[a4anurag]

Originally Posted by Ageing Stud

press harder to get it rectified or atleast publicise it as manufacturing defect which Maruti has a liability to rectify.

Try the suggestion given by Catalyst_delhi but before you do so pressurize MASS to get this issue corrected else escalate the issue higher ups and get a solution.

How does the engine feel otherwise than during idling?

Originally Posted by Catalyst_delhi

strange indeed this must be an electrical fault from the factory.

+1.

Anurag.

[Ageing Stud]

Originally Posted by Catalyst_delhi

You can change the relay for the AC switch, There is a relay which closes a contact when the AC is switched on to tell the ECM to increase RPM. This may be fitted in reverse or the ECM not programmed properly. You can try to re install the software in the ECM/ try some switch like i mentioned above. strange indeed this must be an electrical fault from the factory.

Changing the relay will not help and it is not an electrical fault, as I mentioned earlier in my starting post, the DESIRED IDLE programmed in the ECM itself is lower for Aircon usage, 847 instead of 871 without Aircon.
So as per the programmed software all electrical and electronics parts are working perfect :-(

Also pls note that mine is a 45 day old car with just 1750 kms on the odo so don't think I will void warranties by changing parts or ECM reprogramming.

@Anurag have escalated the issue to the Regional Service Manager, Mumbai level and even talked to some service engineers in Delhi and Gurus on plant, all they say is as per manual and parameters for my car it is working fine :-(

If you can pm me your mail id will forward you the mails exchanged with Maruti.

[a4anurag]

Originally Posted by Ageing Stud

@Anurag have escalated the issue to the Regional Service Manager, Mumbai level and even talked to some service engineers in Delhi and Gurus on plant, all they say is as per manual and parameters for my car it is working fine :-(

If you can pm me your mail id will forward you the mails exchanged with Maruti.

Get the ECU changed or ask them to re-programme that. Get a second opinion with another MASS for this issue.

@Ageing Stud: You are a Newbie bro. I can't PM you and I just checked your profile and it says I can't contact you by email too.

Here is mine.

anuraagshenoy@gmail.com

Anurag.

[audioholic]

Originally Posted by Ageing Stud

Changing the relay will not help and it is not an electrical fault, as I mentioned earlier in my starting post, the DESIRED IDLE programmed in the ECM itself is lower for Aircon usage, 847 instead of 871 without Aircon.

My wagonR did vibrate initially when the compressor used to run and engine fully warmed. Now at 12500kms done, the vibrations are no longer present. Now the RPM dips once when compressor kicks in, surges when it disengages. After a second it stabilises. Moreover, a difference of 30rpm might not be the exact cause for the problem. Under which menu did this info come up? Are these the parameters specified by maruti? In my car, when the engine is fully warmed up,

Coolant temperature - 89deg C
Engine speed: Min: 605rpm, Max: 938rpm, Average: 818rpm
Ac is on without headlamps or any lighting

This is data taken during 1 minute of idling with AC ON.

Without AC, here is a sample run from which I clipped out the idling portion



Average speed for the above data is 841rpm.

[Ageing Stud]

Originally Posted by a4anurag

Get the ECU changed or ask them to re-programme that. Get a second opinion with another MASS for this issue.

@Ageing Stud: You are a Newbie bro. I can't PM you and I just checked your profile and it says I can't contact you by email too.

Here is mine.

anuraagshenoy@gmail.com

Anurag.

You don't get it chief.

The ECM as well as the car is perfect as per MASS and Maruti engineers both. The parameters are common for all Maruti Wagon R and have seen multiple wagon r at MASS and they all have the same desired rpm programmed and do have vibrations though a little lesser than mine.

Thanks for the mail id will forward you my mail interactions with Maruti.

[a4anurag]

Originally Posted by audioholic

Without AC, here is a sample run from which I clipped out the idling portion

Average speed for the above data is 841rpm.

The excel sheet that you have attached is from which software?

Can you please let me know how get the data in such sheet for better understanding.

Anurag.

[audioholic]

Originally Posted by a4anurag

Can you please let me know how get the data in such sheet for better understanding.
.

As I need lots of running data for some project I am using the USB adapter coupled with Scanmaster ELM which can let me record realtime graphs. The data can be exported out of Scanmaster in CSV format which I can easily convert to a worksheet and later use the data and form graphs. Not sure about torque but IIRC torque does let you export data. Not sure though.

