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Spoofing Engine Coolant Temp Sensor for Better Cold Start?

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#1 Robb235



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Posted 05 February 2018 - 05:02 AM

I have a 1999 Toyota 4Runner that I've been running E50 on with good results. Looking at my Long Term Fuel Trims, I don't think I can go much past E50. Stock fuel injectors are 245cc, so to make the E85 conversion I have a set of 315cc injectors to swap in that are 29% larger. These larger injectors should offset the higher fuel consumption requirements, and keep the ECU happy.

My concern is cold starting in the winter time. The Toyota ECU is locked, no aftermarket tuning ability with programs like HP Tuners or Hondata like other cars have. I'm concerned that in cold temps, this non-FFV will not not be able to start on E85.

An idea that occurred to me was to intercept the Engine Coolant Temp with a variable resistor (potentiometer), and make it report a colder temperature than what is actually occurring. The thought being that the ECU thinks it's colder than it actually is, and therefore injects more fuel during cranking. The potentiometer could then be zeroed out for normal operation after the engine starts.

Has anyone tried or heard anything like this? I tried searching the forums and Google, but I don't think I was entering in the right search terms.

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