WHOA!! That's an amazing find, Nick! Credit goes all to you!

So just to be clear... Akebono made the orginal USDM/Export 1993-1998 Supra Twin Turbo OEM brake pads? Are we sure the part numbers they list are for the front and rear TT calipers and not the Supra MKIV NA front and rear sliding calipers?

I see three part numbers listed without reference to Twin Turbo or NA:

ACT619A (Front)
ASP619A (Front)
ACT613 (Rear)

Edit/Update: I have emailed Akebono USA's customer service to get clarification from them on whether these above listed pads are intended for the MKIV TT calipers or the MKIV NA sliding calipers.

However when I go onto the Advance Auto Parts website I am only finding the Akebono ACT619A front calipers listed for the 1993-1998 Supra NA models. They don't carry the other two part numbers.

I'll update when I find out more info.

The alternative Hawk HPS pads are Ferro-Carbon formulated which is said to produce more dust than ceramic formulated pads. Other than the Akebono OE and OEM Toyota TT pads I'm not yet familiar with well regarded ceramic brake pads for these braking systems. However I can vouch for the high quality of the Hawk HPS pads in comparison to the stock Toyota pads in a street application... other than perhaps generating slightly more dust.

Looking around I mostly see Hawk and StopTech pads as true performance alternatives to the OEM Toyota MKIV TT brake pads, should Akebono's aftermarket pads listed above not turn out to be the same thing.

 

Yeah, that’s a fair point. I’m not sure if the parts listed are specific to the TT. In either case, if their website is right and they are the OE supplier of those pads, even if they’re NA, that would indicate to me that they more likely than not made the TT pad too, right? To use to different OEM’s for the pads seems unlikely, back in 1993. Today it’s commonplace with all the name brand braking systems out there, but I could be wrong.

Nick

 

Akebono made two different sets of pads for the 1993-2002 Supra MKIV: one for the Export NA models and JDM NA/TT's that didn't have the Export/TRD upgraded brake package and one set of pads for the Export MKIV TT's or JDM's which got the same upgraded brakes under the TRD banner.

What I found out a few weeks ago was that the OEM Toyota front brake pads for the MKIV TT (USDM/Export) had been discontinued while the OEM Toyota rear brakes for the same cars had not yet been discontinued.

When I went to Akebono's website and looked up all these part numbers and then cross-referenced them through Advance Auto Parts I found that Advance only lists the MKIV TT rear brake pads under their brand name. They do list the front and rear Akebono OEM-spec Ceramic brake pads for the Supra MKIV NA.

...

I think what has happened is that many people bought the Supra TT front brake calipers and OEM TT front pads and exhausted the stock on those at Toyota while the rears are still in stock.

Akebono is more than likely no longer contracted by Toyota to keep producing the Supra MKIV TT OEM-spec brake pads so whatever supply still exists of the rear pads in Akebono's and Toyota's respective warehouses is probably all that remain for purchase.

Thankfully these brake calipers have MANY alternative pad options but it still sucks nonetheless that yet another OEM part for the Supra MKIV seems to be going away. They're really good pads for the street.

 

Well… this happened last night. Just after I did an oil change (no issues there) I took the SC on what was to be a very short drive up the road and back before turning in for the night.




I had recently installed Stu Hagen's adjustable Wastegate Spring Mod using the Dorman #29002 helper spring.

I had taken a VERY gradual cranking up of the adjustment nut to get the old tired OEM wastegate to better hold stock boost pressure. The engine had been responding so much better and was holding boost with fewer and fewer inconsistencies when into the 2nd turbo transition.

There was still a little delay sometimes before I’d get full boost under load after the transition and I always have a little “top in / tip out / tip in again” with the throttle which is a quirk of an old sequential system… but it was overall getting better.

Other than planning my strategy to replace my slightly leaky lower steel oil pan I was at this point pretty happy with the car.

Once I hit the main multi-lane road all it took was two pulls under load into the 2nd turbo boost above 4200rpm at only
7psi and— WHAM— I hit a wall not unlike what I’d felt many months ago when I hadn’t found my cylinder head ground issue that burned igniters.

