Ludikraut

iTrader: (17)

I don't have any logs of this yet, but I wanted to throw this on here to see if anyone has seen this and if it can be addressed.

The scenario: Lift off throttle at lower RPM (<3000) or lift off throttle slowly at any RPM while in closed loop operation.

The result: AFRs go from stoich (~14.7) to reading rich (~12.3) and then slooowly fade to O2, almost like some fuel is still being injected or leftover fuel is slowly burning off.

I've had cases where my LC-1 will read an AFR of anywhere from 29 to 60 for what seems one or two seconds after going off-throttle. I have to admit it sounds hella cool, but the initial rich spike has a tendency to stall the car when I'm putzing around a parking lot in 1st gear. Off the top of my head I'm thinking the culprits might be:
- TB not closing all the way under low pressure situations
- accel enrichment applies to decel as well, or there is a separate decel enrichment (??)
- ISCV somehow messed up
- BISS mis-adjusted

...any thoughts?

l8r)

PS - I'm using a 65mm ported TB from Works (BISS untouched) and an AMS VSR intake manifold...

Spooldyou

iTrader: (52)

mine has always done the opposite, it goes Lean. like 15-17 .

kmcconn9

iTrader: (33)

I just did a log of this this morning. Mine does the opposite, it will go lean upon lifting and decel...which should be normal

gsrboi80

iTrader: (38)

My car goes rich on decel most times as well. Kinda ever since the cams (I think). Not sure of the culprit. My Accel Enrichment is still at the stock setting. Not sure about messing with it. Al did when I first got flashed a couple years back but since being retuned numerous times its back at stock settings

C6C6CH3vo

iTrader: (9)

Maybe EGR system malfunction or leaking injector?

If TB was not sealing it would assist it going up to o2 not richer, I thought

Ludikraut

iTrader: (17)

AMS VSR intake manifold does not support EGR. Maybe that's what's causing it...

l8r)

Spooldyou

iTrader: (52)

great point that would be my estimate.

MalibuJack

iTrader: (5)

I notice its likely due to the slight delay in cutting fuel on decel. Its probably a configurable parameter but I haven't seen it yet.

Remember, the MAF sensor is located some distance away from the Intake, by altering the pipes, intake manifold, turbo size, cams, you have altered the time it takes from lifting throttle actions and MAF signal dropping actions.. Its not a certain answer, but its the most likely theory.

Also, your diverter valve may have some input on this, if it opens and bypasses easily, the signal from the MAF is different than if it doesn't open easily and vent back to the Intake.

I have always seen a slight rich condition from when I take my foot off the gas till it cuts fuel when I was driving. However I have had a wideband on my car when it was completely stock and it did it then also.

chmodlf

iTrader: (19)

Ludi. I have the same exact symptoms. The faster that I lift off the pedal, the worse it is. I think that because the engine is not under load, it is not too bad to go lean.

EDIT: I go lean when I lift. Which is normal?

Ludikraut

iTrader: (17)

So maybe it's just more noticeable with the bigger injectors than it was when it was stock.

chmodif: I would expect the car to go lean when you lift completely off the throttle. It should actually go to O2 very quickly if your clutch is still engaged. Mine gets a short rich spike first and then goes lean.

l8r)

iTune

iTrader: (3)

you will notice this rich condition after lifting stock, this is a fuel over-run delay setting in the ECU. Some cars are more pronounced than others, especially depending on mods. If you have a aftermarket BOV and especially if it's VTA or partially VTA you will notice this overrun being more pronounced. MJ was right on when he addressed the DV or BOV issue. This is because the MAF is metering for air that is being let out of the system.....thus causing there to be less air then the MAF metered for, thus causing the ECU to run richer as you lift the throttle. This carries into decel especially with the overrun cut-off delay that keeps the injectors on more a few hundred MS after you lift the throttle.

It's not hurting anything unless it's going so rich when you lift at very light throttle posistions...if this happens and it goes to 10.5-10.0:1 or lower, it will cause a studder and misfires until you either lift the throttle more or get back on the throttle.

CJ

Titanium

Interestingly enough, I noticed this same situation yesteday my first time logging with a WBo2...

As soon as I lift, I get a spike of 40-60 afr and the it coasts itself down to ~10.3, where it will hold that AFR until I get back on the gas or take in the clutch.

For some reason I thought it would be lean or o2 under these conditions.

E-DUB

I just started logging with the LC-1 and I found the same issue. I was not expecting the rich reading under decel, and I would like to get rid of it. Does anyone have a good explination for this condition, or any way to correct for it? It occured with the stock flash. I am running stock with a RMR cone intake and 3" RMR downpipe & exhaust with stock CAT.

Thanks.

LetItBreath

I'm not familiar with the stock ecu's operation, but I do know that the tuning principal with decel enleanment(not enrichment) is just the opposite as accel enrichment. When you crack open the throttle quickly the rush of air coming in gets to the cylinders faster than the map(and especially) maf sensor can read the event and tell the injectors to give a little extra fuel. For this reason, most accel enrichment will go off the TPS with parameters like deltaT(change in throttle position, or how fast its opening) and throttle position(less enrichment is needed if opening the throttle quickly when already at 50% then say at 10%.

With decel, its just the opposite. Closing the throttle quickly deprives the cylinders of air faster than the maf or map can read. On some systems its possible and practical to actually cut the fuel injectors completely when lifting to 0% throttle.

Again, I'm not familiar with how this would be adjusted with the stock ecu, but if theres some way to have it take the signal from the tps to determine how much decel enleanment, I'm imagining that would be your remedy. Good luck.

E-DUB

That still doesn't explain the 10.3 AFR when the car is in decel. I've read in other postings that people actually use decel to re-calibrate the LC-1 sensor to open air since supposedly under decel the injectors are turned off and only open air is flowing through the exuast. (it does show Injector pulse width of 0 under decel as well in my logs) If this is that case it should not be reading rich. All my other reading seem accurate, 14.3-14.7 during cruise and idle. And close to the projected Open Loop AFR.

Is there anyone else reading ~10.3 on decel with the LC-1?? Any ideas on the cause?