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Old 11th November 2008, 12:21   #1
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Angry Improper Ignition in Optra !!

Problem: Engines seems to be misfiring while igniting in mornings, though i ain't so much sure if it the problem is related to CNG anyhow as car starts in petrol mode (But GM engineer states though, read on for their comments). Engine takes too long ignition, some time it seems engine is coughing.

Considerations:
- Spark Plugs changed recently only with GM OEM one i.e. NGK
- Engine Oil changed at 65K while Car Service
- Fuel Injectors cleaned at 68K
- Battery is perfect
-Engine Decarbonised at 60K

Possible Causes:
- O2 Sensor seems to be conked off - I ain't so much sure about them. But still it can be stated as a problematic area as once ecu is re-setted, it works very fine i.e. Engine starts even at half ignition. But latter once CEL comes up it starts misfiring again. Car has completed 69K, Does O2 sensor has lived up it's life ??
- Ignition Unit needs Service - It might had caught up with Carbon!! It looked like a wild suggestion to me, as after ECU resetting how come everything goes fine ??
- Any further pointers ??

After getting up checked it GM Service Center last morning, GM technician gave some wild cause stating Engine valves are "Short of carbon". He further added that car needs to be ran on petrol for carbon formation so as valves can work properly Once the carbon is formed on valves it will start smoothly !!

While looking at bay, A Crack is discovered in Air-filter box.. can it be a cause of problem anyhow ??

What is your perspectives for the said problem ??
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Old 11th November 2008, 12:34   #2
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Do you get the same problems if you use petrol ??

Try resetting the ECU (as your problems go away after a reset) and run it on petrol for few 100 km's just for the diagnostic purpose.

We first need to diagnose if its related to petrol or CNG usage. Then we can move ahead on the solution part.
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Old 11th November 2008, 12:58   #3
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My friend here in FBD has a optra. He is also facing similar issues , He was told that the fuel pump motor is faulty.
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Old 11th November 2008, 13:45   #4
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Quote:
Originally Posted by dadu View Post
Do you get the same problems if you use petrol ??

Try resetting the ECU (as your problems go away after a reset) and run it on petrol for few 100 km's just for the diagnostic purpose.

We first need to diagnose if its related to petrol or CNG usage. Then we can move ahead on the solution part.
Done the same for few 100s kms. Drove around 4-5Kms on petrol before reaching home in evening. But still looks like a alien problem to me.

It should be related to Petrol as while running in CNG it runs flawlessly. However, problem arises only when one has to crank the ignition.

Multiple and long ignitions, High RPMs after such cranks though settled after a minute idling. I just HATE it

Quote:
Originally Posted by low_bass_makker View Post
My friend here in FBD has a optra. He is also facing similar issues , He was told that the fuel pump motor is faulty.
Mine problem might not be related to fuel pump as fuel flow is normal in injectors and fuel line.
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Old 11th November 2008, 19:33   #5
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Hm.

It's unlikely to be an ignition problem if the car seems to be running fine on CNG. (both fuels use the same ignition mapping from the same ECU and the same ignition components). Also, since Optra runs direct ignition in the form of Distributor-less Ignition, it's highly unlikely that the system in itself is faulty. Besides, CNG has slightly lesser calorific value than petrol, so that probability is ruled out....

Second: Fuelling; Check fuel pressure, injectors and fuel lines, since the problem is only affecting "petrol mode".

Third: A cracked air-box could result in misfires (mostly in carbs, due to air pressure differential; but that happens more in LPG kitted cars). But not to the magnitude that is being spoken of. Nevertheless, a cracked intake box is harmful all the same. Replace it.

Fourth : A faulty O2 sensor could be the culprit as well. But no way to isolate it unless you can check the AFR. A simpler way is to replace the sensor and check for problem recurrence anyways (as a trial-and-error sorts).
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Old 11th November 2008, 22:15   #6
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i have exactly similar issues in my Palio 1.2 which is fitted in CNG. it takes a long self (cold-start) and jerks while running on petrol but runs fine on CNG?
i was also thinking that the o2 sensor has conked off. i havent been able to visit the service center.

can anyone suggest how harmful could it prove to be if i continue running on CNG for a week or so more?
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Old 14th November 2008, 01:32   #7
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well my santro which usually runs on CNG had the same problem last year and it was traced back to a faulty fuel pump. one the pump was changed all was back to normal.
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Old 14th November 2008, 09:21   #8
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Ashish !! Have you been able to track it down ?
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Old 15th November 2008, 00:08   #9
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The problem seems to be due to incorrect setting of CNG . Here it how it goes the ecu has sets short term fuel trims and long term fuel trims ie. when the lambda sensor in the exhaust senses rich fuel mix it shortens the pulse to the injectors to make the mixture lean and vice verse. the long term fuel trim is stored in the ecu and used when cold starting on petrol since during cold start the ecu is in open loop mode because the lambda sensor only starts working when the engine reaches certain temprature . so during cold start the ecu has no feedback from lambda so it relies on the previously stored LFT on deciding upon the duration of the injector pulse. Now if your engine is running rich on CNG during the course of the day the LFT is set to extremly lean as the ecu tries to correct the problem but ecu does not have control over cng mixture so the LFT remains at lean. This LFT info is used by ecuduring next morning cold start on petrol causing a lean mixture where a rich mixture is needed. The remedy is using a lambda for cng which will keep the cng-air mixture within limits or alternately maybe a retune of cng mixture . By the way does the ECU lights up the MIL ( malfunction information Light or the orange check light ) during the course of the day ?
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Old 16th November 2008, 11:34   #10
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Quote:
Originally Posted by veyron1 View Post
Hm.