I didn’t realize at first that I just had NO power at all. I took the engine out of gear and barely managed to coast to a stop into a suicide lane.

The engine would restart but died very quickly each time. It was very cold out and I couldn’t tell what code, if any, that the ECU might or might not register.

I tried swapping in a brand new never used igniter and at that point the engine wouldn’t crank over at all.

I waited a good hour and a half for a AAA tow truck. I was only about 2mi from home, frustratingly but by then it had gotten into 1:45am.

By luck a tow truck driver just off another job pulled over behind me and offered to help. My AAA tow was nowhere to be found so took him up on the offer and got the SC back home safely.

So very frustrating. This came out of nowhere. Or maybe there is still a grounding issue remaining that now only can cause cumulative issues when I go into high RPMs rather than staying at 4K or less RPMs. I have no idea at this point.

Starting into diagnosis at home will have to wait until Monday unfortunately.

I had just taken the car down south on a road trip and back and it was fine other than the long term slight oil pan leak which I kept monitoring and topping off.

That pan was to be the very next fix it project to get underway soon.

….

I think at this point I am just annoyed more than anything. Setbacks happen with vintage cars and especially custom ones at that… but it is becoming apparent to me that no matter how hard I have tried to set this SC up as reliably and near factory stock GTE as possible… I’m not going to be able to truly call it reliable in all situations as a primary car and long distance car as I had hoped.

I don’t know if I have something amiss in my engine harness wiring, a poor ground (still?) or just a bunch of very old and finnicky electronics or a very old bunch of valves on one of the most complicated twin turbo systems ever devised.

…

I’m too tired and frustrated to try right now.

Sorry for a downer update, all. I had wanted to do a quick informative post about the Wastegate Spring Mod’s success.

I hope you all had better post-New Years luck!

C’est la vie…
​

 

Sorry to hear that the SC left you stranded. Knowing you pretty sure you will figure it out. I just hate working on a car too when it is cold out there . Looks like same gremlins you had before .

 

Thanks my friend. Last night wore me out and I was just happy to get myself and the SC back home. It was indeed very cold out (for Florida anyway).

I have no idea what the solution and culprit is right now.

This failure and no-start condition… should not have been possible after all the previous diagnosis and repairs.

I pulled out my spare 6-speed ECUs and the extra set of new capacitors. Hopefully it’s not an ECU problem and hopefully all of them are still in good working shape.

I have an old OEM USDM MAP sensor in the car that I had intended to get a new spare of just in case… but that can’t be the issue.

I picked up another spare good USDM TT MAF the other day… but that also wouldn’t affect a no-start condition.

And I didn’t hit enough boost with the mildly turned adjustable wastegate spring mod to hit boost cut…. which also shouldn’t cause a no-start condition or start-and-quickly-die condition.

Although I will test all these components anyway just to be sure they are all within normal electrical ranges.

​​​​​​…..

If I still have some issue with grounding that I manage to have NOT truly solved…. I don’t feel I have many options.

Maybe I’ll drain the coolant, remove the IACV on the intake side and install the original cylinder head ground wire in a 4GA or 2GA wire.

Or maybe I just need a fresh engine harness built? I still have my car’s original untouched 1993 5-speed M/T engine harness that I could send in as a template reference to some place like Tweak’d, Panic-Wire, Wiring Specialties, etc.

Maybe I need to look into a plug and play aftermarket ECU at this point. One which can be programmed to operate the sequential turbo system and EGR VSV under specific instructions based on how the Supra TSRM breaks down their expected operations. That would be a lot of work.

​​​​​​….

All speculation until I can dig into it. It’s just very frustrating— it was running mostly perfectly until that moment last night.

 

Sucks man, I know, I’ve been there. I just got my FD tuned and it was pulling so hard and felt so fast and then stranded me 2 hours from home. It’s just the nature of these sorts of beasts.

