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Discussion Starter · #1 ·
Greetings my 2 door friends -

I have an Aristo-swapped GTE VVTI engine in my Lexus GS300 (2nd generation). Stock Aristo ECU controls the body, stock 4-speed A340e transmission, and DBW. I have a Haltech running my engine management. The car is well tuned and on a single 6765 turbo. I recently upgraded my fuel pump and fuel lines and bypassed the stock fuel damper. None of this seem relevant to my problem, but it's the only thing I knowingly changed directly before this issue reared it's ugly head.

I am finding that going to WOT with my pedal will result in only partial throttle at the throttle body. I find that consistently the throttle will open fully right around 5,600 RPM and stay open through redline. I have been scratching my head for a few days now, and thought maybe I could get some knowledge here. I have logs that show my VPA (pedal position sensor) and the TPS that illustrate what I'm dealing with. It seems to happen in any gear.

At first I was suspicious of a failing TPS, VPA, or DBW motor. But after all the evidence I've found in the logs as far as consistent behavior, combined with doing a hands-on inspection of the unit and continuity test (although didn't have spec for GTE, only the GE vvti DBW), I don't at this point have a high suspicion of the part being faulty, although it is possible.

I was reading a thread about a very similar problem someone was having with their supra some years back, which turned out to be the knock sensor causing the ECU to restrict the TPS. DBW/ETCS-i problems Similar in the amount of restriction (60-70%) but different, as mine clears up right around 5,600 RPM and gives me 100% to redline. Also different in that I've made no tuning changes since upgrading the fuel pump and fuel lines, and I'm running on e85, so likelihood of too much timing advance resulting in knock is incredibly low / unlikely. I checked my logs and while I'm only logging 1 of my 2 knock sensors, I saw nothing that would indicate it was picking up knock. But I'm still very curious and suspicious that a malfunctioning knock sensor could possibly be my culprit and looking for any insight here as to what could cause the stock ECU to reduce throttle opening.

Other pertinent points: This only happens when I'm moving / driving - with the engine off or in neutral, the throttle behaves correctly. I have no Traction control / stability control functions active on the car that could be the culprits. I can feel as I monitor / log the TPS movement that the car's acceleration is correlated to the throttle movement - which is to say - I don't think I am getting faulty or phantom readings - the TPS readings I believe to be accurate of the throttle/butterfly movement. I checked the stock ECU and I'm not getting any codes related to failures of TPS / VPA / ETCSi.

Here's a look at a log that shows the reduction in the throttle position.
Note: "Nitrous Pressure" is really the VPA / Pedal position sensor and psi = %.

259026


As an aside - Does anyone know how a guy can direct message other SupraForum members these days? I was surprised to see I could not directly contact specific members.
 

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Greetings my 2 door friends -

I have an Aristo-swapped GTE VVTI engine in my Lexus GS300 (2nd generation). Stock Aristo ECU controls the body, stock 4-speed A340e transmission, and DBW. I have a Haltech running my engine management. The car is well tuned and on a single 6765 turbo. I recently upgraded my fuel pump and fuel lines and bypassed the stock fuel damper. None of this seem relevant to my problem, but it's the only thing I knowingly changed directly before this issue reared it's ugly head.

I am finding that going to WOT with my pedal will result in only partial throttle at the throttle body. I find that consistently the throttle will open fully right around 5,600 RPM and stay open through redline. I have been scratching my head for a few days now, and thought maybe I could get some knowledge here. I have logs that show my VPA (pedal position sensor) and the TPS that illustrate what I'm dealing with. It seems to happen in any gear.

At first I was suspicious of a failing TPS, VPA, or DBW motor. But after all the evidence I've found in the logs as far as consistent behavior, combined with doing a hands-on inspection of the unit and continuity test (although didn't have spec for GTE, only the GE vvti DBW), I don't at this point have a high suspicion of the part being faulty, although it is possible.

