Variable resistor adjustment, reading voltage on Vf1
Oct 13, 2014 | 10:29 PM
#1
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Variable resistor adjustment, reading voltage on Vf1
Hi Guys,
I have a 2RZ-FE EFI 2.4 engine which is running very rich - high fuel consumption. I have checked all the sensors and all check out. It has the Pressure in manifold setup. It does not have any oxygen sensors. It does however have a variable resistor mounted on the firewall, part number 89456-30010.
From the electrical diagrams it seems the output of this resistor goes to the Oxygen sensor input of the ECU (E5-6) - so it is a cheap factory method of not having a 02 but still be able to trim the fuel mixture.
Now the two problems/symptoms I had was high fuel consumption and high idle (1000rpm - should be around 850rpm). I checked the CO and it was around 4.6 should be 0-0.5. I replaced the resistor with a generic one because it was not adjusting easily enough - it was still electrically fine and was at around the center position when I checked it, giving about 2.2V to the ECU.
With my new resistor I slowly tweaked it and at around 160mV to the 02 input the rpm dropped to 850rpm adjusting it further down past 70mV the rpm picks up again. I then took it back to 160mV and leaving it there for time being. Previously the o2 input pin was reading 2.2V so I assume my setting is still on the rich side and safe for now.
My question now is how does the Vf1 pin on the diagnostics work? From this site: http://alflash.com.ua/vf1.htm
I think I'm right in my diagnosis from the voltage on the Vf1 pin, mine is at about 30mV. The graph on website says that a lower voltage means an increase in fuel, (the text says the opposite?) This in turn means the ECU is thinking the engine is running lean and needs more fuel than the factory map is supplying. The thing is, the voltage on Vf1 is moving and will also change when I rev the engine - it goes to about 38mV (All these test were done without Te1 and E1 bridged)
My D type injection system is supposed to only have 3 levels on the Vf1 pin, 0, 2.5 and 5V. So I thought the Vf1 is still giving out what the Long term fuel trim is thinking and disconnected the battery overnight to try and reset it. This morning the readings are still the same. So either my Vf1 does not work in steps and instead gives out a voltage proportional to the LTFT or does the ECU still think it is running so lean that it is still enriching the mixture past factory map and giving me 0V (or close to it)?
I know I must take it to my local shop to check Co or even 4 gas analyser but this is broken and sent in for repairs and will only be back next week some time. Anybody with experience with these O2 less variable resistor systems?
I have a 2RZ-FE EFI 2.4 engine which is running very rich - high fuel consumption. I have checked all the sensors and all check out. It has the Pressure in manifold setup. It does not have any oxygen sensors. It does however have a variable resistor mounted on the firewall, part number 89456-30010.
From the electrical diagrams it seems the output of this resistor goes to the Oxygen sensor input of the ECU (E5-6) - so it is a cheap factory method of not having a 02 but still be able to trim the fuel mixture.
Now the two problems/symptoms I had was high fuel consumption and high idle (1000rpm - should be around 850rpm). I checked the CO and it was around 4.6 should be 0-0.5. I replaced the resistor with a generic one because it was not adjusting easily enough - it was still electrically fine and was at around the center position when I checked it, giving about 2.2V to the ECU.
With my new resistor I slowly tweaked it and at around 160mV to the 02 input the rpm dropped to 850rpm adjusting it further down past 70mV the rpm picks up again. I then took it back to 160mV and leaving it there for time being. Previously the o2 input pin was reading 2.2V so I assume my setting is still on the rich side and safe for now.
My question now is how does the Vf1 pin on the diagnostics work? From this site: http://alflash.com.ua/vf1.htm
I think I'm right in my diagnosis from the voltage on the Vf1 pin, mine is at about 30mV. The graph on website says that a lower voltage means an increase in fuel, (the text says the opposite?) This in turn means the ECU is thinking the engine is running lean and needs more fuel than the factory map is supplying. The thing is, the voltage on Vf1 is moving and will also change when I rev the engine - it goes to about 38mV (All these test were done without Te1 and E1 bridged)
My D type injection system is supposed to only have 3 levels on the Vf1 pin, 0, 2.5 and 5V. So I thought the Vf1 is still giving out what the Long term fuel trim is thinking and disconnected the battery overnight to try and reset it. This morning the readings are still the same. So either my Vf1 does not work in steps and instead gives out a voltage proportional to the LTFT or does the ECU still think it is running so lean that it is still enriching the mixture past factory map and giving me 0V (or close to it)?
I know I must take it to my local shop to check Co or even 4 gas analyser but this is broken and sent in for repairs and will only be back next week some time. Anybody with experience with these O2 less variable resistor systems?
Oct 13, 2014 | 10:45 PM
#2
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Just thinking out loud here:
When I trimmed the resistor there was a strange thing: bringing the voltage down from say 2.2V the RPM dropped (around 850) at about 450mV, adjusting the resistor further, the rpm stayed constant (850) but going down further past 70mV the rpm went up again (1000). going the reverse it dropped the rpm again (to around 850) when the resistor was increasing past 70mV but only picked up the rpm (1000) past 1V So the point where the RPM changes going up and going down is not quite at the same point.