My suggestion, to alleviate all possible electrical issues is to get a stand-alone and appropriate harness. Everything will be brand new. Nothing to chase down. It’s mega expensive I know, but you’d be done with electrical issues. I’m sure there’s stock maps for Haltech and MoTec or whoever you choose, and then you can just drive it. If you want more power in the future, you can upgrade turbos and just retune.

Just a thought! Good luck dude!

Nick

 

It feels appropriate leaving this here…



Fuel pump.

 

Thank you Nick. You're right... it can and has happened to all of us who own older modified cars.

Man, I love your old RX-7 FD! One of the most beautiful cars ever made and I'm a big fan of the 13B-REW rotary engine. If I had a spare garage spot I would be strongly tempted to get one myself and set it up as a track car. Such sublime vehicles but they can be very temperamental as you well know but like our SC's it's just such magic to drive when everything is working right.

....

I am considering what you suggest but an aftermarket ECU and totally new harness are out of my immediate range of affordability. However that *might* be the ultimate solution. We will see after I investigate further.

Just 20min ago I was finally able to do a clean TE1 & E1 OBD1 CEL Code pull from the car. Code 14 "Bad IGF or No Consistent IGF Signal". So that same issue with the electrical system must not have been totally resolved after all.

^^^ Gerry-- you called it and you were right!! THe same issue as before came back again... which means it was never totally solved after all

Now this is a test with a brand new Igniter that I kept in the trunk for emergencies and threw in at the side of the road. The Igniter unit that was in the car when the failure occurred needs to be swapped back in to test again... since THAT one at least started the car for a moment every time before the engine would die again.

So this all goes back to the suspects:

--Abnormal grounding issue somewhere causing improper power flow and thus an eventual short
--Potentially an issue with the 6-speed ECU even though it had new capacitors installed a while back
--Potentially a bad igniter unit (again?)
--Potentially an issue with any other major parts in the ignition system such as spark plugs and coil packs

I know that all the wiring paths for the ignition circuit are correct since I went through them all wire-by-wire some time back. A grounding issue must still be at fault somewhere but also it could be something in the harness that... despite all the extensive wire tracing and continuity testing that I have done... is still plaguing the car.

This also makes me wonder if some of the #1 to #2 turbo boost transition issues that I have been experiencing might partly have to do with something in the ignition circuit when I go into high RPMs... but I think that is still likely a separate thing related to 30 year old actuators and diaphragms that are slightly less responsive than new ones.

....

If I could swing it right now I would begin to make arrangements to have my car's original and untouched 5-speed harness rebuilt into a 100% stock OBD1 Supra TT 6-speed engine harness by one of the major professional companies who do this.

Or.... maybe I should find yet another Supra 6-speed USDM harness and build yet another one myself going through each and every wire all over again.

These electrical systems are not THAT complicated. I'm struggling to imagine where I could have gone wrong in the engine harness but if pulling out the IACV on the intake side and installing a 4GA or even 3GA or 2GA ground strap wire in the stock location isn't good enough then anything else will be fair game.

Maybe it's also just other ignition components (a bad coil for instance?) having some issue or the ECU having previous affects from the ground issue that are only manifesting again now.

Teting, testing, and more testing ahead...

 

Just a little update on my progress. I really haven't had time to actually work on the car over the last few days while some other things took precedence.

I rented a Mazda CX-5 to get to and from an out of the area meeting. Aside, it was a good serviceable vehicle but far too high off the ground for my taste and with an incredibly difficult to find AM/FM radio function menu (which isn't even covered in the factory owner's manual!). But I couldn't complain about the good fuel economy it turned in with 87 fuel

However I have been busy with researching this recurring issue again with my SC.

Parts ordered:

--x6 new Denso #673-1200 1JZ/2JZ Ignition Coils
--x6 new Denso #5304 IK20 Iridium Spark Plugs
--1x new 1JZ/2JZ Non-VVT-i factory Igniter (from Driftmotion)
--x2 new OEM #90980-07345 Lexus/Toyota "Cable Bond" cylinder head and transmission case factory ground cables
--x4 OEM 90080-11152 Bolts (for the ground cables)

As of right now I'm still waiting on the new incoming igniter. Tomorrow I will finally have time to begin testing the two igniters I have in the car's trunk right now and see if I can make any progress.

