C7 Running lean, air leak question
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The correct way to diagnose leaking is a pressure test, not smoke. Some leaks will not leak until +10 or -10psi is applied. I always pressure test before tuning a forced inducted vehicle. When they are not forced inducted the leaking will cause high idle speed condition if it is severe leak, which is obvious to the IAC or DBW closing count unable to maintain idle speed. Or cylinder imbalance (roughness, vibration) if the leak is huge near one head port, will potentially set one side of the engine leaner than the other. In which cause it should be obvious there is a leak behavior because one Oxygen sensor will show much leaner all the time due to the leak. So if there is a leak in the exhaust before the oxygen sensor (from maf to oxygen sensor pathway) then that one side of the engine with the leak is obvious detected.
If both sides are leak, well obviously it must be a leaking air before the intake manifold plenum or near that area. However enough of a leak here will cause obvious idle air flow issues as I pointed out, making a leak obvious and uncontrollable engine idle rpm will rise too high.
Based on the lack of presented evidence that any particular oxygen sensor side was affected (if you had that info you did not share or it was left out) I rule out exhaust leaking issues assuming the oxygen sensors are indeed properly flipping 15mV to 1055mV (crossing the median at expected frequency indicating correct fuel control closed loop attempt)
Based on the lack of presented evidence of high idle speed, no high uncontrollable idle, this rules out significant intake manifold leaking.
Therefore the issue does not appear to be any leak related so far with presented information.
Next, I raise the concern or question of the term 'lean'. It is a very strange thing to say to somebody with an engine that needs to be tuned. I mean, if you bring me a fresh vehicle with a new engine and it needs tuning, it isn't going to run properly unless I tune it properly, by which point it will no longer run 'lean' unless I tune it to run lean. I guess what I'm saying is, the initial symptom presented as being 'lean' when the engine is untuned is highly irregular, as why would we expect a modified engine that requires tuning to not run lean or rich before such tuning has taken place.
This leads me to believe the engine has not been modified and a tune is simply being copied down to erase some potentially original tables with new settings. And that no significant modification has taken place, thus the tune is not 'needed' and the original tune is said to be intact and operational, which is the only way one could even assert that it was running 'lean' e.g. the tune is already done, finished, and we noticed that it is too lean for some reason. So why would the tune original be too lean if the engine has not been modified? Here are the possible reasons I can quickly think of
1. Dirty maf
2. clogged injectors (all of them? unlikely. But a few maybe)
3. dropping fuel pressure (did anybody mechanically measure this? Why isnt this being pointed out as a primary potential?)
4. Bad oxygen sensors (would be obvious, so not this)
5. wrong gasoline. You got some E15 or something it will lean out. The gas pump says it might have E15...
6. Misfire. Oxygen and unburnt fuel show up as a lean mixture. Could need maintenance...
6A-F is maintenance related, plugs, wires, balance test, oil test, compression test, etc... do the work to maintain the engine before you suspect "problems"
7. Engine air density changes. Extremely cold or driving down a mountain to more dense air will move trims around. Sometimes inexplicably.
8. Odd friction events causing increased load. It is possible to change engine load and populate less frequent regions of a fuel map due to new vehicle perceived mass, which would take trims for a walk learning this new load at some original operating RPM/velocity.
As a scientist and tuner I would be starting with engine health and misfire detection. plug inspection time. New gasoline. You start easy stuff first. Clean the maf. Try a different maf. Disable one cylinder at a time to watch how the a/f changes and the idle speed changes and engine noise quality changed. Compression test for balance and general health. Pressure test just to rule out tiny leaks if possible. Observe the behavior of the oxygen sensors flipping as they should. Observe fuel pressure using reliable mechanical gauge. Check the general health of the vehicle, brakes, rotating parts, bearings, bushings. Loud cars easily hide noises.
Once I determine the engine is healthy and setup properly for tuning and hardware has been updated maintained then you can see the injector pulse and engine breathing is rationale or not. If everything is rationale and all data looking good then you can tune the engine properly if it needs to be. There isn't any 'fixing a lean condition' before you tune - the engine either needs tuning, or it does not need tuning. It is either healthy or not. Being "lean" isn't a feasible or excusable concern.
