Failed MAF = Intermittent Stumble

[sgod1100]

Do you guys see the same behavior whether the MAF is still installed and plugged in but just failed in the tune, and when it's completely removed (or depinned)?

I have never removed my maf or unplugged it. I've only "failed it" via the tune and the lean spots still exist. Maf only, SD only, OL/CL it doesn't matter they are still there. The part that stumps me is that during that lean spot all three airflows match (MAF air, VE and DYN air).

[Cringer]

Do you guys see the same behavior whether the MAF is still installed and plugged in but just failed in the tune, and when it's completely removed (or depinned)?

Both of these are the same for me on my E38:

• Failed in tune and plugged in
• Failed in tune and removed (using an IAT breakout harness)

[sgod1100]

Do you guys see the same behavior whether the MAF is still installed and plugged in but just failed in the tune, and when it's completely removed (or depinned)?

Here's what it looks like for ref. Notice VE air and MAF air are higher than DYN air. Ignore the KR as this an old log I had

2600 rpm lean spot.JPG

[Cringer]

Do you guys see the same behavior whether the MAF is still installed and plugged in but just failed in the tune, and when it's completely removed (or depinned)?

Oh wait are you talking about the LSA Lean Spot or the original topic for this thread (intermittent stumble)?

As for the intermittent stumble, it happens no matter what.

I believe SGod1100 tested in OLSD and got the same lean spot result.

[sgod1100]

Oh wait are you talking about the LSA Lean Spot or the original topic for this thread (intermittent stumble)?

As for the intermittent stumble, it happens no matter what.

I believe SGod1100 tested in OLSD and got the same lean spot result.

Yup, that is correct...assuming he is referring to the lean spot....sorry Cringer didn't mean to take over your thread

[sgod1100]

log showing it still happening OLSD

OLSD lean spot still happening.hpl

[Cringer]

Yup, that is correct...assuming he is referring to the lean spot....sorry Cringer didn't mean to take over your thread

It is all good. I am interested in the solution to this as well. I still want to try to work on the EOIT angle if you are still willing. I am not sold on the reversion idea. Have you considered it is old school IRL harmonics?

[sgod1100]

It is all good. I am interested in the solution to this as well. I still want to try to work on the EOIT angle if you are still willing. I am not sold on the reversion idea. Have you considered it is old school IRL harmonics?

Sure, I'm just not too confident that's the root cause...lol. Especially since not everyone is experiencing this problem

[Alvin]

log showing it still happening OLSD

OLSD lean spot still happening.hpl

I don't want to junk up this thread as this is a unrelated topic. And the original topic is pretty important IMHO.

I don't see any lean spikes in this. Where are they at? Anytime the pedal moves fast either down or up you'll get a spike one way or the other with the wideband. A perfectly tuned car will do this. When you snap the throttle you are burning fuel that has already been injected.. The injection is always on a delay. Same thing when you lift fast.. What was injected is still in there. It's why people talk about filtering transients when tuning.

[JayRolla]

I don't want to junk up this thread as this is a unrelated topic. And the original topic is pretty important IMHO.

I don't see any lean spikes in this. Where are they at? Anytime the pedal moves fast either down or up you'll get a spike one way or the other with the wideband. A perfectly tuned car will do this. When you snap the throttle you are burning fuel that has already been injected.. The injection is always on a delay. Same thing when you lift fast.. What was injected is still in there. It's why people talk about filtering transients when tuning.

Its right at 2600 rpm. I notice mine are at 1600, 2600 and even a little at 3600. Its when smooth throttling passing those RPMS. It will jump 5-15% lean depending on throttle position. If on the highway in 6th gear and sitting at 2600rpms I run around 1.08 with 1.00 commanded and fuel trims show super positive in that rpm. On his log he is commanding lets say .91 cruise and as he passes 2600rpms he is hitting 1.00. Guessing he set his commanded eq richer to help combat the problem. Here is the original thread and can reply in here.

https://forum.hptuners.com/showthrea...14-ctsv/page10

[sgod1100]

I don't want to junk up this thread as this is a unrelated topic. And the original topic is pretty important IMHO.

