mskibbz-T

I just finished reading the GM article about detonation and pre-ignition and it scared the **** out of me. I have been told by a very knowledgeable tuner that it is typical for the FJO WBO2 to read an AFR of 20.0 on decelleration... I never worried about it since then, but this article claims that after a WOT run when you just give it partial throttle is when you can get horrible detonation. I have gotten into the habit of dropping into neutral after a high speed run and that minimizes the lean condition that my FJO reads, but I need a conclusive answer... Is the FJO WBO2 accurate on decelleration? Or does it display a leaner condition due to the decreasing volume of the exhaust gasses and is therefore only accurate under constant loads and acceleration? How are you guys dealing with decelleration after a hard run? Do you leave it in gear and let off the gas, drop to neutral, slowly ease up on pedal pressure, throw a lot of fuel at it with your decel settings in your standalone? I'm really confused at this point...

http://www.streetrodstuff.com/...I.php
http://forum.aempower.com/bbs/...decel

4cdfedhatchie

can't help you out but, i find that to be really good info.

swlabhot

AFAIK, on deceleration you will always be lean =<20 as your injectors shuts off. So its normal that your FJO reads 20..

GreddySi99

the reason you are seeing a lean condition is because under decel your injectors turn off. your engine is under no type of load and you will NOT get any detionation. this has been covered before. just like an autometer A/F gauge will go dead lean under decel not a problem

mskibbz-T

Sorry man, but you are wrong It also has not been covered as far as I can tell, why don't you post some links to the threads about optimal decel settings please. After a WOT run, for instance a 5th gear pull, cylindrical temps get very high and I am wondering what a good AFR is for decelleration as I can toy with my decel settings in my EMS. The engine wouldn't see load if I dropped to neutral, I am talking about staying in gear, which would make the engine see a load. Any autox guys care to comment?


I could care less what an Autometer A/F gauge reads because it uses the stock O2 sensor, I want to know how accurate/functional the FJO/NTK is under decelleration.

"In the same vein, an engine running at full throttle may be happy due to a rich WOT air/fuel ratio. Throttling back to part throttle the mixture may be leaner and detonation may now occur. Bingo, the piston overheats and scuffs, the engine fails but the postmortem doesn't consider detonation because the the failure didn't happen at WOT." -Allen W. Cline

Thanks for the replies so far

Bottoz

Guys, the injectors do not shut off during decelleration. There is still injector pulse, and with the EMS you can add fuel even with no throttle. Skibbs, I see you've been batteling this for a while now. Here's what I did....on the bottom line of your fuel table, add a little fuel. Under deaccelaration, when my FJO read 16-17 my exhaust would pop like a mug. Also, anything below 12 would pop as well. After a bunch of testing I found that AFR of 15 solved the popping under deaccelaration. Give it a try if you want. I havent played with the Decel/Accel yet, so if you can find a better way Please Share!

Bottoz

mskibbz-T

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bottoz &raquo;</TD></TR><TR><TD CLASS="quote">Guys, the injectors do not shut off during decelleration. There is still injector pulse, and with the EMS you can add fuel even with no throttle. Skibbs, I see you've been batteling this for a while now. Here's what I did....on the bottom line of your fuel table, add a little fuel. Under deaccelaration, when my FJO read 16-17 my exhaust would pop like a mug. Also, anything below 12 would pop as well. After a bunch of testing I found that AFR of 15 solved the popping under deaccelaration. Give it a try if you want. I havent played with the Decel/Accel yet, so if you can find a better way Please Share!

Bottoz</TD></TR></TABLE>

Hey Bottoz,
I am going to go hack away today at my Accel settings because I am dipping too rich initially when I floor it off boost and bogging... Hopefully I can fix that by leaning it out a bit, I'd rather not have to delve into the injector synch settings and all that. I'm going to add fuel at the bottom of the map today too, thanks for the tip Bottoz

simple4012

with the stock honda ecu the injectors shut off during deceleration. this is done to save fuel.


with aems or some systems the decel tables must be tuned.

MIKES

Where does all this talk about injectors shutting off stuff come from? Your car will not start without fuel, your car will not idle without fuel. There is no difference with decel, or when you took your foot off the gas it would just shut off the engine. There is no load on the engine during decel, because your off the gas pedal. But if your program getting you to your top speed is out of wack (ie: really lean or too much timing) then your decel will continue your issues and possibliy case problems in the long run. Add more fuel to that area as another member said and all is good. But to answer your intiall question. Yes the wideband is accurate to a degree. Not exact, but close enough. Because when you let off the gas your exhaust temps will vary large, and it only takes a second and a half to get right back to idle when you put it in neutral after a run. So its not 100%. but its close enough. Tune it right and you will have no issues.

boost3d

It comes from looking at the duty cycle of your injectors, when in gear under decel your injectors shut off under stock ECU. The load from the road keeps your engine running, there is no need for fuel. Plus without fuel there can be no detonation, how can you pre-detonate something that isn't there? The issue the original poster is getting at is that under WOT your running a good air/fuel, then go partial throttle(not NO throttle), the cylinder temps are high from your previous WOT = good condition for predetonation. The car will need to be tuned for low load, 1/4 throttle.

A lot of stock turbo car's ECU will cut fuel completely in the condition of an overboost, NO FUEL = NO DETONATION

mskibbz-T

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boost3d &raquo;</TD></TR><TR><TD CLASS="quote">It comes from looking at the duty cycle of your injectors, when in gear under decel your injectors shut off under stock ECU. The load from the road keeps your engine running, there is no need for fuel. Plus without fuel there can be no detonation, how can you pre-detonate something that isn't there? The issue the original poster is getting at is that under WOT your running a good air/fuel, then go partial throttle(not NO throttle), the cylinder temps are high from your previous WOT = good condition for predetonation. The car will need to be tuned for low load, 1/4 throttle.

A lot of stock turbo car's ECU will cut fuel completely in the condition of an overboost, NO FUEL = NO DETONATION</TD></TR></TABLE>

You, my friend, are understanding where I am coming from The AEM EMS has a bug in the current version that cuts fuel at around 130mph, I've hit that a few times w/o any damage, there is a fix out though and it also has been completely resolved for the latest version 1.03... Nobody has damaged their engines due to the fuel cut that I am aware of, which validates what you are saying about factory boosted cars and overboost protection fuel cuts. I didn't get a chance to play with my decel settings or light throttle today, but I will tomorrow. Thank you for replying with some good and correct info

mskibbz-T

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MIKES &raquo;</TD></TR><TR><TD CLASS="quote">Yes the wideband is accurate to a degree. Not exact, but close enough. Because when you let off the gas your exhaust temps will vary large, and it only takes a second and a half to get right back to idle when you put it in neutral after a run. So its not 100%. but its close enough.</TD></TR></TABLE>

That makes complete sense to me as the O2 sensor is heated, therefore when EGTs change drastically it makes sense that the O2 readings would also change until the O2 controller could compensate for the change in exhaust temp.
Thanks