Got LTFT down, but more tuning questions
First of all, I want to thank the fellow HP Tuners who offered advice and encouragement in my attempt to tune my 03 Z06.
After installing my VaraRam cold air intake, my LTFT were in the +14 to18 range; and my FTC read positive input at WOT. I initially raised the VE table 8%, and then an additional 5%, but couldn't drop my LTFT very much, with just the VE table.
So, I returned the VE table to OEM, and reduced the IFR by 5 %, which immediately dropped my LTFT to about +7 to 9. I didn't want to cut my injector flow any more, so I increased my MAF table by 10%. The MAF table increase and the IFR reduction got my LTFT just a bit negative, which is great. I am stopping here, since my cable interface is being EIO upgraded; and I have a set of long tube headers that I want to install. Then, we will play some more.
Now, the questions. I didn't want to reduce the IFR more than 5%, because I was afraid of running out of fuel capacity. Could that happen? Will 5% less fuel jeopardize the ability to maintain PE needs with my headers? What is the maximum that I could reduce the IFR? What is the maximum that I could increase the MAF? Any disadvantages to what I have done?
I was richening up my AFT above 6,000 rpm. I believe my COT was dumping fuel. Can I just shut off enable COT??? Will this burn up my cats? Turn on engine codes?
When I get my LGM headers installed, and cable back, I intend to get into the tuning. With only the VaraRam and HP Tuners, I have gotten my RWHP from originally 348, to 370; and I know that it had more if I could have fixed my AFR curve, as I believe I can do now.
Paul
Re: Got LTFT down, but more tuning questions
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I didn't want to reduce the IFR more than 5%, because I was afraid of running out of fuel capacity. Could that happen? Will 5% less fuel jeopardize the ability to maintain PE needs with my headers? What is the maximum that I could reduce the IFR? What is the maximum that I could increase the MAF? Any disadvantages to what I have done?
When you reduce IFR all you're telling the computer is that the injectors flow less fuel than they really do. The computer calculates how much fuel it wants in the engine, so if you tell the computer that it has smaller injectors then the computer will increase the pulsewidth (keep them on longer) to still try and dump the same amount of fuel that it 'thinks' is going to go into the engine. But since you lied to it and the injectors are bigger than they are more fuel than was calculated goes into the motor which is why you're LTFTs went down. This is why if you put bigger injectors in the car you have to scale the IFR table to compensate, with the bigger injectors with the same table the computer will inject to much fuel.
Me personally, I don't like lying to the computer because it's just like lying in real life, one lie leads to the next and you have to keep track of them all and in the end you may not get the results you want. You can scale the MAF as much as you want but realize that the further you get away from the 'real' amount of air (and fuel) that is going in the engine, or at least what the computer sees, the more problems that can and most likely will occur. For example spark is airflow depended, so if you start telling the computer that all this air is entering the engine you 'should' slowly start to see your timing drop, just look at your spark table, more air(load) equals less timing.
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Can I just shut off enable COT Will this burn up my cats? Turn on engine codes?
Depends, I didn't burn mine up but it is possible. It totally depends on your driving style. No you won't set a light if you disable it.
Don't get me wrong, what you've done is what alot of people have done. I did it when I first got HPT after I got waxed by my friends sisters '01GT. As you get better with HPT and the more you mess with your car the more you'll start to pickup on everything and get a better idea of what you want to do as far as messing with this table and what that table does. You just have to get the snowball rolling down the hill first which is what you've done :cheers:.
-Mike-
Re: Got LTFT down, but more tuning questions
Hi Paul, I have an 02 Z06 with pretty much the same mods as you're going to have except I have Kooks and a trap. My LTFT's are around +20 right now. Thanks for posting, I'm sure it's going to help me get my car in check. :cheers:
Re: Got LTFT down, but more tuning questions
Thanks for the replies, fellas. I does help me understand tuning.
Screamin03,
I'll leave the IFR where they are for now. I don't want to get any closer to maxing out the injector's pulse width. If after I install the headers the LTFT go positive, I will increase the MAF airflow.
I am getting the idea of this tuning. The factory sets the LTFT close to zero. When we increase the airflow rate by high flow intake or headers, the engine would be running lean (above 14.7), but the PCM adds fuel to bring the AFR back to 14.7. That we see as positive LTFT on the scanner.
When I reduced the IFR table, it was effectively "putting in smaller injectors", which the PCM balanced by commanding a longer pulse width to maintain 14.7 AFR. That move brought the LTFT value down, but was not technically the right thing to do.
Actually, what we did by adding the intake mods is increase airflow, so the increase on the MAF table makes more sense than IFR tuning. I probably should have increased the MAF table by 15%, instead of the 10% that I did; and have left the IFR at OEM, instead of reducing it 5%. After I install the headers, I'll see where the LTFT runs, and possibly go back to OEM on the IFR table and increase the MAF, if need be.
The Volumetric Efficiency table didn't seem to drop the LTFT much at all. I never unplugged the MAF, and I am not too fond of doing that. I am not a fan of SD, at least at this level of tune. Should a small increase in VE be reasonable (after the headers) to reflect the higher efficiency of the motor with greater airflow? Does changing the VE table change the LTFT?
