Hey all,

I've been having problems with my SC400 that has finally gotten my attention. Sorry for the long read.

The Symptoms:
Well, it all starts when I turn on the car. On really cold start ups, there will be white smoke coming out of the exhaust. This smell is really strong and smells like pure unburnt fuel. It idles kind of high: 1500rpm, and vibrates slightly. I constantly check all the fluid levels and they are all where they are suppose to be.

When the car has gotten a bit warmer, but still in Open Loop (not at operating temperature), it will feel fast and quick. It feels really nice and sporty. But as soon as it reaches the normal operating temperature/closed loop, the car starts to feel slower. I have to push on the gas harder to get it going. It feels very sluggish.

Recently I installed a wideband O2 sensor in the exhaust so that I could diagnose it a bit. The car is running very rich under all of these conditions. On those very cold start ups, the car is idling at around 7.4 AFR and below. When normal, idle is around 10~11 AFR. On low throttle it'll go around 8~10 AFR. And on Wide Open Throttle, it goes below 7.4 AFR!

My friends would tell me how the exhaust smell would be unbearable while driving behind me when I punch the gas peddle.
The car has steadily gotten worse over the three years I've had it.

I'm really thinking that its either that the ECU is going bad, or the MAF is. This guy had somewhat the same problem, many said it was a textbook example of a blown headgasket, but it turned out to be that the ECU was bad:
https://www.clublexus.com/forums/per...you-think.html

What do you guys think? Is it the ECU, or the MAF, or something else? I don't think its the headgasket and there is no CEL.

Thank you!

Edit: The Capacitors on my old ecu looked fine. Changed them out anyways. Helped a tiny bit, but not enough to call it a fix compared to the new ecu.

 

had the same issue wit my sc 3 for a lil while...its the ecu...i took it to the dealer and had a test done to it and they told me my ecu was fried and it was causin one of my cylinders to not fire and it was jus fillin one of them up wit fuel...thats where that really bad fuel smell **** from...start the car and rev it for a lil and see if it also has fuel shoot out the exhaust if so...yep its ur ecu...invest in another used sc4 ecu and plug it in and start it and let it idle for a while so that the car will get used to the ecu b4 drivin....

 

I have a similar problem, but it is on a 93 ES, my ecu does not run the spark, just the timing, sooo I don't think its the ecu, but I too have white smoke, no codes, not overheatiing, oil and coolant are fine.... so my thought is one of the cyls are not firing at all, no spark, could be a defective pug, or wire, the plugs are brand new NGK double platinum, the wires are Yaziki hi-grade wires.... no bubbles in the coolant, no overheating, but white smoke, raw gas dripping from somewhere, but not sure where it is coming from. interesting problem..... what do you think?

Capn

 

I've read lots and lots of articles and posts and the conclusion I'm drawing is the ECU. Mainly because my car is very well taken care of. All the necessary mechanical tune ups have been done when I bought it. When I changed the spark plugs not too long ago, I fired it up and that strong rich smell was still there. Its been slowly getting worse over time.

Do you notice that when the car is getting warmed up but still in open loop (not yet at normal operating temp), it feels quicker? more responsive? And then right when it gets to closed loop, if feels really slow.

Just wondering, but if you disconnect the MAF, will the car still start? Or will it just stall?

https://www.clublexus.com/forums/per...ecu-issue.html

Since its not throwing any kind of CEL thats why I think its the ECU. It should be saying something if its running ultra rich...right?

I'm going to get a new ecu and see if that will fix it. I'll keep this page updated if I find anything else.

Thanks for your reply, but I hope I could've helped you too.

 

im tellin u bro its the ecu...cuz i also was keepin up wit the tuning and the spark plugs..wires...02 sensor did nothin...so jus get another ecu and take it from there homie...

 

Yea, I'm going to try and get one.

Thanks for your help man, I hope it works.

 

Thanks 94_soarer! I got the ecu and it made a really big difference in power on the low end. No more white smoke either!

 

so everything worked out??? it was the ecu huh??? yea man i had the same problem and i tried everything and one day a man came into my job and he saw my sc parked outside and he asked whos it was and i said it was mine and he was driving one too...and he asked me did i have the white smoke problem/fuel problem yet and i said no and he was like good...when u do its the ecu...remember that ok and i jus looked at him like he was crazy!!!!LOL about 3 weeks later the car started doing it...i was like awww hell naw!!!!

 

My car has always had that problem and i always wondered if it was normal. Apparently it is caused by leaky capacitors inside the ecu and makes the fuel injectors act all weird.

Thanks a lot bro. Now we both know to pass on this information to every SC owner.

 

yep yep!!!

 

out of curiosity have you tried resetting the ecu? I notice my SC gets crap gas mileage unless I reset the ****. Once I pull the efi fuse and let it sit; she runs great and gets awesome gas mileage....until about a week.

 

yea, i've done that plenty of times and there really isn't any positive effect for me.

If it's ur ecu then you're going to have white smoke that smells like fuel coming out your exhaust on really cold start ups, your car is going to feel faster when the engine temperature is cold, and feel really sluggish when at normal operating temperature.

 

HMMM I'm starting to wonder if this be the issue with my SC300 as well. If I let it sit for a day or so when I start it up there is white exhaust everywhere.....................it looks like a small fire lol. Once the engine warms up the amount of exhaust goes down but is still there somewhat.

 

Since replacing the ECU seems to be the case, here is a link for the part numbers if for some reason you can't read the part number on your ECU:
http://www.siaelec.com/index.asp?Pag...S&Category=380

Even though this is a retail store, it is a good source to find the correct part number especially when buying used. Make sure to get an ECU that corresponds to the one currently installed. The goal is to avoid obtaining the incorrect ECU.

 

I do agree with you on this, but in my case I got a 93 sc300...my ecu fried and a good friend gave me a 95 ecu for free....I use that with no ill affect at all, the 95 ecu is noticeably wider but all the plugs still fit....Now I did that only because it was FREE and I have nothing to loose