I don't see any lean spikes in this. Where are they at? Anytime the pedal moves fast either down or up you'll get a spike one way or the other with the wideband. A perfectly tuned car will do this. When you snap the throttle you are burning fuel that has already been injected.. The injection is always on a delay. Same thing when you lift fast.. What was injected is still in there. It's why people talk about filtering transients when tuning.

Look at the snapshot in my post #83...definitely lean

[InfraRedline]

Options:
1) If the OS patch is not available on your OS, then I think you can either:
1a) ask HPT nicely to port that over
1b) jump over to the 2bar HPT Custom OS
2) MAP^2 fix...
Unfortunately you cannot just zero these out...if you do, it will chance the shape of your VVE curve and that will impact fueling and torque calcs etc, so do not do that. But if you send me or post your tune file here, I can use the "Verlon Mode" in software to convert your normally 6 coefficient VVE shape to use 5 coefficients. The result is that MAP^2 will not be required (and zero'd out properly) while the other 5 coefficients will carry the burden of shaping the VVE.

I still maintain the issue with the LSA lean spots is due to people changing to a standard/straight spray injector, when the LSA requires an angled injector. No one believes me, nor will they put LSA injectors back in to do some simple low RPM testing to see how that changes it. And to a minor extent tuning EOIT can also help.

So...I guess I need to ask, did you swap injectors on your LS9?

Since the stumble issue is so minor on my car and really doesn't bother me since it's usually one quick stumble after a pull I guess I'm not too worried about it. It is nice to understand why it does it though and validates it in my mind that I am not crazy, lol! I do need to log it thought with the airflow calc parameter added just to 100% confirm.

I do have aftermarket injectors in the car, yes. The first thing I did to the car last year when I got it was add a DSX flexfuel kit and ID1300's and put the car on E85 otherwise completely stock and that is when I first noticed the lean spots in the 1600 and mainly the 2600 rpm range at part throttle. Once I got my wideband in and wasn't relying on fuel trims or the dyno sniffer I started to tackle cleaning the lean spots up. When the car was still on MAF right after I did the ported blower and NW102 it was really bad going through those rpm ranges at light to moderate throttle. It got a little better with adding a lot to the maf in those areas, but of course based on the load I would go through those airflow ranges at different rpm at times and would have a rich spot. Once I switched to SD I was able to mask it a little better since there is a bit more resolution to work with when trying to address that type of issue, so I ended up with some decent spikes in the VVE table at 1600 and 24-2600 in the light vacuum to very light boost areas, but the car drives through those rpm ranges pretty close to normal now. After TX2K I'll have to get back at it and see if I can get it a little better yet. Between the issues mentioned here and in this thread and having to find workarounds for transient fueling above 4k rpms to avoid lean tip in when coming into boost so quickly when stabbing the throttle (or on a fast shift) this car is making me work for it! But I'd be lying if I said I wasn't enjoying the learning haha. It is so different from what I usually work on, so it is a nice change of pace once in a while.

In regards to your 1600 and 2600 leans spots...you aren't the only one..lol. I've been trying to figure out the solution to this for a few years now. I'm to a point of just adding some fuel to the maf curve in the hz areas that I'm at when i go through the 2600 rpms and once I'm in PE i'm going to "rape" the table in that 2600 rpms area. I too have to have mountains like you in those two areas and even doing that it will still show slightly lean according to my STFT. Seems that no one has a true fix for it.

https://forum.hptuners.com/showthrea...2600+lean+spot

I just read through that whole thread and it is wild that is such a widespread issue! My car definitely exhibits some of those traits in light to moderate throttle areas. It doesn't seem quite as extreme as some of the guys in there have posted about though, but it is definitely still present. I would say I've got mine 90% of the way where I want it with a couple of little mountains in the VVE table. I no longer feel the hesitation, but can still see a little lean spike on the widebands on both banks. Like I mentioned right above maybe I will tackle it a bit farther after the madness of TX2K and I can get back into a normal schedule. I have a bit more interest and curiousity in it now that I know it has plagued so many people.

[sgod1100]

Since the stumble issue is so minor on my car and really doesn't bother me since it's usually one quick stumble after a pull I guess I'm not too worried about it. It is nice to understand why it does it though and validates it in my mind that I am not crazy, lol! I do need to log it thought with the airflow calc parameter added just to 100% confirm.

