Engine cranks but won't start
 

I had new tires put on my wife's 2008 LS460 and when we picked it up she drove it home (10 miles) with no issues whatsoever. Next morning she tried to start car and after cranking numerous times to no avail she advised me, it was "broken". Started checking obvious culprits , no codes, plenty of fuel, checked oil level in case there is a sensor that would prohibit starting if low and everything is good. I noticed from all te cranking the battery seemed to recharge slow with the 75 amp charger so I had the battery tested which indicated it was questionable, so new battery. DOES NOT CHANGE SITUATION. I have verified the fuel lift pump is supplying adequate fuel pressure to high pressure fuel pumps. Checked on coil for spark=Good. Engine acts like it is trying to fire a cylinder or two when cranking but never starts. I AM BEWILDERED. Has anyone had a similar problem?

Probably not starter or alternator if it is cranking. Check fuses for fuel relay, if the fuse for fuel relay is good see if you need a new fuel relay.

I checked the fuel delivery all the way to the high pressure pumps and fuel rail. ALL GOOD! It is almost like the timing is off. The engine will hit a few times but will never start. Really frustrating... I have been working on cars for 50 years and have worked in electronics nearly as long. Never had something that simply defied reason. HELP!!!!

Please don't be insulted by my comment. It is a mistake that is commonly made.

To start these cars, you need to press and release the START button. If you press and hold the START button, the car will not start.

Alternator. If you have a bad alternator the car will not start. The battery does not have to be completely dead and you can feel like it's trying to turn over

I believe the car will crank longer when you hold it. I could not start my car when my battery drained listening to the radio. Holding down the start gave it the extra crank needed to start it.

If the battery have more than 12volt, with a bad alternator, it should crank.

I'm replacing my alternator right now, when the car is running, only reading around 11.9 volts, should be like 12.4.

I would say that it needs to be more than 12.9 minimum while running; ideally 14 volts cold and no less than 13 hot. But you are right, even with a bad alternator the car should run down to the point of draining the battery. At least that’s my experience with less sophisticated cars.

You are right, I meant to type 14.2 when running and not 12.4

My LS430 was doing the same thing, turn out it was a bad fuel pump

Hey BamaRon, did you ever resolve this? I have the EXACT problem on my wifes car. I own a shop and have 28 years experience and cant figure this out, HELP!! Dan