I looked at the manual and the critical point for the O2 sensor is 0.45 volts. Makes me think then the ECU is standard (Expecting an O2 sensor and not knowing about this resistor thing) and any voltage below say 70mV and above 1V would cause the ECU to think the O2 is not working properly and default to running the engine rich - toyota's failsafe mode? I have removed the resistor before to see if it causes an engine light to come on but did not see anything, maybe that part of the ECU was changed to use the resistor instead of the O2?
When I trimmed the resistor there was a strange thing: bringing the voltage down from say 2.2V the RPM dropped (around 850) at about 450mV, adjusting the resistor further, the rpm stayed constant (850) but going down further past 70mV the rpm went up again (1000). going the reverse it dropped the rpm again (to around 850) when the resistor was increasing past 70mV but only picked up the rpm (1000) past 1V So the point where the RPM changes going up and going down is not quite at the same point.
I looked at the manual and the critical point for the O2 sensor is 0.45 volts. Makes me think then the ECU is standard (Expecting an O2 sensor and not knowing about this resistor thing) and any voltage below say 70mV and above 1V would cause the ECU to think the O2 is not working properly and default to running the engine rich - toyota's failsafe mode? I have removed the resistor before to see if it causes an engine light to come on but did not see anything, maybe that part of the ECU was changed to use the resistor instead of the O2?
Oct 16, 2014 | 12:03 AM
#3
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From: I live in New Tripoli Pa out in the woods
Or you did not drive the vehicle long enough for that test to run.
I have had them take a 100 miles or so
For the most I think we all have no clue what your talking about.
I have had them take a 100 miles or so
For the most I think we all have no clue what your talking about.
Oct 16, 2014 | 01:41 AM
#4
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Let me try again:
Oxygen sensor gives out average voltage of 0.45V when mixture is right. If reading is off ECU makes changes in STFT to correct. Later this STFT becomes the LTFT and the STFT becomes 0. This will only work if the O2 is giving accurate feedback (closed loop) So if the ECU gives more trim it wants to see that reflected on the O2 reading, else it will just give more trim until the O2 gives the correct reading again.
Mine does not have the O2, it has a variable resistor which is supposed to give the 0.45V (or whatever the ECU is expecting the correct mixture to be) to the ECU (My theory). Now if this 0.45V is not what the ECU is expecting it will increase the trim and wait for the change, except that in my case the resistor does not change because it is not an O2. So the ECU thinks it was not enough trim and adds more, and more and more until the trim has reached its max = bad fuel consumption.
Some other toyotas also had this resistor but looking at the electrical diagrams it confirms what the service manuals say about it: that it is only for adjusting the idle mixture. I can bet some good money that these models were fitted with a O2 sensor. Anybody that wants to confirm this?
I have read about Tacomas with the same engine with much better fuel consumption. This makes me believe that the engine is not the culprit. Locally this vehicle of mine is known for its bad fuel consumption and bad performance. This could all be related to the bad fueling execution.
My next step is to install a AFR meter with wideband O2 to monitor what my adjustments are doing to the AFR and as a bonus the one I'm looking at also has a narrowband output which I will wire into the ECU instead of the resistor. If my theory is correct it should give me much better fuel economy and also better overall performance.
BTW. I hear what you say about the 100mile thing, that would be because of the LTFT fuel still affecting the injection time. I did try and reset the ECU by removing the battery but can't say I saw a difference, again without an O2 the ECU is blindly fueling the engine.
Oxygen sensor gives out average voltage of 0.45V when mixture is right. If reading is off ECU makes changes in STFT to correct. Later this STFT becomes the LTFT and the STFT becomes 0. This will only work if the O2 is giving accurate feedback (closed loop) So if the ECU gives more trim it wants to see that reflected on the O2 reading, else it will just give more trim until the O2 gives the correct reading again.
Mine does not have the O2, it has a variable resistor which is supposed to give the 0.45V (or whatever the ECU is expecting the correct mixture to be) to the ECU (My theory). Now if this 0.45V is not what the ECU is expecting it will increase the trim and wait for the change, except that in my case the resistor does not change because it is not an O2. So the ECU thinks it was not enough trim and adds more, and more and more until the trim has reached its max = bad fuel consumption.
Some other toyotas also had this resistor but looking at the electrical diagrams it confirms what the service manuals say about it: that it is only for adjusting the idle mixture. I can bet some good money that these models were fitted with a O2 sensor. Anybody that wants to confirm this?
I have read about Tacomas with the same engine with much better fuel consumption. This makes me believe that the engine is not the culprit. Locally this vehicle of mine is known for its bad fuel consumption and bad performance. This could all be related to the bad fueling execution.