If both sides are leak, well obviously it must be a leaking air before the intake manifold plenum or near that area. However enough of a leak here will cause obvious idle air flow issues as I pointed out, making a leak obvious and uncontrollable engine idle rpm will rise too high.
Based on the lack of presented evidence that any particular oxygen sensor side was affected (if you had that info you did not share or it was left out) I rule out exhaust leaking issues assuming the oxygen sensors are indeed properly flipping 15mV to 1055mV (crossing the median at expected frequency indicating correct fuel control closed loop attempt)
Based on the lack of presented evidence of high idle speed, no high uncontrollable idle, this rules out significant intake manifold leaking.
Therefore the issue does not appear to be any leak related so far with presented information.
Next, I raise the concern or question of the term 'lean'. It is a very strange thing to say to somebody with an engine that needs to be tuned. I mean, if you bring me a fresh vehicle with a new engine and it needs tuning, it isn't going to run properly unless I tune it properly, by which point it will no longer run 'lean' unless I tune it to run lean. I guess what I'm saying is, the initial symptom presented as being 'lean' when the engine is untuned is highly irregular, as why would we expect a modified engine that requires tuning to not run lean or rich before such tuning has taken place.
This leads me to believe the engine has not been modified and a tune is simply being copied down to erase some potentially original tables with new settings. And that no significant modification has taken place, thus the tune is not 'needed' and the original tune is said to be intact and operational, which is the only way one could even assert that it was running 'lean' e.g. the tune is already done, finished, and we noticed that it is too lean for some reason. So why would the tune original be too lean if the engine has not been modified? Here are the possible reasons I can quickly think of
1. Dirty maf
2. clogged injectors (all of them? unlikely. But a few maybe)
3. dropping fuel pressure (did anybody mechanically measure this? Why isnt this being pointed out as a primary potential?)
4. Bad oxygen sensors (would be obvious, so not this)
5. wrong gasoline. You got some E15 or something it will lean out. The gas pump says it might have E15...
6. Misfire. Oxygen and unburnt fuel show up as a lean mixture. Could need maintenance...
6A-F is maintenance related, plugs, wires, balance test, oil test, compression test, etc... do the work to maintain the engine before you suspect "problems"
7. Engine air density changes. Extremely cold or driving down a mountain to more dense air will move trims around. Sometimes inexplicably.
8. Odd friction events causing increased load. It is possible to change engine load and populate less frequent regions of a fuel map due to new vehicle perceived mass, which would take trims for a walk learning this new load at some original operating RPM/velocity.
As a scientist and tuner I would be starting with engine health and misfire detection. plug inspection time. New gasoline. You start easy stuff first. Clean the maf. Try a different maf. Disable one cylinder at a time to watch how the a/f changes and the idle speed changes and engine noise quality changed. Compression test for balance and general health. Pressure test just to rule out tiny leaks if possible. Observe the behavior of the oxygen sensors flipping as they should. Observe fuel pressure using reliable mechanical gauge. Check the general health of the vehicle, brakes, rotating parts, bearings, bushings. Loud cars easily hide noises.
Once I determine the engine is healthy and setup properly for tuning and hardware has been updated maintained then you can see the injector pulse and engine breathing is rationale or not. If everything is rationale and all data looking good then you can tune the engine properly if it needs to be. There isn't any 'fixing a lean condition' before you tune - the engine either needs tuning, or it does not need tuning. It is either healthy or not. Being "lean" isn't a feasible or excusable concern.
“Pressure Testing” may be ONE of the methods but I wouldn’t say it’s the CORRECT way of finding a vacuum leak…over the past 15 years I’ve been through some training classes with some of the best automotive instructors and diagnosticians in the country named John Thornton and Bernie Thompson and never once has that method been discussed…that method may work for you but I consider smoke testing the gold standard for me…and PLEASE don’t say to pressure test for an EVAP leak with 10 psi of pressure !!