.....

I spoke with Gerry about this again a few days ago and reluctantly I do agree with his assessment that at this point it very highly likely may be a wiring harness issue or at the very least a loose connection somewhere that is affecting proper grounding of the ignition firing and igniter/coil circuit.

And so my main focus now will be on finding that anomalous loose/intermittent connection.

Or... possibly having a new engine harness built by Tweak'd Performance using my untouched (and currently in storage) 1993 SC300 5-speed M/T Cali Emission engine harness as a starting basis. Currently with all the options I'd need that's just about $2k USD from them.

I'm going to plan for that but I can't do a whole engine harness purchase at this very moment.

......

Next, some research and double checking:

I had to go back into my earlier posts from about two years ago to confirm that I already did in fact install brand new Denso coil packs when this last occurred. But with an igniter that I had assumed failed at that time. Interesting. At that time in late 2020 I noted that a brand new only 4min used igniter wouldn't start the car but that assumed burned igniter that was in the car when I had my breakdown then DID start the car.

This time, two years later (a new record!) I also found that another brand new never used igniter didn't start the car at all. But the one that died on me would at least allow cranking for a few seconds before the engine died each time.

After that 2020 breakdown I had my "eureka" moment and realized that my cylinder head had no factory ground to the firewall. So I made one and installed it on the outer plain side of the cylinder head. This setup lasted for two years until this newest breakdown.

I had thought that the factory GTE head ground location began on the rear most engine hook bolt (very large bolt and impossible to remove without first draining the coolant and removing the Idle Speed IACV unit).

Well... after searching through yet more original Toyota parts diagrams it seems that is not actually the EXACT location Toyota wanted. For the 2JZ-GTE which uses sequential Coil On Plug ignition they specify the additional ground wire bolting to some spot *inside the coil pack valley* and then terminating at the stock place on a firewall bracket that I used.

After inspecting the inner coil pack valley of the valve covers I found NO unused screw hole as I assumed I would. I just misinterpreted the diagram: Toyota intended it to be interpreted as showing a magical view *through* the valve cover to the other side, where the ground strap does indeed connect to the rear most engine hook bolt.

If you, like me, need to add this AFTER engine assembly while the engine is in the vehicle you must drain the coolant and remove the Idle Speed Control IACV to gain access. There is no other way.


Factory JZA80 Supra MKIV 2JZ-GTE (sequential fire ignition) cylinder head ground to firewall location:



Factory JZZ30 1JZ-GTE Non-VVT-i (batch fire ignition) cylinder head to firewall ground location:



JZZ31 SC300 2JZ-GE Non-VVT-i (distributor and single coil ignition) & UZZ30/31 SC400 cylinder head to firewall ground locations:




And... here's yet another Toyota 2JZ-GTE TSRM diagram showing the factory ground strap location ON THE ENGINE HOOK BOLT.






This is confusing because there are is an official parts diagram showing an affixing location for a cylinder head ground on the 2JZ-GTE inside the coil pack valley.

Yet... when I popped off the coil pack and cam cover to inspect the coil pack valley I saw NO unused hole which would suggest you could affix any additional ground strap cable INSIDE the valley. So this diagram must have been incorrect.

Further, here's another diagram from the TSRM again showing the engine hook ground location:







......

What I find interesting is that not everyone with a stock Supra MKIV or SC has issues when this additional ground is not present. And yet a few owners like myself do have an issue if it is not present. My thinking is that it is there for a good reason.

Yet what reason could this be when the ignition circuit is already grounded at the ECU (which controls each cylinder's firing by completing each ground individually as per the firing sequence) and when the Igniter unit is grounded through that bundle of ground wires that is bolted to the side of the intake manifold?

I began to educate myself as to what this "extra" factory ground at the cylinder head is supposed to do. And I am still at the time of this post continuing to learn about the theory behind it.

So far my takeaways are that it has to do with three things in theory:

1) To additionally ground the coil pack area in case of excess electrical charge buildup that could shock someone working in there with the engine running, since the coils generate something like 40,000V with a very very tiny amount of milliamps.

