has 5 PSI of water pressure, by closing the valve (high resistance sensor) none of the water at 5 PSI gets thru (stays at PCM or house)
When you open the valve on the house (low resistance sensor) the water begins to flow thru the valve thus reducing the 5 PSI at the source. (PCM).
When you completely unhook the water hose (Elec connector) lets assume for this discussion the valve on the house is closed. The water just sets there at 5 PSI.(PCM still senses this 5v)
Best analogy I could muster at this hour, and yes it’s much easier to draw.
Off to another great day of work :rolleyes:
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Race Director
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From: Texas
Re: Am I in open or closed loop? (ericcer)
There should be a datastream entitled "Fuel System Status" for Bank 1 and Bank 2 (Drivers side and Passanger Side) These will capture if you're in Open or Closed Loop.
Short answer...if the fuel trims are at -100%, yes, that typically indicates you're in Open Loop.
What value does the sensor show when it's connected? Watching on Autotap, you should be able to watch the coolant temp increase since that's sensor that the PCM uses (the one in the cylinder head is for the analog gauge)
If you want to e-mail me your file, I can take a quick look at it. Send to Jim.Mason@Boeing.com. I'm certainly not an expert, but sometimes a second set of eyeballs can help.
[edit] On a '96, you can't jumper the pins in the ALDL for system status or codes like previous years. The Factory Service Manual says you can via the CCM diagnostic, but it's in error....OBDII codes (i.e. P0500) are too long to be displayed via the speedometer. [edit]
[Modified by 96GS#007, 7:31 AM 12/9/2002]
Short answer...if the fuel trims are at -100%, yes, that typically indicates you're in Open Loop.
What value does the sensor show when it's connected? Watching on Autotap, you should be able to watch the coolant temp increase since that's sensor that the PCM uses (the one in the cylinder head is for the analog gauge)
If you want to e-mail me your file, I can take a quick look at it. Send to Jim.Mason@Boeing.com. I'm certainly not an expert, but sometimes a second set of eyeballs can help.
[edit] On a '96, you can't jumper the pins in the ALDL for system status or codes like previous years. The Factory Service Manual says you can via the CCM diagnostic, but it's in error....OBDII codes (i.e. P0500) are too long to be displayed via the speedometer. [edit]
[Modified by 96GS#007, 7:31 AM 12/9/2002]
Team Owner
Joined: Aug 2000
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From: San Pedro CA
Re: Am I in open or closed loop?
So, if I am understanding how this works, during open loop, the temp sender is cold, hence, it is receiving 5 volts, but sending nothing back, right?
the 5 volts is being lost in the vapour somewhere.
As it warms, the resister is able to return some of the voltage back, until it reaches the threashold that will switch the engine over to closed loop. Am I close?
the 5 volts is being lost in the vapour somewhere.
As it warms, the resister is able to return some of the voltage back, until it reaches the threashold that will switch the engine over to closed loop. Am I close?
Burning Brakes
Joined: Feb 2000
Posts: 824
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From: Camden SC
Re: Am I in open or closed loop? (bogus)
Our good friend Ben Watson, "How to Tune and Modify Chevrolet Fuel Injection", pages 22 and 24 offers an excellent discussion of variable resistance to pull low circuits. This, along with the other 10 circuit types found on Corvettes will clarify about 90% of electrical issues. $16.95 from Barnes and Noble. You will love this book. Put it on your Christmas list.
And yes, you are close. Other factors for closed loop include time and O2 sensor reaching operating temperature. Some variances between model years are probable.
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And yes, you are close. Other factors for closed loop include time and O2 sensor reaching operating temperature. Some variances between model years are probable.
dlmeyers 90 coupe zf6 3 speed shocks
dlmeyers 90 coupe zf6 3 speed shocks
Race Director
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From: Texas
Re: Am I in open or closed loop? (bogus)
So, if I am understanding how this works, during open loop, the temp sender is cold, hence, it is receiving 5 volts, but sending nothing back, right?
the 5 volts is being lost in the vapour somewhere.
As it warms, the resister is able to return some of the voltage back, until it reaches the threashold that will switch the engine over to closed loop. Am I close?
the 5 volts is being lost in the vapour somewhere.
As it warms, the resister is able to return some of the voltage back, until it reaches the threashold that will switch the engine over to closed loop. Am I close?
The PCM sends a 5v reference signal to the Coolant Temp Sensor. The coolant temp sensor resistance varies as a function of coolant temperature. As the coolant temp increases or decreases, the resistance varies which in turn varies the return voltage to the PCM. The voltage received corresponds to a coolant temperature in the PCM look-up tables.
Think of it as a racetrack...PCM sends out a 5v reference signal to the sensor on wire "x". Reference signal is "changed" due to the sensor resistance. Signal voltage returns to the PCM via wire "y". Return signal corresponds to a known coolant temp.
Also note the the resistance vs temp relationship is not linear.
Coolant temp impacts AFR during start-up and open loop. In addition, the PCM has a table to modify WOT fueling based on coolant temp (PEvsCOOL table in LT1 Edit). Coolant Temp also plays into several other tuning aspects..i.e. When the PCM enters Closed Loop, Limp Home operations, etc.
Burning Brakes
Joined: Oct 2002
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From: Wichita KS
Re: Am I in open or closed loop? (bogus)
Bogus, try to remember the voltage never "leaves" the PCM, so it can't be lost. If you loose that 5v signal the PCM is bad. The PCM simply tries to maintain a 5v reference signal on the wire to the resistor. The PCM actually takes its measurement of voltage on the same line it sends the 5v “out” on.
As the resistance in the sensor changes with temp the 5v goes up & down, try not to think of it as a loop, where as it "leaves" & comes "back" try to think of it as 5v going straight down one wire thru a resistor to ground, when the engine is cold the 5v can't get thru the high resistance in the temp sensor so it never gets bled-off to ground thus 5v still sits at the PCM, as the temp goes up less resistance in the sensor allows more of that 5v signal to ground thus the PCM senses less voltage on that same line it sends the 5v “out” on, or 1.5-2.0 v at 203 Deg. If you remove the wire from the sensor completely the PCM is still applying & sensing 5v as you have only taken away the resistor & the path to ground from the circuit. In short it is called a reference signal for this very reason 5v is the reference it (PCM) tries to maintain on the line "out" variances (thru the resistor to ground) in this signal tell the PCM what the actual sensor temp is.
:)
As the resistance in the sensor changes with temp the 5v goes up & down, try not to think of it as a loop, where as it "leaves" & comes "back" try to think of it as 5v going straight down one wire thru a resistor to ground, when the engine is cold the 5v can't get thru the high resistance in the temp sensor so it never gets bled-off to ground thus 5v still sits at the PCM, as the temp goes up less resistance in the sensor allows more of that 5v signal to ground thus the PCM senses less voltage on that same line it sends the 5v “out” on, or 1.5-2.0 v at 203 Deg. If you remove the wire from the sensor completely the PCM is still applying & sensing 5v as you have only taken away the resistor & the path to ground from the circuit. In short it is called a reference signal for this very reason 5v is the reference it (PCM) tries to maintain on the line "out" variances (thru the resistor to ground) in this signal tell the PCM what the actual sensor temp is.
:)
