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Tried a used one, but it didnt work. Thought it must have been bad. Tried a new one from Lexus. Turns over but does not start.
Jumper FN and +B will start the car.
Am lost on this one. Sounded like it was the problem reading the above posts. Maybe take a minute and re-read.
"Installing a new or known good Fuel ECU will cure the issue. " Thanks
Tried a used one, but it didnt work. Thought it must have been bad. Tried a new one from Lexus. Turns over but does not start.
Jumper FN and +B will start the car.
Am lost on this one. Sounded like it was the problem reading the above posts. Maybe take a minute and re-read.
"Installing a new or known good Fuel ECU will cure the issue. " Thanks
^^ Based on what you said your symptoms were, yes, that USUALLY points to the fuel ECU having a fault... which is cured by either replacing it... (or doing a complete bypass with a +12V & Relay Mod if you want to get into re-wiring).
This has been the culprit 95% of the time for most who experience this issue, especially if the bypass trick allows the car to start and run.
That bypass should be to "FP" and "+B". If your car WILL start and run with the temporary bypass of the entire Fuel ECU then your fuel pump has been temporarily put into direct 12V mode (as opposed to the Fuel ECU controlled 12V on initial start with a switch to 9V for all engine operations until high rpm or full throttle operation when that computer kicks it into 12V high flow mode).
To me this would suggest that there is either a Fuel ECU fault or a wiring fault in one of the wires between the Fuel ECU and main engine ECU or fuse... or possibly even an issue with your main engine ECU's capacitors.
You have put in a new dealer-sourced Fuel ECU. Okay, that leaves it less suspect. Wiring faults between that and the main ecu in the body harness... those are very very rare to occur. You say you have checked the main EFI fuse and that is OK.
Did you have ANY other driveability issues from your car BEFORE you had a no-start issue? Any hard starting or long cranking? Any rough or uneven idle? Rich running condition? Any coming and going odd issues while driving the car? Anything like that?
No issues at all prior to this. Starts right up. Runs fine. Has about 85,000 miles.
Is it an issue driving the car to a shop with the jumper installed? The jumper wire does get hot.
Have not driven jumpered. Just started up with the jumper.
So, main ECU or fault in wiring? Might be a good candidate to bypass the fuel pump ecu.
Will probably have to take it to a shop. As I am running out of ideas / ability if its the main ecu.
Your SC has *only* 85k original miles on the chassis? That's quite low! Actually I'm surprised your car is having this issue at such low mileage. Nonetheless...
The thick paper clip will indeed get hot. What the FP & +B bypass is doing is directly connecting your Denso NA fuel pump to however many amps it draws @ a full 12V. Being a direct connection maybe it's more like 13.8V but I'm not sure. All of that current is going through the little paper clip. For testing it is fine.
Assuming that it is not an incredibly long drive to your repair shop it should be okay... but I have to admit that I've never tried driving with it like that myself.
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I think the car should be looked at first but if everything else checks out OK and you are still having issues with any of the NA FP ECUs you have on hand then sure you could do the 12V mod w/ relay. I don't know how if affects your results on a CA smog testing dyno. This is a reason I would have this system diagnosed first to try to use the stock fuel ecu setup.
Technically though all that would happen at low engine speed operation and idle is that the slower 9V mode pump speed would be bumped up to 12V-13.8V and the return style fuel system and your fuel pressure regulator would be working a little harder than stock. These are not fragile fuel system components.
Mostly though I would say it's the question mark of how it would (or wouldn't) affect smog test numbers when the time comes without the stock 9V/12V fuel ecu setup.
SC owners in other states that don't require testing every two years don't have to worry about this. And my thinking could be overkill but I just wanted to bring it up before you have ruled out ever getting your fuel ecu to work again. It's just weird that you are having this problem at a mere 85k original miles.
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Now the main engine ECU is not something I am certain is at fault. If you have no odd symptoms like rough running or hard starting that come and go or get progressively worse then it's doubtful. However ALL of the ECUs in 1992-1997 SC300's SC400's will eventually need capacitor replacement service due to the type of capacitors that Toyota used in all their pre-VVT-i ECUs from 1985-1997 or so.
