System Too Lean Bank1/Bank2
10-05-2014, 10:20 PM
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System Too Lean Bank1/Bank2 Hello everyone. I own a 2004 CTS-V and also a 2007 Sierra Denali. Currently, I have a concern regarding my CTS-V. I plugged in a dash monitor a couple nights ago to record some 0-60 times and see how the car was performing and noticed I had DTCs. Bank1/2 Lean. So I cleaned my MAF, checked all my intake manifold bolts, Throttle Body bolts, etc... cannot figure it out. I do own HP Tuners and I have logged a couple drives. Looks like at idle and any other time I am not on the throttle it shoots to 25/25 in the Long Term Trims. At a steady 60mph I am around 14.1 (Bank 1) and 10.9 (Bank 2), but it varies as high as 21.9/21.1 Anyone have any ideas? Thanks in advance.
-Steve
-Steve
10-05-2014, 11:37 PM
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I actually just realized I didn't save the " after" MAF cleaning log. This log was before I cleaned the MAF and the reason it is so short is that my right front tire blew apart on the highway. I have a horrible ear infection with blood draining out my ear yesterday and today so I'm not very proactive in trying to track it down. I'm going to check for leaks tomorrow around the throttle body and intake manifold.
10-06-2014, 10:30 PM
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No one has any suggestions or comments? A friend suggested having the fuel system cleaned by a GM dealership and having them test fuel pressure to be sure it is receiving enough fuel. Any thoughts on that?
10-06-2014, 11:54 PM
#4
Sounded like you were going to check a few things and get back to us. Seems like you have too much air, not enough fuel, or something funny with O2 sensors at idle. If you have buildup in your throttle body it might not be closing all the way, letting a little much air in. Also any leak between MAF and intake. Unmetered air causes a lean condition. Beyond that, any other vacuum leaks? I would think that a clogged injector or low fuel pressure issue would only get worse at higher RPM. Fuel requirements are typically lowest at idle. But you can test fuel pressure with a $20 gauge from Harbor Freight.
10-07-2014, 11:02 AM
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I was hoping someone would say it's normal stop pulling your hair out. Since the car starts, idles, runs perfectly fine. If it werent for the codes showing up in HP Tuners, I would have continued driving it as normal.
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10-07-2014, 09:22 PM
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I was told by a mechanic (Honda dealership) to spray starting fluid around the MAF sensor, throttle body, throttle body adapter, intake and injectors and if/when the vehicle revved up from sucking in the ether I would know where the vacuum leak was. I did this and the vehicle's idle never altered at any moment so I determined there are no vacuum leaks in these areas. Anyone have a view on this or other things to check?
Added note : I called the two parts stores in town and neither had a fuel pressure tester in stock, but I did find an automotive repair facility near my home that will test my fuel pressure for $30 on Friday. I will report the findings of that when it has been tested. I believe the pressure should be no less than 55psi with the engine running, if this is incorrect please do chime in. Thanks.
Added note : I called the two parts stores in town and neither had a fuel pressure tester in stock, but I did find an automotive repair facility near my home that will test my fuel pressure for $30 on Friday. I will report the findings of that when it has been tested. I believe the pressure should be no less than 55psi with the engine running, if this is incorrect please do chime in. Thanks.
Last edited by ouchnie; 10-07-2014 at 09:31 PM. Reason: added information.
10-07-2014, 09:53 PM
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So... I started the car and while it was idling I unplugged the MAF. The car idled up slightly, but it idled smooth as silk. I plugged the MAF back in and it immediately bogged down and started to stutter/fluctuate RPMS. Is this normal when a MAF is reconnected to have some stutter or does that indicate a MAF malfunction? Thoughts?
10-07-2014, 10:02 PM
#12
Clean it again..and maybe clean and put some dialectric grease on the connectors before you plug it back in.
I've been a fan of the cigarette smoke test for vacuum leaks. Light one..or your buddy's..and hold it all around the motor and see if the smoke gets interested in any particular spot. Something you can actually watch rather than the carb cleaner method where you listen for idle change which is at least a delayed reaction...and may not be accurate for *small* leaks.
FWIW, I believe the computer will compensate when no signal(or way bad signal) is available from a particular sensor..so no MAF available it may go to speed density mode or similar. May account for different/better idle. So that may not be a true test but is surely interesting!
I've been a fan of the cigarette smoke test for vacuum leaks. Light one..or your buddy's..and hold it all around the motor and see if the smoke gets interested in any particular spot. Something you can actually watch rather than the carb cleaner method where you listen for idle change which is at least a delayed reaction...and may not be accurate for *small* leaks.
FWIW, I believe the computer will compensate when no signal(or way bad signal) is available from a particular sensor..so no MAF available it may go to speed density mode or similar. May account for different/better idle. So that may not be a true test but is surely interesting!
10-07-2014, 10:12 PM
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I have heard of people using cigars for this type of test. I will try to find a smoker and have them indulge me. A tuner I have a lot of respect for told me that unplugging the MAF simply sends the PCM into Speed Density mode which doesn't truly indicate anything to do with the MAF. It still seems odd to me, though.
MAF video
MAF video
Last edited by ouchnie; 10-07-2014 at 10:31 PM. Reason: added video
10-07-2014, 10:30 PM
#14
Well that tells us likely that either MAF is way off or the combo of MAF and other sensors in "normal" mode combines to make a bad situation.
How old are your o2 sensors? Perhaps they are clogged enough that they arent registering properly at low exhaust flow.
How old are your o2 sensors? Perhaps they are clogged enough that they arent registering properly at low exhaust flow.
10-07-2014, 10:33 PM
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The engine has 68K miles on it, I purchased it a few months ago. I am under the impression everything is as it was from the factory - old. If you feel strongly changed the o2 sensors is a good idea, I will certainly do that promptly.
10-07-2014, 11:52 PM
#16
I wouldn't say I feel strongly but they are a wear item. Seems like any kind of sensor gets less accurate as it ages and starts to suffer in the small ranges first. But that may be my imagination or even just my particular experience. They are over 10 years old though..so anything is possible. If you have HPT, could you try enriching the idle mixture and see what happens?
10-07-2014, 11:53 PM
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I honestly do not know how to use HP Tuners for anything beside disabling the Torque Management on my 2007 Denali. I have been afraid to make any changes. I would be willing to try adding fuel at idle, I will have to investigate how to do that.