Front Bank STFT Maxed out Rich-Suggestions

[NOMIEZVR4]

Stock Injectors, Walbro 255 Hotwired Flash ECU

EVOscan is showing front bank is running lean as the Short Term Fuel Trim is +12.5 maxed out. The car has NO boost leaks. New Fuel Filter. Brand new Denso Oxygen Sensor as well on the front bank. o2 Activity is normal as the sensor voltages are fluctuating as they should. New Spark Plug Wires(NGK) and Spark Plugs (NGK Copper R5811a). Car occasionally throws a p0300 I believe because of the Short Trim being maxed out. I would really like to resolve this issue before throwing the big injectors back in. I am aware that it could be a partially faulty injector that could be causing this but just want to make sure I rule out all other possibilities before swapping parts and tunes.

Just for reference, Mid is +5
On the rear bank, Short is +2 and Mid is +6
All help appreciated.

[NOMIEZVR4]

Im running chrome v2 BTW..

[striker2]

check to make sure you dont have a cracked exhaust manifold. although for what its worth mine was maxed the same way, no leaks, no cracked manifold, good O2 sensors. I was able to bring it back down to under +5 on the front and -5 on the rear by adjusting the VE table in chrome.

[NOMIEZVR4]

I re-enforce welded the front manifold when the motor was out...;)

SO relieved to know I'm not the only one...Thank You for chiming in. Anyone else?

[RealMcCoy]

+12.5% is not even close to being maxed out. It's barely above what would be considered 'normal'. Is this at idle?

A 14% variation from front to rear would have me looking for the issue though. Do they come closer together with higher load?

[NOMIEZVR4]

Correct me if I'm wrong but I believe 12.5 is the MAX value that will be displayed although it could be way more than what the number is showing. I'm sure you know this, but the target value is +/- 5% on the trims. Yes, the Short Trim refers to idle. The MID trims are fairly close at 5 and 6 percent respectively.

Maybe you might be referring to the older ECU's which may have a different range displayed, the trims im referring to are in regards to the 99 ECU.

[RealMcCoy]

STFT is not just idle... It is the instant reaction to the oxygen sensor. The long term trim is a reaction to STFT. There are three LTFT's. Low. mid, and high. you want to tune for LTFT as close to 0 as possible, but your instantaneous total trim is STFT+LTFT

At idle, you need to look at front STFT+ front LTFT low = total front trim, rear STFT+ rear LTFT low = total rear trim.

[Greg E]

+12.5% is not even close to being maxed out. It's barely above what would be considered 'normal'. Is this at idle?

A 14% variation from front to rear would have me looking for the issue though. Do they come closer together with higher load?

12.5% is maxed.

[Greg E]

Correct me if I'm wrong but I believe 12.5 is the MAX value that will be displayed although it could be way more than what the number is showing. I'm sure you know this, but the target value is +/- 5% on the trims. Yes, the Short Trim refers to idle. The MID trims are fairly close at 5 and 6 percent respectively.

Maybe you might be referring to the older ECU's which may have a different range displayed, the trims im referring to are in regards to the 99 ECU.

Anything under 100hz is the low trim. Usually that's idle. :)

Few questions:

Do you have periphery 0 bit 2 disabled?
Does the front sensor cycle while cruising?
Hotwired fuel pump with the stock FPR?

[RealMcCoy]

12.5% is maxed.

I don't have a 98-98 here in front of me to check, but I would expect that to be true for any of the LTFT's. I would also expect STFT to have much more resolution.


Anything under 100hz is the short term trim. Usually that's idle. :)



I keep seeing STFT being confused with LTFT low in this thread...

[Greg E]

I keep seeing STFT being confused with LTFT low in this thread...

LOL! Got me there. :)

[NOMIEZVR4]

Anything under 100hz is the low trim. Usually that's idle. :)

Few questions:

Do you have periphery 0 bit 2 disabled? NO
Does the front sensor cycle while cruising? YES, I can go for a drive and double check, but im certain it does.
Hotwired fuel pump with the stock FPR? YES

.......

[Greg E]

Next can you confirm that you are getting 12V at the fuel pump? Talking about actually using a volt meter and measuring at the pump housing itself.

(I know it sounds rediculous but please humor me)

[NOMIEZVR4]

No problem, I'll do that today and report back. Battery is in the trunk too...

The car has no driveability issues BTW, drives great currently making 330whp at 11lbs boost :)

[IPD]

are you running the rails parallel or series (stock) feed? stupid question, i know, but worth asking.

[NOMIEZVR4]

Stock feed

[Greg E]

The issue is probably just FPR over run where you get very uneven pressure between the front/rear banks BUT in my experience, you can still get both O2s to cycle.

The last time I encountered this issue was on a customer car and the cause was a poor fuse connection with the fuel pump Hotwire. This is why I asked you to check the voltage at the pump.

[NOMIEZVR4]

The issue is probably just FPR over run where you get very uneven pressure between the front/rear banks BUT in my experience, you can still get both O2s to cycle.

The last time I encountered this issue was on a customer car and the cause was a poor fuse connection with the fuel pump Hotwire. This is why I asked you to check the voltage at the pump.

OK, just checked. 13.8 at the battery, 13.6 at the pump housing itself on a cold start. So then are we concluding the culprit is the FPR being overun? Shouldn't it be running rich and the trim settling at -12.5 though? Especially on the front bank, relatively speaking..

[Greg E]

Unless there's a serious flow mis-match with your injectors, No. There's a surge of fuel on the rear bank. The front gets trimmed after the rear. So essentially the rear bank is the "base" trim and the front is compensated off that.

I know it's confusing....

Try playing with increasing the values in the MAF Smoothing (VE) table from 100hz and lower. See if that brings that front O2 to life.

[NOMIEZVR4]

Unless there's a serious flow mis-match with your injectors, No. There's a surge of fuel on the rear bank. The front gets trimmed after the rear. So essentially the rear bank is the "base" trim and the front is compensated off that.

I know it's confusing....

Try playing with increasing the values in the MAF Smoothing (VE) table from 100hz and lower. See if that brings that front O2 to life.

Will do. I'll report back shortly.

[RealMcCoy]

I may have missed it, But as the concern is at idle, were the LTFT low, front and rear values posted?

[NOMIEZVR4]

OK, I increased the values in the MAF smoothing table and the trim has come down. Currently at 7% and the rear is at 2%. :) I will drive it some until they settle down completely, but I'm glad I've made progress. Thanks to everyone.

I'm a little confused though, the +12.5 indicated that the ECU was already adding fuel. Further increasing the numbers in the MAF table also ADDS fuel. What am I missing here? Shouldn't I have had to lower the numbers in the MAF Smoothing table?

also, the front o2 was cycling prior to me making any adjustments...

^^
You're confusing me...:p I need to get my head around all the acronyms.

[Greg E]

I'm a little confused though, the +12.5 indicated that the ECU was already adding fuel. Further increasing the numbers in the MAF table also ADDS fuel.

That's right. The trims are adding fuel to get to your 14.7 AFR happily cycling O2s. Adding to the MAF table does what the trims are already doing so the trims don't have to do it anymore.

Simple as that. :)

[Greg E]

STFT = short term fuel trim AKA O2 feedback
LTFT = Long term fuel trim (there are 3 types of these, low, mid, high)

[NOMIEZVR4]

Greg thank you for the clarification!