Car Going To Stoich At 5K RPM! - What the....

[cartman003]

What up fellow tuners.

Car details:
99 LS1 ATI Procharger, 44#inj., Intercooled, A4; 5PSI Boost.

I had tuned this car about a month ago for the supercharger - car left doing about 410HP.

Customer installed the SSI Aluminum Intake manifold and a 90MM TB and came in complaining that the car was not running the same; which makes sense since the vehicle is drawing in more air. Ran the car and put out 360HP. It was hot out here in California that day but 50 hp loss was too much of a loss in my opinion.

Here is where it gets out of control I started to tune the vehicle and out of nowhere the vehicle would "Command" stoich right in the middle of my WOT run; what the hell.

Did a second pull without changing anything in the ECM and did not do it - I've never heard or seen anything like this - check out the attached runs it's mind boggling. Keep in mind that both runs are on the same tune - no changes where made between the runs.

The other issue I have with it is the MAF reading it seems to be bouncing around when boost seems to be pretty consistent.

Is this just a bad ECU?

[WS6FirebirdTA00]

post the tune, that is weird...

[cartman003]

Tell me about it. It was driving me crazy - I thought the car was trying to commit suicide or something. I told the owner to avoid WOT until the issue is resolved or else it can blow.

Here is the file.

BTW, would this be a good time to try to use the "Write Entire" flash function?

[Chris@HPTuners]

my guess is you are throwing a TPS code related to the new throttle body. i've seen that before when people grind the throttle stop down to get more rotation at WOT.

when you get that code the PCM estimates the throtle position very low which someimes puts you out of PE mode.

[WS6FirebirdTA00]

that was going to be my next question, if you were throwing any TPS codes

[cartman003]

I had just flashed it and after the run it did not throw any codes. If the TPS was going out would it have not also changed the TPS signal to 20% or 30% reflecting the the output of the TPS signal. Through out the run the TPS is displaying 100%.

[Chris@HPTuners]

unfortunately no. If a TPS high/low voltage code is set the TPS value used by the PE calculation (and others) is set to a default value (which in many cases is 0).

The PID will continue to display close to the measured TPS value from the TPS Sensor.

Chris...

[cartman003]

Do you think if I physically back probe the TPS sensor with a volt meter that I would see the drop in voltage when it commands stoich?

Could the new TB be the cause of the TPS drop?

BTW, on a side note that aluminum SSI intake heat soaks the engine really bad. After the car cooled down with the help of a few bags of ice and a few fans we where finally able to make a pass without the car commanding stoich and the power came back up to 380hp - not exactly what he was doing before but at least we knew that when the car is commanding the correct a/f the power is somewhat still there.

He's actually contemplating changing it to the LS6 intake.

This car has truly been a nightmare it is the same vehicle that I had posted a thread on (http://www.hptuners.com/forum/showthread.php?t=17477
) with the VATS killing the injectors because the BCM was not receiving the appropriate 5V reference. And the only fix for that was to remove the VATS.

I feel for this guy it has been one thing after another.

[Chris@HPTuners]

you can log the TPS sensor voltage in the scanner. my guess is you need to change it so that the blade doesn't quite rotate as far at WOT, it sounds like you are right on the limit. Some aftermarket TB's have a setscrew you can use to adjust this, others don't. You won't see a volatge drop, it's just the voltage is exceeding the limit the PCM uses to detect open circuit (high voltage) on the sensor.

Try putting something there to stop the throttle opening just the last little bit at WOT and see if it fixes it.

I see this a lot when people grind the throttle stop off a stock TB thinking that extra 0.5 degree rotation will by some miracle give them 20hp... but it sets the code and almost detonates their engine instead...

[cartman003]

Thanks Bill,

This makes perfect sense. I'll be working on the vehicle tomorrow and I'll update you on the outcome. I appreciate the help.

Something new to look for when dealing with a newly installed ported TB.

I wonder how many cars have actually gone out like that. Imagine a nice 250 shot of NOS and the car commanding stoich at 5200 RPM.

[MMGT1]

unfortunately no. If a TPS high/low voltage code is set the TPS value used by the PE calculation (and others) is set to a default value (which in many cases is 0).

The PID will continue to display close to the measured TPS value from the TPS Sensor.

Chris...

well i'll be damed......good info guys!

[cartman003]

Here is the follow up and outcome. As Chris pointed out the throttle stop screw was set to the minimum by the installer/customer. When he dropped off the car he expressed to me that he wanted the TB to open as much as possible.

I measured the voltage using the PID and it was reading 4.89v at WOT. The vehicle considers 4.27v as 100% therefore allowing the voltage to go up as high as 4.89v is overkill and exceeding the TPS voltage capacity.

I reset the throttle stop screw so that wot is at 4.40v.

The car ended up putting down 430RWHP/405ft.lbs of torque and the commanded never went back to stoich.

Thanks again Chris.

[WS6FirebirdTA00]

sweet

[Chris@HPTuners]

glad you got it sorted. usually the threshold is set somewhere between 4.75 - 4.90V

[Bill@HPTuners]

Although a rare case I believe this thread to be deserving of a sticky

Thanks for the great info Chris!

[Y2K WS6]

It might not be so rare, I just competed my first couple of scans and have one of those throttle bodies that has been slightly modified..... and i think it might have done the same thing... i say think because i'm still very new learning fast though.

[josh mcclelland]

car i am tuning has same problem , checked voltage and at wot it is 4.89 i am going to calibrate wot at 4.40 and hope that is the fix. thanks josh

[RWTD]

Yeup, I bet that'll fix it ! I, too, had the same damn problem.

[jimmyblue]

4.75V is the fault-trip threshold, under 4.7 consistently
(4.65 is good) and you'll be fine.

[3831badls1]

hey i am brand new to hp tuners and i had a question that reminded me of my issue im having with my car that was somewhat similar to this. First of all i am having bank 2 o2 sensor issues that are exactly the same as the log from this persons car, my b2 sensor stays at 447 only jumps to 451 occassionaly, which is screwing with the b2 fuel trims and making the car run crappy, exactly like this persons. I replaced the o2 sensor and still the same, i am also having some tps issue, basically my tps is not reading 100% under wide open throttle. can anyone help?