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

[Consynx]

What Bitter said: if you’re reading the AFR’s from the gauge, they’re not showing what’s really happening.
You need to log the data at the highest frequency allowed.

Additionally, I skimmed the post, so i am sorry if this was answered, but your turbo; if it’s a t25-28, you’re probably hitting full boost around the rpms mentioned, so I’m curious if you’re boost controller is hooked up properly. A leak could cause some issues at idle and in controlling boost, but if the controller isn’t hooked up correctly, you could be trying to spoil your turbo to Infiniti and beyond.

I’d triple check the boost controller. If it wasn’t ever controlling boost property yet, i would target something like the waste gate’s base pressure (7-10psi probably), and make sure I can hit that to Help rule some things out.

Edit: I read the whole original post...I’d throw plugs into the list of things to check, and I don’t know if you have the setup, but I’d try to document boost when logging the AFRs.

I once had a setup try to spool to the moon...probably the only time I was happy to have clutch slip.

This post has been edited by Consynx: Jan 31, 2021 - 9:26 PM