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Old 13th March 2007, 10:54   #1
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Angry MIL Light glows while running on CNG in Honda city

We have converted one honda city to run on CNG. the kit fitted is italian Landi renzo. The car is running absolutely fine on CNG as well as petrol. Mileage is good pickup and acceleration is also good. But the problem is when it run on CNG it shows MIL light in dash. When we checked the ECU with scantool it shows error code which suggest mixture is too lean. When we checked the voltages generated by both the o2 sensors it gives 0.975 volt while running on CNG.
Now we want that the MIL light should not glow when running on CNG. What can we do. We have tried to insert resistor of different values on the output of o2 sensor to reduce the output voltage to ecu but it's not working. Is there any way to solve this. Can we make some arrangement such that no change is made when it runs on petrol but when it runs on CNG the reading given to ECU is altered so that it doesn't glow the MIL light.
While driving with scantool connected it was observed that the short term fuel trim remains high while running on CNG and long term fuel trim is low compared to the same when run on petrol. So how to reduce the short term fuel trim which is making th MIL ON on CNG.
Kindly suggest some solution to this problem if anybody has come across

Thanking you.
regards,


Rajeev Patel
p_raj14@hotmail.com
Ankleshwar, Gujarat.
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Old 13th March 2007, 16:10   #2
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What I know is that running too lean means you are running too hot also. And running too hot is not good for engine.

I think the car needs a retune to burn CNG.

There are guys here who can provide you good direction.

Last edited by Pankaj401 : 13th March 2007 at 16:12.
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Old 13th March 2007, 23:35   #3
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If its a new kit, You need a Lamda controller with Stepper Motor, Basically it will Pump Required Gas only and is ECU Based Controller which is set using MUT or OBD..!

Ocassionally, I did get Check Engine Error on my CNG XETA, Which was Lamda Error, Got the System Retuned, Lacking the Lamda as Shrimanker Bedini keep on delaying Lamda Control..!
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Old 14th March 2007, 01:13   #4
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One should not fiddle around with O2 sensor & ECU, the kit you bought should have support to tackle such kind of problems please get in touch with the installer, putting resistor of different values without knowing its outcome is pure experimenting any wrong connection can result in permanent failure of O2 sensor or your ECU.
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Old 14th March 2007, 02:46   #5
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Watch the engine temps. As long as its within the safe zone, you are OK. I have seen many OHCs with gas kit showing check engine light.
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Old 14th March 2007, 04:06   #6
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I have not worked or had experience with CNG systems but atleast I know that playing with signal to ECU is not the right way to supress MIL.


Quote:
Originally Posted by rajeevpatel View Post
Now we want that the MIL light should not glow when running on CNG. What can we do. We have tried to insert resistor of different values on the output of o2 sensor to reduce the output voltage to ecu but it's not working. Is there any way to solve this. Can we make some arrangement such that no change is made when it runs on petrol but when it runs on CNG the reading given to ECU is altered so that it doesn't glow the MIL light.
The voltage of the o2 sensor should not be altered, there is a reason why the MIL is coming on, by artificially altering the o2 voltage the problem will not go away.The reading must be brought down by increasing the fuel and not by masking the voltage.You will be simply causing engine knock or engine damage with those lean fuel ratios..


Quote:
Originally Posted by rajeevpatel View Post
While driving with scantool connected it was observed that the short term fuel trim remains high while running on CNG and long term fuel trim is low compared to the same when run on petrol.
How high is it ? Im assuming your STFT has maxed out and the LTFT is more than 20% which is triggering your MIL.


Quote:
Originally Posted by rajeevpatel View Post
So how to reduce the short term fuel trim which is making th MIL ON on CNG ?
The STFT is being increased by the ECU based on your voltage which is screaming out that it is leaning out.
Either reset the ECU and let the ECU add the STFT to the LTFT on its own and see if STFT becomes stable. BUT this is obviously not working as it has already gone above acceptable range of LTFT.

By the way can you check your IPW how long is it on for ? or if your OBD2 software shows IDC , how much IDC % your injectors are on for ? are they maxed out ?
If it was a petrol engine ..u could have increased fuel by increasing injector size, fuel pressure with bigger fuel pump, used a piggback AF controller etc to alter fuel delivery with help of a wideband etc ...similar may be applicable in case of CNG.. ? (maybe similar)
Basically try increasing your fuel/CNG supply..
(Try getting hold of a wideband AFR meter)

Is there a way your CNG system understands/compatible/takes feedback from 02 sensor/obd2 port/ECU ? if NOT then Im confused how the system is designed to work on a existing MPFI engine.. ?
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Old 14th March 2007, 04:10   #7
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Quote:
Originally Posted by Mpower View Post
Watch the engine temps. As long as its within the safe zone, you are OK. I have seen many OHCs with gas kit showing check engine light.
I would panic if my MIL came on..
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Old 14th March 2007, 04:33   #8
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your MIL light being on is a clear indication of an adjustment to be made for optimal performance make sure you fix the issue instead of using a workaround only coz you may spend less on cng but if you blow a cylinder or something then theres no point having CNG.
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Old 14th March 2007, 10:23   #9
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I have'nt worked on CNG systems, but this seems like a normal closed-loop behaviour of the sensitive Euro 3 (and some Euro 2) spec ECUs. If ECU detects the afrs do not behave as per ECU predictions and actions, it usually throws a MIL. Nothing to worry about, unless something else is kaput.

