o2 removed, ecu still showing vf

[grimreaper]

trying to force open loop for maftpro ptt here and for the last 3 days pulling the nbo2 sensor has worked perfectly. However tonight i went to get a few logs and the ecus showing a vf signal and tossing my tune out the window....
anybody seen this before? o2 is not on the car!
89 7mgte stock ecu and electronics.

 

[turbobob]

I'm not sure how the supra ecu determines that the O2 is there and working. On a GM car the O2 is biased by resistors to .4v as the O2 heats up it begins to be able to overdrive the bias resistors. So a missing O2 sensor just hangs mid scale and never triggers the lean/rich thresholds in the ECM (<.3 = lean, >.5 = rich)

My Mitsubishi (Dodge Stealth RT/TT) O2 voltage starts at 0 with a cold sensor and creeps into the normal range as it heats up.

So perhaps you are getting some stray noise coupling into the O2 input making the ECU think there is a sensor attached.

Try putting a resistor to ground on the O2 sensor input and see if that changes anything.

Bob

 

[CRE]

An open or short to ground on the O2 sensor line should result in a Vf reading of around 0... BUT, there's still going to be fluctuations as the TCCS presents more information via that line than just basic fuel corrections... they're just more minute so you're going to need a scope to read them.

If you're seeing a reading much higher than a half a volt or so it may be due to an error code. I'm pretty sure that those fuel adjustments appear on the Vf line as well. Look for correlations if this continues to happen... Does it only happen when logging after a warm start? Does it correspond to a change in weather? Does it continue if you turn the car off and reset the TCCS (pull the EFI fuse)? Are there any error codes present when this is happening?

Don't forget, the Vf line is a diagnostic output for the TCCS. Not all of the data it presents is related to the O2 sensor.


I think that to satisfy the 89+ TCCS after removing the O2 sensor you have to install a resistor across the heater lines... I think people were just using a 1K&#937; resistor; do a search to be sure.

 

[Supra_Villan]

i'd like to know this as well.

 

[CRE]

i'd like to know this as well.

You would like to know what?



Grim, Bob is right; an errant current could be causing your Vf issue as well. Test the OX line for voltage the next time this occurs.

 

[grimreaper]

no codes at the time (i checked), the car litterly ran perfect in open loop and then the next start up showed a vf reading of 3.5 V. This took about 3 days before i ran into issues. I have gone back to closed loop ecu control and no codes yet (about a month iirc). As soon as the vf reading showed up i had major issues with tuning where as before that i had a near complet open loop maft-pro tune.

I pulled the pin out of the o2 to ecu harness that sent the signal to the ecu. So the heater circuit was still hooked up but the o2 signal was not connected. I removed the o2 completly but decided to keep it on the car in case such and issue arose. (blue wire sepreated at connector, identical to cutting the blue wire at the o2 sensor). There is no way the sensor would have fed any info to the ecu.

warm starts or cold starts, it didnt matter. weather was stable during that time frame (mid 80's).

I did not try a reset to see the outcome but when i get more time to look at this issue i will try that.

The issue that there was a possibel code did strike me but the fact that the ecu adjusted fuel trims is what throws me off.

 

[grimreaper]

Ill pull out the volt meter tomorrow and play with this again. The simple fact that ecu actually adjusted fuel on me is what has me wondering why... even a code present shouldnt let the ecu adjust fuel should it?

 

[nacho8705]

I have been having a similar issue. I have a reading of about 2 volts on VF no matter what.

-Maf pro is on its own circuit powered before ecu. no code 24
-stock o2 blue wire is cut, heater lines still in place

After i reset the codes, i got it to stay at 0 volts. I let the car get up to temp idling, still stayed at 0. I turned it off and restarted, and sure enough, 2 volts started showing after about 15 seconds.

When the ECU is outputting that 2 volts, its like it is in a wierd mode. If i adjust the VE table to get 14.7:1 at idle, then rev, it doesn't come right back to 14.7. it goes lean then slowly comes back down.

Anybody have any ideas?

 

[CRE]

Grim, sorry for not following up... did you get this solved? Yes, there are a number of codes which cause the ECU to adjust fuel regardless of whether there is a valid OX signal or not.

Nacho, I've noticed the same behavior when working with GE electronics. It's as if the ECU has a different open loop fuel map for running after a cold start and another for after a warm start. I tested all related sensors and wiring and went so far as swapping in a few different temp sensors and three different ECUs. The only solution I found was rather lacking in sophistication... a push button which I have to hold for 10 seconds after cranking to makes the ECU see a cold start situation, then release. If I do this it all works fine and there is no shift in my fueling. The level of enrichment is such that without this solution the MAFT Pro can't pull enough fuel to come back to my tune (it's internally limited as to how much fuel it can pull when PTT is active). I've found that the effect isn't seen when the stock O2 sensor is present, BUT it is there when in open loop. If you've found anything further about this behavior I'd like to know.

The Vf feedback in my case does correspond to the amount of fuel that's being added.

