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Old 01-13-2020, 01:06 AM   #1
BurninSTI
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Default What's really wrong with the sti stock tune?

Just started getting my feet wet in real tuning. Did the cobb university thing so now I can mess with the ecu..hooray Anyways I have read a lot about old school efi tuning and have been thinking what's the real difference between upping the fuel pressure while retaining stock injector table values : changing latency and all the other measures. Seems to me like more air=the need for more fuel. How it happens shouldn't matter that much as long as all the fuel is dispensed and sucked into the cylinder before the intake valve closes or am I missing something? I am looking for more power but more importantly doing it safely.
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Old 01-13-2020, 01:50 AM   #2
viper_crazy
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Increasing fuel pressure will increase flow through the injectors, yes. I'd probably upgrade the fuel pump as it will also see that increase in pressure. I wouldn't know how much of an increase it can take or for how long but if you're increasing fuel demand, fuel pump should be apart of the upgrade package.

As you likely know, there's several ways to increase fuel flow. Higher flowing injectors, increase injector duty cycle (if you can do so safely), increase fuel pressure. Fuel pump will increase supply, but doesn't necessarily mean increase in fuel pressure, because the regulator is controlling pressure, which means a high flow pump won't necessarily reduce injector duty cycle.

If you increase air flow by increasing target boost, just make sure you don't run the compressor outside of its efficiency range. When you reach that limit, you're now getting into turbo upgrade territory, which means more air flow at lower boost.

It's important to note, as I don't remember if this was covered in that course, that fuel is only sucked in while the manifold is under vacuum. Under boost, it's forced in. When you've built boost, that pressure is forcing fuel back up the injectors which is why a rising rate regulator is necessary, to increase fuel pressure to offset the boost pressure 1:1.

Supplemental info:
Total fuel pressure on rising rate regulators is calculated as Base Fuel Pressure + manifold pressure. At idle, there is roughly -10psi, which means total fuel pressure at idle is 33.5psi. If there's a 15psi boost target, total fuel pressure is 58.5psi.

Last edited by viper_crazy; 01-13-2020 at 02:02 AM.
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Old 01-13-2020, 11:38 AM   #3
BurninSTI
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Thanks Viper. Forgot to say I did just install the AEM pump a few weeks ago, seemed to really help acceleration down low, idk how that would work unless my old pump was tired, currently the fuel pressure is regulated by the stocker. Last night I ordered the radium fpr, hoping it will bring those idc's down. Will update this post with results. Also considering getting a wideband or just moving the afr sensor#1 to the endo of the downpipe so it can actually read the afr's accurately. I have a sneaking suspicion that the stock tune might be better than we all think, maybe a bump in fuel pressure/port the wastegate is all that's needed to get the car running safely at <300 whp. I can't see a company custom tuning each engine they drop into rally cars when one blows during a stage, maybe I'm wrong, idk but if stock jdm homologated sti's are running 53 base fuel pressure why are we running 43?
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Old 01-13-2020, 01:25 PM   #4
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I would get a wideband as the stock sensor #1 isn't a wideband. From my understanding it's more of a narrowband supposedly, so even if you do move it, readings likely wouldn't be as finite as a wideband. You can also run a wideband through the rear O2 wiring and log on your Accessport.

Cobb tuning has tech doc on how to disable rear O2. If you have a GR era body style, the rear O2 actually has some influence on fuelling. Not a lot, but enough that you have to set the rear O2 parameters to 0. The doc explains it all.

You can also log fuel pressure via tvg wiring and Flat Irons Tuning discussed being able to tune in a failsafe if ever fuel pressure dropped preventing you from running lean. I'll try and find that video and edit this post.

Last edited by viper_crazy; 01-13-2020 at 01:31 PM.
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Old 01-13-2020, 02:43 PM   #5
BurninSTI
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Just read last night that the stock #1 sensor is actually a wideband, but functions as a narrowband due to the pressure and heat from where its located.
https://forums.nasioc.com/forums/sho....php?t=1922848.

I'll have to check that out do you have a link?
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Old 01-13-2020, 02:57 PM   #6
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There's a lot of back and forth what the front sensor is. Some say narrowband, other say wideband, and I've read that others say it's in the middle of the two...middleband? I'm sure moving the front O2 to the rear would work, but that would require extending the harness so the ECU sees the front O2 circuit. Less tuning headache that way. Considering the undecided topic of what the front O2 is, I'd say go with a reputable wideband kit that's 100% for sure a wideband. I'd be curious to know what you can do as I haven't come across anyone using a relocated front O2. Quite possibly there's a reason no one has tried? Not sure.

