RomRaider

Hello all,

I have a 2003 JDM Legacy Spec B which is not controlling boost correctly. I am overshooting to 16-17psi, target is 2.01Bar abs. Max error on the logs is around -2.

I have an IAM value of 0.6875 currently, the ROM says that disable is set at 0.3125 and re-enabled at 0.5625.

The FLKC looks good, I have 3 cells populated in the 1.15<1.5 column have a look at the screeshot.

No codes are set from overboosting (which should cause fuel cut anyway i believe).

So what is causing the disable, and why am I overboosting?

Any hints on what best to log to quickly disagnose the root cause?

Some more background is that the vac line btween the t-piece (Actuator to Manifold) was broken when I bough tth car. It was boosting to only 0.7 Bar however. Reconnecting the BCS into the system saw the boost rising again, but I dont understand how!! Surely the wastegate was only controlled by the size of the hole left in the damged pipe and the BCS canot make that hole bigger!

When boost is disabled, I still see 0.7Bar.

Hi. Not sure if I understand what you saying but reset your ecu to get it back to Iam 1 and log the basic parameters with boost, wgdc's, target boost etc. Also log flkc and fbkc and take it from there to see why your iam is dropping in the first place.

What do you mean by "causing the disable" do you mean boost cut? What is your boost limit (fuel cut) set at?

Cheers

Fuel cut is 2.28Bar, so I am getting close to that. I have logged almost 18Psi Max, but 2.28 is almost 19psi so I havent had a fuel cut issue.

That is not the problem.

The problem is the boost control is disabled, so BCS goes open and I get WG spring pressure only.

The question is, if the IAM value is dropping and causing the cut, then why dont I see more knocking in the FLKC table?

I guess it is due to a recent new value being set for IAM, and the table is empty. At the time of the snapshot, Boost was OK as I had recently reset with battery disconnect.

I will try your suggestion. Start from a reset (so IAM is 1 and no knock) and log those parameters until the boost control is disabled again.


Thanks for the reply!

look at your A/F corrections :
-11 at idle
+8 on mid cruise

Is it possible you have a leak somewhere - perhaps intake or headers?

*edit* or too/from the boost control solenoid and that's why your overboosting?

Possibly. The large +8 and -11 corrections definitley need investigation, something is not right. But the 40+ correction is small.

This weekend I will take the manifold off so I can really get to the vac lines and replace all with silicone. For now, I will keep the restrictor pill, but I have a GM 3 port to install once I iron out this issue.

It is extremely possible that if the plastic of 1 t-piece was old enough to break, then there could be other issues...

I will report back.

Hello all.

After 3 port bcs install i have reliable boost pressure control, however i still have some issues. During the bcs install ibremoved the intake manifold and all vac lines and hoses have been replaced or fastened correctly. But i still have a large negative value for learrning #a and #b.

Naturally i have been reading up online abiut the possible causes but the information i have been reading seems quite contrary. Let me think Out loud:

Intake leak

LV values are negative when fuel is removed from the calculated requirement based on maf voltage. Positive when fuel is added. So negative value means o2 sensor reads rich vs calculated fuel req from maf voltage. To reset the maf voltage vs airflow conversion we can change the calibratable curve. If the correction value (af learning #1 for example) is always at a maximum correction most advice online suggests an intake leak.

My thoughts why this doesnt stack up---

At idle everything after tb is vacuum. Before tb is in light vacuum. the whole system is sucking air in. Losing air through a hole in the intake system aka a boost leak is not possible, we cannot lose air from the system when it is all under atmospheric pressure.

To reach rich fuelling condition at idle (negative lv values for learning #a) due to 'boost' leak at idle is impossible. Because a leak can only add more air to the system under vacuum, it is impossible that maf is over-reporting actual airflow. So large negative value at idle is maf scaling or injector scaling.

Even up to 40g/s range is almost all vacuum and possible very very light boost. All zones are below meanigful positive boost. We can prove this by plotting g/s vs manifold pressure.

Please could you double check my thinking here????

Cheers

Have you tried testing with another front 02 sensor?

Yes also changed for new.