NightmareTA

iTrader: (20)

Hey all. I have a turbo 5.3 in my car, and for some reason, the AFR under WOT changes with the weather, and it is pissing me off hardcore. I get on it when it's hot outside and it's perfect, and other times when it's much cooler out, like at night mostly, it leans out bad. I'm getting sick of constantly having to watch the wideband in fear of blowing this engine up, and I'd love some insight on why this problem is possibly happening.

Setup is as follows...

-stock bottom end 5.3
-317 heads
-LS6 cam and intake
-T76 turbo at 11 PSI
-60 lbs mototron injectors at stock fuel pressure
-twin walbros
-T56

Tune currently uses a stock F-body MAF sensor which has been re-scaled to be able to make the power the car is at. I also am running no O2 sensors currently....could this be the issue? The car has never run great with thie current tune while normally driving, since it's always rich. It rarely goes much above 11.8 AFR when just cruising. When going WOT on a hotter day, it starts around 10.9 AFR and maxes out at about 11.4. On a cooler day, WOT gets dangerously lean, and I have seen it hit low 13's once or twice, and it really is scaring me.

Anyways, can somebody PLEASE give me some ideas as to what is causing this, and I would greatly appreciate it!

ACCLR8N

Short answer: Yes, no O2 sensors are the problem. You are missing out on short and long term fuel trims to compensate for variables.

I have found temperature has an impact, though backwards. I am finishing up my tune and I have had to make compromises. Over the course of 30-40 minutes my LTFTs lean out. I have ended up tuning it -3% LTFT for the first 20 minutes with it ending up +2% after 40 minutes of driving. Temperature increase resistance altering readings of sensors. Temperature alters springs rates affecting fuel pressure regulators and wastegate boost levels.

Re-scaling the MAF has also introduced more variables. I'm not sure how the F-Body MAF works. My LS2 GTO MAF outputs a frequency based on airflow. The frequency is limited to 12200 Hz which is scaled to 492.9 g/sec. If I were to fudge the scales to give a specific AFR at a given VE cell, at a cooler temperature (denser air) it would be flowing more air and consequently leaning out.

I think you would be happier Speed Density adding an O2 sensor or two and not have the smallish F-Body MAF. I am at 7 psi on my stock LS2 and I am at the limit of my larger MAF (11900 Hz).

danieloneil01

Your tuner shouldn't be tuning. No front O2 sensors is retarded. They help during part throttle to maintain stoich. I would also ditch the MAF and go SD and find a new tuner.

In the meantime pull your plugs and see what they look like. If you dont have tuning software I would not go WOT. Lord knows if you have any knock considering your tuner is inept.

NightmareTA

iTrader: (20)

Thank you very much for the detailed answer! That's basically exactly what I was looking for, since I have heard the O2 sensors make significant changes based on weather and temp. The car has never had them hooked up though, so I had nothing to go off of. I actually plan on ditching the MAF very soon and going to a 2 bar SD operating system in HP tuners which I recently bought. As for the MAF sensor, I have heard that when you re-scale one, it loses a lot of low RPM frequency, so the car will never drive quite as good down low. I can't wait to ditch it and go SD!

In my tuners defense, it was my choice not to run O2 sensors off the bat, because I have heard they don't live long on a turbo car, and he thought we could work around them. He also really didn't have much time to tune the car honestly....like I said above though, I do own HP tuners now and plan on going to a 2 bar SD tune very shortly and will be tuning it myself for the future. I think the car will run much better overall and lose a lot of the annoying problems I have now.

I am running very conservative timing and have had my scanner on HP tuners on the car plenty of times and have not seen any knock yet, but I haven't scanned any of the lean runs either, so it definitely could have seen some knock the few times it happened on cooler nights.

As far as O2 sensors, I am assuming a SD tune requires them as well to maintain a consistent AFR during part throttle? If so, do they have to be located in the merge pipe, or can they be put on the downpipe? If I have to add them, I want to know the best spot where they'll live the longest!

Anyways, thanks a bunch for the info guys!! Keep it coming!

ACCLR8N

To make the sensors survive longer, they need to be mounted further away on a FI car. My passenger side O2 is 8-10" from the exhaust manifold in the cross over before the turbo. The bank 1 unfortunately is in the downpipe after the turbo. My WO2 is even further away in the downpipe per Innovates 18" from turbo suggestion. Bank 1 and the WO2 are reading a combined exhaust from both banks after turbo. When I tune, I tend to tune based on the bank 2 readings. WO2 readings tend to lag 1 frame behind in my logs.

https://ls1tech.com/forums/forced-in...keeping-c.html
post #7 has a picture of my bank 2 front O2
post #14 you can just see my bank 1 front O2 bung in the downpipe. My WO2 is actually in my cat pipe right after the downpipe.

NightmareTA

iTrader: (20)

I have a truck manifold setup with a merge pipe thats pretty much equal length piping on both banks right into the merge at the turbo, so locating the sensors right in the merge on both sides should be very doable. I'm sure I can get them both at least 8" from the manifolds. My wideband (LC-1) is about 2 feet from the turbo outlet on the downpipe, so it may very well be slightly laggy on the readings as well. I guess the O2 sensors are mandatory so I will be adding them in before switching over to the SD setup.

