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robertcope

1999 Lexus SC400 - I messed up good this time

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Ha! I know Andrew. We should sneak that dyno chart into his WRL file.

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1 hour ago, joesurf79 said:

That 2jz now wants to destroy all tires, fulfilling the destiny of the drift monster SC! 

This is the SC400, which has the 1UZ-FE (4.0L V8) motor in it!

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8 minutes ago, robertcope said:

This is the SC400, which has the 1UZ-FE (4.0L V8) motor in it!

For some reason I was thinking it had been swapped, my bad Robert! Cool car either way 🙂

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Car is home. I have a few things I want to do tomorrow, but it should be ready to run on Sunday. So excited!

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Back from MSRH. I'd say today was a success; the car got me to the track, ran a few sessions, and got me home. Drivability was fantastic both on the road and the track. As usual, there is always more work to do, but it's damn fun as it sits. The next item on the list is Koyo radiator; to be fair, it's been the next item on the list for a while now, but now that I am logging coolant temps, it's gonna happen ASAP. I was running about 235F today!

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Given the conditions this weekend, I'd think your cooling system was juuuuust enough!  probably worst-case scenario there.

But yeah, I'd definitely be putting a more effective radiator in there if I had the ability.

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image.thumb.png.1102dd7aabe6ca5e1e3e26455cefdc55.png

Better graph, now that I have the dyno files. It's not bad. But I'm convinced the tune was pretty quick and dirty. I plan to do a few things -- remove the MAF sensor from the intake path, possibly redo the exhaust, get the knock sensors working -- and take it back and do some testing/tuning of my own.

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This thread is awesome and thanks for sharing your SC400’s progress with us.  🙂  How does it compare to your NSX now that you’ve spent more time driving your SC400 “spiritedly?” 

 

I ask because I have a turbo 2JZ sc300 with original Toyota Soarer “r154” transmission and am debating whether to sell it for an NSX or keep it and try some track days with it.

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1 minute ago, StraightEdge said:

This thread is awesome and thanks for sharing your SC400’s progress with us.  🙂  How does it compare to your NSX now that you’ve spent more time driving your SC400 “spiritedly?” 

I ask because I have a turbo 2JZ sc300 with original Toyota Soarer “r154” transmission and am debating whether to sell it for an NSX or keep it and try some track days with it.

Oooooh, tough choice! I would say that the NSX is certainly more exciting to drive, but I do not feel as free to drive it as I do the SC400 because I don't want to hurt it. The Lexus is also a lot more comfortable to drive because it has a proper seat and harness in it. If I had to own one, it would _probably_ be the NSX, mostly because it is more versatile... fun on the track, fun to show up to meets with, _probably_ not going to lose much value, etc.

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One issue I have been having since doing the ECU is the battery dying rather quickly. When I've measured draw with the car off, it is always rather low, 25-35mA or so; and yet, the car sometimes dies overnight. This weekend I decided to at least start trying to figure this out. Obviously, the ECU is among the only things I've done in recent history, so started there; I also remembered seeing it stay powered on while at Mayco dyno testing it. 

With that in mind, I went out and checked to see if I could get it to "fail". In testing, I found the following: if I turned the key on (but did not start the car) and then back off before the fuel pump finished priming, the ECU would power off; if I turned the key on (but did not start the car) and back off after the fuel pump finished priming, the ECU would stay powered on; if I started the car and turned it off, the ECU wold power off. Very confusing.

I had really not done any reading on how to power the Link ECU -- remember that I'm using wiring harness that uses the OEM ECU wiring and it "just worked". So, I started reading that. One of the things that stuck out to me was that the wiring for an e-throttle setup was a little special, and they particularly called out Lexus/Toyota cars for needing a relay setup. I have an e-throttle, but as noted earlier, it's disabled and I'm just using the cable. So... I took a wild guess and simply unplugged the connection to the throttle motor. This seems to have changed the test results from earlier; I cannot find a way to get the ECU to stay on with the key off.

I don't really understand what's going on, but I'm assuming there is some kind of "back flow" of power that was happening. I've read threads on the Link ECU forums where other people had similar issues. Again, I don't claim to understand it in this case, even though I've looked through the wiring diagrams and such... just not that smart, I guess, or maybe I just don't care.

I charged up the battery overnight and am going to let it sit until next weekend, hopefully it will start then.

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Electrical problems can be a real PITA. Good diagnosing.  Now as far as the "e-throttle", I do know that with computers you don't leave flying leads open; as in if it's not being used it shouldn't be connected to computer.  That's more of a IT thing referring to cabling, but it's prolly to prevent a similar event. To really understand you can label all the "Ethrottle" cables to get a idea of how that circuit is used. I'm assuming a 4 wire connector; 2 for powering throttle body, 2 for resistance circuit to see TPS.  Just guessing.

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can you post a link/image to the e throttle wiring diagram(s)?  maybe the interwebs can assist with info..

if I had to make an ASSumption, the ethrottle spits out a signal voltage to indicate throttle position while it's operating..  that voltage needs to be stabilized somehow and read by the ECU.  i.e. pull-up/ down resistors.   depending on the voltage and current, that could be requiring a fair amount of juice..  just a quick calc says 25-35mA (I used 30mA) / 12V = 400ohms.  *typical* pull up/down resistors are in the 300-1k ohm range, so that's not far out of question.

However, 30mA load on a standard car battery (say 65Amp-hours) should last well over a month before discharging-- maths says 2166hrs = 90 days to full discharge.

So I suspect there's likely something else happening somewhere that you just haven't found quite yet.  

