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ECU behaviour ?
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jbalat Offline
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Post: #1
ECU behaviour ?
I noticed on the fuel saver document it was mentioned that by measuring the o2 sensor voltage you can tell if it goes into open loop when the value stops jumping around...

Not sure how this is possible or whether it is true but a funny thing happened which through me

As I was trying to read the maf signal and output a modified signal to the ecu.. the engine light came on due to a poor signal. All of a sudden the input signal flatlined ? Is this normal behaviour.Hmm
07-25-2009 03:33 AM
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colchiro Offline
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Post: #2
RE: ECU behaviour ?
By "input signal flatlined" do you mean your o2 voltage flatlined?

It's very common to go into open loop if an important sensor fails, like the o2, maf or map.

Rick

Links: Documents / Tuning for Mileage | Toyota Sensors | Autoshop Sensor Tutorials
07-25-2009 05:24 AM
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jbalat Offline
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Post: #3
RE: ECU behaviour ?
I mean once the engine light came on while I was trying to send the ECU a modified signal... The MAF wave coming in from the sensor wire also went dead ?
07-25-2009 03:18 PM
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colchiro Offline
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RE: ECU behaviour ?
I'm only guessing but maybe if the ecu thinks the maf signal is bogus, it cuts the power to it? This is the first I've heard of that tho.

You might find more info on my Autoshop Tutorials link, under "airflow sensors".

Rick

Links: Documents / Tuning for Mileage | Toyota Sensors | Autoshop Sensor Tutorials
07-25-2009 08:34 PM
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jbalat Offline
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Post: #5
RE: ECU behaviour ?
colchiro please see this pic from my wiring manual (left) and from the autoshop tutorial on the karmen sensor (right). I am trying to compare so I can make sense of which wires I should be using as an input and output for my small computer to modify the square wave.
[Image: karmen.jpg]

I have cut wire 3 at the sensor (wire 10 at the ecu) since I thought this was an output from the sensor. ie. While harness is plugged in I use the oscilliscope and I get the square wave at wire3.

If I unplug the harness...Then from the ECU side at wire3 I get dc +5v. From the sensor at wire3 I get nothing since there is no power to run the Karmen flow meter ?

This is my dillema I guess... How can I intercept the square wave and change it on wire3 when the ECU needs to supply +5V from the same wire ?..

Looking at my diagram wire7 looks like it may be relevant but when I measured it plugged or unplugged I got nothing on the oscilliscope not even a dc voltage (wire 7 could be the ref earth?)

BTW. Wire4 provides +12v. Wire5 is a common black/earth for all the other sensors including o2

Can you have a think for me. I'm sure you have a better idea than me..
(This post was last modified: 07-26-2009 04:26 AM by jbalat.)
07-26-2009 03:55 AM
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colchiro Offline
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Post: #6
RE: ECU behaviour ?
Hi JB.

I just read this from "Tuning for Mileage", regarding modding a frequency based sensor:

"The other type of MAP sensor used almost exclusively on the Ford based systems is frequency based. It has a 5 volt VREF, ground, and frequency signal output. The method of dealing with the frequency based MAP sensors is different than that used for the DC voltage based MAPs. Simply cut the ground wire going to the sensor, then add a small amount of resistance. A good starting point is about 10 ohms. Your upper limits will be between 15 and 20 ohms, depending on the ECU’s calibration. The more resistance, the more offset. Notice I didn’t say 10K ohms. It takes very little resistance to accomplish the job."

If that doesn't work, you're dealing with something that Mike might know more about and is beyond my basic electronics experience.

Rick

Links: Documents / Tuning for Mileage | Toyota Sensors | Autoshop Sensor Tutorials
07-26-2009 07:35 AM
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jbalat Offline
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Post: #7
RE: ECU behaviour ?
Colchiro, that trick didnt work.. Can you contact Mikle to see if he has any ideas

Just looking at my schematic it appeared to me that mitsubishi tried to save a few cents by combining the 5v power going into the sensor and the pulse signal coming back from the sensor in the same wire ??

In that case I will need to use 2 wires from the ecu to the sensor with diodes so that 5v will only flow one way to the sensor and a diode on either side of my black box to ensure 5v cannot flow into it but the pulse can flow in and the modified pulse can flow out..

ECU +5 ---->----D---------> Power to Sensor
ECU Sig <---D---BOX---D----< Pulse from Sensor

What do you think ?
07-26-2009 04:21 PM
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mike Offline
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Post: #8
RE: ECU behaviour ?
I've finally deleted that part of Tuning For Mileage. I'm afraid it just doesn't work. That article is the one article on my site written by someone else, and I had posted it because it has a lot of useful information in it. But the frequency based MAPs and MAFs don't respond to the resistor. I'm sorry.

We are prototyping a frequency based MAP/MAF board now. It actually samples the incoming frequency, and outputs a different frequency based on the position of a pot. It's the only solution that I know of for frequency based units.

Our board will be universal in that it will also handle voltage based MAP/MAFs as well. But the frequency function is the reason we created the board.

It will be at least 5 or 6 weeks before we have them available for sale, however.

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07-27-2009 10:43 AM
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jbalat Offline
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Post: #9
RE: ECU behaviour ?
Mike,
that is exactly the same thing I am doing.. I have purchased a BS2 Stamp (by parallax) and a PWMPal
http://www.fuel-saver.org/Thread-HHO-woe...6#pid29406

The problem I get is that when the incoming frequency changes (as it does quite often in a car) the command to the PWMPal re-triggers so that the previous output wave has not yet completed.

I have tried to read the output pin and loop until it has gone from hi to low before re-triggering the next frequency however I dont think the BS2 is fast enough or the PWMPal doesnt respond fast enough upon receiving the new command

I am now thinking that the parallax Propellor may have been a better choice although it cant output more than 3 volts..

Mike...
Now that I have built the board and it is close to responding with a nice 0-5v square wave output, I still have an issue trying to get it back into the ECU.. My ECU is sending 5volts back down the same line to power the MAF sensor. Then somehow the sensor sends the pulse back the opposite way ?
07-27-2009 03:58 PM
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hhoelectronics Offline
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Post: #10
RE: ECU behaviour ?
(07-27-2009 10:43 AM)mike Wrote:  I've finally deleted that part of Tuning For Mileage. I'm afraid it just doesn't work. That article is the one article on my site written by someone else, and I had posted it because it has a lot of useful information in it. But the frequency based MAPs and MAFs don't respond to the resistor. I'm sorry.

We are prototyping a frequency based MAP/MAF board now. It actually samples the incoming frequency, and outputs a different frequency based on the position of a pot. It's the only solution that I know of for frequency based units.

This product already exists on the market.

There is a lot of missleading information here, it is good that you deleted that part.
(This post was last modified: 07-28-2009 12:43 AM by hhoelectronics.)
07-28-2009 12:38 AM
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