Fiesta ST - Part-Throttle Surge
- on April 06, 2020
- Categories: Tech Articles
I have had isolated reports of what I like to call a “part-throttle surge” on the Dizzy Tuning Fiesta Flash Tune. You can reproduce this surge by going into 3rd, 4th, 5th (or really any) gear, with the RPM around 2,000. If you then lay into it fairly aggressively, but only to about 60% throttle position, and hold the pedal there. You will experience a surging, regardless of the intake or exhaust modifications. Aftermarket intakes that are much noisier, will make the issue much more pronounced/audible. Testing with aftermarket actuators is coming soon, but I have confirmed it is NOT the actuator causing the surge.
I also want to state up front that my Flash Tune is not the only calibration that exhibits this behavior. I have confirmed that it is present in the Cobb OTS maps (v500, I have not yet tested the v504 for this phenomenon), as well as other Protuner maps. I will not go into much detail here, but have spoken with numerous customers using various other tunes, and they have noticed it as well. I do think the intensity of this surge may vary by tuner, but it is always still there (in my opinion, and I have seen datalogs).
So what causes this surge, and why has no one addressed it? This is something I have been working on over the past few months, and plan to implement in my upcoming Fiesta Flash Tune V2! **article written in 2018, V2 is released**
Let’s go into a little more detail, shall we. The ECU uses what is called a torque (or load) targeting strategy, rather than the old school boost targeting strategy. Torque targeting is fantastic because it allows your engine to run consistently in virtually all weather conditions. Some of you may notice that your boost values may be slightly lower in the winter, and higher in the summer. This is cause the colder denser air requires less boost to achieve the same torque values that it would have in the warmer months with higher boost levels. But the overall underlying issue (in my opinion) is the overly aggressive torque targeting tables, coupled with a VERY small turbo that spools almost instantaneously.
So if we think about the processes in slow motion, it would look something like this:
So how can we fix this? We can modify the Throttle Requested Torque tables to target torque more appropriately based on turbo size and flow modifications on the vehicle. The result is smooth ETC (Electronic Throttle Control) operation that more closely matches APP (Accelerator Pedal Position). Enjoy!
I also want to state up front that my Flash Tune is not the only calibration that exhibits this behavior. I have confirmed that it is present in the Cobb OTS maps (v500, I have not yet tested the v504 for this phenomenon), as well as other Protuner maps. I will not go into much detail here, but have spoken with numerous customers using various other tunes, and they have noticed it as well. I do think the intensity of this surge may vary by tuner, but it is always still there (in my opinion, and I have seen datalogs).
So what causes this surge, and why has no one addressed it? This is something I have been working on over the past few months, and plan to implement in my upcoming Fiesta Flash Tune V2! **article written in 2018, V2 is released**
Let’s go into a little more detail, shall we. The ECU uses what is called a torque (or load) targeting strategy, rather than the old school boost targeting strategy. Torque targeting is fantastic because it allows your engine to run consistently in virtually all weather conditions. Some of you may notice that your boost values may be slightly lower in the winter, and higher in the summer. This is cause the colder denser air requires less boost to achieve the same torque values that it would have in the warmer months with higher boost levels. But the overall underlying issue (in my opinion) is the overly aggressive torque targeting tables, coupled with a VERY small turbo that spools almost instantaneously.
So if we think about the processes in slow motion, it would look something like this:
- You press the accelerator pedal aggressively, while rolling at a constant rpm
- The ECU uses the Throttle Requested Torque tables to lookup/determine what torque we want to achieve, based on current RPM and APP
(The tables are aggressive, so they request a high torque value) - The throttle opens abruptly and the wastegate closes, spooling the turbo
- You then overshoot your torque lookup target in the Throttle Requested Torque tables, due to the initial overly aggressive target
- Now the ECU closes the throttle and reduces boost, via the wastegate
- The process may repeat depending on the above conditions
So how can we fix this? We can modify the Throttle Requested Torque tables to target torque more appropriately based on turbo size and flow modifications on the vehicle. The result is smooth ETC (Electronic Throttle Control) operation that more closely matches APP (Accelerator Pedal Position). Enjoy!
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