JDM 3rd Gen 3SGTE Closed Loop Lean Misfire / Poor Idle, Engine Goes to Closed Loop EFI, it Coughs, Stumbles, and Misfires Options

[J3rkyBoy]

About 6-8 months ago, I installed an EBC solenoid for the already-wired in Greddy ProFec B Spec II in my ST205 front clip conversion (JDM 3SGTE, 3rd Gen, stock ECU) 1996 GT. During the week I had it in, it developed a misfire at idle (and a sputtering cutout between 2800-3100 RPM). The misfire appears to be as soon as it switches into closed-loop EFI mode and is as dramatic as someone flipping a switch: one second it is fine, and the next: cough, sputter, choke and AFR usually around 16-18 from 14.7. It is usually worse the hotter the engine is. It seems to be intermittent and can go a day or two without issue. As soon as I step on the gas and get it north of 3k it is typically fine and I'm good.

Please advise.

Aaron

[enderswift]

This sounds identical to what I was dealing with for a long ass time.

Try bypassing the stock fuel pump resistor by the battery. Mine was causing sputtering and heasitation issues when coming onto boost. Bypassed it at the connector and problems solved. Like you, it was an issue that seemed related to heat. Turns out the older these resisters get, they more they drift their resistance values with temperature, something I verified with a heatgun and multimeter.

doesn't really matter if the fuel pump runs at full 12V all the time. Your FPR will ensure your injectors get the correct fuel pressure regardless



Edit: for context, the fuel pump resistor is solely intended to allow the ECU to switch the fuel pump from 9v operation off-boost, to 12v operation on boost (I'm guessing toyota did this to keep the pump quiet when just cruising). Its completely unnecessary, and will momentarily kill fuel pressure when switching voltages if the resistor is old and drifts its resistance value.

This post has been edited by enderswift: Feb 1, 2021 - 3:06 PM