And yes, the fuelling goes into open loop under certain conditions (i.e.: WOT) because of Exhaust MAP, temps, etc. Considering the importance of that sensor, I'd leave it where it is and utilize a wideband in the rear as mentioned above.
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Old 01-14-2020, 07:56 PM   #7
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Yeah, a widebands probably next on the list... As for right now, I got and installed the radium fpr and gauge. Ta-da no more cylinder roughness counts or knock. Idc's went from the high 3's at idle to mid to low 1's and never went above the 60's at everything but full throttle much meatier exhaust sound as well and the thing PULLS. For some reason unbeknownst to me it isn't overboosting anymore either.
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Old 01-14-2020, 07:57 PM   #8
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Curious, what pressure did you set it at? What's your AF learning?
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Old 01-14-2020, 08:06 PM   #9
BurninSTI
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I went with 48-49 base with the regulator giving a 1:1 increase per lb. of boost. Once I get the wideband I'll start playing around more with it... I didn't check to see. I'll check when I drive it tomorrow. The air fuel correction was hitting around 7.5-9 because of the Cobb Sf intake that's on it so I figured I the increase in fp would cover that and some more... idc if it's a bit rich now. Safety is my #1 atm.
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Old 01-14-2020, 08:47 PM   #10
firebane
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Quote:
Originally Posted by viper_crazy View Post
I would get a wideband as the stock sensor #1 isn't a wideband. From my understanding it's more of a narrowband supposedly, so even if you do move it, readings likely wouldn't be as finite as a wideband. You can also run a wideband through the rear O2 wiring and log on your Accessport.

Cobb tuning has tech doc on how to disable rear O2. If you have a GR era body style, the rear O2 actually has some influence on fuelling. Not a lot, but enough that you have to set the rear O2 parameters to 0. The doc explains it all.

You can also log fuel pressure via tvg wiring and Flat Irons Tuning discussed being able to tune in a failsafe if ever fuel pressure dropped preventing you from running lean. I'll try and find that video and edit this post.
My understanding rear o2 can't do the proper voltage it would require? Again a lot of back and forth on this. I debated wiring this way but could find no solid answer.
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Old 01-14-2020, 09:33 PM   #11
viper_crazy
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Quote:
Originally Posted by firebane View Post
My understanding rear o2 can't do the proper voltage it would require? Again a lot of back and forth on this. I debated wiring this way but could find no solid answer.
The factory rear sensor itself can't do it, but with a little tuning with Cobbs Custom features, the ECU will the see 0-5v output from the wideband controller. You'll effectively be deleting the stock rear O2. Alternatively, you can use the TGV left or right for this as well. Again, you just have to use the Cobb Custom Features to "program" that function. All you need is to hook up the wideband 0-5v output into the factory sensor signal wire (not power or ground). Most wideband controllers have you hooking up to a switched 12v source anyways so all you're looking for is the signal wire.

If you still have TGV's installed and active, that part gets a bit tricky if you want to retain TGV's, but using TGV Dupication mode will help with that.



Here's that video I mentioned earlier and forgot to look for:

It may be possible to run closed loop all the time using a wideband hooked to the rear O2. That was a project a local-to-me tuner was looking into. I don't know remember if he said he succeeded in doing that or if he was testing it. That was a few years ago now.
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Old 01-14-2020, 10:17 PM   #12
BurninSTI
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I hadn't considered just swapping the sensor... sounds nice but atm I can't. I probably should just get a tactrix and pull the rom out of my ecu because I can't edit the map I am currently using.. like its some super duper secret. For 300 I should be able to eff my motor up playing with tables... I "highly" doubt the tuner I got it from didn't utilize cobbs ots map to make mine. On top of that the worst customer service I have experienced although it is much better than the cobb map! Rant over... when I hit the dyno in a few months I will probably have them start with an unlocked ots map so I can edit it myself in the future.

I think that an auto tuner would be awesome for our cars. I ride road track when I get the chance and many guys have the power commander auto tuner on their bikes. It would be a dream come true.
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Old 01-14-2020, 10:18 PM   #13
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Do you still have the tgv's on your suby viper and if not any noticeable difference?
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Old 01-14-2020, 10:24 PM   #14
viper_crazy
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No, I deleted mine. Not much of a power difference, but then again my car was apart for the better part of a year so I lost the feel of what it felt like before and after. I deleted them while I built my engine and the intake was off. It's something I was going to do so no time like the present as everything was apart. I've deleted them out of my map so no limp mode or check engine lights and avoid any headaches related to malfunctions down the road.
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