1999 Ls400 Cranks, Won't Start, No Spark

[DigitalBuddha]

My wife's LS400 suddenly wouldn't start the other day.

Cramked just fine and strong but no spark getting to the pluigs. Not getting any codes.

Towed it to the mechanic (certified Lexus independant shop) and of course it started right up for him. We discussed the issue and agreed to replace the crankshaft position sensor.

Drove home just fine and the next day, same thing. Won't start, no spark. I checked resistance on the camshaft sensor and it is within spec (1400 ohm).

I'm at a loss as to what to look for next. I would rather not pay for another tow and only to have the intermittent problem not reveal itself again. Any suggestions on what to do next?

[landar]

Don't you just hate when that happens? ^_^ The sad thing is that your mechanic seems to be out of ideas as well. It sounds like he took the "shotgun" approach to throwing a part at it. Sometimes that works but its generally a crapshoot. If you are certain that there is no spark then I would suspect a bad connection, perhaps at the ECU, or a sensor. It will take some sleuthing to get to the root cause. If it were mine, I would have an oscilloscope on points of interest (like cam and crank signals). You have a vehicle with coil-on-plug so it is something common to all eight cylinders of course. You might consider hooking up a some diagnostic software to the OBDII port which will give you some active parameters whereas a cheap scanner only gives codes. I also wonder about anti-theft acting up. With any intermittent situation such as you have, it is vital to have everything (that you want to see) instrumented at all times so that when an 'event' occurs, it is captured.And finally, WELCOME, DigitalBuddha! (is that vs. an AnalogBuddha? :whistles: )

[DigitalBuddha]

unfortunately, i dont have an oscilloscope or any obdII software/dongle, etc.

i was just out at the car again and followed these steps:

Pulled plug and again tried to see if there was spark (none)

Checked the resistance (again) at crank and camshaft sensors (within spec)

With ignition switch on, checked for voltage at the coil (there was)

I'm not a fan of the shotgun approach either, but since the car was already towed to the garage and it seemed to be fine again, I figured why not replace something simple that might clear up the intermittent problem. Oh well!

So now I am going to trace to see if there is a signal being sent via the ECU. Does that seem to be the most logical choice?

Where is the best place for me to test for signal along the IGT from the ECU?

Can you give me insight into anti-theft?

Thanks for the welcome!

[landar]

The anti-theft is a long shot. It probably would not even crank if that were activated. So, it is now at a point where it will not start at all? BTW, be very careful with running your battery down cranking it. Lead acid batteries do not 'like' to be run dry and can fail forever after that. So, put a charger on when not using it to keep it from going completely dead or you will be buying a new battery soon.

If you do not have access to test equipment and do not want to invest in same, I would probably start with gathering more symptoms. You said that it started for the mechanic. Was the battery disconnected prior? What happens when you disconnect the battery overnight then reconnect and try to start? Can you locate the ECU and wiggle on some connectors while trying to start and see if anything happens? Just wiggling various wire harnesses in general (while cranking) might provide some clues. Does it start when it is warm? Or cold? I know it is getting colder with Fall in full swing. You might bring it into a heated garage or use a hair blower to heat certain parts/sensors.

And finally, I agree that replacing the crank sensor is a reasonable thing to do. And even though you have done a DC resistance check on the Cam sensors, that does not mean the dynamic portion is working. That is why I mentioned the oscilloscope which will show you a waveform from the sensor.

[DigitalBuddha]

Wow, you're not going to believe it but it's fixed!

It took all my cunning and acute sense of perception.

We purchased the car over a year ago and within 2 days my wife lost the lone key. We had a locksmith come out and make us 2 new keys. Of course, you know where this is going. My wife found the original key in the bottom of a purse and tried using it. Long story short, I gave the mechanic one of the new keys, which is why it ran just fine for him.

So, if you've found this post via search and have a crank, no spark...try using another key

[landar]

So you mean a mechanic made you two new keys and reprogrammed the ECU to accept the new keys? Then the old key would no longer work but that is the key you were using when it would not start?

[VBdenny]

In the future keep in mind that almost every auto parts store has and OBDII scanner that they let you use for free.