It's unlikely to be an ignition problem if the car seems to be running fine on CNG. (both fuels use the same ignition mapping from the same ECU and the same ignition components). Also, since Optra runs direct ignition in the form of Distributor-less Ignition, it's highly unlikely that the system in itself is faulty. Besides, CNG has slightly lesser calorific value than petrol, so that probability is ruled out....

Second: Fuelling; Check fuel pressure, injectors and fuel lines, since the problem is only affecting "petrol mode".

Third: A cracked air-box could result in misfires (mostly in carbs, due to air pressure differential; but that happens more in LPG kitted cars). But not to the magnitude that is being spoken of. Nevertheless, a cracked intake box is harmful all the same. Replace it.

Fourth : A faulty O2 sensor could be the culprit as well. But no way to isolate it unless you can check the AFR. A simpler way is to replace the sensor and check for problem recurrence anyways (as a trial-and-error sorts).
-Fuel Pressure seems to be perfect as car run smooth as well in petrol mode too.
-I might be visiting Service Center this week for the O2 trial-and-error method after doing the CNG Lambda trial-and-error method.

Quote:
Originally Posted by coolmob View Post
well my santro which usually runs on CNG had the same problem last year and it was traced back to a faulty fuel pump. one the pump was changed all was back to normal.
How was your santro behaving while on petrol ?

Quote:
Originally Posted by Shashank.A View Post
Ashish !! Have you been able to track it down ?
Not yet, though i have been doing the temp fix now-a-days, instructed driver to reset the ECU every morning

Quote:
Originally Posted by ask77 View Post
The problem seems to be due to incorrect setting of CNG . Here it how it goes the ecu has sets short term fuel trims and long term fuel trims ie. when the lambda sensor in the exhaust senses rich fuel mix it shortens the pulse to the injectors to make the mixture lean and vice verse. the long term fuel trim is stored in the ecu and used when cold starting on petrol since during cold start the ecu is in open loop mode because the lambda sensor only starts working when the engine reaches certain temprature . so during cold start the ecu has no feedback from lambda so it relies on the previously stored LFT on deciding upon the duration of the injector pulse. Now if your engine is running rich on CNG during the course of the day the LFT is set to extremly lean as the ecu tries to correct the problem but ecu does not have control over cng mixture so the LFT remains at lean. This LFT info is used by ecuduring next morning cold start on petrol causing a lean mixture where a rich mixture is needed. The remedy is using a lambda for cng which will keep the cng-air mixture within limits or alternately maybe a retune of cng mixture . By the way does the ECU lights up the MIL ( malfunction information Light or the orange check light ) during the course of the day ?
This is another wild guess running in my mind, CNG Lambda might be an issue as i had read somewhere that it too might create the issue. I am planning to visit the CNG installer in this week.
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Old 16th November 2008, 22:07   #11
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Try running on petrol at the end of the day for the last one kilometer or so ( the ECU check lite should not be on ) If the problem is with CNG running rich then the last km run on petrol will ensure that the LFT will normalize and you will get a good cold start in the morning on petrol.
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Old 19th November 2008, 14:22   #12
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Well I just reached office and a surprise was waiting for me

Had fixed up an appointment with Shrimankar Auto Gas people in morning, driver went over and after various trial-error shots Lambda unit found faulty. Unit replaced with a new one and Car running/igniting smoothly as previously. cheers:

Called up the supervisor and after a brief discussion with Shrimankar Auto Gas supervisor I got to know that it is basically error codes which develops in Lambda ECU and cannot be restted without appropriate tools. It is not something which can resetted by shorting battery terminals which we usually do in ECU cases. As a matter of gesture he replaced the unit rather than resetting the same Lambda.

Thanks for all who inputted their valuable suggestions !!!
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Old 23rd November 2008, 00:45   #13
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how is the optra performing now ? can you let me know the make and price of the lambda you are using ?
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Old 24th November 2008, 09:35   #14
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Car is performing very well, Car starts at half crank

Price was included into the total price of the CNG kit so cannot scrutinize the price of Lambda from the total cost.
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Old 24th November 2008, 11:14   #15
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Quote:
As a matter of gesture he replaced the unit rather than resetting the same Lambda.
I smell a colony of rats bro. But all's well now

He's not a charity, is he?
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