I am quite new here, but I have also done quite a bit of homework. I have a 2006 EVO IX (15 ROM id) with the following mods...

Ebay TBE (no O2 housing yet)
Hallman MBC (set at 21 psi)
AEM Intake

I have noticed a phenomenon in my logs since I installed my TBE/WBO2 sensor that is quite strange to me. Whenever I release the accelerator from a steady cruise, my AFRs will go pig rich. Most of the cruise logs that I have come across on EvoM show AFRs becoming lean after the accellerator is released. Does anyone have any idea What could cause my AFR to become so rich?

The ideas that I have so far are
1. blow by from the lack of exhaust backpressure after installing the 3" TBE
2. faulty stock BOV
3. boost leak (not likely, just tested this)

 

i go rich as well, not sure why, never got a problem and its been 20,000kms.

 

is the bov recirculated? is the hose leaking the connects it back to the intake, as this wouldnt be a boost leak and would show on a boost leak test. how rich? 11-12 or under 10?

 

That's normal....the butterfly has closed and there's still fuel in the system. Then, if you keep decelerating in gear, it should go peg lean. No worries. You will always see a swing in AF between gear shifts.

 

wats your TPS Volts closed?

 

like already stated, its not that abnormal but check your BOV make sure its recirculating and go from there

 

Retard the ignition in the low load/higher rpm colums and get rid of that fuel

 

My comment was assuming you're running the stock/recirc BOV.
Between shifts, the gauge should swing rich and then peg lean if still decel in gear, or go back to stoich if you resume normal driving.
If you have something going on different than that, then you have an issue.

 

what????????????

 

Just curious... does it have the same problem if you let off the throttle abruptly? Mine has had the same issue with either of the open intakes I have tried and seemed to get worse when I traded up to the E9 BOV. If I let off slowly as you did mine will stumble a bit drop to 10-11 afr then back up to stoich. Never worried about it much though

 

^ Normal

 

Thanks... I figured as much. WOT to 0% throttle is fine

 

My BOV is a stock IX BOV and it is recirculated, when closed my TPS reads around 15.

I was curious if anyone else with similar mods (TBE, cone Intake) has any logs that they can send me that shows this problem on their car, so I can compare it to my scenario.

I am still a bit paranoid about this because I have only found this problem on 2 of the 50 logs that I have downloaded from this site. Also, will the oil that develops on the walls of the cylinder only be washed away when the engine is running rich for extended periods of time, and will small spikes that I am seeing have any affect?

 

does your car stutter when this happens, as if bov is trying to vent but cant? Im on stock IX valve thats crushed mine does this only at light throttle, its annoying.

 

I get this and an RPM drop sometimes. It is directly attributable to the intake pipe.... i can almost 100% guarantee that.

I had a full bolt on car that never had problems, then switched the stock pipe to a metal one (already had an open filter) and the problem came up. For a while I thought it might be the blowoff pushing air backwards over the MAF, but I don't think that is the case anymore. I tried creating some restrictions for the BOV air to be directed toward the turbo and slowed... didn't seem to help. Besides that the problem happens when out of boost also.

Obviously my trims are spot on for regular idle, so I've been wondering if lowering the ISCV adder could help (more open ISCV = low vac = higher requirements to maintain idle). I'm speaking specifically of the same two that cause rev-hang.

Adjusting MAF compensation would help temporarily, but then the trims would re-settle for correct airflow and the problem would be back (and drivability and idle would suffer). I always wondered if it was the peak in the maf compensation table near idle, but my testing showed that it personally did not help much.