Pin 2I and erratic idle
10-03-11, 08:49 PM
#1
Pin 2I and erratic idle
Car is a 90 NA vert converted to a Lemons racer. Engine has street port, headers and 550 secondary injectors. Sometime during the last race the car had difficulty idling hot. At lower RPMS's no load the engine speed cycles. The wideband jumps from normal to infinity during the cycling. Otherwise it seems to pull ok under load but cycles at constant throttle under no load.
Here's what I've done so far -
1. Adjusted TPS to spec
2. Checked voltage at white/green wire (pin 2I ?) and had none. It does have continuity to ground.
3. Swapped ECU with spare, still no voltage at white/green wire
4. Removed water temp sensor from thermostat housing and checked it's resistance cold and warm. I had a used spare and both had similar resistance. I reinstalled the spare.
5. Made a jumper wire and plugged one end into the white/green wire in temp sensor connector. The other end I ran into the car and checked continuity between my jumper wire and the white/green wire at the ECU connector. I had continuity but there was a little resistance measured.
6. Used same jumper wire on the other temp sensor connector (brown/black?) and tested against any similar colored wire at the ECU connector. No continuity. Checked jumper wire against chassis ground and had continuity.
7. Tested BAC by disconnecting connector and applied 12v and ground. It gives a satisfying sounding thunk each time.
So, where do I go next? Cut/replace the white/green wire? I assume the ECU is supplying the voltage.
Thanks
Here's what I've done so far -
1. Adjusted TPS to spec
2. Checked voltage at white/green wire (pin 2I ?) and had none. It does have continuity to ground.
3. Swapped ECU with spare, still no voltage at white/green wire
4. Removed water temp sensor from thermostat housing and checked it's resistance cold and warm. I had a used spare and both had similar resistance. I reinstalled the spare.
5. Made a jumper wire and plugged one end into the white/green wire in temp sensor connector. The other end I ran into the car and checked continuity between my jumper wire and the white/green wire at the ECU connector. I had continuity but there was a little resistance measured.
6. Used same jumper wire on the other temp sensor connector (brown/black?) and tested against any similar colored wire at the ECU connector. No continuity. Checked jumper wire against chassis ground and had continuity.
7. Tested BAC by disconnecting connector and applied 12v and ground. It gives a satisfying sounding thunk each time.
So, where do I go next? Cut/replace the white/green wire? I assume the ECU is supplying the voltage.
Thanks
10-03-11, 10:08 PM
#2
The voltage on that pin is an input value so it is coming from the sensor itself and "not the ECU." The non G/W wire is a ground wire. Make sure the plug connected to the sensor does not have either of its two pins pulled back within the plug. This is likely the problem w/the inaccurate reading.
10-04-11, 10:12 PM
#5
Ok, new update. I disconnected the connector from the sensor and created a mini loom with a new connector. I wired it the same as the OEM connector with the wires in the same position. One wire I ground to the intake manifold. The other wire I ran to pin 2I in the ECU connector (i cut the existing white/green wire). Turned key on, no voltage and the resistance was the same as the sensor measured cold. Fired car up, no voltage and the resistance changed as the car warmed up. Car ran like crap, wouldn't idle and the wideband was pegged at 18. I shut the car off, removed my loom, plugged the OEM sensor connector back in and reconnected the wire at the ECU. Fired it up and it ran as before I messed with anything, the cycling bit.
I find it hard to believe that the sensor generates it's own electricity. It seems to me the either the ECU is supposed to supply the voltage or the other wire in the sensor connector (brown/black?) is supposed to be supplying the needed juice.
Thoughts?
I find it hard to believe that the sensor generates it's own electricity. It seems to me the either the ECU is supposed to supply the voltage or the other wire in the sensor connector (brown/black?) is supposed to be supplying the needed juice.
Thoughts?
10-04-11, 10:54 PM
#6
You need to give it a rest as the sensor creates the voltage. Does it make sense that a sensor is used to provide "input" for the ECU? Say yes. What would be the purpose of the ECU sending voltage to the thermosensor to tell it what the coolant temp is when it is the job of the sensor to do just that. Just look at the FSM wiring diagram to illustrate that the Black wire is the ground. And as far as the G/W wire is concerned the FSM shows that the connection at the ECU is an "INPUT" signal and not an output one. There is also a procedure listed in the FSM to see if the sensor is in spec.