I do have aftermarket injectors in the car, yes. The first thing I did to the car last year when I got it was add a DSX flexfuel kit and ID1300's and put the car on E85 otherwise completely stock and that is when I first noticed the lean spots in the 1600 and mainly the 2600 rpm range at part throttle. Once I got my wideband in and wasn't relying on fuel trims or the dyno sniffer I started to tackle cleaning the lean spots up. When the car was still on MAF right after I did the ported blower and NW102 it was really bad going through those rpm ranges at light to moderate throttle. It got a little better with adding a lot to the maf in those areas, but of course based on the load I would go through those airflow ranges at different rpm at times and would have a rich spot. Once I switched to SD I was able to mask it a little better since there is a bit more resolution to work with when trying to address that type of issue, so I ended up with some decent spikes in the VVE table at 1600 and 24-2600 in the light vacuum to very light boost areas, but the car drives through those rpm ranges pretty close to normal now. After TX2K I'll have to get back at it and see if I can get it a little better yet. Between the issues mentioned here and in this thread and having to find workarounds for transient fueling above 4k rpms to avoid lean tip in when coming into boost so quickly when stabbing the throttle (or on a fast shift) this car is making me work for it! But I'd be lying if I said I wasn't enjoying the learning haha. It is so different from what I usually work on, so it is a nice change of pace once in a while.



I just read through that whole thread and it is wild that is such a widespread issue! My car definitely exhibits some of those traits in light to moderate throttle areas. It doesn't seem quite as extreme as some of the guys in there have posted about though, but it is definitely still present. I would say I've got mine 90% of the way where I want it with a couple of little mountains in the VVE table. I no longer feel the hesitation, but can still see a little lean spike on the widebands on both banks. Like I mentioned right above maybe I will tackle it a bit farther after the madness of TX2K and I can get back into a normal schedule. I have a bit more interest and curiousity in it now that I know it has plagued so many people.

Yeah, when I first started that thread so many guys thought I was just doing something wrong. At first I thought I was too. But then after chasing my tail forever and talking with other guys that are experiencing the same problem I realized that there is something else going on. Like you when I first saw that I was like "welp, need to massively richen up the maf". After I did that and hit those hz ranges at a different rpm I was running in the high 10s (afr scale). Then I went back and forth trying everything I could think of, but still no dice. I've just kind of cheated my maf curve in the close loop areas where I go through that rpm the most (around 5400-6000 hz). I have an m6 trans too so I typically shift right around the 2600-2800 when I'm just accelerating normally.

Are you currently catless?

[L1FTD]

Do you guys see the same behavior whether the MAF is still installed and plugged in but just failed in the tune, and when it's completely removed (or depinned)?

Interesting, first I?ve seen of an engine other than the LSA doing this. Always wondered if the LS9 or LS3 + LSA blower had the same problem.

I only speak for MAF de-pinned, running VVE or 2Bar OS. Seems the problem doesn?t differentiate between MAF, blended, or VE.

I can confirm lean spots present after just headers, no cats, intake. I thought it was after injectors, but checked old logs and saw the trims going +10-15% after just first round of mods.

Wish I had a log of the car stock. If only someone had a log of completely stock car, could see if it?s from GM or as a result of mods.

If it doesn?t do this stock, must be from either intake, headers, or no cats. Big injectors probably amplify it.

Here?s an example of 2Bar OS, no MAF, all the weight of the lean spots on VE fuel.

I?ve tried pretty much everything in HPT. Tried putting the stock ?accordion? tube back on intake. Haven?t tried the whole intake, but the stock tube made no difference.

Seems most likely a test or diagnostic that?s not mapped in HPT.

The cat efficiency test requires a minimum cat temp. to run, and my logged temp without cats is 30c lower than the minimum.

The cat test is already turned off, but maybe there?s other parameters that need minimum cat temp. to be met. So much we can?t see in HPT.

I can still hit COT threshold if I turn it on though, so don?t know if the logged cat temp. is the only factor.