Something else I was curious about was the MAP sensor itself. I'd like to use a 2 bar MAP and I bought a stock replacement for a 2006 cobalt SS. I have heard from some that this particular sensor is in fact a 2.5 bar, but I am not 100% sure. Will this screw with the tuning on a 2 bar setup? And if so, is there some other sensor I should be using? The one I have is BWD P/N EC1636.

danieloneil01

Post your tune

NightmareTA

iTrader: (20)

Heres whats in the car currently.

danieloneil01

VE table, 80kPa @ 2800rpm. I would change that to 41. Looks like a sinkhole.


The map sensor you have I believe is in fact a 2.5. I believe my meth kit comes with a 2 bar. If it does I would send it to you for free minus shipping. The amount of boost you're at is MAFless territory.


Map sensor look up.
http://www.robietherobot.com/storm/mapsensor.htm



I'm by no means an expert on tuning but it's been fun learning. Just wished most people were more open with giving help. If you don't use front O2 sensors then a tuner can do a SD tune that will still run correctly no matter the IAT temps. I'm still trying to tune mine which is a PITA. But if it blows up it's because of me and not someone else. And truthfully, you care more about your car and will take the time to tune it right.

Good luck and I love that body style of that gen Camaro. My buddy when I was very young had one with a 2.8 or 2.6 can't remember but it was a weak engine and I would get my parents '88 Blazer with the 4.3 and make it my bitch.

ACCLR8N

Sounds like you will have a better position for your NBO2's. Ever have trouble with your LC-1 doing a free air calibration while the car is running? Mine occaisonaly resets at start-up.

2.5 bar MAP in a 2 bar tune will mess you up. They all are 0-5V scales. There are two tables that have to be adjusted in your tune. With key on engine off, your scanning software should read 99-102 kPa for normal atomspheric pressure. Could be your first excersise with HPT.

NightmareTA

iTrader: (20)

Def let me know about the MAP sensor! Is it a direct fit for an LS6 intake, or a universal one? And thanks for the tips. I never understood why nobody that tunes likes to give out help. It really pisses me off, because the whole aspect of tuning is treated like some big top secret cult. I've been slowly learning HP tuners and actually just finished tuning my brother's H/C 6.0 in his firebird. With the exception of it idle flaring once in a while, it runs great and put down 435 rwhp after I tuned it. It's not the same as a turbo car, but it was a nice way to get me familiar with the program!

Thanks for the compliment too. These cars were pretty pathetic in V8 form even lol, so the V6 ones were absolute dogs!

I've never done a free air calibration while it was running. It's always with the key on accessory, but I've never had an issue with it resetting after one. I am guessing I did get the wrong MAP based on some quick research I did on here. Apparently the one on advance auto's computer is incorrect for a cobalt SS and they gave a true part number which was directly cross referenced from GM's 2 bar number. I'll have to swap it when I get back to advance!

Thanks again guys.

ddnspider

iTrader: (26)

I see no reason to ditch the MAF on your setup. I am running a scaled LS7 MAF in a 4" tube because I maxed out both the airflow and frequency on a stock MAF. I have a similar setup with twin walbro's, 60# Siemens injectors, T76 turbo, but a forged 383. My OLMAF tune has the car running smoother than it ever has and I'm not done tuning it, even with the "loss of resolution". You not having front O2's is definitely not helping when the weather changes, but in 99+ tunes there is supposed to be a table for air/fuel correction based on intake temperature. That table is where I would look if you trust your MAF curve.

PS....Also curious why it looks like you have your tuned scaled over 50% when you're only running 11psi. This is just going off of your IFR table that has your 60# injectors(which are rated at 60# at 3 bar of fuel and LS cars run 4 bar of fuel), but they look like ~35#er's in your tune.

danieloneil01

Yes it'll fit but you will need to trim it. I had to on mine but it takes about 1 minute to trim.

NightmareTA

iTrader: (20)

I honestly just don't care for MAF tunes period since they never have the throttle response of a SD tune, and I plan on upping the boost at some point as well. A local guy has a 750+ HP turbo 6.0 that he tunes in SD and he says he will never look back. He also offered to help me get started on tuning a turbo car that way so it's nice to have someone thats "been there done that" locally. I love the ease of tuning in SD as well.

As far as the MAF scaling on my current tune, the original guy that tuned it basically just input the scaled data from his old 700 rwhp turbo camaro and told me that it's not even close to being maxed out, but it'll work for now. The car runs pretty decent, but it's constantly rich and I'm getting terrible gas mileage for a stock 5.3 with a turbo on it. I'm lucky to get 14ish while I should be getting 18-19 around town easily in a light third gen bird.

And just for my own knowledge, what should the actual injector numbers be if they were input correctly as a 60 lbs injector?

I honestly broke down and ordered a 2 bar sensor from the local advance auto. It was a BWD part number that crossed over from the GM 2 bar sensor number. Thanks anyways though man, I appreciate it!

ddnspider

iTrader: (26)

Wait....so you're not a fan of maf tunes and hate the way your car runs and get terrible gas mileage, but you don't even have a proper maf tune in the car?