I was reading a thread about a very similar problem someone was having with their supra some years back, which turned out to be the knock sensor causing the ECU to restrict the TPS. DBW/ETCS-i problems Similar in the amount of restriction (60-70%) but different, as mine clears up right around 5,600 RPM and gives me 100% to redline. Also different in that I've made no tuning changes since upgrading the fuel pump and fuel lines, and I'm running on e85, so likelihood of too much timing advance resulting in knock is incredibly low / unlikely. I checked my logs and while I'm only logging 1 of my 2 knock sensors, I saw nothing that would indicate it was picking up knock. But I'm still very curious and suspicious that a malfunctioning knock sensor could possibly be my culprit and looking for any insight here as to what could cause the stock ECU to reduce throttle opening.

Other pertinent points: This only happens when I'm moving / driving - with the engine off or in neutral, the throttle behaves correctly. I have no Traction control / stability control functions active on the car that could be the culprits. I can feel as I monitor / log the TPS movement that the car's acceleration is correlated to the throttle movement - which is to say - I don't think I am getting faulty or phantom readings - the TPS readings I believe to be accurate of the throttle/butterfly movement. I checked the stock ECU and I'm not getting any codes related to failures of TPS / VPA / ETCSi.

Here's a look at a log that shows the reduction in the throttle position.
Note: "Nitrous Pressure" is really the VPA / Pedal position sensor and psi = %.

View attachment 259026

As an aside - Does anyone know how a guy can direct message other SupraForum members these days? I was surprised to see I could not directly contact specific members.
low post count could be your problem with messaging other members. Post more. Reply to me.
 

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Discussion Starter · #3 ·
LOL yes a low post count for sure. But I used to be able to send and receive messages. No longer see the option to do so. :unsure:
 

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LOL yes a low post count for sure. But I used to be able to send and receive messages. No longer see the option to do so. :unsure:
hrm I’m not sure I click on the name and then message in lower right corner of the box that pops up
 

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Discussion Starter · #5 · (Edited)
I did a little more research and experimenting.

I took the car out for a drive today and logged both knock sensors. While I don't necessarily know what high vs. low amounts of noise looks like out of the knock sensors, I'm not seeing a meaningful correlation between the reduction of the throttle plate and the knock volumes. I'm still seeing that very sharp point in the RPMS where the ECU releases it's grip, allowing the throttle to open to 100% at around 5,600 RPM.

259043


One insight from today's trip is I was watching my dash a little closer during the pull, and the check engine light was illuminating during the throttle reduction, and then at that 5,600rpm mark when it opened up, the light went out.
I can reproduce the light in my garage - notice it goes out right around that 5,600 mark:

I am not finding any codes from the ECU that appear to have anything to do with knock sensors / knocking. I have list of codes having to do with the MAF and O2 sensor - which are no longer present on the car - nor have they been for about a year since I went to the single turbo.

The other insight is that I went back and checked my logs pre-fuel pump / line upgrade. At the VERY tail end of the logs, I found one example of this behavior. Which is to say, I am all but counting out the fuel upgrades having anything to do with this behavior.

This may bring me closer and more focused to what could be the problem, but I'm still grasping. I wish I could understand what parameters the stock Aristo ECU is referencing for manipulating the DBW system. I'd also be interested to know what failing knock sensors look like from a logging perspective? If they just flatline, I can probably assume they're still functioning fine and they may not be the culprit.
 

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Discussion Starter · #7 ·
That's an innovative solution I've not seen before. It would work for the sole purpose of ensuring 100% throttle. The catch is - at least for me, is I want to retain the stock ECU control to soften the shifts (reduces TPS during WOT shifts) on the old 340e if possible.
 

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Discussion Starter · #8 ·
As an update, after disconnecting and reconnecting the battery, this issue seems to have resolved itself. Not sure why. Still curious what the factory ECU was doing and/or what the trigger was.
 
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