There?s an intrusive fueling test in the FSCM as well. Constantly tests for fuel pressure variation, fuel flow <22g/s, 5-12s duration, every 60s after test passed.

These lean spots always show the fuel pressure going jagged then smoothing out (since corrected with a Radium fuel pulse damper, very good addition, quietens the ?sewing machine?, great for smoothing the pressure on heavy throttle).

Problem may be tied into specific FSCM?s, of which we have very limited access in HPT or anything else.

I?ve got a few more ideas to try in the tune, but I?ll need to make my own XDF?s for those next week.

Sorry, long post. I?m very passionate/annoyed about these lean spots.

Screenshot (34).pngWOT.pngWOT (2).pngPart-throttle.pngScreenshot (37).png

[InfraRedline]

Yeah, when I first started that thread so many guys thought I was just doing something wrong. At first I thought I was too. But then after chasing my tail forever and talking with other guys that are experiencing the same problem I realized that there is something else going on. Like you when I first saw that I was like "welp, need to massively richen up the maf". After I did that and hit those hz ranges at a different rpm I was running in the high 10s (afr scale). Then I went back and forth trying everything I could think of, but still no dice. I've just kind of cheated my maf curve in the close loop areas where I go through that rpm the most (around 5400-6000 hz). I have an m6 trans too so I typically shift right around the 2600-2800 when I'm just accelerating normally.

Are you currently catless?

I didn't stay MAF long, but I was surprised when it still did the same thing on SD. My first event in the car was roll racing at StreetCar Takeover and I noticed it happening really bad when I would quickly try to accelerate through 1st to get up to 40mph by the starting line and it would fall on it's face so hard crossing over 2600. I didn't have the widebands wired in to be able to log yet, but I knew it had to be going lean. I had just barely street tuned the car just enough to make the event so I thought I just needed to refine it a bit. So when I started chasing the issue down after the event just on the street I would roll into 1st gear fairly quickly like that and would see the widebands go crazy lean, and then I realized I could replicate it in other gears and load areas as well so I started adding fuel and thought something must be wrong. So I changed where the fuel pressure ramps up from low flow to normal flow, and moved that higher and lower with no change. Then I changed my injector data a couple different times just to test that out with no change (tried not scaling the ID1300's back and just maxing out the flow rate table once it hit 127 lb/hr just for testing). I tried going back to MAF, I tried blended, and ultimately left it SD and worked the VVE table to the point where it isn't pretty, but it is functional. Last time I had it on the dyno I took some time to just sweep through that area over and over to get it pretty close, and I will say now besides an ugly VVE table I don't have any rich dips and it still just goes barely lean enough to see it, but I don't feel it anymore, so I'm getting close for sure. Still very odd though!

I am catless currently. But while I had the stock headers on the car most of last season I had all the downstream o2 codes still turned on and that is when I was doing most of this testing since I was waiting for my headers to show up. So for me, catted or catless, codes turned on or off made no difference. The only difference was the rate of response for the wideband readings since there were no longer factory cats before them.

[L1FTD]

I am catless currently. But while I had the stock headers on the car most of last season I had all the downstream o2 codes still turned on and that is when I was doing most of this testing since I was waiting for my headers to show up. So for me, catted or catless, codes turned on or off made no difference. The only difference was the rate of response for the wideband readings since there were no longer factory cats before them.

Beautiful! So you had factory headers, factory cats, o2 codes untouched, and still had these lean spots?

Another first, had no evidence of a stock car doing this.

Maybe it?s a test/diagnostic in the FSCM specifically? Or GM strategy to push extra oxygen through the cat for burn off?

Either way, just have to find the parameter they are doing it through. If it is in the FSCM, not much chance.

[GHuggins]

Beautiful! So you had factory headers, factory cats, o2 codes untouched, and still had these lean spots?

Another first, had no evidence of a stock car doing this.

Maybe it?s a test/diagnostic in the FSCM specifically? Or GM strategy to push extra oxygen through the cat for burn off?

Either way, just have to find the parameter they are doing it through. If it is in the FSCM, not much chance.

