Supra Forums banner

1 - 20 of 37 Posts

·
Registered
Joined
·
182 Posts
Discussion Starter #1
Went back to the dyno this morning.
Results
This pull was at a max boost of 1.3 bar.
HP 490.7
TQ 454.9
Most other pulls produced about 480HP

Issues:
1. My VPC was working backwards?
If I richened the curve with the Gain knob, it would lean the curve. I tried this several times with the same results.
2. My igintion was giving me fits when I tried to turn the boost past 1.3 bar. The car would start missing bad.
I believe my plugs have about had it. I have been running Denso Iridiums at stock gap for 20k miles with no issue.

Can someone please advise.
1. Why my VPC works backwards?
2. What plugs and gap do you recommend.

I have one last question.
I tuned with a Fields SFC-R and had no problem fattening the AF curve up but when I am under light throttle my AF is so rich it chokes the car out and it stalls. Does anyone else have this problem with fuel computers. Do any allow you to adjust for throttle position or are all an on-off switch, meaning you either run the modded curve or you don't?

All in all I was fairly happy with my results today and I can tell this turbo has A LOT left in it. My HP curve just kept going up and when I tried to turn the boost up further I gained over 40HP and 40 TQ below 5000 RPM's but all those runs had to be aborted due to missing. If I could have stayed in it I believe I would have made well over 530HP.
I am going to change my plugs and go back to the dyno in a couple weeks.
Thanks
Josh
 
P

·
Guest
Joined
·
0 Posts
sounds good, I have no problems with the VPC, but all my settings are at 0 and I use the GCC for tuning (but they are at 0 too, because I have the ecu upgrade)

anyway, I have the NGK 3330's and I am very happy, no problems at all gapped to .032, I run about 1.4 bar

congrats :)
 

·
Moderator
Joined
·
3,148 Posts
I would also recommend about a .032 gap.

Later, Steve
 

·
Registered
Joined
·
182 Posts
Discussion Starter #4
What do you all use for fuel control? Any issues?
 
B

·
Guest
Joined
·
0 Posts
Are you resetting your ECU with every pass? Get 3330's and try it again. I'd know when i forgot to reset the ECU between passes when I'd change fuel settings and it'd do the opposite of what I wanted it to do. My AFC works great and so does the VPC. I make big changes with the VPC and then smooth out the curve with the AFC. Good luck
 

·
Registered
Joined
·
362 Posts
Keller,

Larry from SP recommended NGK 3330's gapped at 0.028". This solved my misfire problems although idle is a little erratic at the moment.

BTW Today I got 540rwhp at 1.6bar (6th gear, in 4th and 5th gear boost did not go over 1.2 bar) on a Bosch dyno (don't know how that compares to a 'real' Dynojet).

Flavio
 

·
Registered
Joined
·
182 Posts
Discussion Starter #7
Brad
Your saying that if you didn't reset your ECU that if you turned the gain up on the VPC it would actually lean out the curve?
This is what happened to me.
Flavio
I am gettting boost in 4th. In fact I'm getting so much so early it is amazing. Have you tried to adjust your wastegate screw?
I just ordered a set of 3330's;)
I am going to try an initial gap of .32 to see if that help preserve my idle quality.
540 is awesome, the little turbo that could. I bet this turbo will hit 580+ at 2 bar. Enough for me for now:D Of course I need a fuel system first.

Thanks For the help guys.
 

·
Registered
Joined
·
362 Posts
Josh,

I can get plenty of boost on the street but the dyno I went to today just wasn't suitable for the Supra with the fast spooling SP57. It just didn't load the engine long enough to get boost up to high levels.

Flavio
 

·
Registered
Joined
·
1,022 Posts
Reseting the ECU is not a good idea, unless you've made broad changes and give the ECU a chance to re-learn everything. When you reset it, all fuel trims go back to zero. On a stock MAF car this may not change much, but in a VPC car the ECU is probably applying a good amount of correction to the fuel trim to keep it running right.