Since you're in CA the closest service facility for the ECU will be Driftmotion in Montclair. They regularly do repairs on these and other Toyota/Lexus ECUs there. Alternative to that is mailing it out to Tanin Auto Electronix in Wisconsin. Both DM and TAE are excellent for this type of repair and are very familiar with these ECUs.
But if you have no obvious symptoms pointing to the engine ECU then I do not think that is it at this time, no. Should you address having your main engine ECU serviced in the future anyway? Yes, absolutely as a highly recommended preventative measure.
Getting your main ECU serviced is a VERY common SC300/400 and MK4 Supra issue. It just doesn't happen to all at the same mileages or chassis age. For the ECU capacitor issues that people have it doesn't matter how many miles are on the odometer.
It is a possibility... but right now I think the focus should still be on the fuel ecu and its circuitry since you seem to have no issue once you apply the FP & +B bypass.
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I was based in Los Angeles for many years until recently and for shops I don't have any Lexus dealers I'd recommend. Avoid Keyes Lexus like the plague. Lexus of Glendale is OK but pricey as you'd expect. I had good experience with Kerechuk Motor Service in Alhambra in the past but they are sometimes difficult to schedule with. I also like Tyerman's Automotive & Suspension in Burbank.
Not the cheapest recommendation or most convenient but I always had good experience with Carson Toyota servicing my SC300. If it's an option I'd call them to verify that they still service Lexus vehicles but they did before and they sell parts for both brands.
What I am thinking in any of these recommendations is what shops I can recommend to you that I know would be familiar with the unique 9V/12V fuel ECU setups in SC's and Supras (and a couple of the more recent Toyota trucks). And who would have access to the official Toyota TIS (Toyota Information System) documents that would provide every single service manual for your car.
(*Actually any of us can access the Toyota TIS system from the web and download anything we want for a small fee).
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What I would recommend right now is to keep the fuel ECUs that you have currently. Your original, the dealer-bought OEM replacement and whatever other one you just trued. Keep them ID'd as such.
They're not really serviceable in an easy way. Tanin Auto was asked to look into the possibility of repairing these but found that Toyota didn't make it easy to internally.
The new dealer-sourced fuel ECU that you have is likely fine... because so far no matter which fuel ECU you try you're getting the same result.
I am not sure and really would need to think on this further after reviewing the SC300/400 troubleshooting TSRM. The culprit is likely something else in the same electrical setup that isn't working right.
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For me here it is late. I will see if I can find the troubleshooting guide PDF if I have it somewhere.
Thanks for the info. I use a local auto shop about 10 miles from home. Small shop, sharp guys. Will probably go there.
Short drive, but I didn't want to fry anything driving jumpered. So I had to ask. Will probably go for it with a jumper / rather than tow.
Will ask around.
Tha story:
This car was parked in good running cond in the driveway 3 doors down for 11-12 years.(and not started or moved)
When the owner purchased a new Lexus. I bought it with 69k. Started leaving notes on it yrs ago.........
Drained 8 gallons of the worst smelling gas ever. Replaced the FP, brake job, and all normal maint as it had none with only 69k.
But it was 22 yrs old then. TB, WP, belts, etc. The car runs and drives like new.
I did recover the leather seat seats from sun damage, and tires and wheels. But have had zero problems the last 15k miles. Till this.
Really appreciate the help! Too bad Its not part of the 95%. lol lol
This is where it was parked for 12 yrs. The int off gassed and tinted the inside windows. Also had moss on the right side from the sprinklers...Had it towed 300 feet to my driveway on Superbowl sunday 2017. Driveway still has stain from where it was parked.
How it looks now. Great car! (when it starts)... Ha Ha.
Your SC looks fantastic! You could almost call that a time capsule! And the wheels you've put on it are very fitting. Having recovered the leather I am sure the interior is no exception despite sitting out for 12 years.