Not trying to muck this thread up anymore, but if it is an oxygen storage parameter taking place you'll notice the issue a lot at idle. If that's a problem after cat removal and thus making this issue more pronounced it will idle about 10% lean according to the wideband vs the O2 switch points. I deal with these issues a lot on gen V platforms..... You should also see it adding a decent chunk of fuel on decel. Again, if it's cat removal related making an already existing issue that much worse.

[InfraRedline]

Beautiful! So you had factory headers, factory cats, o2 codes untouched, and still had these lean spots?

Another first, had no evidence of a stock car doing this.

Maybe it?s a test/diagnostic in the FSCM specifically? Or GM strategy to push extra oxygen through the cat for burn off?

Either way, just have to find the parameter they are doing it through. If it is in the FSCM, not much chance.

I did have a completely factory exhaust and untouched o2 codes, but I did have 1300cc injectors. I first tuned the car completely stock and never noticed any weirdness in those rpm ranges, but as soon as I put the 1300's in I could feel the lean spots pretty apparently and the trims would try to chase them briefly, but I didn't have a wideband in the car yet since I used the dyno sniffer for WOT tuning that first go around. I kind of just wrote it off as needing more dialing in since I was about to put more parts on and put my widebands in, so I didn't spend much time with the car in stock + 1300cc flexfuel form. When I added my next round of parts which included the ported blower, IC bricks, pulley, intake, and 102mm TB I put my dual widebands in and that is when I really could see the lean spots happening and started down the path of all the testing. At that time I did still have factory headers and cats in place for at least a few months and they were still factory when I did all the testing I mentioned above. However I did not have the rear o2's in place at that point since I put the widebands in their place. But going by feel and fuel trims they made no difference as the stumble from the lean condition was definitely there just as noticeably before I put the widebands in.

[L1FTD]

I did have a completely factory exhaust and untouched o2 codes, but I did have 1300cc injectors. I first tuned the car completely stock and never noticed any weirdness in those rpm ranges, but as soon as I put the 1300's in I could feel the lean spots pretty apparently and the trims would try to chase them briefly, but I didn't have a wideband in the car yet since I used the dyno sniffer for WOT tuning that first go around. I kind of just wrote it off as needing more dialing in since I was about to put more parts on and put my widebands in, so I didn't spend much time with the car in stock + 1300cc flexfuel form. When I added my next round of parts which included the ported blower, IC bricks, pulley, intake, and 102mm TB I put my dual widebands in and that is when I really could see the lean spots happening and started down the path of all the testing. At that time I did still have factory headers and cats in place for at least a few months and they were still factory when I did all the testing I mentioned above. However I did not have the rear o2's in place at that point since I put the widebands in their place. But going by feel and fuel trims they made no difference as the stumble from the lean condition was definitely there just as noticeably before I put the widebands in.

Perfect! Great info!

So you had the problem stock exhaust, but injectors added.

Myself and others had the problem with stock injectors, but exhaust/intake mods.

Seems like it is pointing to a factory intention, worked in there by GM for emissions most likely.

Whatever is going on, big injectors and possibly no cats just amplifies whatever GM intended to do with the leaning out.

Very consistent, could be an oxygen storage thing like GHuggins mentions. Need to find the parameters. If it is in the FSCM, not much chance.

So many variables have been discussed in sgod1100 thread. Everyone noticed the issue at a different point in their mods, no one could confirm if the car did it completely stock.

[InfraRedline]

Perfect! Great info!

So you had the problem stock exhaust, but injectors added.

Myself and others had the problem with stock injectors, but exhaust/intake mods.

Seems like it is pointing to a factory intention, worked in there by GM for emissions most likely.

Whatever is going on, big injectors and possibly no cats just amplifies whatever GM intended to do with the leaning out.

Very consistent, could be an oxygen storage thing like GHuggins mentions. Need to find the parameters. If it is in the FSCM, not much chance.

So many variables have been discussed in sgod1100 thread. Everyone noticed the issue at a different point in their mods, no one could confirm if the car did it completely stock.

Yes sir I can definitely confirm I had the issue on 100% stock exhaust with factory rear o2's in and turned on. If I get some time later on I will revive that thread and add my case in there. I feel bad sort of hijacking this thread and it could be good to bring that thread back with some additional info.