Wrx stumbles at wot.

_Broken_WRX_

New member
So I just had to get a new trans and in my ignorance I managed to lose my harness to my rear O2 sensor, Cruise, and traction control. Since then as soon the car hits boost it stumbles for a second until smoothing out. I watched my afrs on a pull and it seems like as soon as I give it the beans the afr spikes to about 16 (sketchy). Thats when it stumbles. After that my afr continues to fall back down to the low 11s until I let off. Ive quit driving the car in boost for now until I get that harness. Is this something just caused by not having that sensor? I thought the rear sensor was just for emissions. Possible vacuum leak?


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Alin

Diehard Car Enthusiast!
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HolyCrapItsFast

Drinks beer!
The rear O2 definitely affects fuel trims. If you have a Cobb accessport you can monitor A/F correction #3 and A/F learned #3 to see it's contribution. This is why we disable it when we tune. That the harness is damaged the false reading being given is only complicating matters. I am not sure but I think this may force your car into open loop all the time.
 

_Broken_WRX_

New member
The rear O2 definitely affects fuel trims. If you have a Cobb accessport you can monitor A/F correction #3 and A/F learned #3 to see it's contribution. This is why we disable it when we tune. That the harness is damaged the false reading being given is only complicating matters. I am not sure but I think this may force your car into open loop all the time.

Thanks. Since I dont have the harness rn it doesent read at all. I did do a smoke test and found one fairly significant vacuum leak around my blowoff valve. Should I hold off driving the car at all or just not in boost for now?


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Eagleye

Tinkerer
Yeah if your rear O2 sensor isn?t communicating It will effect fuel trims as holy said. He can correct me if I am wrong, but the rear can be turned off until you get it fixed which should correct your problem. The ecu should then just rely on the front o2 for A/F corrections.
 

Eagleye

Tinkerer
Thanks. Since I dont have the harness rn it doesent read at all. I did do a smoke test and found one fairly significant vacuum leak around my blowoff valve. Should I hold off driving the car at all or just not in boost for now?


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I take it this is an actual problem with the bov and not the line running to it? If it is the lines, try to re seat them and fix it before driving. Personally I would park it until you can get it fixed right if you have another car to use.
 

_Broken_WRX_

New member
It was the gasket between my intercooler and the blow off valve that was bad. I made a new gasket out of some gasket paper and it seals now.


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HolyCrapItsFast

Drinks beer!
Yeah if your rear O2 sensor isn?t communicating It will effect fuel trims as holy said. He can correct me if I am wrong, but the rear can be turned off until you get it fixed which should correct your problem. The ecu should then just rely on the front o2 for A/F corrections.

Aaaa fuck it. I just leave it off all the time. It does no good except for emissions and CAT efficiency and the fuel trims are much smoother without. :tard:. If you are catless then turn em off for sure. Your tuner should be able to do this for you.

It was the gasket between my intercooler and the blow off valve that was bad. I made a new gasket out of some gasket paper and it seals now.


Check your cruising fuel trims now. I bet this was most of the problem. Reset the ECU before you do and give it some time on the road before you log. I wouldn't go wide open throttle till you know your fuel trims are proper.
 
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