+1 ^

 

Just a stab in the dark, but have you checked the vacuum line onto the fuel pressure regulator? If it doesn't see vacuum on idle or cruise its going to keep the fuel pressure higher than it should be.

 

I will get a good datalog sample showing the condition I described. It will be very simple as the car is always doing it.

All hoses are in place for the EGR. Also verified the tables and they are indentical to any stock rom. The thing that is killing me is that no CEL has been triggered! Oh well!

Does the fuel pressure solenoid has an inlet and outlet? Sort of like the BOVs that the air flows on one direction only. I remembered replacing this hoses as maintenance when I did the turbo swap.

Also, does anyone knows if I can bypass the solenoid and place the vacuum source directly to the fuel pressure?

Here is a diagram for reference:

 

Well! Here is a quick update and some logs as promised.

1. Checked Fuel Pressure Regulator and it is working fine. Bypassed the FPR solenoid and I still get the same problem. The Fuel Pressure is around 40-45 PSI with the vacuum hose connected, 50-55 PSI with the hose disconnected.

2. Please note that the first log based on time is on 1st and 2nd gear. Second log is on 6th gear inthe highway. Please note when the JDMMAP is or above zero, there is a big jump in AFR even when the injector pulse is higher.

Check them and let me know what you guys think!

 

Sounds like front O2 sensor failure.

 

Even in Open Loop? I forced the ECU to run open loop all the time disabling that on Periphery FAA. So no trims are adjusted or changed.

Thanks for replying!

 

When did this all start happening? Was it after an install of some part?

 

Well... I was swapping the green for a red and a BR TBE to a BR V-Band TBE. However, I kept the Ex Mani and the O2 Housing. New gaskets thou!

In addition to that, I replaced the vacuum hoses for the EBC, BOV and FPR ones as a maintenance step.

Right after the swap I noticed the rich condition with a P0172 (System too rich) code and the weird idle/cruise. After a lot of minitoring, I finally noticed that the rich condition is only while the car is in vacuum and suddenly jump to stoich (or near stoich) causing the erratic acceleration.

There is another member here (Cali2MDevo8) that is experiencing a very similar trend and we are working together to find a solution for this culprit.

I should be getting an AEM EMS ECU tonight and will be testing the symptoms tomorrow hopefully.

 

Check for exhaust leaks before 02 sensor, since you changed the turbo.

 

I checked for leaks in the manifold/turbo area and could not hear/find anything.

Since I disabled closed loop, would still matter? If the ECU is not taking in consideration the O2 feedback to balance the mix to stoich, why an exhaust leak will cause the symptoms mentioned above? Why rich only when the car is @ vacuum and not at atmosphere or pressure?

Just something to think about!

 

Ok got u. Let us know if u find the problem, this one is baffling.
good luck.

 

It is very strange! There is another user here (Cali2MDevo8) with a similar problem and has not been able to solve it yet.

I disabled closed loopto ensure that the AFRs that I am seeing is not based on O2 Feedback correction. If I enable closed loop, the car will go into stoich for hours or maybe a day. Right after enough time for the car start to learn idle and cruise trims, it will go into P0172. Before, the code is triggered, the cruise will get affected because of the sudden jump from rich (10.8-11.2) into the expected values (14.0-13.0... which is normal for the tune) . At that time, the jump will be from mid 13s and 12s into 16.9 AFR becuase the ECU trims are very negative substraction a lot of fuel. This leading to rough acceleration during partial throttle.

The solution right now is to leave the closed loop disable to find out the root cause. At least is driveable during cruise in the city.

I still need to find out what is causing this!

 

being u swapped the 02 housing and the turbo as well check for a small exhaust leak either pre turbo or possibly downpipe to 02 housing, small leak and its prolly not gonna run right n u havin the ability to retuned are tryin to tune out a problem thats not electrical...check all ur exhaust bolts and retighten them all up...gl

 

similar problem, just scaled some injectors (770s) got the trims in nice, however, when the car is at idle the WB is seeing 15AFR - good. once u start driving between 1500-4000 RPM the car goes rich - to 11-12AFR. then back up at 14-15 @ 4500RPM.

weird stuff. any ideas?

 

Hey I just noticed in one of your posts you mentioned you were using the SD patch correct? If so, what map sensor and scaling are you using? Here's why I ask...

When I first started playing with SD for my 8 I never had any logs to go from to set my RPM VE and Map/kPa VE. For a while I would make a change and see how it reacted and go from there. Along the way I ended up with a Map/kPa setting that made my full throttle map run perfect, but my cruise and idle were in the 9.8-10.3 afr range, which sounds very similar to the issue you're having. If you're on SD I would suggest looking closer at the Map/kPa VE table and adjust that instead. Once you get it set semi-close you can drop your RPM VE table down to keep a normal Low and Mid LTFT without popping a DTC for an overly rich condition. FYI, the trims do tend to bounce negative like you mentioned on SD when you don't have the RPM VE set properly either.


*Edit: I just noticed he also said he was getting an AEM ems. Wonder if he ever found out the problem?