The thumbnail is for an S4 but the S5 works the same way.
EDIT: You mentioned pin 2I in your first post, but pin 2E is the correct pin designation for an S5. So, if you've been messing with pin 2I you were dealing w/the wrong pin.
The thumbnail is for an S4 but the S5 works the same way.
EDIT: You mentioned pin 2I in your first post, but pin 2E is the correct pin designation for an S5. So, if you've been messing with pin 2I you were dealing w/the wrong pin.
10-05-11, 10:28 AM
#7
Give it a rest? Love to. Just as soon as I can get this working.
I agree that the ECU is accepting an input from the white/green wire and it's not outputting any voltage to that pin. I agree that pin 2E is the correct pin for an S5 and note that I've been checking the wire color, not the pin location. The pin 2I bit came from reading other posts in the forum. I don't agree that the sensor creates the voltage. That makes no sense.
If the sensor is generating the voltage, why is the part listed as a thermistor? By definition a thermistor is a resistor that changes it's resistance with temperature. http://en.wikipedia.org/wiki/Thermistor Resistors change voltage as it passes through. They generate heat, not voltage.
If the sensor is generating voltage, why does the test in the FSM (F1-83) involve testing the resistance? Why wouldn't the FSM test of the sensor alone be to test the voltage? Why do you need to have the key turned on or the engine running to test the voltage if this thing is generating juice? If the sensor is generating voltage, why can't i just stick in it my bathroom with it's willie in a glass of water and 2 wires running up to my Hello Kitty nitelight?
What does make sense to me is that since the FSM thermosensor test is to measure the resistance of the sensor and the resistance is reduced the hotter the temperator AND the voltage values at pin 2E of the ECU rise with temperature that voltage is being PASSED through the thermosensor. The simplest way to change voltage is to pass it through a resistor. This whole testing procedure only makes sense if you introduce voltage to the resistor and let it change the voltage with temperature changes. That said, to solve my problem I need to find out where the voltage is coming from.
There are a couple of things that may or may not be interesting or pertinent. One is that when I first measured the continuity/resistance of the white/green wire from the sensor back to the ECU connector that I got continuity but some resistance. The wiring diagram shows it to be a straight shot but why would there be resistance unless it was partially grounding or there is some other device on the wire? The other thing is the brown/black wire. From the wiring diagram I can see that it runs around to several of the other sensors on the engine but I can't really see where it terminates. There's a brown/black wire that terminates in the same ECU connector as the white/green wire. Any relation? And if this sensor was a stand alone unit generating power and I isolated it by making it's own wiring loom, why did the car run so bad and immediately run better when I hooked it back up to the OEM loom?
Or someone can convince me that this little $40 sensor really is a self contained nuclear power generating mothereffer.
I agree that the ECU is accepting an input from the white/green wire and it's not outputting any voltage to that pin. I agree that pin 2E is the correct pin for an S5 and note that I've been checking the wire color, not the pin location. The pin 2I bit came from reading other posts in the forum. I don't agree that the sensor creates the voltage. That makes no sense.
If the sensor is generating the voltage, why is the part listed as a thermistor? By definition a thermistor is a resistor that changes it's resistance with temperature. http://en.wikipedia.org/wiki/Thermistor Resistors change voltage as it passes through. They generate heat, not voltage.
If the sensor is generating voltage, why does the test in the FSM (F1-83) involve testing the resistance? Why wouldn't the FSM test of the sensor alone be to test the voltage? Why do you need to have the key turned on or the engine running to test the voltage if this thing is generating juice? If the sensor is generating voltage, why can't i just stick in it my bathroom with it's willie in a glass of water and 2 wires running up to my Hello Kitty nitelight?
What does make sense to me is that since the FSM thermosensor test is to measure the resistance of the sensor and the resistance is reduced the hotter the temperator AND the voltage values at pin 2E of the ECU rise with temperature that voltage is being PASSED through the thermosensor. The simplest way to change voltage is to pass it through a resistor. This whole testing procedure only makes sense if you introduce voltage to the resistor and let it change the voltage with temperature changes. That said, to solve my problem I need to find out where the voltage is coming from.
