So I’m in the process of getting a Diablo tune from Lew and after my road test and data collection for him, he says it’s running lean and I probably have an intake or exhaust leak. It’s a 2014 Stingray Z51. Anyone have experience with this and where I might look first? What might be the most probable source of the leak?

 

Has any recent maintenance been done on the car ??…are your Long Term Fuel Trims elevated on one bank or both ??…if both banks could be an vacuum leak anywhere downstream of the MAF sensor to the throttle body….could also be a fuel delivery issue or a bad MAF sensor…if exhaust leak it can be anywhere from the exhaust manifold to the front O2 sensor…if fuel trims are elevated at idle but decrease under load you have a vacuum leak…if they are normal at idle but increase under load you have either a fuel delivery issue or a bad MAF sensor….this is basic engine diagnostics 101…Lew should know this stuff and if he doesn’t he shouldn’t be tuning cars…if you don’t see anything obvious find a diagnostic shop and they will find it quickly…using a smoke machine is the gold standard to finding vacuum leaks…a shop vac hooked up backwards to blow air out with a soapy water solution is my method to find exhaust leaks.

 

2 recommended diagnostic shops.

 

An ultrasonic leak detector has always worked for me to find vacuum leaks.

 

Curious in knowing more about this. My quick research point to ultrasonic leak detector for pressure leaks, wasn't able to find much about their use with vacuum. As @C5 Diag suggests, I have used a smoke machine and shop vac for the same purposes he stated - with success, but always like to hear about other options.

 

Pressure and vacuum leaks both produce ultrasonics at approximately 150 KHz.

These detectors can hear this frequency

 

I use this ultrasonic leak detector mainly for EVAP leaks if the smoke machine can’t locate it and you may be able to pick up a used one on EBay…they are sold by Kent Moore who supplies almost all of GM’s specialty tools…I never used it for a vacuum leak since a running engine may have too much noise…I need quiet.

 

Great info guys, thanks! I did not expect them to be so pricey. I need neighbors like you guys

 

I just bought a smoke machine, could you lead me to a location of here to insert smoke into the system? Will I mess anything up with the smoke? I was thinking I’d just try starting at the beginning the air filter…it has this huge cone I can stick in it and see if there’s any obvious cracked lines or connectors. I’d sure appreciate any detailed directions on places to push smoke.

 

I’d say remove the brake booster hose and insert the smoke machine hose there or upstream of the throttle body…get a baggie and remove the rubber boot and block off the area just upstream of the throttle body if using the brake booster…if not the smoke will escape there…smoke will not harm anything.

 

So I purchased a smoke machine and I have an air leak on the bottom of the air filter box where it seats into the tabs…so I’ll resolve that myself no big deal, but I also have a couple exhaust leaks, one in on driver side just up in front of the muffler at a clamp and another larger leak right in the middle of the car. But it looks like there’s a plate blocking it and a major PITA to attempt on jack stands so think I’ll take it to a local shop. Would you have a recommendation for a shop you’d trust around the lake St. Louis area for sealing the exhaust? I think it’ll be a simple fix on a rack. Maybe even some exhaust rap would do it. But evidently little leaks like that can cause it to go lean a little and affect the tune I’m getting so like to get this done before I do another data log and send to Lew for his tune. Want it to be as good as it can be.

 

I actually went in a few locations injecting the smoke and it’s all completely tight other than the bottom of the airbox where the air filter housing seats into the tabs. So I’ll check that and I’m sure I can resolve that no biggie. I also put smoke into the exhaust and had a couple leaks to fix. One in front of the drivers side muffler at the clamp and one right in the middle of the car, like maybe there’s another clamp or x-pipe or something there that needs to be sealed. But not sure I’d want to try that on jack stands… looks like a big plate has to be removed to get access.

 

Only unmetered air downstream of the MAF sensor will affect the fuel trims.

 

So since the filter is in front of the MAF, that’s not the issue, ok. But I’m sure the MAF is original and 10yrs old, 80k miles so for $65 for a new AC delco MAF I went ahead and got one in case it’s got issues.

And I’ll fix the exhaust leaks.

 

How are you going to know if you have a MAF sensor issue ??

 

@C5 Diag This is not a fair statement and you should refrain from makeing them when you dont know who you are talking about

Lew has been around a long time and does know his stuff ... he is a good remote tuner and will help anybody but he is not on site , he told the guy he has vacuum leak ...he cant diagnose it from afar just like you cant , all u can do is offer suggestions which I am sure he did , he does not know the mechanical ablity of the people he is working with as he has 100's of customers most of which cant turn a screwdriver and if somebody messes with the wrong thing ... right away .... it would be his fault . Remember it's different when you are on a forum offering suggestions for free than when you are in business and getting paid for a service. He is getting paid to tune not to fix a vacuum leak

Dave

 

Sorry, but I don’t know who “Lew” is and what is capabilities are !!…all “Lew” said the car is running lean !!..he should have been able to tell OP how to diagnose these elevated fuel trims.

 

@C5 Diag No problem I figured you did not know . Lew has been around a long time and specialized the un modified or slightly modified engines doing remote tuning for those that use a Diablo tuner , most of his customers have just got into mods or just want their stock motor and trans tuned without spending a fortune on a dyno tune or they may not have a tuner in their area . He , along with Mike from Diablo were great supporters of the GM truck and C6 forums for a long time then they moved over to the C7 platforms

He can tell folks how to fix stuff but maybe he choses not to , he is not getting paid to diagnose ....he is getting paid to tune . It's no different than my remote tuner who told me I was not makeing enought boost ... I had to figure it out...

I am sure they do this because of the " you told me it was this ... " syndrome, i am also sure you have ran into this ...

Also you don't know what he told the OP ... you are assuming that he did not ... or did the OP even ask him what it was ?

Just don't assume 👍
Dave

 

[QUOTE=Jamie316;1608015032]So I’m in the process of getting a Diablo tune from Lew and after my road test and data collection for him, he says it’s running lean and I probably have an intake or exhaust leak. It’s a 2014 Stingray Z51. Anyone have experience with this and where I might look first? What might be the most probable source of the leak?[/QUOT

Check the torque on you intake manifold bolts. They tend to loosen plus it’s quick and easy.

 

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.