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AFR Adjustment Questions / I think I need help

This is a discussion on AFR Adjustment Questions / I think I need help within the Computer & Tuning forums, part of the LSx Technical Help Section category; Hi Guys, I'm kind of a newbie but I'm starving for anything that i can learn from you about my ...

  1. #1
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    Exclamation AFR Adjustment Questions / I think I need help

    Hi Guys,

    I'm kind of a newbie but I'm starving for anything that i can learn from you about my LS1. My car has some bolt-on's currently. Fast 92mm intake, 92mm TB, Full Length headers, Cats deleted, 160 degree thermostat, K&N open air filter (I also have ram air hood so the IAT is always between 42-72F). By the way; My car is a 99 Chevrolet Camaro with AT.
    I am a real fanatic for LS1 so I want to be best at it in Turkey.
    And I want to be really really good at it because currently I'm swapping a 98 LS1 with AT to my 74 Pontiac Firebird Formula. Honestly it has a freshly built 400 Poncho engine with a TH-400 but to me nothing is better than an LS.

    My question is about Air Fuel Ratio:

    I am trying to learn about the idea behind it but i'm quite confused at the moment. This Rich and Lean stuff is bugging me at the moment.
    This is what I shortly know; There is a factory setting like 14.7:1 for the best emissions rate. Now if I take this as Point Zero, which side is rich? And which side is Lean.
    My second question:
    What is a safe margin that Your engine should be around to get the most out of it?

    Currently my car has 11,8:1 / 12,1:1 at idle speed, cruising around 2000 / 2500 rpm it is around 12,6:1 / 13,1, at WOT it is like 11,3:1 / 12,4:1

    As far as I understand, my car is running way too rich. Right?
    So, according to the general theory as i was able to understand up until now is that, right now my car should be down on power. Is that right?
    But on the contrary, I personally feel that after I have come up with these values, my car has become much more responsive. The moment i step on the gas pedal, there is really good reply. No stalling. Actually in order to achieve these values, I have spent hours with my diablo sport handheld. And now I don't know if I have succeeded something or fucked up everything. The only thing that was bugging me was the car was kind'a like stalling in neutral. The rpm value was changing between 502 & 645. As if like a person breathing... Then I adjusted the idle rpm value to 700 and it passed....


    I would be grateful for any guidance.


    PS: I have no dyno values because i can not trust the dyno read outs in Turkey. Turkish Market which is all into either Ricer stuff or all out carburated stuff. Sadly People in this industry have any means of education (all they do is trials and mostly errors) and normally the LS engine is really a big phenomena for them. And by no means I am willing to sacrifice my car as a test mule for them. As a person who owns two LS engines, I have to know everthing.

  2. #2
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    Welcome to the site!

    The 14.7:1 you referred to is what is called the stoichiometric ratio (stoich) of air to fuel. Setting aside differences in gasoline blends, it is the theoretical ratio at which every molecule of fuel in the combustion chamber is consumed. Adding alcohol to the fuel (not sure about your country, but here we have about 10% alcohol in all our pump gasoline these days) actually changes the stoich to around 14.4:1.

    Under light cruise conditions, a normally aspirated engine (no power adders) will see AFR's of up to 15.3 or so as excess air in the combustion chamber isn't an issue. However, stomp the pedal and the PCM will go into fuel enrichment mode and AFR's will drop to around 12.8 or so - which is less air and more fuel. Engines with power adders will go even lower and may end up around 11.8 or so under load. As you drop back into cruise, the AFR's should then come back up and down from stoich -- it is essentially a moving target.

    It does appear that you are running a bit on the rich side, but don't always bank on a gauge reading. What type of gauge do you have? I assume it is a wideband? Can it be calibrated for atmospheric oxygen (models by Innovate have this feature)? Do you have black smoke out the exhaust? How do the plugs look? All of these will confirm if in fact the engine is running rich. Another tell is exhaust gas temperature as a leaner mixture will burn hotter than a rich mixture. Lean under load is bad and that is where you get detonation and can potentially damage your engine.

    There are a couple of tuning books on the market that really go into detail on this stuff -- I highly recommend the series by Greg Banish of Calibrated Success.

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    Hi Pajeff02 and Thank You so much!

    Yes, so it turns out that my logic turns out to be quite right.
    In Turkey we have 95 & 97 octane unleaded. I use 97 octane regularly.