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
[QUOTE=Kingtal0n;1608045349]
Next, I raise the concern or question of the term 'lean'. It is a very strange [Quote]
Wow .. nothing like a over compllcating a diagnosis lol lol
It is not a new engine, it is one that has been running on a factory tune , And a preasure test will tell you you got a leak but on a NA car , smoke test will tell you where the leak is
😀
Lew is an experenced and well known remote tuner , he is not onsite , he is seeing the "lean" information in the tune logs .
Considering that OP makes no mention of the car running bad before sending Lew the logs one can assume it was running fine but what the OP did not know was his short term or long term fuel trims were out of wack
There is also no mention of a CEL which would pop on if several conditions you presented above were happening ....
You get a little deep on your trouble shooting , i always use the KISS principal. The OP's car is not supercharged (Lew does not tune supercharged or highly modified cars) nor is it modified again because you would need a wide band and the fact that nobody uses a Diablo tuner for modified cars , just small bolt ons if anything , most are just looking for a few more HP and better drivablity
Yes there are 100 things that could cause the readings , thats why Lew said ... you got a lean condition....and he did not diagnose it
Before jumping off the deep end here with all your scenarios, It would be better suggest someone do a simple scan with GDS2 or the like as it would show all the PIDs and point him or his mechanic in the right direction. It might be something as simple as a slight exhaust leak or a O2 sensor going bad
Do you know how many exhaust leaks I have come across that caused the 02 sensor to wig out ...
OP if you have not figured it out yet just have you car scanned , present your findings and we can help you from there
Dave
Next, I raise the concern or question of the term 'lean'. It is a very strange [Quote]
Wow .. nothing like a over compllcating a diagnosis lol lol
It is not a new engine, it is one that has been running on a factory tune , And a preasure test will tell you you got a leak but on a NA car , smoke test will tell you where the leak is
😀Lew is an experenced and well known remote tuner , he is not onsite , he is seeing the "lean" information in the tune logs .
Considering that OP makes no mention of the car running bad before sending Lew the logs one can assume it was running fine but what the OP did not know was his short term or long term fuel trims were out of wack
There is also no mention of a CEL which would pop on if several conditions you presented above were happening ....
You get a little deep on your trouble shooting , i always use the KISS principal. The OP's car is not supercharged (Lew does not tune supercharged or highly modified cars) nor is it modified again because you would need a wide band and the fact that nobody uses a Diablo tuner for modified cars , just small bolt ons if anything , most are just looking for a few more HP and better drivablity
Yes there are 100 things that could cause the readings , thats why Lew said ... you got a lean condition....and he did not diagnose it
Before jumping off the deep end here with all your scenarios, It would be better suggest someone do a simple scan with GDS2 or the like as it would show all the PIDs and point him or his mechanic in the right direction. It might be something as simple as a slight exhaust leak or a O2 sensor going bad
Do you know how many exhaust leaks I have come across that caused the 02 sensor to wig out ...
OP if you have not figured it out yet just have you car scanned , present your findings and we can help you from there
Dave
Last edited by Dcasole; Aug 2, 2024 at 07:08 AM.
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
“Pressure Testing” may be ONE of the methods but I wouldn’t say it’s the CORRECT way of finding a vacuum leak…over the past 15 years I’ve been through some training classes with some of the best automotive instructors and diagnosticians in the country named John Thornton and Bernie Thompson and never once has that method been discussed…that method may work for you but I consider smoke testing the gold standard for me…and PLEASE don’t say to pressure test for an EVAP leak with 10 psi of pressure !!
I use it first even on boosted applications and only if I think I have an issue do I preasure test
Dave
Safety Car
Joined: Oct 2007
Posts: 4,225
Likes: 1,080
From: South Florida
“Pressure Testing” may be ONE of the methods but I wouldn’t say it’s the CORRECT way of finding a vacuum leak…over the past 15 years I’ve been through some training classes with some of the best automotive instructors and diagnosticians in the country named John Thornton and Bernie Thompson and never once has that method been discussed…that method may work for you but I consider smoke testing the gold standard for me…and PLEASE don’t say to pressure test for an EVAP leak with 10 psi of pressure !!
