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Is it safe to do a performance tune (reflash ECU) with only factory sensors?

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Hi everyone.

My son is talking about getting his V7 WRX road tuned again, but I am concerned that his tuner is only using the factory sensors for doing a performance tune.

This is his 3rd engine, which we haven't long finished doing a forged rebuild on. He had his last engine tuned by the same guy, and it threw a rod out the block a few weeks later. The current engine is out of a V7 STi (EJ207), and is is obviously much stronger being forged, but I very much doubt it is 'detonation proof'!

I am only new to HPA, but from very early on I became aware of how critical ignition timing and AFRs are when going for maximum power and reliablity, where ideally a stand-alone AFR monitor and audio knock monitor should be used.

His tuner seems confident he can tune the new engine using just the existing factory sensor inputs to ECU, but to me it seems very dodgy as the o2 sensor is an unknown quantity and the factory knock setup is apparently pretty average at the best of times.

So my question is, "Is there any safe/acceptable way to do a road tune using only the factory sensor inputs on the above engine?"

I think not, but I told my son I would ask the experts, then it's not just Dad's opinion. :-)

Many thanks in advance for your advice.

Kind regards,


I wouldn't be loading a built sti motor on boost without knock listening and a wideband. Given your investment in the motor (time and money) the cost of that additional gear seems very modest compared to losing an engine. Is if a standard or sti driveline?

Hi Michael, thanks for the quick reply.

That was my thought exactly!

At this stage it's just the sti engine & clutch. 6spd is next on his wish list. I'm trying to convince him to invest in a proper tune, or some tuning tools, before doing anything else.

That is what I'll be doing. I have wideband and plex knock listening setup, plex combustion logger (I appreciate this is beyond most people's budget) and will be using a 4 channel thermocouple system on my rx7. A built piston motor should be more tolerant of approaxhing knock if the tune and boost levels are progressed slowly. I'm just getting itchy feet waiting to have room to work on it properly. Best of luck with it, I know I didn't always take heed of my father's advice as a young fella but try to make him realise his mate/tuner is probably a bit full of himself and gets off on ego boosting sweet talking people about his skills.

I'm not sure what your background is but i would recommend both of you going over fault finding/disgnostic resources for both mechanical/auto electrical stuff from your trade training colleges or automotive mechsnical engineers institution or similar. Deciphering faults is by far the harder part of tuning than understanding air/fuel or ignition mapping.

The stock O2 sensor in the V7 STi is narrowband and hence is totally useless for tuning under load. The knock control system is effective to a point on the Subaru engines but I'd still strongly recommend using audio knock detection equipment to validate logging from the stock ECU. So I guess the short answer to your question is no, you can't rely solely on factory sensors.

Thanks very much for input guys! I have sent him a screenshot of your reply Andre, so hopefully common sense will prevail. :)

There are no faults or issues with the car Michael, at least not prior to the tune. I would love your tuning tool setup, but is indeed a bit cost inhibitive. I have an Innovative wideband hard wired in my car and am making a cheap audio knock pickup at the moment. I was considering a getting a 4 channel CHT & EGT monitor for road tuning my Civic when I finish the turbo build, but now considering an oscilloscope instead. Basically looking for the best option to help find MBT while road tuning. A local Uni does an automotive oscilloscope course, so will be finding a bit more about that soon. I want to tune my N/A (DOHC ZC) engine as well, as I had it dyno tuned recently with very poor results, hence joining HPA. It has been warmed up a bit with high compression, "lumpy cams", ported head, lightened flywheel etc. My general automotive & auto-electrical knowledge is pretty good, but tuning is new to me.

Cheers, Wayne