If the plug matches ok then that's what I may just go ahead and do. Make life easy!

 

I’m curious if I’ll need a new o2 sensor. The one on my donor is a 4 wire. Was that the same one when it was running in your old car?

 

Billy,

I'm running a four wire now and have been told by a few of these guys that it will not work with the JDM vvti ecu. I ordered a three wire (part number is a couple of posts up) that I'll be trying tonight or Saturday. I'll report back with how it works.

 

Tried grounding the 4-wire o2 sensor and still got the “21” code to flash at me with a CEL as soon as I go over a few thousand rpm. The wiring on the harness side doesn’t match colors, so I may need to get creative and cut some of it back or trace it to see how to wire the new one. It IS wired for a 4-wire plug which is odd too.

Also installed the new MAF. Still goes into limp mode. I disconnected the battery before starting it. Warmed up and idled well, part throttle felt great, full throttle hit 12 pounds and went into limp mode immediately. Tried again and it happened at 8 pounds.

Definitely disappointed, and just have no clue where to go from here lol.

 

Maybe a bad map sensor?

 

It's certainly crossed my mind, but based on how people have described boost cut it doesn't seem like the symptoms match up. Unless boost cut can activate limp mode... I'd think that putting the car into limp mode would leave a hard code in the ECU that would show up instead of simply the 02 sensor code. I've always driven cars that were able to operate just fine even if an 02 sensor was bad... However, perhaps I've been overthinking this and maybe the bad or possibly unreadable 02 sensor can cause limp mode under full throttle/boost conditions?

I'm going to cut back some of the Tweak'd harness tomorrow and trace the wires for the 02 sensor. I'll get the new 3-wire one hooked up and see if that's enough to alleviate the issue. I'm so close, but yet it feels so far! haha.

I keep reminding myself that at least the motor is good, and regardless of what a frustrating last few weeks it's been, I got a screamin deal on everything from that parts car.

 

For whatever it's worth - the car is idling high as well. I turned it off and re-started it a few times after reading a few old threads. The idle did come down from 1900 rpms down to more like 1100/1200, but still seemed a little high. Throttle cable is adjusted, the throttle body closes all the way, and I don't think I'm having TPS issues because the pedal works great, allows me to rev freely, and part throttle driving is super smooth and drama free. I'm going to try the "Ali" method of adjusting the TPS by feel tomorrow to see if perhaps that's the issue. My TPS is turned nearly all the way clockwise which sounds like it could cause the high idle. And who knows, maybe that's a factor in hitting limp mode at WOT. The car feels great and pulls pretty hard at 75% throttle.

 

^^ You definitely need to adjust your TPS sensor. It seems like this little thing that you just install and screw down any way you want but it's surprisingly very critical to get its adjustment right. I think Ali must have mentioned the method in the manual where you use a multimeter on one of the Ohms settings (1K Ohms? I'd have to look it up in the manual again as it's been a while for me) with little alligator clip wires on two specific sensor terminals while it is installed on the intake manifold. Then you turn it with the hold down screws a bit loose until you reach and surpass infinity resistance. Then you need to dial it back again until you're JUST before the deflection point of infinity. From there you tighten the sensor down. You do have to have inserted a feeler gauge of a specific thickness in between the stopper on the half-wheel that holds the throttle cable end in place before starting the deflection point procedure.

It could be that this has contributed to your fuel cut issue but I think it may be related to excess current draw by having that Denso TT fuel pump on the same EFI1 circuit as your injector system and spark/ignition system. It's a lot of electrical load on that circuit (up to 20 Amps of current draw from the TT Denso fuel pump alone). The primary reason for doing the +12V Fuel Mod w/Relay with a 10ga fused separate power wire direct from the battery into the cabin and to a 30/40A relay near the fuel ecu is that it takes that high current draw load off the EFI1 circuit and onto it's own circuit that you have created for it (and with its own in-line 10ga fuse holder with a 20A fuse). This is also why Toyota built a separate "EFI2" electrical circuit from for that high flow / high current pump from the factory on the Supra TT's.

I could be wrong but it's possible this might have something to do with your EFI Fuse clicking on and off if the TT Denso fuel pump's extra electrical load at full speed is pushing the SC300's stock EFI fuel circuitry to its maximum.

The idle issue might have something to do with the TPS being misadjusted or it could have to do with the GTE Idle Air Control Valve. Starting cold at 1900rpm seems more like the ECU isn't getting what reading it wants from the IACV and so is going to a default high idle as a fail-safe measure before going to a default high idle in open loop mode once the engine has come up to temperature. Again, I could be wrong about that but it's a guess.