 

[turbobob]

Grim, sorry for not following up... did you get this solved? Yes, there are a number of codes which cause the ECU to adjust fuel regardless of whether there is a valid OX signal or not.

Nacho, I've noticed the same behavior when working with GE electronics. It's as if the ECU has a different open loop fuel map for running after a cold start and another for after a warm start. I tested all related sensors and wiring and went so far as swapping in a few different temp sensors and three different ECUs. The only solution I found was rather lacking in sophistication... a push button which I have to hold for 10 seconds after cranking to makes the ECU see a cold start situation, then release. If I do this it all works fine and there is no shift in my fueling. The level of enrichment is such that without this solution the MAFT Pro can't pull enough fuel to come back to my tune (it's internally limited as to how much fuel it can pull when PTT is active). I've found that the effect isn't seen when the stock O2 sensor is present, BUT it is there when in open loop. If you've found anything further about this behavior I'd like to know.

The Vf feedback in my case does correspond to the amount of fuel that's being added.

how is the switch wired? We could probably set the pro up to do it for you.

B

 

[CRE]

C to NC the signal runs straight through, C to NO adds a small resistor... I'll have to double check what value. I'm sure you could manage it with the Pro, much like the ETPS pass the signal through except for the first 10 seconds after the RPM are above 500 or so. You don't want it to present a false cold signal to the ECU WHILE cranking though... it can cause starting issues due to excess fuel; I haven't noticed any issue after cranking though.

 

[turbobob]

so you are connecting a resistor in line with the coolant sensor?

cool.

On the Buick, the coolant sensor is used with selectable pullup resistors, so there was not a 1:1 relationship between voltage and coolant temp.

One experiment on the Supra would be to watch the coolant sensor during warmup and see if its voltage range changes.

If it doesn't then we can do some real cool stuff.

Bob

 

[CRE]

I'm sorry, actually I remember I elected not to run the resistor in series... the switch swaps the sensor for a resistor (I think the value is 1.2K&#937.

I'm not terribly familiar with the inner workings of the GE ECU in this area. However, now that I have a second voltage monitor free in the Pro :icon_bigg I can log it.... interested?

It would be REALLY cool if we could replace the blind afterstart enrichment using the actual temp to control the quantity and duration... or even a boost control scaler... Hmmm... lots of ideas.... Engine temp logging and display in the Sensor Monitor would be great. (okay, sorry... I'll get a grip....)

I don't know if these help you find precisely what you need to know, but it's a start until I can log the temp signal.

The temp sensor is THW:
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=32
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=113

The Temp sensor sits across THW (ECU temp input) and E2 (ECU sensor ground).



On a somewhat unrelated note, what's the highest resolution possible with the voltage monitors, hundredths or is it possible to monitor to the thousandths (is the hundredths a limitation of the Pro or can I just adjust the definitions in TP)?

 

[turbobob]

if we knew the voltage during warmup we could tell if the ecu is changing pullup resistors in the middle somewhere.

If you log it, make sure you have disabled the aux2 pullup.

Bob

 

[turbobob]

On a somewhat unrelated note, what's the highest resolution possible with the voltage monitors, hundredths or is it possible to monitor to the thousandths (is the hundredths a limitation of the Pro or can I just adjust the definitions in TP)?

The aux input is "10 bit", so it has a resolution of about 5mv. Since the input is 'single ended', i.e. it shares the ground with other circuits, there is a small amount of noise mixed in.

The number of digits displayed in TP is set in the ADS file, but if editing the ADS file, you need to reset the baud rate with a text editor after you finish the edit.

Bob

 

[CRE]

I've already disconnected R9 when we previously spoke about making Aux In 2 usable. I'll probably wire this up and make a log tomorrow.


Is the baud fix still required in TP 5? I've been thinking about trying it out anyway.

 

[turbobob]

I've already disconnected R9 when we previously spoke about making Aux In 2 usable. I'll probably wire this up and make a log tomorrow.


Is the baud fix still required in TP 5? I've been thinking about trying it out anyway.

Ok, cool.


TP5 doesn't have the baud rate issue, but its a totally different animal (ads and xdf files don't transfer over ), so lets tackle one project at a time.

B

 

[CRE]

I know about TP5, I'm working with your files (and reworking them as needed) and not using it for anything critical. The higher resolution thing was just for something I want to monitor later on. I'll post back after i have a to wire up and make a log.

 

[3p141592654]

To clarify one thing with the Vf line. It is actually just connected to a PIO on the microprocessor, so it can only be 0 V or 5V. The way it get the "in-between" voltages is to modulate the number of 0V and 5V intervals, and then uses a low-pass filter RC filter to smooth out the signal. The high frequency ripple you see on a scope is each time it updates the PIO signal, which is every 30 degrees of crank rotation and every 4.096ms of time.

 

[CRE]

Thanks Pi. Have you found, in your extensive investigation of the TCCS, anything which might be responsible for the difference in fueling depending on whether the car was started warm or cold? Do you happen to have any additional information about the THW design or operation?