And you're welcome! I am sorry I couldn't help you solve the fuel/starting problem easily though. Based on those initial symptoms you described that is almost always the fuel ecu. However it's just a little more in depth it seems. It's still not a complicated circuit and I've been through the electrical diagrams for that fuel ECU many times.
Speaking of which, thinking on the time it sat before you got it... IF your mechanic cannot find anything wrong with the fuel pump circuitry or the fuel pump ECU itself, keep it in the back of your mind that it is still entirely possible that your main engine ECU might need to have the capacitors serviced. It's a remote possibility but still a possibility.
The ECU sitting and not being used for so many years could contribute to that but you would only know by sending it in for service. The casing is opened up (carefully so as to not introduce any static electricity!) and the boards are checked for any signs of capacitor leakage or damage to the board traces from any cap leakage.
The replacement capacitors are VERY specific and are pretty a much special order from Japanese electronics parts suppliers. This is why if it comes about that you do need it serviced I strongly recommend either driving or mailing the ECU to Driftmotion or mailing it to Tanin Auto. They do those ECU repairs regularly and have good reputations.
The reason I am bringing this up again just to keep in mind when you get the car diagnosed with your mechanic is because the main engine ECU does have pins in its harness that connect all the way to the back of the car into that Fuel ECU which control its functions. It's basically a big main solid state computer controlling a much smaller solid state computer (and a very simple one at that).
But it looks like you took care of most everything else that could have aged badly from the important parts of the fuel system to the tires. Just monitor any major hoses you didn't replace but they should be fine as long as they're still supple.
^^ They will take care of getting your ECU fully checked out . They keep SC, LS and ES shop cars specifically to final QC test out all their Lexus ECU repairs.
Hopefully this will resolve your issue for good. Either way by now your ECU is just as old as any other SC's ECU so replacing the capacitors will future proof it.
I do not suspect it is your wires between the main ECU and fuel ECU. It is technically possible that it could be but the likelihood is extremely low.
Some advice for shipping your ECU: when you have them return ship back to your CA address, please do not use Fedex Overnight or any overnight mailing service. Sending to them should be fine if you already have but do not use Fedex Overnight or any overnight service for the return shipping of your ECU. Also, give it about $300 of shipping insurance to be safe.
That is the only thing I would definitely warn you to avoid (Fedex Overnight for shipping TO CA). Any other Fedex shipping service tier is fine.
Probably the capacitors on the ECU are bad, just open and look if any are bludged and replace them.
That was it. main ECU repaired by Tanin.. Runs like normal.....Starts right up.
Bought a new ecu relay for $400.00 but didn't need it.
If anyone needs one in great working cond, with 90k orig miles let me know...........
See photo below.........................
^^ Very glad you got it solved!! So the main ECU's circuits that control the Fuel ECU were the problem all along. It also would not hurt to hold onto that new fuel ECU but given what it cost... I don't blame you for selling it. Being in CA with emissions it could come in handy for a rainy day in case whichever one you have in the car now does truly fail.
This thread is adding to my growing suspicion that due to the age (not mileage) of SC's now, regardless of any issues that may need to be solved (or not) I think a baseline recommendation to anyone who is a new SC owner from now on must be to get their main engine ECU capacitor serviced. Because it's the one aspect that can throw off almost all other engine electrical diagnosis.
Up date, at 475 miles (2 weeks ago) 4 days after installing the reworked main ecu the car quit running on the FWY at night in L.A. (Not fun)
Drove the last 60 miles with the jumper installed in the port.
Mailed the main ecu back to Tanin, and it worked for them in there test car.
Due to its unpredictable / ness. They recommended I purchase a different one from them.
$169.00 as they gave me credit for the rebuild of my old one. Its in the mail.
Will know soon............ P.S. Always carry a small piece if wire, a string and a flashlight. Saved my bacon...
Plugged a "new to me rebuilt main ecu" from Tanin Sunday. Works fine!
On the two times I have used the car. Hopefully, this will be my last post on the subject.
10-31-18, 01:00 PM
. They keep SC, LS and ES shop cars specifically to final QC test out all their Lexus ECU repairs.
