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

Vacuum leak? That's one thing that gets better at higher RPM, as the engine is gulping more air and the leak has less affect on the engine. The AFR is really lean, too, which means you've got more air and not enough fuel, naturally. There are several backyard methods to test for this, depending on how well equipped you are with tools (everything from a spray bottle to a smoke machine).
Or, bad O2 sensor reporting incorrect readings. What's the history of the O2 sensor? Do you have a scanner capable of reading the O2 output? I know things are a bit weird with JDM ECU's using a different protocol, but never had one so don't know.
My hunch is on the O2 here. When the ECU switches into CL, it starts running off O2 output rather than pre-set maps, and it sounds like too much for it to be just a vac leak. Could be both though.

If you can't get live data from the O2 it's pretty trivial to probe it with a meter, though a graphing meter or an o-scope is best to use. Being able to see fuel trims and airflow sensor data would be good to.

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 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.

I want to say thank you to all you guys who responded. I had an illness in the family and duty called. Please accept my apologies for this late reply.

Okay.

Well, with every forum post, one has to balance the length of their post and its provision of sufficient facts to let others make the assessments we seek. No doubt, we have all asked questions, received answers, and rebutted with facts not known to the responder at the time of their response. This is one of those replies.

To Slavie, the original responder (and fellow 6GC'er, who said via PM "post this to the forum") I say: I do believe you are on to something. All I have available to me at the moment is my multitester. I do know it is not the correct tool, but in this case, it is better than nothing and, I believe, shows something interesting. I uploaded a video to YouTube and am posting the link. Please take a look if you have the time.

To Bitter: man, all I have in my possession is my trusty multitester. I know it ain't the right tool, but I think I do see something odd in its reading. If you might also check out the YouTube video I published, I would appreciate it. Maybe there is something of a clue.

To Consynx: Stock turbo for JDM ST205, so, CT26? The EBC solenoid is not the issue right now (unless it damaged something and this is the outcome) as I removed it after a week, as soon as the misfire started. Plugs have been changed ... twice. Good to hear someone had a positive experience with a slipping clutch; mine always meant money, and pulling the engine (which I just did two months ago).

To Enderswift: resistor has been gone since before this started. 12v constantly (and yet I still find the strength to go on ... listening to my Walbro sing at full-tilt boogie whenever the engine is running ... by simply opening my exhaust cut-out and punching the gas! ;-) ). One of the first things I checked was fuel pressure consistency. It appears to be within spec (BGB). One oddity regarding fuel pressure: when I physically touch the rubber fuel line after the fuel filter on its way to fuel rail, I can feel a definite hard "clicking" type pulse to it. If I had to describe it, it would be, like, someone smacking the line 5 times per second with a pencil, or a screwdriver. Listening to it with an automotive stethoscope yielded a definite, loud, clicking/metallic smacking sound ... existing only in the fuel hose. Have no clue. I would ask you as well to please watch this YouTube video and see if it provides any clue.

And now, since I spent so much time on my computer without charging it, I have to get going to my home so I can charge it again and provide new information/hopefully read a reply which knows why my O2 sensor is spiking to 2-3 volts as my engine stumbles and goes lean. I realize this video is boring, so just say so and I will post either a link to me almost wiping out in my Celica in Ohio on the way back from NJ to Seattle, a link to me giving the business to a Lamborghini Gallardo who decided to flex on me for no reason, or, and this one is probably the most interesting and funny, what happened when a hot girl came up to me and said "I'll su** your di** for a ride" last year ... just sayin' ;-)

Thank you all for your replies. I need them.

A@ron

https://youtu.be/aafZE3G5oV4

The pulsing on the fuel line is probably normal. The pump is pumping, you're feeling the individual pumps.

As for your multimeter video, either the multimeter is not responding fast enough or the o2 is dropping out. No way to tell without a graphing function.

You're either gonna have to start investing in some tools and learning some more, or start throwing parts at it and hope something sticks. The latter is not ideal, of course, but many find themself in your situation.
You could try to bring it to a shop, but it's very, very hard to find a shop these days with a qualified tech that has the knowledge to diagnose anything, especially on an older car. Most shops these days just throw parts at the problem and never bother to diagnose.