There are a couple of things that may or may not be interesting or pertinent. One is that when I first measured the continuity/resistance of the white/green wire from the sensor back to the ECU connector that I got continuity but some resistance. The wiring diagram shows it to be a straight shot but why would there be resistance unless it was partially grounding or there is some other device on the wire? The other thing is the brown/black wire. From the wiring diagram I can see that it runs around to several of the other sensors on the engine but I can't really see where it terminates. There's a brown/black wire that terminates in the same ECU connector as the white/green wire. Any relation? And if this sensor was a stand alone unit generating power and I isolated it by making it's own wiring loom, why did the car run so bad and immediately run better when I hooked it back up to the OEM loom?
Or someone can convince me that this little $40 sensor really is a self contained nuclear power generating mothereffer.
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10-05-11, 12:50 PM
#9
I am taking the voltage reading through the back of the ECU connector at the G/W wire with the car running and the plug connected to the ECU. To see whether or not I am actually making contact with anything useful within the connector, I switched the multimeter over to ohms and was able to see the resistance change as the car warmed up. I did this when I had my temporary separate sensor loom wired up but not when the OEM loom sensor loom was being used. I guess I should disconnect the ECU connector and measure resistance between 2E and 3D to make sure it matches what I measured at the sensor alone. I still have no clue where the voltage is coming from.
10-05-11, 07:49 PM
#12
Rotary Freak
Pin 2E is the input from the water thermosensor on a SERIES FIVE car. Wire is green/white.
Power is from the guts of the ECU and that voltage is pulled down by the water thermosensor. As the temp of the water increases the ground from the water thermosensor varies which results in the reading at the pin 2E to vary. Once the water temp gets up to normal the reading at 2E will be 0.4 to 0.5 vdc.
The plug has to be on the ECU when you read the voltage at pin 2E of the ECU.
On a series four this wire would be on pin 2I instead of the 2E you have on your series five car.
Even if the plug was off the water thermosensor you would still read approx 5vdc when you backprobe pin 2E, IF the ECU is any good and it probably is good. I suspect your middle elect plug that has pin 2E in it, is not connected to the ECU when your doing this. Right? If so then plug it in and turn the key ON and then backprobe the pin/wire in 2E with a fully warmed up engine.
Power is from the guts of the ECU and that voltage is pulled down by the water thermosensor. As the temp of the water increases the ground from the water thermosensor varies which results in the reading at the pin 2E to vary. Once the water temp gets up to normal the reading at 2E will be 0.4 to 0.5 vdc.
The plug has to be on the ECU when you read the voltage at pin 2E of the ECU.
On a series four this wire would be on pin 2I instead of the 2E you have on your series five car.
Even if the plug was off the water thermosensor you would still read approx 5vdc when you backprobe pin 2E, IF the ECU is any good and it probably is good. I suspect your middle elect plug that has pin 2E in it, is not connected to the ECU when your doing this. Right? If so then plug it in and turn the key ON and then backprobe the pin/wire in 2E with a fully warmed up engine.
10-06-11, 08:17 AM
#17
Rotary Freak
The water thermo sensor is a THERMISTOR who's resistance varies with the temperature of the water.
The voltage seen at 2E comes from the ECU's vref.
The device in the ECU that the 5vdc ref voltage comes from decreases in value as the resistance to gnd thru the water thermo sensor decreases. As that resistance of the thermistor (water thermo sensor) decreases the 5vdc decreases til it reads approx .5vdc when the engine is fully warmed up(180*F).
IF the wiring to the sensor is open b/t the ECU and the sensor, the ECU defaults the reading to 180*F. So I'm saying that if that is the case then there is no degradation of the performance of the engine once the engine if fully heated up and as long as it STAYS heated up. Once the water cools down........your going to have starting problems along with driveablility problems til the water gets up to 180*F.
It ain't no thermosensor. Creates no voltage whatsoever.
The voltage seen at 2E comes from the ECU's vref.
The device in the ECU that the 5vdc ref voltage comes from decreases in value as the resistance to gnd thru the water thermo sensor decreases. As that resistance of the thermistor (water thermo sensor) decreases the 5vdc decreases til it reads approx .5vdc when the engine is fully warmed up(180*F).
IF the wiring to the sensor is open b/t the ECU and the sensor, the ECU defaults the reading to 180*F. So I'm saying that if that is the case then there is no degradation of the performance of the engine once the engine if fully heated up and as long as it STAYS heated up. Once the water cools down........your going to have starting problems along with driveablility problems til the water gets up to 180*F.
It ain't no thermosensor. Creates no voltage whatsoever.
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