97 Lexus LS400 turned off while driving about 50-55 mph. Engine would crank and start for a second and immediately turn off. I hooked it up to a MODUS scanner at my mechanics and tried to see what codes were being displayed and found out there were no codes. I saw a similar post at your site from a guy that had the same symptoms and he stated that the engine would start if I would disconnect the driver or passenger cam sensor. Sure enough It did. Still had no codes. The post indicated a possible problem with the ECM and gave instructions on how to test the ECM. I did not understand how to test the ECM, so I purchased a rebuilt ECM. Installed it and had the same result... with no start and no codes. Tested the cam sensors and the crankshaft sensor. They tested fine within parameters. When I started the engine without the crank sensor plugged in I received a code flagging the crand sensor. ECM working possibly? Talked to the company who sold me the ECM and they suggested a possible problem with the rebuild. Going to return for exchange. Is there anything else I could look for before I send the ECM back for exchange? Is there something I am not understanding or missed? At your earliest convenience. Thanks. South Texas.

 

next thing I would check is if the engine is getting fuel.
do you hear the pump? does it start if you spray starter fluid in the intake?

 

Pump is working. I can unplug one of the camshaft sensors and the engine will start and run... I can even move the car around the mechanic shop. Once I plug the cam sensor back in. The engine will start and quickly turn off.

 

Seems like I am asking this a lot today. Is your key cracked or broken from the plastic housing? When you unplug anything on an LS you have to disconnect the battery ... or the computer gets confused.

 

How did you test the sensors?

 

The ECU is an unknown based on your statement of the sensors checking out. The other thought may be the transponder key or receiver.

 

Thanks for responding. I have a crack on top of the eyelet of the key, otherwise no cracks on any other part of the key. I have a spare key that has no cracks, but to no avail. I did unplug the battery every time I unplugged the ECU. I also took my ECU apart to look for leaking capacitors and did not find any. Looked Clean...

 

Yes I can hear the pump. I also sprayed starter fluid in the intake, and it would start and turn off.

 

I tested them for resistance. I looked in a program call AllData and found the range required for the sensors. They were within range. I did not take the sensors off of the motor before testing.

 

Something is throwing off the timing. I'd just try a new cam sensor.

 

When you move the car unplugging one of the camshaft sensors, does the engine run as it supposed to be?
Or does it run poorly and you have to push the pedal deeply to reach the mechanic shop?

If it runs poorly, I suppose that the engine is in the back-up mode due to the reason that something serious has happened in the engine management system. I can't say what is the root cause of your problem at the moment but I'd be happy if my past posts below were some aid for your further trouble shootings. I'd check the circuit opening relay is triggered or not as a first step.
https://www.clublexus.com/forums/ls-...ml#post9195875
https://www.clublexus.com/forums/ls-...l#post10010327

 

Thanks for your reply. When I unplug one of the cam sensors, it runs as if some of the cylinders are not all firing. I do not have to change the way I press the gas pedal. I can drive it around the shop without much effort. You can just feel the engine running as if it is missing. I will check out your past posts and look into changing the cam sensors. Thanks again for your help.

 

Is the battery old? weak? cheap? If not, then I tend to suspect fuel delivery on any of my vehicles that start only on starting fluid. You can rent fuel pressure gauges and the like, but I have never done this on a lexus, so I am no help there. I have changed the fuel filter on my 98, and the hardest part was "be somewhat soaked in gas" and getting the bolts back into the mounting bracket. Honestly, It was quite dangerous. Lots of patience is required to empty the gas tank, prehaps even running way below empty. If you don't, then you are in a situation of being under a car soaked in explosive gasoline. Things that spark like disconnected battery cables that find there way back to the terminal, passerby with a lighter, cigarettes, and the like could go horribly wrong. Anyway, just my 2 cents. So be very careful if you go the route of a fuel filter change.

 

You said it definitely DID restart after it died? If it did not that sounds like a broken timing belt but if it did restart then that would not be the case.

 

Your description reminds me of the off timing. When the crank and cam timings are not well synchronized, the ECU is confused and can't control the engine and forced to stop it. Unplugging the cam sensor, the ECU can't check the timing phase but in this case it uses the internal data instead of the real cam signal. So the engine can run but not well enough. I suggest you to check the timing belt carefully removing the cover.