From what I know, the idling speed is not fixed and the ECU tries to keep idle speed close to the desired value. When the compressor is running, it will cause a dip in engine speed which the ECU then compensates. This is contrary to older cars wherein the Idle speed was made to rise once the compressor was coupled. As long as the dip in engine speed is compensated by the ecu, that is fine and need not necessarily mean that engine speed must be higher when compressor kicks in. I dont find logic in that. Maybe in the era of carburetted engines where idle speed was to be set manually andthere was no automatic adjustment, engine speed rose once the compressor kicked in. But definitely not the same in both my cars. There will just be a fluctuation when the compressor engages and disengages.

[a4anurag]

Originally Posted by audioholic

From what I know, the idling speed is not fixed and the ECU tries to keep idle speed close to the desired value. When the compressor is running, it will cause a dip in engine speed which the ECU then compensates. This is contrary to older cars wherein the Idle speed was made to rise once the compressor was coupled. As long as the dip in engine speed is compensated by the ecu, that is fine and need not necessarily mean that engine speed must be higher when compressor kicks in. I dont find logic in that. Maybe in the era of carburetted engines where idle speed was to be set manually andthere was no automatic adjustment, engine speed rose once the compressor kicked in. But definitely not the same in both my cars. There will just be a fluctuation when the compressor engages and disengages.

If the idle is say 830 rpm without the AC, once the AC button is pressed the rpm goes upto 900 - 920 and after a second or two it settles down to 880 - 890 rpm. The engine increases the rpm to take the load of the compressor and once the ECU understands it seeks down at a lower rpm.

Anurag.

[audioholic]

Originally Posted by a4anurag

If the idle is say 830 rpm without the AC, once the AC button is pressed the rpm goes upto 900 - 920 and after a second or two it settles down to 880 - 890 rpm. The engine increases the rpm to take the load of the compressor.

I beg to differ. Do you mean to say the engine cannot take the load of the compressor at the same speed and hence idling speed increases? That's not correct. If 850rpm is the idle speed without AC, the engine can still run with the compressor at the same RPM, only at the cost of more fuel. Thats it. Its like applying more accelarator input.

Let me explain what happens in my car.

1. Compressor starts.
2. Engine speed falls below desired value. ECU reads Actual value<desired value and then increases Throttle position.
3. Engine speed comes in range of desired value. Minor correction is done after that to keep idle constant.
4. Compressor disengages. Due to increased throttle position the engine speed rises.
5. ECU detects that Idle speed>Desired idle speed and reduces throttle opening.

I havent observed much related to this so I will probably run a test sometime and closely monitor changes and post it when possible. Most of the times I acquire data without AC on.

[a4anurag]

Originally Posted by audioholic

I beg to differ. Do you mean to say the engine cannot take the load of the compressor at the same speed and hence idling speed increases? That's not correct. If 850rpm is the idle speed without AC, the engine can still run with the compressor at the same RPM, only at the cost of more fuel. Thats it. Its like applying more accelarator input.

I agree on what you say but what I have observed in my car with the OBD reader is that the idle RPM dips a bit and to compensate that the ECU alters the RPM and makes it a bit higher than the desired idle RPM.


Anurag.

[DerAlte]

Originally Posted by audioholic

I beg to differ. Do you mean to say the engine cannot take the load of the compressor at the same speed and hence idling speed increases? That's not correct. If 850rpm is the idle speed without AC, the engine can still run with the compressor at the same RPM, only at the cost of more fuel. Thats it. ...

Huh? Maintain RPM and produce more torque to by consuming more fuel? How /Why? Are you equating the idle load increase with you pressing accelerator harder to maintain speed while going uphill?

At idle, there is no manipulation of Acc pedal to accommodate higher load, right? The ECU sets RPM based on load when Acc pedal is at 0. ECU cannot arbitrarily change fuelling as it doesn't directly know *how much* load has come on - there is no 'load sensor'! ECU has to incrementally increase injection, wait for RPM to change, and then reduce it to 'just enough for the load'. All this is done based on RPM reading only, and RPM increases / reduces based on quantity of fuel injected (it never stays constant and quietly drink more fuel).