    As far as I know, as octane rises, you should retard timing right?
    But on the opposite of this theory, I have advanced the timing +1 in both 2k-4k and 4k-7k rpm range and my engine has come much more responsive.
    And there are no sign of knock readings on diablo sport either.

    My basic thinking was shortly like this (please correct me if I'm wrong); The engine is basically a pump. The moment I was done with the induction, I started getting huge air into the engine. This 92 mm intake & 92mm TB together with an open filter is like having a vacuum cleaner under the bonnet. So I thought I am complete with air, so I should add equal amount of fuel accordingly. That's why I adjusted my injector slope down to -14 in value by diablo sport. And on the other hand, I have adjusted the power enrichment for wot somewhere like %4 in order to get it balanced... I don't know... For the moment I'm saying the car has become much more responsive but maybe if these adjustments were done with knowledge, I would have been much more happier....

    I have bought this car in 2010. It was in pretty beat up shape. But I am guessing that the car had already a cam in it. Because my previous 98 Z28 (which I totaled) was nowhere close to this ones power. The car still retains it's #243 heads but in near future, I am planning to stuff heads & cam combo. Which, of course will be another discussion topic.

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    Ah! Sorry, forgot to write my wideband...
    I have installed AEM uego wideband gauge.

  5. #5
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    With the AEM you should be seeing reliable AFR's. I am not familiar with the Diablosport and its capabilities. HP Tuners is really the best way to tune and probably offers a ton more parameters than the Diablosport. As you said, the engine is an air pump, but its pumping efficiency through the rev range does not remain a constant. Therefore, an across the board adjustment of plus or minus a certain percentage may get you in the ballpark, but it will not be precise. At different RPM and load conditions you will be either lean or rich. The feedback loop utilizing the stock O2 senders will compensate for this and you can look at your short and long term fuel trims to get an idea of what your PCM is doing with fuel. Ideally, the trims should be close to zero, plus or minus a point or three. Trims greater than that indicate an issue with the tune (or other problems).

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    Like Jeff said....if you're serious and really want to have full control of your engine then hptuners is the way to go. I would have to look and see what the advance is for the 99's at WOT......I believe it was 26 degrees. You can always had a couple degrees to that. The key is to then log your knock retard to make sure you're not getting knock. To compare hptuners to a diablo would be like comparing a ferrari to a horse and buggy. You have a ton more control over your engine. The trade off is you can't just plug it in and immediately know everything. There's a ton of reading involved and a learning curve mixed with some trial and error. Fortunately the forums are full of people who are willing to answer questions and help you.
    Dzel likes this.

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    Good Morning.
    I already have bought HP Tuners. I have registration for both of my engines.
    But have i tried to use it..?
    That program scares the shit out of me.
    I honestly have zero knowledge of how to use it.
    I think it would be much wiser to pay $250 for a Greg Banish DVD.
    I really want to learn how to use it.

  8. #8
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    I have all of Banish's books, his DVD and have attended his calibration school... and I still feel about the same way as you. It is very intimidating when you open the program for the first time. Start slow -- open the VCM Editor while plugged into your car, click on Flash and then Read Entire. This will download the current PCM tune to your laptop. Save that file as your base tune and make a spare copy with another name. Then, open the spare copy and start looking at tables and going through everything. That will give you an understanding of what all is available and what your current tune looks like. You can play with this spare copy and practice making changes to get comfortable with how things work. Since you will not be uploading this spare copy back to your car - there is absolutely nothing you can hurt. Another easy thing to do is run VCM Scanner and open up the gauge panel while hooked to your car with the engine running. This is all your real time engine data and is pretty cool to play with. First step would be to install a PID for your AEM wideband -- something that Banish covers in his DVD. Since primary engine calibration is based on adjusting the VE Table for your engine's actual airflow, you need to be able to see the AFR.

  9. #9
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    I agree with Jeff....start slow and take it one step at a time. I also agree that one of the first things you should do is get familiar with the scanner so you can make proper logs of the car. The logs are the whole key to tuning. They tell you what needs done. Set up your wideband and practice logging that and different parameters like spark advance, fuel trims, MAF, and map. Since you're an auto you can also play with the tranny settings like removing torque management and adjusting shift properties.

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