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lexpert, Lexus Master tech
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Experience:  Master Certified with lexus, 8 years experience with Lexus
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1992 Lexus SC400: this means the Engine ECU is gone

Resolved Question:

1992 Lexus SC400 V8.
When turn on the ignition with the key, the engine light does not come on? Is this means the Engine ECU is gone? When the engine light does not come on, I can't start the engine. Just crank but won't start. Thanks.
Submitted: 4 years ago.
Category: Lexus
Expert:  Skyvisions replied 4 years ago.

Was all the work listed to correct the no start and no check engine light situation?

 

Skyvisions

Customer: replied 4 years ago.
I replaced the Fuel ECU, Alternator, Spark Plug Wires, Fuel Filter to fix the no start and no check engine light. Thanks.
Customer: replied 4 years ago.
Also, when I takes out the battery negative for 8 hours or more overnight, reconnect it back in the morning seems to fix the no-start issue for a while. After the engine is warmed up, I can't restart the engine anymore. It cranks but no-start and the check engine light does not comes on when turn the key ignition to "on" position. Pressing the gas pedal and release it after the engine start seems to kill the engine.
Customer: replied 4 years ago.
Once the engine is warmed up, I can drive around with no issue. As soon as I turn off the warm engine, I can't restart the engine again. Also, no check engine light or engine codes after that.
Expert:  Skyvisions replied 4 years ago.

I am going to defer on this one Have not heard of this problem.

 

Skyvisions

Expert:  lexpert replied 4 years ago.

You stated that the check engine light does not illuminate correct?

Any issues with fuses blowing?

Do you have an aftermarket alarm on this car?

 

Customer: replied 4 years ago.

As far as I have checked, no fuses are blown. The car alarm is from the manufacture, not aftermarket.

 

As for the check engine light, it does illuminate once a while, but not all the time. Most of the time, it doesn't illuminate when you turn the key to the ignition on.

 

 

Expert:  lexpert replied 4 years ago.
Ever have the check engine light on but the engine starts normally?
Customer: replied 4 years ago.

Everytime the engine light is on, the engine starts easily. Only when it's not on when the ignition is on that is when the engine won't fire, just cranks.

Expert:  lexpert replied 4 years ago.

Ok, that is what i figured you would have but I wanted to be sure.

have you done any electrical tests on the car yet?

Customer: replied 4 years ago.
No I haven't done any electrical tests.
Expert:  lexpert replied 4 years ago.
Some complex tests would need to be performed here and while the condition is happening to confirm this but it looks like you may be having an issue with the engine ECU as this is a somewhat common issue on the 1992-1993 models. No check engine light means the computer is not powering up.
Customer: replied 4 years ago.

Thanks, XXXXX XXXXX think it's the Engine ECU. Is there a way to test the Engine ECU to know it's still active/alive or not?

 

Expert:  lexpert replied 4 years ago.
The only real tests are to confirm power at the ECU, in most cases on these older ones when in question we kept a "tester" ecu at the dealer, I know you do not have this convenience but that is what I have to offer.
lexpert, Lexus Master tech
Category: Lexus
Satisfied Customers: 9973
Experience: Master Certified with lexus, 8 years experience with Lexus
lexpert and 2 other Lexus Specialists are ready to help you
Customer: replied 4 years ago.
Got a new Engine ECU today. I installed it and the car ran normally again. Thank you for your bull-eye support.
Expert:  lexpert replied 4 years ago.
Great! glad to hear of the success, let me know if you need future assistance.
Customer: replied 4 years ago.

Peter,

 

I have a high idle with me 92 Lexus Sc400. What could be the problems?

Expert:  lexpert replied 4 years ago.
Did this only start after the ECU replacement?
Customer: replied 4 years ago.
Yes it is. It idle at 1025 RPM and in Drive/Reverse at 1000 RPM.
Expert:  lexpert replied 4 years ago.

Even after warming up?

Any signs of vaccum leaks?

Customer: replied 4 years ago.

If I force the TPS all the way down (counter-Clockwise) then it idle around 800-850 RPM & get CEL code 13 RPM signal. Also, when in Drive/Reverse it goes to 650-700 RPM with a bit rough idle at stop lights/signs.

 

If I reset the ECU, and leave the TPS back to normal position w/ idle at 1025 RPM, then there is no CEL at all. No rough idle at this normal setting.

Customer: replied 4 years ago.

I just replaced all of the vacuum tubings but it didn't help.

Expert:  lexpert replied 4 years ago.
If you get a code #13 this is not a RPM signal issue, it means that the timing belt is not propelrly positioned.
Customer: replied 4 years ago.

What about the setting without the CEL # XXXXX at idle 1025 RPM? I'm not sure which route to take at this moment.

Expert:  lexpert replied 4 years ago.
You need to pull the timing belt covers. Messing with the throttle does not cause a code 13, timingbelt position or a damaged crank/cam sensor will. Sounds like your timing belt is off one tooth.
Customer: replied 4 years ago.

Thanks, I'll try that tomorrow. Will keep you updated.

Expert:  lexpert replied 4 years ago.

Ok

lexpert, Lexus Master tech
Category: Lexus
Satisfied Customers: 9973
Experience: Master Certified with lexus, 8 years experience with Lexus
lexpert and 2 other Lexus Specialists are ready to help you
Customer: replied 4 years ago.

Peter,

Once again, you are dead on the problem. It was off-timing as you said it was. The timing was off by two teeth. I fixed it and the car runs smoothly once again. No more rough idle and CEL #13. Thank you once again for your expertise.

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