o2 tuning and various questions regarding AFR

[blueman803]

Is the o2 used to control timing in anyway? I am reading about this megasquirt system and it has the capability to tune using a wideband 02. So I am wondering if I can simply unplug the stock o2 and run a wideband since the MS would be taking care of fuel delivery. If not I guess I would need to weld an extra bung until I get MS to take over ignition as well correct?

What is a good target afr for idle and cruise. I have seen values ranging from 14.7 to 17. Do you simply continue to lean it out until EGT's rise or look for knock? Whats the correct way to determine a good AFR?

Any links to a beginners guide to tuning would be appreciated.

Thanks,
Brandon

 

[Coup D E'Tat]

I am unaware of this as far as MS-specific stuff, but -

your O2 sensor controls fuel, and consequently timing under part throttle conditions. If you replace your narrowband O2 with a wideband, the wideband needs to have narrowband (simulation) capabilities in order to provide the ECU with useful information. Personally, I'd leave the narrowband in and weld another bung in for the wideband.

Stoich is 14.7, and is the general number to shoot for. Obviously, your results may vary, but it'll give you a starting point. Fuel trims will be the easiest thing to go off of. Watch them, and adjust accordingly based on the readings.

Later,

 

[Quasimondo]

Here's a link to a page full of other MegaSquirt links:

http://megasquirt.sourceforge.net/

 

[blueman803]

http://www.powertraincontrolsolutions.com/content-26.html

This would be capable of narrowband simulation?

And from my readings it says that stoich is not necessarily the most efficient afr. 14.7 just allows the catalytic converter to do its job easier. For better fuel economy and idleing, I saw reports of using AFRS as low as 17 to 1. Just wondering how to determine what is too lean or too rich, what results from both, and what to target under varying loads, throttle positions, and pressure. I guess basically a newbie guide to a stand alone system. The megasquirt system didnt seem to really cover that, like it assumes you should know this already before you attempt to mess with the system.

Under the MS tuning it does say aim for 16.5 to 17 under no load and cruising? So do you start with a target 14.7 and lean it out until the engine will no longer idle and then back it down a bit? I imagine at idle EGT's would be of no concern correct? But for light load such as cruising they could be an issue?

After reading back the Corky Bell's book, he says to shoot for 14 to 15 for idleing and cruising, and go for 12.5 to 13 under WOT. Is that not a lot leaner than most ECU chips are set for? Should start with around 11 to 1, then lean it out and monitor knock and EGT correct?

 

[OverboostXS]

Your last statement is correct. 14.7 is stoich but it is not desirable in any way when under load, this area is dangerously lean and could give you problems. Like you said tho leaner for idle and cruise then start at around 11:1 and lean it out from their monitoring knock and timing. Good Luck.

 

[GVR4592]

I am unaware of this as far as MS-specific stuff, but -

your O2 sensor controls fuel, and consequently timing under part throttle conditions. If you replace your narrowband O2 with a wideband, the wideband needs to have narrowband (simulation) capabilities in order to provide the ECU with useful information. Personally, I'd leave the narrowband in and weld another bung in for the wideband.

Stoich is 14.7, and is the general number to shoot for. Obviously, your results may vary, but it'll give you a starting point. Fuel trims will be the easiest thing to go off of. Watch them, and adjust accordingly based on the readings.

Later,

How does an O2 sensor control timing?

 

[andymoraitis]

Brandon,

I'll be putting together a beginner's guide to tuning in the next couple of weeks and posting it in the tech section. In the meantime, you can reference this thread which will tell you appropriate targets:

http://www.dsmtuners.com/forums/showthread.php?p=1658205#post1658205

From a technical standpoint, you don't need a standalone to control A/F and timing maps. I know I sound like a broken record, but an EPROM ECU is all it takes as long as the chip contains a leaner A/F and more timing. This is my only "tuning" device and it's served me very well and helped me make huge gains as you'll see by clicking the above link. The beauty of the EPROM setup is that it allows for changes to take place with a simple chip swap. As an example, I have two chips. One is set for an 11.7:1 A/F and 23 degrees advance (higher octane fuel) and the other is a basic street chip with 11.7:1 A/F and 19 degrees of timing for 93 pump.

If you find that you're interested in going fast with less, drop me a line and I'll help you with custom chip settings that will allow you to make maximum horsepower reliably. You can still add a wideband (weld in another bung on the downpipe) so that you can see the state of tune, but the target A/F ratios run in Jeff's chips are very close to what he programs for.

Hope that helps,

Andy

 

[blueman803]

Andy, thanks for the link and I look forward to your guide.

About the standalone, the main reason I am staying away from eprom chips is the fact that I don't have an eprom ECU. For me to get one would cost 200 or so dollars, plus getting the chips and replacing the capacitors. So probably talking about an investment of around 250 dollars give or take some just to start.

I don't know how familiar you are with the Megasquirt system, but it looks like the best thing since sliced bread to me. If you see any downfalls with the system let me know.

The MS ecu uses a speed density calculation to determine fuel, so it requires running a vacuum line back to the map sensor on the MS ECU and installing an IAT. Are there any drawbacks to a MAP system over a MAF system? I only see the MAF as being more restrictive to airflow?

I can get the entire MS ECU put together for roughly the same price as the socketed ECU with chips, not to mention the megatune software displays active values so you know exactly what is happening with your car. There is also the option to later hook the timing up and move away from the stock ecu altogether. The MS ecu even has a way to monitor knock and retard timing as well. Its a bunch of reading, but I feel that learning how to set this system up properly is a great idea because it so universal and inexpensive compared to other systems with the same capabilities. Also has the option for water-injection controlled based on the map sensor, which I plan to use eventually.


Brandon

 

[Coup D E'Tat]

How does an O2 sensor control timing?

O2 voltage is used to determine how much fuel to give. When needed, based on the fuel/airflow/O2 readings, the ECU will add/pull timing.

 

[andymoraitis]

Brandon,

I have no experience with Megasquirt setups, however I have read of instances where people were able to make good power. If you really like on the fly tuning where you can make tiny tweaks, then I would go for it, pending a consultation with a qualified Megasquirt tuner. Just do your research and make what you believe to be the best decision for you based on your mods and goals and then move forward from there.

If it were up to me, I'd stick with the EPROM setup and Keydiver chip, simply because that removes any headaches for me. It's a simple and proven combination that's worked wonders, especially when custom A/F and timing maps are used. Paying $100-200 more for something that I know will work is better than spending less on something that may not be what I want, but again it's your money and your call.

Hope that helps,

Andy