Any diviation from the predicted value in closed-loop operation (ie whenever the O2 sensor reads something that doesn't agree with the ECU's airflow input) can effect WOT fuel trims as well.

Also, if your car is missfiring the wideband will read leaner. I'd keep your same plugs just gap lower.
 
B

·
Guest
Joined
·
0 Posts
I've always reset the ECU every pass. If i forget to it acts up. I always reset the ECU between passes at the track too. I'm gonna go ahead and say that the car likes it, cause if I dont the car makes less power or goes slower.......
 

·
Registered
Joined
·
1,022 Posts
Brad Mayo said:
I've always reset the ECU every pass. If i forget to it acts up. I always reset the ECU between passes at the track too. I'm gonna go ahead and say that the car likes it, cause if I dont the car makes less power or goes slower.......
Then maybe you should tune it w/o reseting until it stops acting up? :)

What is the difference in trap speed with reseting and not reseting? My car would always go 1 mph slower if I reset the ECU.
 
B

·
Guest
Joined
·
0 Posts
You CANT tune a car right without resetting the ECU. If you try to change settings after a pass without the ECU going back to baseline you cant make it do what you want it to. Think about it, you make a pass, the computer sees things it doesnt like and changes them. Before the next pass you go make changes on top of the ECU's changes and it ends up being different from what you wanted to happen. When you reset it you go bakc to zero and only the changes you made are what effect how the car runs. Anything else is shooting in the dark.....
 

·
Registered
Joined
·
1,022 Posts
Brad Mayo said:
You CANT tune a car right without resetting the ECU. If you try to change settings after a pass without the ECU going back to baseline you cant make it do what you want it to. Think about it, you make a pass, the computer sees things it doesnt like and changes them. Before the next pass you go make changes on top of the ECU's changes and it ends up being different from what you wanted to happen. When you reset it you go bakc to zero and only the changes you made are what effect how the car runs. Anything else is shooting in the dark.....
How can the ECU "see" anything? You are tuning for WOT operation right? As in open loop? The ECU does not use O2 sensor information for feedback, it only uses MAF input, throttle position and RPMs to select injector duty cycle.

The following is a post by Lance W. put on the main list a long time ago, about how the ECU works w/ fuel trims and all that:


Reg Riemer posted on this subject a while back and even linked a few pages
from the Toyota Technical Training Manual regarding long and short term fuel
trim. The following text is quoted from the manual.

Fuel Trim

Fuel trim is a term used to describe the percentage of correction to basic
injection duration based on oxygen feedback. There are two different fuel
trim values which affect final injection duration; long fuel trim (Long FT)
and short fuel trim (Short FT).

Long FT is after the basic injection duration calculation. It is determined
by how closely the fuel system achieves the theoretical air/fuel ratio.

Long FT is a learned value which gradually changes in response to factors
beyond the control of system design. For example, fuel oxygen content,
engine wear, air leaks, variations in fuel pressure, and so forth.

Short FT is an addition to (or subtraction from) basic injection duration
and fuel trim calculation. Oxygen sensor information tells the ECM how
close it comes to the ideal air/fuel ratio and the Short FT corrects for any
deviation from this value.

How Short FT Works

Short FT is a temporary correction to fuel delivery which changes with every
cycle of the oxygen sensor input. Under normal conditions, it fluctuates
rapidly around it ideal value of 0% correction and is only functional during
closed loop operation.

Short FT is a parameter on the OBD-II data stream, that can be displayed in
the Diagnostic Tester. Its normal range is +/- 20%, but under normal
operating conditions rarely goes beyond +/- 10%.

Short FT responds to changes in oxygen sensor input. If basic injection
duration + Long FT results in a lean air/fuel ratio, then Short FT responds
with positive corrections (+1% to +20%) to add fuel or enrich the mixture.
If basic injection + Long FT is too rich, then Short FT responds with
negative corrections (-1% to –20%) to subtract fuel or lean the mixture.

