I came across this comment in the faq:

"The standard scan and retune doesn't work for PE or WOT tuning because at WOT the system goes into open loop. Standard O2 sensors aren't much good beyond the proper stoichiometric ratio. Because the desired A/F ratio during PE is 12:1, a wideband sensor or other method of measurement is required."

Does this mean I have to install a wideband O2 sensor in place of the existing sensor to tune?

 

Or run car on a dyno to accurately measure WOT AFR
For want of a better description a NB O2 is a only a " management" device that reads rich or lean very closely each side of 14.7.
A WB will accurately read 10 -20 AFR

http://www.thirdgen.org/techboard/po...867-post8.html

 

I am just thinking that buying all this tuning gear is a bit pointless on its own if it can't tune for acceleration. Watching the car idle or cruise in closed loop is a bit pointless.

Why does the target afr go from 14.7 to 12.1 when you go from closed loop to open loop?

How does a dyno accurately measure WOT AFR? I thought it measured torque and hosepower!

 

You can learn alot from reading datalogs and making adjustments.
In my case spark advance was the biggest problem, I had too much SA going through 3K @WOT giving me knock counts and timing being pulled out that I wasn't aware of until I run the logs.
Fueling on MAF cars ( stockish ) doesn't seem so bad because MAF reads actual air flow and will self adjust to mods ( within reason )

 

In this example the spark was retarded to stop the knocking (ie: auto adjust). Isn't this just like the fuel self adjusting?

 

All dyno operators have a WB sensor they stick up the exh pipe so they can tune AFR

Correct
But the "cause" of the knock was TOO much spark advance to start with.
Once I reduced SA in that area, WOT; I got no knock counts so no spark retard

http://www.thirdgen.org/techboard/di...ml#post3669051
http://www.thirdgen.org/techboard/di...ot-tuning.html

 

This looks like a good answer to why the mixture needs to be richer under load:

A stoichiometric mixture (14.7:1) unfortunately burns very hot and can damage engine components if the engine is placed under high load at this fuel air mixture. Due to the high temperatures at this mixture, detonation of the fuel air mix shortly after maximum cylinder pressure is possible under high load (referred to as knocking or pinking). Detonation can cause serious engine damage as the uncontrolled burning of the fuel air mix can create very high pressures in the cylinder. As a consequence stoichiometric mixtures are only used under light load conditions. For acceleration and high load conditions, a richer mixture (lower air-fuel ratio) is used to produce cooler combustion products and thereby prevent detonation and overheating of the cylinder head.

 

What are the modes the ecm has?

Are there 4 distinct modes?:

1.Closed Loop
2.Open Loop
3.Wide Open Throttle
4.Program Enrichment

 

Is it necessary to buy a wideband afr meter to stick up the exhaust pipe when tuning for WOT?

 

WB makes it MUCH easier to dial in WOT when tuning, especially if you do street tunning.

ELSE you need to make guesses and watch for spark retard. Set the timing table to a typical value like 34-36 deg or a sbc chevy for max power at WOT ranges.

Go WOT and keep playing with the tune. A dyno is absolutely best for this, even if it doesnt have a wideband o2 on it. Just keep tuning until its running max power. Much easier said than done. You can do the old fashion way and just do a WOT pass and shut motor off immediately and read the spark plugs

A simple check to see if things are running right is look at your 02 sensor output while under WOT. its not used in WOT for fuel but will READ constantly. Normal operation its rapidly switching from 100-200mv to 800-900 and anywhere in between. Under WOT, It should peg out somewhere in the 850mv to 950 mv range and hold there across the rpm range. A common rule i've seen was tune for 900mv while in WOT.

My friends car runs in the low 10's to 1 air fuel ratio on a rough tune and his narrow band o2 voltage was reading in the 950-976 range thru the high rpms. So in the high 900s is rich. Tune for that and then back off while on the dyno or at the track and keep backing off to see if MPH increases or hp increases on dyno. If it does, you can feel confident you are in the right area.

Its funny that its 10's to 1, since its commanding 10.76 air fuel as target at those higher rpms under WOT. Interesting...

NOT the most accurate thats for sure. Its the only thing in the logs you can go by to get an indication of what WOT is doing.

Well, maybe not, there is base pulse width of your injectors. You can go by what they are putting out, and estimate actual air fuel ratio i believe but I dont know the formula off hand. It ratios it to stoich I believe which is 14.7 to 1 and with all the other ecm parameters, spits out the target air fuel and in my case, its pretty darn close

 

Thanks for all this good advice. My first challenge is to work out how the fuel and spark tables work. Which ones to change, how much etc.

I have just changed my chip to one running the arap bin. Do you know whether the arap tune is identical to the original 87 one or whether there is a difference?

 

More spark advance in ARAP for starters

Open them both up in TunerPro and do a "compare "
Shows the difference between them

 

Thanks. What is the easiest way to get the 87 bin? Jack Didley mentioned it was available from Moates. I will check it out.

 

Check your email

 

There are a bunch of different MAF L98 codes used. Some are $6E based in 89 and some are $32 and $32B masks. I think 87 would be a 32B mask and I thought ARAP was a 89 bin but doesnt matter, either one will work. ARAP is very aggressive on spark but can work well on the right combination.

Friend of mine has a 360 cu.in stealth ram motor with old style AFR 190's and 280XFI cam that runs very well on a mild modded ARAP bin. The 190 heads are very similar to L98 113 heads just ported. Timing tables ran ok on that car. MAF handles fuel very well and it only needed a few % increases in PE mode to handle WOT.

 

If the goal is for maximum possible spark advance across the rev range then maybe ARAP is a good start. I suppose one just has to look at the datalogs to ensure knocking isn't coming in to play and adjust as necessary. I am running 98 octane due to my higher compression from the Al 128 heads being shaved so that should also hopefully help with the knocking issue from spark advance.

BTW I am using the $6E mask.

 

I don't believe I have received anything!

 

How high is your compression? You may want less timing right now and work your way up with high compression motors as they can be more detonation sensitive. But with your 98 octane gas, it may be ok.

 

After I first got it back after the heads were serviced it was knocking on first start up (open loop). I was then advised to go to 98 octane. Seemed fine after that. Tha ARAP bin hasn't caused any obvious signs of knocking but I haven't done any datalogging on it.

Not sure what the compression ratio is. Equivalent to one shave I suppose. Any way to check?

 

What motor are you running? If its a 350 with flat tops then mildly shaving the heads down to even 54 cc would give upwards of 11.5-11.7 to 1 which is high for a mild cam and would need high octane gas or possible a very safe tune with less timing..alot less than what arap has to offer.

you can do a compression test to see what cranking pressure is. If its real high then yes you will need alot of octane to prevent detonation. Else you will need to up the cam size alot to bring effective dynamic compression down