When AC comes on, ECU increases RPM to a higher value, finds it too high (crankshaft still accelerating), reduces it till it is too low (crankshaft continuing decelerating), increases slightly again and holds that injection level till load changes again. The new RPM is what is sufficient for increased or decreased load. One can read up Control Theory, specifically P, I and D control strategies to know the maths behind it. (y)

[audioholic]

Originally Posted by DerAlte

When AC comes on, ECU increases RPM to a higher value, finds it too high (crankshaft still accelerating), reduces it till it is too low (crankshaft continuing decelerating), increases slightly again and holds that injection level till load changes again. The new RPM is what is sufficient for increased or decreased load. One can read up Control Theory, specifically P, I and D control strategies to know the maths behind it. (y)

I agree with the logic sir. How is this increase in RPM brought out then? By increasing the air flow right? I am not from the mechanical background so I can only analyse the electronics part. In my car the idle speed relates to the Absolute throttle position value. Sadly I dont have access to injector pulse width so I cant understand what happens there. Relative throttle position will not change as I have observed it is related to the accelarator input. So when I switch on AC, there is a change in the absolite throttle position which changes to accomodate the load of compressor. Average idle speed remains more or less the same.

[DerAlte]

Originally Posted by audioholic

... How is this increase in RPM brought out then? By increasing the air flow right? I am not from the mechanical background so I can only analyse the electronics part. In my car the idle speed relates to the Absolute throttle position value. ...

I was describing the electronic control part! In "drive by wire" the Acc pedal is not connected to throttle valve / vane. It is controlled by a motor which is controlled by the ECU. The ECU sets the opening based on fuel quantity to maintain the right fuel-air ratio. Effectively, one calculates fuel first from the map, and the opening follows the corresponding air requirement. That opening factors in altitude (air pressure) and air temperature.

Originally Posted by audioholic

... Average idle speed remains more or less the same.

"more or less the same" is not the same as "same" or "equal"! 50RPM is a significant difference.

[Ageing Stud]

Originally Posted by DerAlte

I was describing the electronic control part! In "drive by wire" the Acc pedal is not connected to throttle valve / vane. It is controlled by a motor which is controlled by the ECU. The ECU sets the opening based on fuel quantity to maintain the right fuel-air ratio. Effectively, one calculates fuel first from the map, and the opening follows the corresponding air requirement. That opening factors in altitude (air pressure) and air temperature.

"more or less the same" is not the same as "same" or "equal"! 50RPM is a significant difference.

Sorry Guys being a newbie all my posts are posted only after being approved by a moderator and hence I cannot participate in realtime.

1. My wagon r vibrates at idling only after attaining the Optimum running temperature as while cold, the rpm is usually much higher.
2. The desired idle and actual rpm readings in all my post have been taken by a Suzuki SDT which is there diagnostic tool at a MASS and it shows the desired idle rpm programmed in the ECM also.
3. Have seen other wagon r at the same MASS with the same idle rpm settings but apparently with a lesser vibration maybe due to reason that those cars' engines were not warm enough.
4. What is the logic for decreasing desired idle With Aircon, I can understand fluctuating rpm and ECM controlling it but if the ECM itself is programmed to accept lower rpm then...?
5. I am not a technical person but my last 2 cars had ECU, and I remember the last one a Getz 1. 3 gls was reprogrammed by hyundai, and I could see that the tacho used to show around 800 without AC and around 900 with ac, so I can assume a) It is not a big deal for a company to reprogram their ECM b) Even in cars where rpm and injection is controlled by ECM normal is to increase idle rpm when ac load is switched on.

[DerAlte]

Originally Posted by Ageing Stud

... What is the logic for decreasing desired idle With Aircon, I can understand fluctuating rpm and ECM controlling it but if the ECM itself is programmed to accept lower rpm then...? ...

At idle, there is only just about enough fuel injected to keep the engine rotating. AC doesn't form part of this initially. When the AC kicks in, the load presented by it to the engine exceeds the load handling capacity corresponding to idle fuel injection. This causes RPM to decrease.

The ECU is not "programmed to accept lower rpm" - it is programmed to take appropriate action at different RPM. Incase of AC coming on, it increases the injection to take care of increase in load.

Originally Posted by Ageing Stud

... so I can assume a) It is not a big deal for a company to reprogram their ECM b) Even in cars where rpm and injection is controlled by ECM normal is to increase idle rpm when ac load is switched on.

Correct, but an ECU is programmed to behave like that from start, it is not 'reprogrammed'.