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Old 26th April 2013, 10:24   #1
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Default Trouble with the Zen's ECU

Hi,

Im trying to fix low mileage and erratic idling problem with my Maruti Zen 2005 MPFI model. (i have been trying to troubleshoot the problem for more than a year).

After replacing, IAC value, TP sensor, Throttle body, gaskets..etc..
I have finally narrowed down the issue to incorrect and fluctuating TP sensor Voltage
The voltage keeps fluctuating on its own.

I followed the troubleshooting steps given in the service manual.
Please refer to the attached image for my observations.
The test involves disconnecting TP sensor connector and measure the voltage from the ECU end.
Im observing 2.5V instead of 5V specified in the manual.


Is the replacement of ECU the only possible solution?

or

My half baked knowledge says i can connect a pull up resistor outside the ECU between terminal 'a' and 'b' to pull up the voltage to 5V.
Will this solve my problem?, in that case what should be the resistor value?


Im looking for an alternate solution, I dont want to spend on money on a new ECU :-(

Thanks
T1000
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Trouble with the Zen's ECU-tp-sensor.jpg  

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Old 26th April 2013, 11:24   #2
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Default re: Trouble with the Zen's ECU

Quote:
Originally Posted by T1000 View Post
Is the replacement of ECU the only possible solution?

or

My half baked knowledge says i can connect a pull up resistor outside the ECU between terminal 'a' and 'b' to pull up the voltage to 5V.
While repairing an ECU is possible, it is very tough to get such expertise in India unless you are willing to take the risk.
I would suggest you get in touch with someone who is good in FMCG electronics since they function in a similar manner and see if that person can check the resistance required and source it.

Since you will anyway need a new ECU, you will not lose anything if you end up blowing your existing one. For all you know, you might be able to get it repaired.

Keep us posted.
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Old 26th April 2013, 11:35   #3
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Default re: Trouble with the Zen's ECU

How did you check "incorrect and fluctuating TP sensor Voltage "? At which point? Using what instrument?

There are 2 possible reasons - and they are mentioned in the table under NO.

1. Disconnect the connector near ECU (careful - don't pull the wire harness), and inspect the pins. Don't use any abrasives - use a typewriter eraser (those old round ones) to remove dirt from pins. Make sure all pins are straight (use forceps if they aren't) and reconnect the connector

2. Check the harness wires for obvious signs of cracking or fraying. Use electrical tape to cover those areas

"can connect a pull up resistor outside the ECU between terminal 'a' and 'b' to pull up the voltage to 5V": No you shouldn't - you will make the problem worse.

* 'a' is the supply point, and it reads 5.20V - that is what it should be
* Voltage at 'b' should vary with demand. If it is varying with pedal at rest, quite likely the position sensor is at fault (dirty wiper inside the pot), especially at either end of travel.

You can check this by checking resistance, with ignition switch off, between points 'b' and 'c' with and analog multimeter (DMM has higher time constant) while moving the vane - you should be able to detect jitter

Last edited by DerAlte : 26th April 2013 at 11:38.
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Old 26th April 2013, 12:27   #4
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Default re: Trouble with the Zen's ECU

Quote:
Originally Posted by n.devdath View Post
Since you will anyway need a new ECU, you will not lose anything if you end up blowing your existing one. For all you know, you might be able to get it repaired.
Keep us posted.
True, Thats the motivation to play with ECU, you dont get many chances :-).
BTW, Im mentally getting prepared to buy a new ECU, the cost is Rs 12700.
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Old 26th April 2013, 12:52   #5
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Default re: Trouble with the Zen's ECU

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Originally Posted by DerAlte View Post
How did you check "incorrect and fluctuating TP sensor Voltage "? At which point? Using what instrument?
Well, Ive been driving with a digital multimeter connected to various points at the ECU harness side for the last 15 days.
Im cross checking the values with the service manuals.
The multimeter probe is connected to ECU end.

Its like for two days i monitored O2 sensor values, then another two days with TPS sensor.

The tps sensor value is within range when the ignition is ON and engine is OFF.
The voltage fluctuates when the engine is running even with no movement in accelerator pedal.
While driving everytime the pedal returns to idle position the voltage read is anywhere above 0.8 to 1.2 where as the manual says the it should be 0.78 to 0.83


Quote:
Originally Posted by DerAlte View Post
1. Disconnect the connector near ECU (careful - don't pull the wire harness), and inspect the pins. Don't use any abrasives - use a typewriter eraser (those old round ones) to remove dirt from pins. Make sure all pins are straight (use forceps if they aren't) and reconnect the connector
The connectors at the ECU looks clean and straight.