2. Smoke testing is done at atmospheric pressure. Which is literally the only pressure an engine can experience where the leaking makes zero difference.
E.g. remove the intake manifold from a vehicle at wide open throttle and the head ports experience atmospheric pressure. The "leak" is actually desirable at that pressure setting, as is removal of the intake system to some extent. Of course I am neglecting conservation of energy considerations but I believe the scenario correctly pointing out why smoke testing is inadequate with respect to #1 and #2 combined
3. The symptoms don't fit the leak theory, as I point out a leaking manifold noticeably would raise idle and present with imbalance engine fuel trim if later in the tract, (specific side trim where the leak is) and no mention of this was made leading me to believe the problem is global (both sides of the engine) which rules out leaking air with the adequate idle control position(dbw/iacv)
it is merely logic applied at fundamental physical chemical mechanical in nature, I do not follow procedures. I make them based on how machinery operates.
Since all combustion vehicle engines operate on similar principles these may be applied to almost any engine in the world.
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
1. Almost if not All factory intake manifold systems will handle at least 15psi of boost pressure. Thus, there is no other logical way to test for pressure leaking without applying that same pressure the intake experiences. Intake vacuum is just as stressful as positive intake boost pressure.
2. Smoke testing is done at atmospheric pressure. Which is literally the only pressure an engine can experience where the leaking makes zero difference.
E.g. remove the intake manifold from a vehicle at wide open throttle and the head ports experience atmospheric pressure. The "leak" is actually desirable at that pressure setting, as is removal of the intake system to some extent. Of course I am neglecting conservation of energy considerations but I believe the scenario correctly pointing out why smoke testing is inadequate with respect to #1 and #2 combined
3. The symptoms don't fit the leak theory, as I point out a leaking manifold noticeably would raise idle and present with imbalance engine fuel trim if later in the tract, (specific side trim where the leak is) and no mention of this was made leading me to believe the problem is global (both sides of the engine) which rules out leaking air with the adequate idle control position(dbw/iacv)
it is merely logic applied at fundamental physical chemical mechanical in nature, I do not follow procedures. I make them based on how machinery operates.
Since all combustion vehicle engines operate on similar principles these may be applied to almost any engine in the world.
2. Smoke testing is done at atmospheric pressure. Which is literally the only pressure an engine can experience where the leaking makes zero difference.
E.g. remove the intake manifold from a vehicle at wide open throttle and the head ports experience atmospheric pressure. The "leak" is actually desirable at that pressure setting, as is removal of the intake system to some extent. Of course I am neglecting conservation of energy considerations but I believe the scenario correctly pointing out why smoke testing is inadequate with respect to #1 and #2 combined
3. The symptoms don't fit the leak theory, as I point out a leaking manifold noticeably would raise idle and present with imbalance engine fuel trim if later in the tract, (specific side trim where the leak is) and no mention of this was made leading me to believe the problem is global (both sides of the engine) which rules out leaking air with the adequate idle control position(dbw/iacv)
it is merely logic applied at fundamental physical chemical mechanical in nature, I do not follow procedures. I make them based on how machinery operates.
Since all combustion vehicle engines operate on similar principles these may be applied to almost any engine in the world.
Dave
Safety Car
Joined: Oct 2007
Posts: 4,225
Likes: 1,080
From: South Florida
17 inches of vacuum (17"Hg) is reducing that pressure to around 14.5psi minus (17/2)psi, to about 8.349psi absolute pressure. The intake manifold will see this as stress, outside vs inside pressure, e.g. pressure over area = stress. Pressure is a scalar and the result of elastic molecular collisions of gas with some surface. It is these collisions with gaskets and parts that find leaks, the diameter of a gas molecule can even diffuse through a leak or into solid structures without a pressure difference because of natural random motion and effusion. It is these random molecular collisions to which I ascribe and pay close attention to their behavior for diagnostics such as these, the core of my thought process.
