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Old 07-14-2020, 09:56 PM   #126 (permalink)
Cyborg ECU
California98Civic's Avatar
Join Date: Mar 2011
Location: Coastal Southern California
Posts: 6,092

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
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Reducing throttle reading variability

There is a small problem with this great and clever method in that the throttle position readings vary irregularly sometimes in some cars. Here is a solution.

Problem: I often got significantly different throttle position readings in successive applications of the throttle as I shifted to my test speed and then between different test runs: 16.1, then 15.6, then 17.0 and so on. Sometimes there was wide variation, such as 16.1 to 18.8. Once 17.1 became 20.1. Were the readings a real indication of movement of the throttle plate or was it meaningless sensor or gauge error? Was there "stretching" of the braided cable, shifting of the stopper, or compression of the carpet and sound deadening under the gas pedal? It was hard to tell on the road, so I spent time tinkering with the build and testing.

Testing results: The different readings are caused mostly by compression of materials under the gas pedal and by inevitable, slight shifting of the stopper's position due to engine and road vibration. However, the TPS reading variability is also partly caused by imprecision in the sensor itself. When the spring throttle on the intake is limited by securely-mounted metal pieces, the TPS's own imprecision can still yield variations in its readings but they become slight.

Conclusions: to me, this means that the throttle stop under the pedal can be a source of error in road test results. It would be better to control (1) carpet and sound deadening compression and (2) movement of the stopper relative to the pedal a little more rigorously. These sources of error may not be fully apparent to the driver because the throttle stop movement might allow the throttle to open a little more while the throttle position sensor's imprecision might mask the extra opening. Maybe this only applies to D16y7 Civics, but it likely applies to almost any gasoline car built in the 90s & 00s with cable throttle, electronic fuel injection, and carpets and sound deadening on the fire wall.

Safety: I'm a little concerned about the safety of the under pedal stopper. In an emergency, it could end up under the brake or clutch pedal. Many years ago that happened to me and it was terrifying.

Solution: I made a simple throttle limiter and mounted it on the engine itself. I'll write that up in a new thread, with credit to Julian and to Vekke, hopefully soon.

Here is the under pedal stopper I built and will now scrap. The black end fit into a slot on the floor for precise placement and the wood and rolled tape "legs" rested on the carpet for stability. It works quite well, but it could be better and safer at speed.

Hoping this is all helpful to someone else...
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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