Stft very high at WOT

[Rob777]

Do you worry about extremely high stft at WOT in 4th? I'm still learning but from what I've gathered the ecu is running closed loop mode and the AFR is what matters at WOT not stft??
The question arise's from some of my logs I have just seen which I'm not sure whether to be concerned about or not.
At 5435rpm I'm hitting 17.5psi, AFR 10.79, FP 1692.31psi and STFT +47.7!!!! LTFT is 0.
At 6163rpm 16.1psi, AFR 9.79, FP 1759, STFT +58.6 and 0 for ltft again.
Now that +58 means the ecu is adding a heap of fuel correct??
So if its adding tons of fuel it's because there is more air going in than the maf says it has seen go in correct??
Am I on the right path in thinking I STILL MUST have a small boost leak?
Running Cobb SRI, TIP and Hypertech.

[SarcasticOne]

i'd say ou have a boost leak, so, something between turbo and throttle plate
gen 1 doesnt have WOT fuel correction (gen 2 does... bastards)
whilst it's saying +STFT it's not actually adding fuel...

[Rob777]

i'd say ou have a boost leak, so, something between turbo and throttle plate
gen 1 doesnt have WOT fuel correction (gen 2 does... bastards)
whilst it's saying +STFT it's not actually adding fuel...

Thanks sarcasticone, most of my learnings have come from your various posts and MSF. You seem like the man when it comes to data logs!

So if the +value is actually removing fuel why does my AFR go into the nines? That means there is lots of fuel in engine right?? I would of thought it would make the AFR higher?

Now I have never touched anything post turbo or post TIP. So I'm gonna do another boost leak test tonight when I get home and look for leaks around turbo to cooler to throttle plate etc.
Would you expect a leak in that area to make a noise when boosting? I had a leak in TIP before and that was obvious noise but now it's replaced there is no noises.

[SarcasticOne]

all of my knowledge comes from MSF
i read the posts with data logs, and see what the experts have to say

i'd just go through, tighten the hoses from turbo -> intercooler and intercooler -> throttle plate
would expect some noise yes... but guess it depends where/if it's leaking...
i dont know what AFR the HT commands up top, but i doubt it's in the 9's

just looked at my STFT from logs, im often in the +30 range

[Rob777]

Interesting.. Thanks for checking that. So maybe a minor leak I suppose as no noise but still stft almost double yours.
After checking and tightening if I get time ill post a log of 3rd and 4th wot and get your opinion again if you don't mind?
Thanks again!!

[Rob777]

No log yet sorry no time.. Just wondering what is a typical reading of vacuum on a boost gauge at idle? Pretty sure the pressurized air is escaping, would this show on a boost gauge in this instance? At idle even?

[shaneski]

No log yet sorry no time.. Just wondering what is a typical reading of vacuum on a boost gauge at idle? Pretty sure the pressurized air is escaping, would this show on a boost gauge in this instance? At idle even?

Around -10.30.

[Rob777]

Around -10.30.

Thanks. Same as me so there goes that idea.

[shaneski]

It would probably have to have a big leak for it to show a different reading on idle.
Check the small hose that goes from intake to the boost controller for tightness, i had a corksport intake and it was running crap in 4th WOT, turned out that small hose that came with the intake was not a tight fit and was sucking unmetered air to the intake, i put zip ties around it and it solved it.

[Rob777]

all of my knowledge comes from MSF
i read the posts with data logs, and see what the experts have to say

i'd just go through, tighten the hoses from turbo -> intercooler and intercooler -> throttle plate
would expect some noise yes... but guess it depends where/if it's leaking...
i dont know what AFR the HT commands up top, but i doubt it's in the 9's

just looked at my STFT from logs, im often in the +30 range

Sorry the late response to this, I've been incredibly busy.. I'll post my 4th wot log tonight too.
By throttle plate do you mean throttle body? I'm thinking I might remove throttle body tonight and clean and re tighten. Would u bother with that coolant bypass?
The last major service I had at mazda not long ago, whilst costing a bomb, they cleaned my fuel system, this would cover throttle body area? I'm thinking it just wasn't put back together very well.
Also when boost leak testing I put it on SRI and soapy water everywhere. Intake def does not leak but I cannot replicate the noise I hear when driving. Air does eventually leak out at oil cap though.
Hope u understand what I mean. Being articulate is def not one of my high points..