2) To protect the circuit from other electrical interference.

3) To protect the system from excess current flow buildup during engine operation which might have nowhere else to go but through the ECU's six ignition driver MOSFETS.... and/or... nowhere else to go but back into the Igniter Unit.


I hope my assessment is so far correct as to why it is there in the first place.


.....

It has also been suggested in at least one thread that I am reading that a bad coil pack can cause this IGF 14 failure condition..... but since I installed new coils when the engine was first started and since I replaced those with all new ones in 2020 I highly doubt a bad coil STARTED this issue I have been having. Maybe I *damaged* a coil due to improper or poor or loose grounding but the coils themselves definitely didn't start this recurring issue.

In one or more of those threads I have been researching it has also been suggested that in *can* happen that an ECU malfunction of some kind might cause an irregularity in the ignition firing circuit such that the repeated irregularity might eventually burn out one or more components in that ignition circuit. "Dwell Time" was mentioned in one thread as to ignition coil firing but I am still learning about that concept.

Yet I have had this issue show up when switching between more than one identical ECU so I am not convinced it is necessarily that either.

....All of which leads me back to the discussion that Gerry and I had about this a few days ago. That and definitely moving my cylinder head ground to the EXACT place that Toyota specifies in their parts diagram for the 2JZ-GTE immediately.

....

My current research threads on this so far:

https://www.supraforums.com/threads/dwell-time.671538/

https://www.autospeed.com/cms/a_1131...populararticle

https://www.toymods.org.au/forums/th...-JZGTE-igniter

https://www.supraforums.com/threads/...lready.566570/

https://www.supraforums.com/threads/...solved.681083/

http://www.toyota-supra.info/forums/...lp-please.html

https://www.supraforums.com/threads/...seless.296877/

https://www.supraforums.com/threads/...lpacks.573415/

https://forum.miata.net/vb/showthread.php?t=703708

https://www.supraforums.com/threads/coil-pack-ground.314348/

https://www.supraforums.com/threads/lets-talk-about-grounding.1117621/


......


I'll update more as I can finally get into testing, moving that cylinder head ground and when the rest of the parts I ordered show up.

Looks like I'll put the battery on my tender for now to keep it topped off

Ultimately if nothing I can address right now in all these regards prevents this from happening for good then the final straw would be commissioning a brand new USDM 2JZ-GTE engine swap harness from Tweak'd Performance and swapping it in. My feeling now is that I am committed to the intention of ordering one from them regardless as soon as I am able to.

My self-modified swap harness *should* be fine and seems to have been in all other aspects since I first started up the new engine in 2018 and corrected my couple of minor mistakes since everything it connects to works perfectly until this specific failure happens.

However as Gerry has pointed out to me the other day: after all of my troubleshooting it may in fact come down to something harness related that I just haven't been able to diagnose or identify yet.

We'll see!

My very next project was to have been finally getting my slightly leaking lower oil pan replaced with the new one I already have on standby with fresh FIPG. That'll have to wait just a bit longer than I anticipated.

 

Over the last few days I have done some work on the car.

x6 all new Denso coil packs went in. Battery was recharged fully after being drained when the car died on the road with multiple staring attempts. I'm going to test igniters shortly.

I removed this irregular temporary ground connection and re-fashioned the end with a standard 8GA 3/8" hole ring terminal and affixed it to the rear engine hook bolt as the Toyota diagrams instruct. Hoping that will be the end of it.

To get to that engine hook bolt with the engine assembled and installed the coolant must be drained, EGR VSV and EGR Vacuum modulator disconnected to make room, then the Idle Speed IACV has to be unbolted, disconnected from the small fat rubber hose, that fat IACV rubber hose has to be removed temporarily and the metal rear coolant pipe that it connected to had to be slightly pushed out of the way. Then the #6 injector connector and rear camshaft sensor connector both have to be temporarily unclipped and pushed out of the way. A 14mm long closed end wrench (do NOT use the open end of the wrench) can loosen the rear engine hook bolt to remove it. Slide the 8GA 3/8" ring terminal over the bolt and reinstall in reverse order.

