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Old 15 August 2009, 14:21   #1
mrwrxcar
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Default My car is running lean

I've noticed lately, my car has been running lean. Could this be due to the lambard censor? I've checked the pipe work for leaks, unplugged the AFM and engine stalls, checked the spark plugs, and it does look like it's running lean. Any ideas? I've fitted a K&N panel filter, have an open mouth down pipe and a standard ECU (not chipped). Would it be possible to have a lazy lambard censor? Just one more thing, when the engine is hot, and I let it idle for 2 or 3 minutes, the air/fuel ratio gauge will start going up and acting normally. Have I missed something?

Any advice greatly appreciated.
Thank you
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Old 15 August 2009, 14:44   #2
dabow
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Originally Posted by mrwrxcar View Post
I've noticed lately, my car has been running lean. Could this be due to the lambard censor? I've checked the pipe work for leaks, unplugged the AFM and engine stalls, checked the spark plugs, and it does look like it's running lean. Any ideas? I've fitted a K&N panel filter, have an open mouth down pipe and a standard ECU (not chipped). Would it be possible to have a lazy lambard censor? Just one more thing, when the engine is hot, and I let it idle for 2 or 3 minutes, the air/fuel ratio gauge will start going up and acting normally. Have I missed something?

Any advice greatly appreciated.
Thank you
id have the car rolling raoded. they would give you a better idea mate
or pm some of the tuners on here for better advice mate

if running lean, dont push her
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Old 15 August 2009, 14:50   #3
al02uk
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does it say bank 1 running lean by any chance?
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Old 15 August 2009, 14:58   #4
Splitpin
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Originally Posted by mrwrxcar View Post
I've noticed lately, my car has been running lean.
What makes you think that, and what model and model year is this car?

Quote:
Could this be due to the lambard censor?
If it's running lean under boost, no. Under boost the mixture is calculated via rpm and the airflow meter only. The O2 sensor only affects the mixture during off boost/low speed cruise.

Quote:
I've checked the pipe work for leaks, unplugged the AFM and engine stalls,
The "unplug the AFM and see if the engine stalls test" is complete bullsh*t. Unfortunately it has been repeated by enough people on here long enough that it has come to be regarded as "fact", which is a problem when it gives false confidence and can (both ways) do more harm than good.

It proves nothing, one way or the other so if you are using this as evidence that your air flow meter is "good", I'm afraid it simply doesn't work in practice. At this point, for all you know, the MAF might be good, or it might not be, this "test" doesn't help you determine either way.

Quote:
checked the spark plugs, and it does look like it's running lean. Any ideas?
Do all four plugs look the same? From what you've said so far we know a couple of things. First of all you have an AFR meter, that, presumably, piggybacks onto the standard lambda sensor for its input, yes? Is this telling you that your AFR's has recently leaned off under load? If so there are two possible explanations:

First of all, your lambda sensor has degraded a little (or reads wrong when it gets very hot) and as a result, the reading on your AFR meter is showing lean but the actual mixture is correct.

The other possible explanation is that either due to the engine being able to ingest unmetered air somewhere (check the induction pipework again), or due to a failing airflow meter, the mixture is being set too lean.

Are you monitoring knock? If so, has the activity you see there also increased?

Quote:
Would it be possible to have a lazy lambard censor? Just one more thing, when the engine is hot, and I let it idle for 2 or 3 minutes, the air/fuel ratio gauge will start going up and acting normally.
The stock narrowband sensors tend to become unresponsive and/or inaccurate when got really hot (i.e. foot down for extended periods of time) so this may explain what you're seeing - the reading recovers as the sensor cools back down.

However, as mentioned the lambda sensor has nothing to do with setting the mixture once into positive boost/high revs. If the plugs tell you that it's lean, then your best next move would probably be to beg, borrow or steal someone's DeltaDash (etc) and actually monitor the readings from the MAF sensor (and the final mixture value) as the car is being driven.

Last edited by Splitpin; 15 August 2009 at 15:05.
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Old 15 August 2009, 15:00   #5
mrwrxcar
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does it say bank 1 running lean by any chance?
Sorry, I've never heard of this term. Could you explain it please.
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Old 15 August 2009, 15:09   #6
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Sure,

a common fault code for a faulty O2 sensor is P0171 which is "sytem too lean (bank1)"
If you plug a diagnostics machine into your car it could be that.

I had the same a couple of years back
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Old 15 August 2009, 15:11   #7
mrwrxcar
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Originally Posted by Splitpin View Post
What makes you think that, and what model and model year is this car?



If it's running lean under boost, no. Under boost the mixture is calculated via rpm and the airflow meter only. The O2 sensor only affects the mixture during off boost/low speed cruise.



The "unplug the AFM and see if the engine stalls test" is complete bullsh*t. Unfortunately it has been repeated by enough people on here long enough that it has come to be regarded as "fact", which is a problem when it gives false confidence and can (both ways) do more harm than good.

It proves nothing, one way or the other so if you are using this as evidence that your air flow meter is "good", I'm afraid it simply doesn't work in practice. At this point, for all you know, the MAF might be good, or it might not be, this "test" doesn't help you determine either way.



Do all four plugs look the same? From what you've said so far we know a couple of things. First of all you have an AFR meter, that, presumably, piggybacks onto the standard lambda sensor for its input, yes? Is this telling you that your AFR's has recently leaned off under load? If so there are two possible explanations:

First of all, your lambda sensor has degraded a little (or reads wrong when it gets very hot) and as a result, the reading on your AFR meter is showing lean but the actual mixture is correct.

The other possible explanation is that either due to the engine being able to ingest unmetered air somewhere (check the induction pipework again), or due to a failing airflow meter, the mixture is being set too lean.

Are you monitoring knock? If so, has the activity you see there also increased?



The stock narrowband sensors tend to become unresponsive and/or inaccurate when got really hot (i.e. foot down for extended periods of time) so this may explain what you're seeing - the reading recovers as the sensor cools back down.

However, as mentioned the lambda sensor has nothing to do with setting the mixture once into positive boost/high revs. If the plugs tell you that it's lean, then your best bet would be to beg, borrow or steal someone's DeltaDash (etc) and actually monitor the readings from the MAF sensor (and the final mixture value) as the car is being driven.
Thanks for the quick replies.
This actually happens when I'm just cruising, just off boost. When I put my foot down it actually registers nothing, just goes very lean. I understand that when you put your foot down it will run lean. This is on a '94 Impreza WRX. I may have to borrow parts of my wife's car to compare. I may have to have it on the rolling road, as suggested.
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Old 15 August 2009, 15:25   #8
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Originally Posted by mrwrxcar View Post
Thanks for the quick replies.
This actually happens when I'm just cruising, just off boost. When I put my foot down it actually registers nothing, just goes very lean. I understand that when you put your foot down it will run lean. This is on a '94 Impreza WRX. I may have to borrow parts of my wife's car to compare. I may have to have it on the rolling road, as suggested.
have you wired the afr gauge up the correct way? ie not back to front?
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Old 15 August 2009, 15:25
 
 
 
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