Consistent Negative STFTs
Thread Starter
Teching In
Joined: Jul 2009
Posts: 33
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From: La Porte, TX
Consistent Negative STFTs I recently cammed my m6 02' z28, about 1700 miles ago. (230/236 .612/.604 111+4). I got dyno tuned (at a VERY reputable shop) and the car runs really great up top (steady 12.8-12.9 AFR as seen during the pulls). It made 398/380, which i cant complain, it made 340 before the cam with full bolt ons minus an ud pulley.
The problems: The car runs like *** when it's cold, and forget about the a/c when it's cold or when I try to start it. Even hot it struggles to hold a steady idle for a minute after I turn the a/c on. Which i guess is pretty normal, especially with the amount of overlap. When the the car is at op temp, the car will hesitate if i give it more than 50% throttle, and sometimes pop and backfire. It smells super rich also, that's the first thing people say about my car.. "man your car is running super rich!!!!". I cant even have the a/c on (not recirculating) at a stop light because the fumes are overwhelming (no I dont have cats). I get the P0121 code for the tps and the asr light comes on when I have the a/c on longer than 2 min. Cold idle: 850-900rpm, warm idle: 900-950 rpm. With a/c on: 950-1000rpm.
I cleaned my MAF and replaced the o2s with new Densos. Neither helped at all. The plugs were new with the cam. The fuel pressure has an interesting problem, probably a bad check valve in the tank. I put a gauge on the fuel rail and noticed the pressure leaks down to 0 after about 20 seconds with the key on. And I have been having hard start issues. It is usually okay if I start to crank right at the end of the priming. I have also pulled the intake with the rails attached and hit the key to see if injectors are leaking and they are not. I did this about a year or two ago, and the leak down problem wasnt near as bad, it would take about a minute to leak down to zero.
So i have hooked up a scantool (OBDWiz) and logged some data. I have found that the STFTs are consistently negative. I cant get any readings on LTFTs, maybe the tuner turned them off?? I have attached an excel spreadsheet with the data showing about 30 minutes of city driving. I plotted bank 1 and 2 STFTs and again showing a close up of about 3.5 minutes of driving (idle to cruise). My MAP is around 8.9 at idle and my timing tries to hang around 21.5 deg. My o2s are switching properly but it's not doing the trick, they read rich hoping it will pull enough fuel but it cant ever get to 0%. Then they switch back lean after a couple seconds (at idle) and my stft hits -10% to -12%. Bank 2 seems to be a little worse than bank 1. When i hit the gas and let off my stfts hit up to -25% to -40%. WOT I see 0% after about 3000rpm, and constant acceleration under ~50% throttle i see positive 5% to 7% give or take. And no I do not have a wideband to monitor the AFR.
Anybody have any thoughts? I am thinking maybe I have a leaky or stuck injector? Anything else I should be monitoring?
Cruising on the highway at 70 I was getting 23.5 mpg, city is around 16-17mpg. My goal is to get HPTuners/wideband and due a lot of part throttle tuning with the VE tables and timing. Surely my commanded AFR is around 14.7..?
Thanks in advance!
EDIT: It wont let me upload an xlsx file or csv file so I attached a screenshot.
The problems: The car runs like *** when it's cold, and forget about the a/c when it's cold or when I try to start it. Even hot it struggles to hold a steady idle for a minute after I turn the a/c on. Which i guess is pretty normal, especially with the amount of overlap. When the the car is at op temp, the car will hesitate if i give it more than 50% throttle, and sometimes pop and backfire. It smells super rich also, that's the first thing people say about my car.. "man your car is running super rich!!!!". I cant even have the a/c on (not recirculating) at a stop light because the fumes are overwhelming (no I dont have cats). I get the P0121 code for the tps and the asr light comes on when I have the a/c on longer than 2 min. Cold idle: 850-900rpm, warm idle: 900-950 rpm. With a/c on: 950-1000rpm.
I cleaned my MAF and replaced the o2s with new Densos. Neither helped at all. The plugs were new with the cam. The fuel pressure has an interesting problem, probably a bad check valve in the tank. I put a gauge on the fuel rail and noticed the pressure leaks down to 0 after about 20 seconds with the key on. And I have been having hard start issues. It is usually okay if I start to crank right at the end of the priming. I have also pulled the intake with the rails attached and hit the key to see if injectors are leaking and they are not. I did this about a year or two ago, and the leak down problem wasnt near as bad, it would take about a minute to leak down to zero.
So i have hooked up a scantool (OBDWiz) and logged some data. I have found that the STFTs are consistently negative. I cant get any readings on LTFTs, maybe the tuner turned them off?? I have attached an excel spreadsheet with the data showing about 30 minutes of city driving. I plotted bank 1 and 2 STFTs and again showing a close up of about 3.5 minutes of driving (idle to cruise). My MAP is around 8.9 at idle and my timing tries to hang around 21.5 deg. My o2s are switching properly but it's not doing the trick, they read rich hoping it will pull enough fuel but it cant ever get to 0%. Then they switch back lean after a couple seconds (at idle) and my stft hits -10% to -12%. Bank 2 seems to be a little worse than bank 1. When i hit the gas and let off my stfts hit up to -25% to -40%. WOT I see 0% after about 3000rpm, and constant acceleration under ~50% throttle i see positive 5% to 7% give or take. And no I do not have a wideband to monitor the AFR.