The rear engine hook takes 29 ft-lbs but it's hard to get a torque wrench or torque adapter in there so tight. The fuel rail prevents pretty much any 14mm short socket and 3/8" torque wrench from clearing so tightening up with a guesstimate of what 29ft-lbs might feels like is all that can be done in such tight confines.







Also I removed the extra ground wire that I had made to go from the chassis to the ground on the side of the intake manifold rear (where the Igniter Unit ground wire terminates).

New coolant is going in. I sincerely hope that now this will be the end of this specific problem.

At the same time I replaced my 30 year old coolant overflow tank hose (reusing the outer protective sleeve) with a new OEM part and two new OEM clamps. Just siphon out the old coolant in the overflow tank, remove the old hose from the protective outer sleeve and cit the new one to the same length as the old one. Reassemble and… no more leaking overflow hose!

 

Well… that didn’t work.

No start even with a brand new igniter, brand new coil packs, a correctly placed cylinder head 8GA ground at the engine hook bolt and a freshly charged battery.

I wasn’t expecting them to work but all three of my 6-speed ECUs produce the same result. Only one of them still hasn’t been capacitor serviced.

I’ll open up the rear seating area and check/test my fuel pump relay and the TT Fuel ECU to see if those are all okay.

​​​​​​….

I suspect Gerry is right. Maybe there is a wiring issue or bad solder joint in my harness that is causing this as well as the previously missing and/or previously poorly placed cylinder head ground.

I was so thorough so I can’t imagine how or where right now but I have to consider it as a possibility.

I will need to buy a fourth engine computer to rule that out too but now I kind don’t even want to use it yet until I’ve gone through my current engine harness or until I’ve had an entirely new one made which cannot possibly be suspicious in any way.

​​​​​​…..

Just so frustrating. It was running near perfectly.

Right now I don’t have time or physical space to pull out and diagnose an engine harness.

I’ll hunt for another computer just to hold onto until I can determine more.

 

Craig , I will hold on looking for a USDM 6speed ecu since they are a bit pricy . I don't think those 3 ECUs are all bad .

Check these out to isolate the problem to pinpoint your course of action so you don't keep buying expensive parts here and there buddy.

a) is there fuel being injected on the cylinders ? First check fuel flow and pressure . Even if there is flow but not enough pressure , it won't start. How old is your fuel filter that can cause low fuel pressure ? If flow and pressure are both good , Is there actual injection (fuel coming out of the injectors). If not, then you know it is an electrical problem which can be a myriad of things... grounding , ecu and so forth. Get noid lights to check fuel injector pulse.

b) is there spark from the spark plugs ? If none , then another electrical problem which could be related to the electrical problem above like a grounding issue. If there is good spark , then you know it is not a grounding issue as you suspected.

c) do compression test (unlikely your problem since that car was never abused and doesn't have tons of miles)

 

Craig so sorry to hear about your troubles. I think Gerry has it right - his approach is old school but despite all the electrical nonsense in these 90's 2J's I think it will truly help you narrow down which system you're having issues with. Clearly you have a lack of fuel or spark (I'm with Gerry about the compression - I HIGHLY doubt that's the case). Best of luck on your search and hopefully going through fuel and spark will help you track down the culprit before you pull the trigger on any big upgrades. On that note - mine didn't start the first two times this morning and had an odd hesitation when hitting boost driving it home the other day. Sounds like we both are in for a little messing around with these things. I'd like to take your route of going standalone and replacing all of the proprietary sensors/throttle body/etc with simpler more available parts. However, that is such a huge nut to dish out that it's hard for me too to justify it at this time.

Let us know what you find and I'm sending some good diag vibes your way!

 

I must be luckier than you because mine appears to have magically fixed itself literally overnight. Cranked just fine, purred like a kitten, and no hesitation on accel... It did sit for a couple weeks due to the horrible cold/icey/gererally ****ty weather we've had lately. I really think this car HATES to sit and always seems to act up if it's not driven regularly. You guys experience that with your GTE motors at all?