My next step is to install a AFR meter with wideband O2 to monitor what my adjustments are doing to the AFR and as a bonus the one I'm looking at also has a narrowband output which I will wire into the ECU instead of the resistor. If my theory is correct it should give me much better fuel economy and also better overall performance.
BTW. I hear what you say about the 100mile thing, that would be because of the LTFT fuel still affecting the injection time. I did try and reset the ECU by removing the battery but can't say I saw a difference, again without an O2 the ECU is blindly fueling the engine.
Jun 22, 2020 | 04:25 PM
#5
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Hello
Let me try again:
Oxygen sensor gives out average voltage of 0.45V when mixture is right. If reading is off ECU makes changes in STFT to correct. Later this STFT becomes the LTFT and the STFT becomes 0. This will only work if the O2 is giving accurate feedback (closed loop) So if the ECU gives more trim it wants to see that reflected on the O2 reading, else it will just give more trim until the O2 gives the correct reading again.
Mine does not have the O2, it has a variable resistor which is supposed to give the 0.45V (or whatever the ECU is expecting the correct mixture to be) to the ECU (My theory). Now if this 0.45V is not what the ECU is expecting it will increase the trim and wait for the change, except that in my case the resistor does not change because it is not an O2. So the ECU thinks it was not enough trim and adds more, and more and more until the trim has reached its max = bad fuel consumption.
Some other toyotas also had this resistor but looking at the electrical diagrams it confirms what the service manuals say about it: that it is only for adjusting the idle mixture. I can bet some good money that these models were fitted with a O2 sensor. Anybody that wants to confirm this?
I have read about Tacomas with the same engine with much better fuel consumption. This makes me believe that the engine is not the culprit. Locally this vehicle of mine is known for its bad fuel consumption and bad performance. This could all be related to the bad fueling execution.
My next step is to install a AFR meter with wideband O2 to monitor what my adjustments are doing to the AFR and as a bonus the one I'm looking at also has a narrowband output which I will wire into the ECU instead of the resistor. If my theory is correct it should give me much better fuel economy and also better overall performance.
BTW. I hear what you say about the 100mile thing, that would be because of the LTFT fuel still affecting the injection time. I did try and reset the ECU by removing the battery but can't say I saw a difference, again without an O2 the ECU is blindly fueling the engine.
Oxygen sensor gives out average voltage of 0.45V when mixture is right. If reading is off ECU makes changes in STFT to correct. Later this STFT becomes the LTFT and the STFT becomes 0. This will only work if the O2 is giving accurate feedback (closed loop) So if the ECU gives more trim it wants to see that reflected on the O2 reading, else it will just give more trim until the O2 gives the correct reading again.
Mine does not have the O2, it has a variable resistor which is supposed to give the 0.45V (or whatever the ECU is expecting the correct mixture to be) to the ECU (My theory). Now if this 0.45V is not what the ECU is expecting it will increase the trim and wait for the change, except that in my case the resistor does not change because it is not an O2. So the ECU thinks it was not enough trim and adds more, and more and more until the trim has reached its max = bad fuel consumption.
Some other toyotas also had this resistor but looking at the electrical diagrams it confirms what the service manuals say about it: that it is only for adjusting the idle mixture. I can bet some good money that these models were fitted with a O2 sensor. Anybody that wants to confirm this?
I have read about Tacomas with the same engine with much better fuel consumption. This makes me believe that the engine is not the culprit. Locally this vehicle of mine is known for its bad fuel consumption and bad performance. This could all be related to the bad fueling execution.
My next step is to install a AFR meter with wideband O2 to monitor what my adjustments are doing to the AFR and as a bonus the one I'm looking at also has a narrowband output which I will wire into the ECU instead of the resistor. If my theory is correct it should give me much better fuel economy and also better overall performance.
BTW. I hear what you say about the 100mile thing, that would be because of the LTFT fuel still affecting the injection time. I did try and reset the ECU by removing the battery but can't say I saw a difference, again without an O2 the ECU is blindly fueling the engine.
Jun 22, 2020 | 11:21 PM
#6
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Hi,
So I installed the oxygen sensor and wired the narrow band output to the resistor input of the ecu.
It made no difference to the fuel economy. I never tried wiring the 0-5v output of the sensor to the ecu to see if that voltage range will work better.
Either way the oxygen sensor readout says it is running very rich. Another thing I still need to try is replacing the ignitor module inside the distributor and maybe also the coil as I've heard they do also give problems. The aftermarket replacement is not good, I was told to only go with OEM.
If you can afford to replace them do that and let me know!
So I installed the oxygen sensor and wired the narrow band output to the resistor input of the ecu.
It made no difference to the fuel economy. I never tried wiring the 0-5v output of the sensor to the ecu to see if that voltage range will work better.
Either way the oxygen sensor readout says it is running very rich. Another thing I still need to try is replacing the ignitor module inside the distributor and maybe also the coil as I've heard they do also give problems. The aftermarket replacement is not good, I was told to only go with OEM.
If you can afford to replace them do that and let me know!
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