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Originally Posted by DerAlte View Post
2. Check the harness wires for obvious signs of cracking or fraying. Use electrical tape to cover those areas
Wiring looks clean

Quote:
Originally Posted by DerAlte View Post
Voltage at 'b' should vary with demand. If it is varying with pedal at rest, quite likely the position sensor is at fault (dirty wiper inside the pot), especially at either end of travel.
Agreed. As per the manual when you disconnect the sensor and measure the voltage from terminal 'b',(ECU harness end) the voltage should be 5V.
My understanding is, this means the line is internally pulled up using a resistor to maintain 5V and the voltage reduces as the pedal is moved.
Is my understanding correct?..is it worth to take the risk?

Quote:
Originally Posted by DerAlte View Post
You can check this by checking resistance, with ignition switch off, between points 'b' and 'c' with and analog multimeter (DMM has higher time constant) while moving the vane - you should be able to detect jitter
I changed the throttle body and TPS sensor yesterday. The resistance values are within range.

Im going to check the ECU for visible damages during my lunch time, will come back if i find anything interesting :-)
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Old 26th April 2013, 13:34   #6
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Default re: Trouble with the Zen's ECU

Quote:
Originally Posted by T1000 View Post
... The multimeter probe is connected to ECU end. ...
Connected how?

Quote:
Originally Posted by T1000 View Post
... The voltage fluctuates when the engine is running even with no movement in accelerator pedal. ...
Shouldn't you be also observing whether the throttle valve is moving or not (in the TB)? It is controlled by the ECU (drive by wire?), and may be continuously positioned based on situation. The TP sensor only senses the throttle valve's position.

Quote:
Originally Posted by T1000 View Post
... While driving everytime the pedal returns to idle position the voltage read is anywhere above 0.8 to 1.2 where as the manual says the it should be 0.78 to 0.83 ...
So what would be the inference?

Quote:
Originally Posted by T1000 View Post
... Agreed. As per the manual ...
Is my understanding correct?..is it worth to take the risk? ...
What if it was a "Pull Down resistor"?

Inside the ECU, one cannot get a reliable reading with ADC if a point does not have definite voltage, i.e. if in an input line is open. That high value (as compared to the TP sensor) resistor is only a protection to ensure one gets a reliable reading if the point is open, or senses an error if the wire shorts to ground (in which case the resistor will limit the short circuit current). You putting another resistance in parallel (effectively reducing that resistance) is going to do zilch - it will only make things indeterminate in the ECU, which will now read a different open state voltage corresponding to the TP input point. It may even declare that line faulty.

Quote:
Originally Posted by T1000 View Post
... Im going to check the ECU for visible damages during my lunch time, will come back if i find anything interesting
If the ECU has to go bad, LOT more stuff would have gone bad - to the point that the engine wouldn't be running smoothly, or it would have either gone kaput or running in 'Limp Home' mode. Anyhow, happy hunting.
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Old 26th April 2013, 13:44   #7
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Default re: Trouble with the Zen's ECU

Sorry I don't know any of the technicalities, but a gone ECU is a gone ECU unless you can get someone to repair it, which will also be surely expensive as I had faced this situation with my car in the US. I ended up getting myself a refurbished ECU off of eBay that cost the same as the repair, which worked well until I sold the car away.

Since India's eBay hasn't matured, you might want to ask salvage yards or car mechanics to see if they have any ECUs from the cars they salvage from accidents. 12K is too much to pay for a chip.
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Old 26th April 2013, 14:24   #8
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Default re: Trouble with the Zen's ECU

Quote:
Originally Posted by hellmet View Post
Sorry I don't know any of the technicalities, but a gone ECU is a gone ECU unless you can get someone to repair it, which will also be surely expensive as I had faced this situation with my car in the US. I ended up getting myself a refurbished ECU off of eBay that cost the same as the repair, which worked well until I sold the car away.

Since India's eBay hasn't matured, you might want to ask salvage yards or car mechanics to see if they have any ECUs from the cars they salvage from accidents. 12K is too much to pay for a chip.
Agree with you, 12K is too much and im not sure if it will solve my mileage problem.
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Old 26th April 2013, 15:05   #9
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Post Re: Help needed from ECU gurus!

