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I am new to the WRX world but I know my turbo basics. Most of my knowledge comes from turbod MR2 and Supras in which case you can use a boost controller to raise boost past the Fuel Cut point without even thinking about the ECU. Why are these WRXs so delicate to raising boost? On an MR2 you can raise boost from a stock 12psi to 17-18 psi safely only requiring an upgraded intercooler, spark plugs, and a Fuel Cut defender and any other type of basic bolt on (downpipe, exhaust, etc) all on a stock turbo with no piggybacks or reflashing.

edit* ok i just read stileguy's response and that is exactly what I was getting at. It shouldnt matter that you raise your stock boost slightly. your MAF sensor is there to detect the amount of incoming air and adjust fuel pressure accordingly. Thats the whole reason behind fuel cut. The ecu will cut fuel and retard timing at a preset boost level (17psi i hear in wrx) as to prevent from knock. So why not use a boost controller to raise boost to 16psi or 17 with a fuel cut controller like the HKS FCD. In cold winter conditions boost tends to creep higher simply because of the cold air. The ecu knows this and adjusts fuel accordingly.
 

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most hotwire airflow meters use an output voltage from about 0-5v (0 being engine stopped and 5 being the highest airflow that sized airflow meter can maintain the hotwire temp at.) once this "wall" is reached it is time to get either a bigger airflow meter (pipe diameter) or change to a completely different meter (ie nissans use Q45 infinity meter) or go for map sensed load axis. either way you will need a retune on your ecu. it is possible to max out an airflow meter on a nissan without hitting the boost cut by using an aftermarket turbo with stock boost levels, the subaru ecu does not have af meter out of range cut, only a boost cut, when you disable the boost cut with an fcd the ecu will adjust fuelling to excessively rich to the point where the fuel system is not capable of maintaining. ie as boost is raised the stock ecu gets excessively rich to a point where the fuel system runs out of flow and results in a lean condition often ending in cracked ring lands or melted piston crowns or both. this is why the stock ecu shows little extra power when boost gets above 15-16psi on a stock turbo as it runs air fuel ratios in the low 10:1s to protect itself and looses power because of excessive rich mixtures. the subaru engineers have tuned the fueling within the confines of the factory turbocharger and factory boostcut with an excellent compromise between safety and power. if you go beyond the factory boost cut with an fcd or aftermarket boost control you can measure the life of your engine in seconds or minutes. anytime boost or airflow (via turbo replacement) exceeds the factory limits (boost cut) a full ecu retune should be done. no exceptions. So the obvious conclusion is that boost controllers dont kill engines, boost controller USERS kill engines.
 

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This is true. There is some important info in the original post though, and that's the part about part-throttle boost.

With a boost controller you'll be able to hit full boost at part throttle (the ECU normally prevents this). Since the ECU is expecting you to be off boost at part throttle it's still aiming for a 14.7 : 1 AFR (way too lean for on boost).

I seriously doubt the 19:1 claim though, that seems impossible and I've never heard anyone else say anything about AFRs leaner than 14.7 : 1 as a result of a boost controller.
 

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Discussion Starter #24
codemonkey said:
I seriously doubt the 19:1 claim though, that seems impossible and I've never heard anyone else say anything about AFRs leaner than 14.7 : 1 as a result of a boost controller.
When I get a chance, I'll show you the logs showing insanely high AFR's. Granted, they only hit them for a split second, but, as you know, sometimes it only takes a split second to do damage...

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Noob question. You state that the air fuel ratio is controled by the tps sensor. Isnt there a map or maf sensor on thies cars? I would think a map sensor has more to do with air fuel ratio then the tps. Cause how is the computer supose to know how much air is going through the throtle plates when all it know is how much you have the throtle open.
 

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Iroc-Z said:
So wouldnt the maf be able to compensate for the extra air?
Its not so much compensating for extra air as it is for a condition called PTFB (Part Throttle/Full Boost).Plus the ECU controlls the boost amount in correlation to ambient temps & barometric pressure.The MBC or some self programmed EBC's just won't allow the ECU to correct for all the conditons listed above.This could be bad fo da engine.Its allways best to let the factory ECU do as much as possible.Spend the money for some engine management and let it control the boost safely.
 

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and if the ecu is tuned to boost 12psi and the boost controller is set to boost 18, they will fight each other the whole time causing lag and sudden power loss (the ecu doing everything it can to stop boost)

but if you still want a boost controller... haha my friend is selling his... and for a reason.
 

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Okay i hear everyone saying theyre getting 12psi stock, my 03 stock is only pushing 6psi for reasons unknown. i just ordered a perrin MBC to up it to 12psi, would this be a bad idea considering its what stock levels are set to?
 

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It sounds like you're only getting wastegate boost pressure, meaning that you might need to put the pill back into the line, you have a faulty bcs, or a leak. It sounds like your wastegate is controlling boost instead of the bcs.

Also, adding a mbc isn't a good idea.
 

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Cosmo said:
No. The "learning" is based on how you drive, and it only works if the ECU is still in control of everything. It may adjust the fuel and timing slightly over the course of a few months, but not nearly to the extent everyone says it does. And, not nearly enough to compensate for the extra boost. Especially at lower rpm and load points.

I have a question about this. I intend on purchasing an 03 WRX and since this is the case, how could I reset the ECU so that when I start driving it, the ECU will tailor to me and not stay with the settings of the previous owner?

Thanks
 

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is this the same for 06 model? im wondering cause i know that in a DSM you can safely go to 17 and all i want is to go to 15 right now. also on a side note a guy i know threw a electronic boost controller on his 02 wrx and he never had a problem. well thanks and i hope someone can help me on my decision.
 

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trktwrx said:
is this the same for 06 model? im wondering cause i know that in a DSM you can safely go to 17 and all i want is to go to 15 right now. also on a side note a guy i know threw a electronic boost controller on his 02 wrx and he never had a problem. well thanks and i hope someone can help me on my decision.
DSM's and Subarus are two totally different animals when it comes to ECU's, simply invest in some engine management if you want to safely increase boost levels over stock. For the money that you'll spend for a good EBC, you can pick up the AccessPORT and handle your business that way.
 

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soundline said:
I have a question about this. I intend on purchasing an 03 WRX and since this is the case, how could I reset the ECU so that when I start driving it, the ECU will tailor to me and not stay with the settings of the previous owner?

Thanks
If you want to reset the ECU, unplug the negative battery terminal and step on the brake pedal for 5 seconds. However, the ECU constantly learns. It didn't learn the previous owner and then stop learning. It will (probably has) learn around your driving as much as possible even without a reset.
 

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Well you CAN, but the car's computer is controlling the fuel input, independant of what the fuel pump is supplying (unless something is wrong, of course). If fuel pumps oversupply what the car tells the injectors to put in, the rest just gets dumped back into the tank.
 
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