When Short FT is varying close to +/- 0%, this indicates a neutral condition
where the basic injection duration calculation is very close to
stoichiometry, without any significant correction from the oxygen sensor
input.

How Long FT Works

Long FT is a data parameter on the OBD and OBD-II data streams. It is a
more permanent correction to fuel delivery because it is the correction
right after basic injection duration calculation. Long FT changes slowly,
in response to Short FT. Its normal range is +/- 20%, positive values
indicating rich correction and negative values indicating lean correction.

If Short FT deviates significantly from the +/- 10% for too long, the Long
FT shifts, changing the basic injection duration. This shift in basic
injection duration should bring Short FT back to the +/- 10% range.

Unlike Short FT which affects injection duration calculation in closed loop
only, the Long FT correction factor affects the basic injection duration
calculation in both open and closed loop. Because Long FT is stored in
NVRAM and is not erased when the ignition is switched off, the fuel system
is able to correct for variances in engine and fuel conditions even during
warm-up and wide open throttle conditions.

LEARNED VALUE (Vf) OR FUEL TRIM

At the same time the ECM is controlling the fuel injection duration using
input of feedback from the oxygen sensor, it is also “learning” about the
amount of fuel correction that is taking place. This learned value (Vf) is
used by the ECM during both open and closed loop operation to help fine tune
the fuel control in relation to engine wear, sensor wear, and air leaks.

Basic Injection Duration and Oxygen Sensor Input

The basic injection duration value is the ECM’s best guess at the actual
injection time necessary to achieve an ideal fuel/air ratio. Generally this
basic injection calculation is very accurate, typically within +/-20% of
what is needed. Once within this range, the ECM can trim the air/fuel ratio
to stoichiometry based on oxygen sensor input. Depending on many different
factors, the amount of correction required for Ox feedback will vary. If
the amount of necessary correction remains relatively small, for example
less than 10%, the ECM can easily adjust the mixture. As the Ox feedback
correction reaches the +/- 20% limit, the ECM fuel correction range becomes
limited. The ECM then uses its “learned memory” to adjust or trim the basic
injection calculation. By increasing or decreasing the basic injection
duration, Ox correction can be held within an acceptable range, maintaining
the ECM’s ability to correct over a wide air/fuel ratio range.

Please don't argue about the content here. It is directly from the horse's
mouth, word for word, I just retyped it because the original jpegs were all
but illegible.
 
B

·
Guest
Joined
·
0 Posts
Thats all fine and dandy, but why whould you want to fight the ECU when you can take it back to zero and make things easier?
 

·
Registered
Joined
·
182 Posts
Discussion Starter #19
Andi
Why would my VPC work backwards?
Also could you please resond to the issue I posted at the beginning of this thread about my SFC and stalling when down shifting.
Also did anyone notice that Short FT is an OBD II perameter only?
This would mean that Brad's ECU is going to react differently to fuel changes then our OBD II ECU's.
 

·
Supra OG
Joined
·
1,002 Posts
Keller said:
Andi
Why would my VPC work backwards?
Never tune w/ the gain, in the end after a couple minutes of learning it will do NOTHING. Tune with the secondary RPM based fuel computer only above 4000RPM.

Also could you please resond to the issue I posted at the beginning of this thread about my SFC and stalling when down shifting.
Likely: bad oxygen sensor.

Also possible: bad or wrong VPC chip.. or bad VPC pressure sensor. or resistor fell out of the VPC harness that sets the temp to 80F.

Also did anyone notice that Short FT is an OBD II perameter only?
93-98 Supra TT's all have a long term FT, and long term FT is computed from short term FT....

This would mean that Brad's ECU is going to react differently to fuel changes then our OBD II ECU's.
He's still wrong on this.....

Andi
 
1 - 20 of 37 Posts
Top