You might have to get a CNG kit capable of maintaing at least a stoich mixture, if not closed-loop controller, as wolfenstein said. Most of the LPG/CNG guys tend to go on the leaner side for efficiency, which should'nt be a problem with the typical non-stressed street engine.

Last edited by rdkarthik : 14th March 2007 at 10:38.
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Old 14th March 2007, 13:31   #10
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I guess the NHC does not come with a temp. gauge?
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Old 14th March 2007, 14:09   #11
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Quote:
Originally Posted by GTO View Post
I guess the NHC does not come with a temp. gauge?
Nope, it does not - just an indicator for cold/hot.
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Old 14th March 2007, 22:24   #12
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Quote:
Originally Posted by goldie_malhotra View Post
Nope, it does not - just an indicator for cold/hot.
yes..
what "rajeevpatel" needs on his CNG/petrol engine car is a EGT gauge..
the temp indicator gauge is just useless in this case..
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Old 24th July 2012, 16:16   #13
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Default Re: MIL Light glows while running on CNG in Honda city

Specifically for Honda Cars, online forums are full of complaints about the check engine light remaining on all the time, more so than other brands. I have a 2005 Honda City iDSi, (non VTEC) and am planning to go for a CNG kit with this single issue holding me back. Searched through Team-bhp.com and other online forums, but did not get any conclusive user feedback about their Honda Car Check Engine problem being solved. I would appreciate if any user has such feedback. Observations so far:

As noted in the thread above, the error code points to "mixture too lean" - the associated risk is engine over-heating.

Across forums, there are two patterns to this:
1) The check light stays on all the time
This would in most cases be due to the CNG fitter tuning it for efficiency. This should be easily resolved by tweaking the peak speed adjuster.
Are there any other reasons why this could happen? Is there a common mis-wiring that anyone has gotten rectified to resolve this issue?

2)The check light comes on when braking, decelerating from 80 to 20 etc.
This would be more complex - during deceleration, when you suddenly leave the accelerator, the gas supply presumably decreases more abruptly than the Honda ECU's tolerances allow for.
I am not sure from the comments I went through whether this pattern occurs with open loop systems only, or closed loop as well.
Any ideas on how this could be resolved? The normal tuning/setting on the kit is unlikely to resolved this fully - only decrease its occurrence. Are there any tweaks on the timing advancer/lambda, or completely outside the kit that could resolve this, without affecting performance when running on petrol?

Finally, my problem is when I called CNG fitters in Thane, they say that the light normally comes on in Honda cars, and that is "normal". I am not ready to settle for that. Nor do I want to go for a sequential kit which involves cylinder drilling. Can anyone suggest a solution, or a fitter who is more knowledgeable than these?
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Old 17th August 2012, 15:02   #14
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Default Re: MIL Light glows while running on CNG in Honda city

I have been using CNG kit on my Lancer for last 1 year and absolutely no issues at all. I can't speak the technical language but the Engine or MIL light is ON whenever it runs on CNG. And goes off when I shift to petrol.

The fitter said that this is normal. I did an MUT setting / engine diagnostics recently at Aquest Auto - Mitsu *** and everything is normal ..all parameters I mean.

So i am not worried about that light being ON during CNG run.
It possibly only means a deviation from pre-set parameters which is designed only for petrol use and it recognises CNG as 'foreign'..

Does that help ? I could be wrong
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Old 17th August 2012, 22:45   #15
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Default Re: MIL Light glows while running on CNG in Honda city

Quote:
Originally Posted by ijeff View Post
I have been using CNG kit on my Lancer for last 1 year and absolutely no issues at all. I can't speak the technical language but the Engine or MIL light is ON whenever it runs on CNG. And goes off when I shift to petrol.

The fitter said that this is normal. I did an MUT setting / engine diagnostics recently at Aquest Auto - Mitsu *** and everything is normal ..all parameters I mean.

So i am not worried about that light being ON during CNG run.
It possibly only means a deviation from pre-set parameters which is designed only for petrol use and it recognises CNG as 'foreign'..

Does that help ? I could be wrong
Thanks for the input - reassuring to know that there are no issues over a 1 year period with the light remaining on all the time!
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