After I get my cable interface back after EIO, and the headers installed, it is back on the dyno. I would like a more level AFR curve. My curve dropped to rich above 6,000 rpm. I think the COT may have been kicking in. When is the COT activated? How can we tell if it goes on? I am thinking of doing a pull as is, then shutting off the COT enable. Is that the only way to see if it goes on, and how much the COT affects the AFR?
Also, I heard that some of the professional tuners are setting the PE delay to zero. How do you do that through tuners? I didn't think that there was a delay. I would have thought that when the TPS and g/cyl load settings are tripped, PE would kick immediately. What are your thoughts on PE delay, and how do you drop the delay to zero?
Thanks
02Z06,
You see the changes that I did to get the LTFT down. Maybe less or none on the IFR reduction would have been better, with more MAF; but I don't think that the combination is that bad. Also, there might be some logic in increasing the VE table due to the greater efficiency in the intake and headers now.
Good luck,
Paul
Re: Got LTFT down, but more tuning questions
03_Z06_Blue,
In regards to your COT enable, It is best to leave it on to prevent any undue melting of your cats, what I do is to set enable temp higher.
ie. 1000, 1100, 1200, 1300.
This way it only comes on if really needed.
Mark :cheers:
Re: Got LTFT down, but more tuning questions
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Screamin03,
I'll leave the IFR where they are for now. I don't want to get any closer to maxing out the injector's pulse width. If after I install the headers the LTFT go positive, I will increase the MAF airflow.
You won't change anything with the injector pulse width by messing with the IFR. If the LTFTs are +10 with the IFR stock and you scale it to get the LTFTs to zero the pulse width will still be the same, it's just now the computer is making the change in the root fuel calcualtion instead of after(LTFTs). Think about it, If the motor is running at 800RPMs with a 14.7:1 AFR with nothing else altered, there is only one injector pulsewidth (amount of fuel) that can get it there. All you are changing when you mess with the IFR is how the computer sees it. Does this make sense at all?
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I am getting the idea of this tuning. The factory sets the LTFT close to zero. When we increase the airflow rate by high flow intake or headers, the engine would be running lean (above 14.7), but the PCM adds fuel to bring the AFR back to 14.7. That we see as positive LTFT on the scanner.
Correct
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When I reduced the IFR table, it was effectively "putting in smaller injectors", which the PCM balanced by commanding a longer pulse width to maintain 14.7 AFR. That move brought the LTFT value down, but was not technically the right thing to do.
Correct, me and alot of others feel you should leave your stock IFR to match your stock injectors, why lie to the computer.
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Actually, what we did by adding the intake mods is increase airflow, so the increase on the MAF table makes more sense than IFR tuning. I probably should have increased the MAF table by 15%, instead of the 10% that I did; and have left the IFR at OEM, instead of reducing it 5%. After I install the headers, I'll see where the LTFT runs, and possibly go back to OEM on the IFR table and increase the MAF, if need be.
Think of it this way, the VE table is a chart of the airflow of the motor and it will be wrong with any airflow change to the motor. The MAF sensor measure the incoming air, if the amount of air coming in the motor matches what the MAF sensor is saying then there shouldn't be any reason to alter this table. This is why the feature in this thread was asked about:
I think alot of the problem stems from the fact that the computer blends both VE and MAF below 4K. Be careful when you add 15% to the MAF table as far as spark is concerned, the computer will now think more air is flowing into the motor and will operate on a different part of the spark table which will most likely be spark values that are lower than you're running now.
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The Volumetric Efficiency table didn't seem to drop the LTFT much at all. I never unplugged the MAF, and I am not too fond of doing that. I am not a fan of SD, at least at this level of tune. Should a small increase in VE be reasonable (after the headers) to reflect the higher efficiency of the motor with greater airflow? Does changing the VE table change the LTFT?
I had the same problem when I did my car. When I disconnected the MAF sensor the VE table then had an effect. After I got the LTFTs where I wanted them I plugged the MAF back in and scaled it (I believe x1.10) to get the LTFTs back where I wanted them. This kind of goes against what I just said above but it worked.
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After I get my cable interface back after EIO, and the headers installed, it is back on the dyno. I would like a more level AFR curve. My curve dropped to rich above 6,000 rpm. I think the COT may have been kicking in. When is the COT activated? How can we tell if it goes on? I am thinking of doing a pull as is, then shutting off the COT enable. Is that the only way to see if it goes on, and how much the COT affects the AFR?
I'll be starting a thread about COT because I'm not sure of how it works as far as when and how it determines to kick in.
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Also, I heard that some of the professional tuners are setting the PE delay to zero. How do you do that through tuners? I didn't think that there was a delay. I would have thought that when the TPS and g/cyl load settings are tripped, PE would kick immediately. What are your thoughts on PE delay, and how do you drop the delay to zero?
For a Z06 I don't see an actual delay setting, the only thing I see that can affect it would be 'Enrichment Rate-small number means more time until final AFR is achieved' and 'Mode Delay RPM-PE mode is delayed if RPM is below this value'. For the mode delay it doesn't say much about how it works and I don't see any other tables that you can mess with. This would be a good question for the GMV8 Tuning Forum.
Hope this helps,
-Mike-