When the gas molecule strikes the inside of a tire at a higher frequency or with higher velocity (temperature and density of the gas) the tire inflates, the tire experiences stress. That is how a map sensor works, it has an atmospheric container sealed and a movable wire which bends with increasing molecular collision freq/strength to bend the wire which changes voltage. It doesn't matter if you remove molecules (vacuum) or add them (pressure) at a constant temperature (kinetic energy of gas) because either way the wire experiences a force and direction with linear relationship to the input pressure scalar. It does not depend on flow or momentum like a maf sensor.
And it is this physical phenomenon which tells me that producing 18"Hg of vacuum inside the intake manifold will give approximately the same stress as adding ~9psi of 'boost' pressure during a pressure test. E.g. if you want to find leaks which only appear at 18"Hg of intake vacuum you will need to apply at least 9psi of boost pressure to the manifold to detect them. It is very easy to hear these leaks in a quiet setting. I frequently pressure test engines from the compressor inlets all the way through their intake systems to find all leaks. And it is very easy to tell when they seal up properly, they will hold that pressure like a balloon. Here is example video of me pressure testing stock LS1 intake manifold system for an stock engine to show it quite easy to perform
You can agree that under this much vacuum a small leak could be present that would not alter the idle enough where the OP might have just thought this was normal
.... , also you are not concentrating the obvious that would cause a "lean" condition . You can apply all the theory you want but there are proven diagnostic trees that we follow
Dave
Dave
Race Director
Joined: Apr 2000
Posts: 15,344
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From: Texas
I still want to know the fuel trims. Might be trouble-shooting a problem that's not there. Seems like an easy question to ask Lew 
If he says he's seeing average LTFTs of +20% (or -20% for that matter) then yes it's an issue. If it's on one bank, the issue is narrowed to that side of the engine. If it's on both, it points to the intake or something that affects all cylinders.
Have some of you guys seen some of the stuff with factory cars? People run around trying to get stuff to +/-2% (self included) yet as delivered factory results can be upwards of +/-12% or even a little worse and are considered acceptable. That's why knowing the LTFTs is important.
If he says he's seeing average LTFTs of +20% (or -20% for that matter) then yes it's an issue. If it's on one bank, the issue is narrowed to that side of the engine. If it's on both, it points to the intake or something that affects all cylinders.Have some of you guys seen some of the stuff with factory cars? People run around trying to get stuff to +/-2% (self included) yet as delivered factory results can be upwards of +/-12% or even a little worse and are considered acceptable. That's why knowing the LTFTs is important.
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
I still want to know the fuel trims. Might be trouble-shooting a problem that's not there. Seems like an easy question to ask Lew If he says he's seeing average LTFTs of +20% (or -20% for that matter) then yes it's an issue. If it's on one bank, the issue is narrowed to that side of the engine. If it's on both, it points to the intake or something that affects all cylinders.
Have some of you guys seen some of the stuff with factory cars? People run around trying to get stuff to +/-2% (self included) yet as delivered factory results can be upwards of +/-12% or even a little worse and are considered acceptable. That's why knowing the LTFTs is important.
If he says he's seeing average LTFTs of +20% (or -20% for that matter) then yes it's an issue. If it's on one bank, the issue is narrowed to that side of the engine. If it's on both, it points to the intake or something that affects all cylinders.Have some of you guys seen some of the stuff with factory cars? People run around trying to get stuff to +/-2% (self included) yet as delivered factory results can be upwards of +/-12% or even a little worse and are considered acceptable. That's why knowing the LTFTs is important.
I know Lew well and I am sure that Lew provided details on what he saw but remember most people who use a Diablo are usually not mechanically inclined . Lew knows and understand LS and LT motors so he is not chasing a non existent problem. Nobody will tune a car that has a mechanical problem
Its not rocket science as the guy above is trying to make it.....
Also from what he is staying above I am not sure he understands exactly how a LT motor is tuned ... especially the statement that he shoots for 15.2 to 15.8 AFM for starting, Idle or cruise lol lol
I also don't need a lecture on how to find a vacuum leak or how to use "air preasure " lol lol but if it makes him feel good, so be it. lol
If it is running lean its a simple diagnostic procedure to find out why ...and without seeing the car or being able to perform any tests .... all we can do is talk ....and guess
Dave
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