Fix one issue at a time and note the behavior of the car each time for any differences.

 

Craig,

Before I had a chance to read your post, a buddy of mine came over to give me a second opinion yesterday. We wired the 02 sensor correctly (turns out someone has re wired the harness side and it was bizarre), and then we adjusted the TPS by feel as Ali described in an old post I found. We got the idle set correctly (although I need to adjust it a hair again as it’s a tad low at this point), and then....

No more limp mode or cutout!! The car had oddly also stopped turning the efi relay on and off after removing the key.

The ecu was definitely bad in the beginning causing its own odd issues... but you guys nailed it early on with recommending the tps adjustment.

I was so excited I also took the time to install my boost gauge and auto extrude gauge pod (which to be honest, would not buy again). It was a PITA, fits poorly, and IMO isn’t quite worth the extra work.

I’ve got a few little odds and ends to wrap up, however, it feels so good to drive this bad boy. I’m super impressed with the drivability on the stock ECU, and it pulls like a freight train especially in 3rd/4th gear.

Special shout out to Gerry for taking the time to text me and hooking me up on a much needed ecu.

You guys rock! More pictures and adventures to come with this bad boy.

 

Hell ya happy to hear you got it worked out!

 

Thank you very much! I'm absolutely stoked. A few little things to wrap up and we'll be in business.

 

Gald it worked out! Weird someone would have messed with the o2 wiring, that was probably a big part of the problem if it was getting the wrong signal.
Tps by feel is the best way once you figure it out

 

Ali,

I'm so glad I found that thread where you described how to do it. MUCH simpler and more intuitive than doing it by the methods you find elsewhere.

I've got a few little things to sort out, but it's all coming together. There's a small coolant leak that only shows up once in a while from a heater hose that I'm having trouble getting eyes on. Otherwise, I am getting codes "42" and 89" still causing a CEL. Sounds like they relate to the VSS and TRAC systems. Not sure if this is because I'm running an automatic ECU, or what, however, they don't seem to be affecting driveability in any way.

This thing sounds so tough and pulls as hard if not harder than I was hoping it would. I can't wait to get it out to the local road course, and I'd love to strap it down to a dyno and see how it does in stock form.

Can't thank y'all enough for taking the time to comment and help diagnose. I'll be sure to update as I continue to tune/tinker throughout the year.

 

The vss code for the missing automatic is normal. Not sure about the trac but if everything else is working wouldn't mess with it yet.

 

Wow! Excellent work Rudy! And thanks to Ali and Gerry for the expert diagnosis as always and to Gerry for hooking you up with that good ECU!

The O2 sensor wiring being modified is definitely strange. I encountered some very weird re-wiring areas of my 2JZGTE harness as well though so it doesn't really surprise me honestly. Given enough time as we get wiring harnesses that have seen one or more cars by now some previous owners do some really weird things that can strain one's understanding as to why they did it.

Glad you got it all sorted out and have the car running smoothly now!!

...

Regarding the Autoextrude vent gauge pod I kind of agree but there's also no other way to have designed it to be installed unless removing the entire dashboard were a normal and appealing thing to most owners. If so those little tabs could have been made fixed (I think) and then it could be installed while dismantling the entire A/C vent assembly as a whole removed from the dash. Next to nobody wants to do that and so I think it was an acceptable compromise of the design. Theoretically I do feel it could have been made to fit much more snugly in there but the consequence would have been a very, very unappealing installation process and thus that would have made it a non-starter aftermarket part.

I also wish it were a little less moveable while it's installed but it's okay and makes much better use of the space unless the full blast of A/C on your hand or face in very hot summers from the OEM original vent is a must (and this may be a legitimate concern for some even though there is still plenty of airflow with the gauge pod vent). The main thing with it is that I think only shallow depth 52mm gauges should be used with that custom mounting assembly so as to allow full travel of the A/C flapper just behind it.

Personally I feel it was worth the extra work to install once the "eureka!" moment was hit upon to understand how to remove the OEM vent first. But I agree that it may not be a modification that's right for everyone's SC. It is a pricey part after all. Still, a pretty good option that doesn't involve a pillar pod or steering column mounted gauges. Additional gauges in the ashtray area or in one of the stereo DIN slots round out a nice understated look I think.

...

Now, if that highway picture from your interior is any indication I hope you'll be able to take it out more now and fully enjoy the fruits of your hard work!