After swapping the exhaust on my Evo 8, now when I come to a stop, the engine drops to 500 RPM and practically dies every time unless I give it gas, which is kind of unsettling. Is there any easy tweak I can make with ECUFlash to make this go away?

 

most possibly nothing to do with your exhaust. what part of exhaust? cat back? manifold?

i guess you need to tune your idle and/or check for vacuum leaks

 

One detail I forgot about is that my battery died and I had to replace it, so it's possible that I need to just drive it around and hope that the fuel trims get re-learned.

 

Is your car tuned? Might have dual maps?

 

Could be, but if your trims are that off you have other problems. I would probably start with a boost leak test and go from there. What in all did you do with the exhaust? If you messed with the 02 housing you might have an exhaust leak effecting the 02 sensor.

 

Exhaust swapping is not your problem, even if there is a leak, it would merely sound like it and that's it. O2 sensor is not affected by any leak, such as a gasket not sealing well, as it only needs a very small quantity of gasses to read properly. Before anyone else mentions oxygen mixing with co2, it does not affect the sensor, for the reason I mentioned. Just think that your exhaust is full of oxygen when the engine is off. The only way to affect the sensor is to have a very short exhaust pipe with the sensor placed at the edge of it.


Check the O2 though as it might need to be replaced. Also check your TPS sensor, that might also needs to be replaced, or it is not getting the right voltage. Also check the wiring of O2 that it has not been damaged while you were changing exhaust parts, and that it is properly plugged back at its place.








Marios

 

No battery replacement or removal for charging, does affect the ecu. The ecu has two types of memory, surfacial/ temporary, and solid/deep memory. Only the first type is affected from removing the power source, the second type does not as the ecu stores energy for it but also because it is the same type of memory such as your pc has, the one that stores your personal settings on your windows software. In the same way it stores your fuel and timing maps trims and settings.Idle area is on the fuel and timing maps, and its settings belong to the solid memory. When you remove the battery for some time, a few hours i.e both the TPS , IDCV and O2, sensors need re-calibration. A process which is initiated and takes place automatically, the moment you re-connect the battery and start the car, this is for idle, but it might also take a spin around the block for things to be fine-tuned and back to normal. This is for voltage to increase through rpm and sensors to get the full 5v they need, and also some extra time for ecu to finish its fine-tuning. This is only a few minutes of driving, no more, and it might not even need that. It depends, on the battery type and properties , the condition of your alternator, and the condition of wiring.







Marios

 

I was always under the impression that a pre-02 sensor leak could draw in ambient air and mess with the 02 readings. I don't want to argue with you, this isn't first hand knowledge but was passed on to me. If you disagree that's fine.

Fair enough description, If you don't mind i'll just elaborate. What you describe as "solid/deep memory" is called EEPROM (Electronically Erasable Programmable Read Only Memory) and "surfacial/ temporary" is RAM (Random Access Memory). If everything is mechanically sound then the calibration stored in EEPROM should be good enough to run the car without any noticeable issues, the narrowband is very fast and the ECU employs short term feedback trims almost immediately. It's only when things are beyond the bounds of what the ECU can compensate for in short term trims alone that you get immediate issues on a clean slate calibration (No Long term trims).

 

This is not the case, and there is no reason in arguing, everyone is entitled to their opinion. In order for that to happen it needs to be on short pipe right after the turbo, an open dump that is so short that there is a lot of oxygen affecting the exhaust gasses. Also the opening does not matter if it is before the sensor or after it. The sensor by default on our cars is located on the top of the o2 housing, so unless someone does not bolt the o2 housing on the turbine housing but leaves hanging there having an inch of open space in between, a leaking gasket will not affect it as it is too small of a leak. Also the amount of gasses is so thick, and so much, with so much force at that specific area, that the actual forced pulsing of the gasses pushes outwards and allows no oxygen in. Besides we are talking about a a 2mm thick metal gasket of oem quality, personally I have never seen either a manifold to turbo or turbo to o2 housing gasket fail.


Whoever told you this, is mistaken. The reason for his malfunctioning idle i.e was something else.







Marios

 

It seemed plausible enough for me to believe it because of Bernoulli's Principle and the scavanging effect.

 

I always try to keep things simple for others to understand. I know what eeprom or ram is. I've also replaced the Power fc one on mine with a Power fc Pro version one, along with a couple of parts that needed to be replaced. The narrowband is as fast as a wideband sensor, such is the bosch 5 wire one, of course it depends on the wideband as there are types of wideband sensors,so I would agree that the oem o2 can be faster than some wide band ones out there.

I do not use a narrowband sensor on my setup, I have mapped and configured the whole thing on a wideband only.









Marios

 

Scavenging does not apply on the specific case, gasses or oxygen from the leak are not drawn from, they are forced frontwards/outwards. Scavenging would apply much later down the pipeline of the exhaust system. But still even if there is oxygen drawn into the pipe by a leaking gasket it will not affect the o2. You can actually try it if you want actual first hand evidence. Just loosen up the bolts of your o2 housing a bit so that a thin piece of paper can be squeezed in there and then start the car. You will notice no difference in idle. You can also do the same by removing one pipe of the sas system i.e on the exhaust manifold, or the bolt if you have removed the system, you will also notice no change in idle, but you will notice the extra sound frequency and pitch.





Marios

 

I had a crack in the exhaust manifold on my honda- it threw my fuel trim positive for this exact reason. When I replaced the cracked manifold the trims returned to near zero.

 

Well I find that hard to believe, as I have seen noumerous cracked exhaust manifolds on various cars, including hondas with no idle issues nor afr changes.

Here is a random example :




Marios

 

Thanks for weighing in with your first hand account.