 

also, how old is the battery?  any chance it's just getting old?   batteries typically die in the hottest part of summer and the coldest part of winter.  they'll be fine one week and then *bam* crap battery that won't hold charge a week later.

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I think you misunderstood or I didn't communicate well. The 30mA test was done using the typical "disconnect battery, place meter between terminals, read amps" method. In that case, the ECU has been shut down because the battery was disconnected before running the test. What I found was that the ECU was staying on in some cases. I don't know what it draws, but obviously enough to drain the battery fairly quickly. That's fixed now, at least in the test cases I found. I don't understand why actual "mechanics" of how the e-throttle setup was "back feeding" the ECU, but other than intellectual interest, I don't really care.

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ahh ok.  yeah that makes sense.   I was only partially paying attention since I was posting from work and pretending to actually be working. 😉

 

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Well, so far the battery has not died on me since "fixing" the ECU power issue. I'm going to call it fixed.

I took the car out to MSRH today and ran some laps before the rain hit. My main goal was to get the knock sensor working. I did get it mostly working and tuned, unfortunately, I'm going to have to do it again... the gain was set too high and it's maxing out under normal conditions. But at least I had a little fun, validated that the knock setup does work correctly, and learned a bit more on how to tune it. It shouldn't be hard to do it again.

At this point, I think it's basically a functional, fun car to drive. There are still many things I want to do to it, of course.

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Replaced brake rotors and pads today; Centric Premium rotors and G-Loc R12 pads. I don't expect to like the G-Loc pads, but we'll see.

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1 hour ago, robertcope said:

Replaced brake rotors and pads today; Centric Premium rotors and G-Loc R12 pads. I don't expect to like the G-Loc pads, but we'll see.

How much does the lexus weigh with you in it roughly?

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43 minutes ago, Hollywood said:

How much does the lexus weigh with you in it roughly?

3642lbs, give or take. Remember I've been on StopTech Sport and it is mostly okay. I think the brakes on this thing are not working that hard. I guess we'll find out.

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12 hours ago, robertcope said:

3642lbs, give or take. Remember I've been on StopTech Sport and it is mostly okay. I think the brakes on this thing are not working that hard. I guess we'll find out.

I converted to Gloc and loved it, but I don’t think the literature out there on compounds aligned with my style. In other words, I’m curious if R12 is going to be enough for you. We’ll see!

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So far, so good on the brakes!

My right-rear wheel bearing, OTOH, is trash. I've ordered a Timken replacement. The problem I'm running into now is that nobody makes a damn hub for this thing except for Lexus, which is a $250 item! Hopefully I pull it apart and find that the hub is just fine.

I have about 15 sessions on the R888Rs. I think they may be starting to cycle out, although the track may have just been super green today, too. I figure they have one or two days left on them. I really need to work on figuring out how to get some 255s or 275s on the car in a square setup.

DKUwTtbD8PoPOsEPKIOgX5NxYEfSI98MFO2jqpBdPZRWnMtLi_8_2sZPxtg0nlTmCSQXviaBUzJBYG7--m-MdvJ_z2WcgWXijVMEY6xvmFBoOLeWmPZyhZUC18kVYT9KEnWCSqZ5GwbFWCbYN1mLC8sq9QJDOad6XhHDVKY2Nf2qZbyc3n4Xs1lxQ-MN1ptIm_NH5OGxQ5lqWsapvyLJ-_Rz_yI5ugc2Y0yWymi1wjl9VVzzegHYRC5hFTRbxr6Syo1qu7iPPNQPJM6escKETbOaxQfC-ZbY4xnpEPmYFdTm8rjXuoY7xancx8tedKHCnOrVeYo9JY0-Crk6THiuhA19WZujtRbvZZkkie5ElGd_G1MpZooNnhpg6iLIcSizy6SI2ze0g9NUXL_EF1HRCbBe-6T1A_mueIWcXfYqMgjmBlOEtBdktgwENZz4EmPI2EHvykO4zMzp6gvz1I1dQ7oG950Pdp4wWpOQwy_GhMwpyF6bbcm7PV4UH4sIUN_fOQUx9RtM38wc-mmc2XnwTralhvV0VJLnNmEJUtkMdoX6GbTGi8x17pVWnj0YODQl7h0XpyNypCxaR2eE4fvTDmn8QFgKYeMxkg28skAe5rCbkZkqaPzYNiuvYkEUNoNDjGV6Nt9ymiZrjUitUek17W4edPpl0sMtlJ8U-jG9ef4WBk_W_v-dwvA7=w2134-h1602-no

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Might be a bit late or you don't want to use Chinesium, but Rockauto has hubs for the car at a whopping $22/ea.

I likely wouldn't trust them myself.

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6 hours ago, Matt93SE said:

Might be a bit late or you don't want to use Chinesium, but Rockauto has hubs for the car at a whopping $22/ea.

I likely wouldn't trust them myself.

Not for my car, they don't. They have front hubs, this is a rear hub.

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this is fun..  when I searched this morning, it only showed me rear hubs.  When I searched this afternoon, it only showed me front hubs.  I remember they were rear since they had the splined ID to secure the CV axle..  Then I noticed my search parameters..

If you search for "1999 lexus sc400 4.0L V8"  it showed front hubs only.

If you search for "1999 lexus sc400" and then use the 4.0L V8 drop down, THEN it only shows rear hubs..

image.thumb.png.988a08811bb29b60c5bb61cb493ccabb.png

 

now I've reloaded the page a half dozen times and it only shows rear hubs.. I can't repeat it to show only fronts...   :shrug:

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