Quote:
Originally Posted by DerAlte View Post
Connected how?
I just insert the positive terminal of the multimeter to the connector.
A crude way of doing, but i dont have a choice.


Quote:
Originally Posted by DerAlte View Post
Shouldn't you be also observing whether the throttle valve is moving or not (in the TB)? It is controlled by the ECU (drive by wire?), and may be continuously positioned based on situation. The TP sensor only senses the throttle valve's position.
Throttle is controlled by mechanical linkage. TP sensor only senses the position of the butterfly value. ( i installed a new throttle body and tp sensor yesterday).
I ensured that the throttle is fully closed many times, i even checked it from the throttle body end.


Quote:
Originally Posted by DerAlte View Post
So what would be the inference?
My *Guess* is as follows,
When the throttle is closed , TP sensor value should be in the range of 0.78 to 0.83V
The values im observing are way above, in the range of 0.88 to 1.2V.
It makes ECU think that the throttle is open and uses incorrect fuel ratio and it may also affect fuel cut off operation or mishandles idle air supply.
This increases fuel consumption.

Few more observations,
- i get very good mileage on the highways, 22km/lit and 8-9km/lit in city(without much traffic). earlier i used to get 15km in city.
- No carbon buildup or oil observed in the spark plugs - i assume O2 sensor is working fine.
- Engine runs smoothly

My conclusion is, cos of incorrect TP sensor values, ECU gets confused during idling.

Quote:
Originally Posted by DerAlte View Post
What if it was a "Pull Down resistor"?
:-) This is again a guess, Pull up/down resistors are used to give a default value to a signal probe. When the TP sensor is disconnected the signal line must give 5V. if it gives 0V then we can assume its pull down.

Some info
http://www.seattlerobotics.org/encod...97/basics.html
http://cnmat.berkeley.edu/recipe/how...ontroller_i_o_


Quote:
Originally Posted by DerAlte View Post
Inside the ECU, one cannot get a reliable reading with ADC if a point does not have definite voltage, i.e. if in an input line is open. That high value (as compared to the TP sensor) resistor is only a protection to ensure one gets a reliable reading if the point is open, or senses an error if the wire shorts to ground (in which case the resistor will limit the short circuit current). You putting another resistance in parallel (effectively reducing that resistance) is going to do zilch - it will only make things indeterminate in the ECU, which will now read a different open state voltage corresponding to the TP input point. It may even declare that line faulty.
I got what you are saying, im not going to try it until im sure of what im doing.

Quote:
Originally Posted by DerAlte View Post
If the ECU has to go bad, LOT more stuff would have gone bad - to the point that the engine wouldn't be running smoothly, or it would have either gone kaput or running in 'Limp Home' mode. Anyhow, happy hunting.
Agreed. But my problem is even if i change the ECU there is no guarantee that my mileage problem will be solved.

I opened the ECU now, the circuit looks clean , no visible damages or loose connections.

Last edited by T1000 : 26th April 2013 at 15:08.
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Old 26th April 2013, 15:44   #10
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Default Re: Trouble with the Zen's ECU

As per my information during servicing my Zen at MASS Zen Euro II and Euro III had different setting/values for TP sensor .For Eg if you get a new TP sensor then they can program it via the Suzuki scan tool for different values.
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Old 29th April 2013, 14:29   #11
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Default Re: Trouble with the Zen's ECU

An Update and sharing my experience with ECM!

I removed the ECM circuit and used my macro lens to get a closer view of the circuit.
I noticed lots of tiny metal dust particles(see attached picture) on the circuit, must be lead dust which wasnt cleaned after soldering.

I suspected these metal fragments have the potential to short circuits. I cleaned the circuit board with isopropyl alcohol using a tooth brush.

I quickly tested the cleaned ECM in the vehicle...It solved one of my problem!!!
TP sensor voltage which used to fluctuate on its own was stable and the sensor was behaving as expected.

Now everything seems to be normal, i'll have to check the mileage in couple of days.
-----------------------

Now the only pending issue is, As per the service manual, voltage level with the TP sensor disconnected should read 5V, but im still getting 2.25V. (Step 2 in the "trouble shooting TP sensor circuit" section )


Can this point be overlooked?
Attached Thumbnails
Trouble with the Zen's ECU-ecu.jpg  

Trouble with the Zen's ECU-dsc_4201.jpg  


Last edited by T1000 : 29th April 2013 at 14:30.
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