[Rob777]

To update this: finally had the time to remove throttle body. Looked fine.. Reinstalled and no difference.
Did a boost leak test, again, and no leaks though a very strong smell of fuel is noticed. Gonna check out the injectors next chance I have. I've read somewhere about injector seals being dodgy?? And pretty sure that's an area Mazda touched last time someone other than me was under the bonnet.
Still got to post that log as well.

[Harry LuvzDrift]

To update this: finally had the time to remove throttle body. Looked fine.. Reinstalled and no difference.
Did a boost leak test, again, and no leaks though a very strong smell of fuel is noticed. Gonna check out the injectors next chance I have. I've read somewhere about injector seals being dodgy?? And pretty sure that's an area Mazda touched last time someone other than me was under the bonnet.
Still got to post that log as well.

U read write abt injector seals, here's mine torn into pieces

[richierichness]

Why don't you post a couple logs and I'll check it out


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[Rob777]

U read write abt injector seals, here's mine torn into pieces

Thanks Harry. What were your symptoms, if any of that seal??
From what I said where I can smell fuel when boost leak testing would this happen in that case of a crap seal?

Why don't you post a couple logs and I'll check it out

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Thanks for your offer dude! I'll get one up tonight.. Promise! Not logged with an AP though, using dash command and scantool.

[Rob777]

logs.. for some reason fuel pressure and spark advance didn't log. FRP will be fine, I put in HPFP tonight and was fine beforehand anyway.

thanks @richierichness

[lup15]

hey Rob, good to see you got the HPFP installed. I'm still learning about fuel trims and found a good little overview below
Fuel trim can be a valuable diagnostic tool - Eastern Manufacturing

have you checked your LTFT? I've got Hypertech as well and know they run a safe rich tune. my LTFT have consistently been around -12 regardless of the mods I have been doing, though I find that very rich and may have leaks somewhere too. I'll monitor my STFT to see how they are compared to yours

[Jmac]

Hpfp in, without reading the whole thread, is it possible there is a leak from the fuel line that has to be removed to install the pump?

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[Oldhead]

Hpfp in, without reading the whole thread, is it possible there is a leak from the fuel line that has to be removed to install the pump?

Sent from my GT-I9505 using Tapatalk 4

+1 fuel line to fuel pump connection is critical to be seated correctly as it it easy to crossthread the nut !!!!! you would easily notice fuel spraying > leaking > use torch with engine running and put fingers around connection>also check seal point at fuel pump housing > hope you tightened all long bolts equally and gradually !!!!

[richierichness]

logs.. for some reason fuel pressure and spark advance didn't log. FRP will be fine, I put in HPFP tonight and was fine beforehand anyway.

thanks @richierichness

Rob,

I've never seen someone's LTFT or STFT go beyond 25% but that may just be an AccessPort limit. That being said, once in open loop the ecu follows the MAF curve and doesn't do much if any compensation based on STFT. I suggest your read up on closed loop to open loop transition with our vehicles to fully understand.


I assume your not running any kind of tuning solution? I would highly recommend the AccessPort as it is preferred for us tuners and easy for you to use. You can buy an AP and e-tune through me as RichTune is a vendor here.

Your car is running pig rich as most OEM cars and most people don't log with your solution so I wouldn't get too worked up about the high STFT.

If your worried i recommend you find a friend with an AP and load up a map and take some logs.


Sorry for the late response I've been on vacation


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[Rob777]

hey Rob, good to see you got the HPFP installed. I'm still learning about fuel trims and found a good little overview below
Fuel trim can be a valuable diagnostic tool - Eastern Manufacturing

have you checked your LTFT? I've got Hypertech as well and know they run a safe rich tune. my LTFT have consistently been around -12 regardless of the mods I have been doing, though I find that very rich and may have leaks somewhere too. I'll monitor my STFT to see how they are compared to yours

Hey lup thanks man, read it, really understanding now! Could you please if u have time, tell me ur ltft at idle? I'm up near -18 at idle and -7 at part throttle which I understand is normal anyway but the idle confuses me. Also does ur AFR go into the nines at WOT?

Basically the the -17/18 ltft at idle, the +56 stft at wot and the noise which comes and goes at around 4000rpm are all related. I'm positive. I'm also positive there is no leak in the intake. The cause is between TB and exhaust. Im thinking injector seals (mazda did something here last time they looked at it). It holds boost fine but somewhere along the way, after being cooled it has to be escaping. To me this will explain everything.