Anybody have any thoughts? I am thinking maybe I have a leaky or stuck injector? Anything else I should be monitoring?
Cruising on the highway at 70 I was getting 23.5 mpg, city is around 16-17mpg. My goal is to get HPTuners/wideband and due a lot of part throttle tuning with the VE tables and timing. Surely my commanded AFR is around 14.7..?
Thanks in advance!
EDIT: It wont let me upload an xlsx file or csv file so I attached a screenshot.
Last edited by Aggie_Ls1; Jun 13, 2012 at 02:11 PM.
With all the mods you have done, you need to get a real street tune, not a dyno tune. The most important part of tuning is cold starts, idle, part throttle, idle with a/c on; idle with a/c off, throttle cracker, throttle follower,. All that stuff is what takes time, but is very rewarding if done properly. A good tuner should be able to get your problems fixed up pretty easily.
Thread Starter
Teching In
Joined: Jul 2009
Posts: 33
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From: La Porte, TX
I agree. I planned on buying HPTuners, but I then decided to go buy an engagement ring.. lol.
So you think all of this could be resolved, including the rich condition, with proper tuning? I am afraid that I have a problem not related to the tune. (although I know I have plenty that ARE tune related)
So you think all of this could be resolved, including the rich condition, with proper tuning? I am afraid that I have a problem not related to the tune. (although I know I have plenty that ARE tune related)
Thread Starter
Teching In
Joined: Jul 2009
Posts: 33
Likes: 0
From: La Porte, TX
This is what I have found on the TPS issue, so I think i am okay there.
Now, that 65kpa map figure comes into play in nearly every LS1 Car/Truck because its the max map setting in most of the calibrations for the sanity test
Under normal circumbstances a stock cammed A4 will probably idle at around 35-40 map. When switching to a larger cam with more overlap your map readings could go up to as high as 70 or more kpa map which is way outside of the normal boundries. On a stock cammed car you'd probably need to be at around 30% tps to hit that same map number which is where that predicted throttle angle quote comes into play.
Now onto the last quote the 20 second timeframe. This will Usually come into play more often than not at idle with large cammed vehicles because many times your steady state map will be within the map sanity guidelines so there is a good possibity you might not see this code pop up immediatly.
There are a few ways you can cure this issue
a. Do as suggested in the help file which is to just set the min to 0 & max to 100
b. Adjust them to YOUR liking so you'll be within a reasonable limit. This will help determine if there IS a real issue with your TPS sensor later down the line.
So there you have it, as good an explanation I can come up with for that bastard code. So the next time you go WOT in your auto LS1 with a large cam & you go from 1st to 4th by 40mph or just a nagging p0121 code for no obvious reason you now have the info needed to fend it off.
Well, have a good night & Stay Tuned!
Under normal circumbstances a stock cammed A4 will probably idle at around 35-40 map. When switching to a larger cam with more overlap your map readings could go up to as high as 70 or more kpa map which is way outside of the normal boundries. On a stock cammed car you'd probably need to be at around 30% tps to hit that same map number which is where that predicted throttle angle quote comes into play.
Now onto the last quote the 20 second timeframe. This will Usually come into play more often than not at idle with large cammed vehicles because many times your steady state map will be within the map sanity guidelines so there is a good possibity you might not see this code pop up immediatly.
There are a few ways you can cure this issue
a. Do as suggested in the help file which is to just set the min to 0 & max to 100
b. Adjust them to YOUR liking so you'll be within a reasonable limit. This will help determine if there IS a real issue with your TPS sensor later down the line.
So there you have it, as good an explanation I can come up with for that bastard code. So the next time you go WOT in your auto LS1 with a large cam & you go from 1st to 4th by 40mph or just a nagging p0121 code for no obvious reason you now have the info needed to fend it off.
Well, have a good night & Stay Tuned!
This doesn't affect anything other than setting a light (f-body), so it's definitely not the cause of any poor operation...
Thread Starter
Teching In
Joined: Jul 2009
Posts: 33
Likes: 0
From: La Porte, TX
My logs are .csv files, not .hpt, so I can't upload them. I attached a screenshot of my STFTs and RPM. What would you prefer to see? I can log STFTs, timing, throttle position, o2 voltage, MAF, speed, rpm, load, MAP, IAT, and fuel economy.
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Thread Starter
Teching In
Joined: Jul 2009
Posts: 33
Likes: 0
From: La Porte, TX
Here is another screenshot. This is really weird behavior at idle after an hour long drive on the highway. I can't make any sense of it. (The rpm, throttle position, timing and speed are all scaled way down to fit on the plot with the fuel trims, and x-axis is in seconds.)
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