marcellomax

2 new battries new starter, still when cold it cranks and start fine, when hot it will only crank once one turn over and thats it nothing else. and if you hold the key like starting a regular car it will turn once and then 1 second pause then turn once again, check the video out

ItalianJoe1

Crank sensor ever been changed?

marcellomax

I ordered one new crank sensor and all 4 cam sensors. will find out on Friday, But dont you think if it was the crank sensor at least it will crank but not start?

ItalianJoe1

Depends. If it's not seeing RPM signal right away it may kill signal to the starter. I don't often see crank sensor failures on the newer cars like the old ones, but if you have good batteries and starter, I don't know where else to go without having the car in front of me.

Check for good grounding of the engine, I've seen issues where a broken/corroded ground strap caused things like that, the starter would just start to engage but then it would stop, checked from the engine to a ground point and found appx 200 ohm, went to remove the ground cable at the body and the stud snapped off, was all corroded underneath, couldn't see it. Ran my own ground wire, fired right up to drive to the bodyshop and have a new stud welded in.

marcellomax

It only does it when its hot, when cold it cranks very good and fast has a very strong crank let me go down stairs and try starting it after it cooled off give me a minute.

Ok here you go after it cooled off it started like a charm.

Rudeney

A bad CPS will not prevent the starter from rotating the crankshaft. If the starter stops after one rotation, then it's either a bad starter (yes, I know it has been replaced - new parts can be bad). or it is not getting voltage. That could be be a bad battery, or starter relay. I'd start diagnosing it by putting a voltmeter on the starter solenoid feed. If it has +12v the entire time the crankshaft "should be" rotating, then it's the starter or solenoid. If voltage drops out, then go upstream and check the solenoid ("L" on the right SAM).

marcellomax

The old starter did what the new starter is doing the car has a Brand new Passenger side SAM Brand new SAM fuse box with its fuses and relays all brand new. I am puzzled why this happen when the car is HOT?

Rudeney

Are you going to diagnose and fix this yourself? If so, then I stand by my suggestion to test voltage at the solenoid. If you paid a shop or dealership to do all that work recently, then I'd take it back to them as it will be one of the things they replaced that is the culprit.

marcellomax

Tomorrow i will drive it get it all warmed up then put it up on the lift and crank it and see what the voltage is at the starter thats a brilliant idea. you know how it is i give it to the mechanic and it starts just fine i pick it up and bring it home and i get here and turn it off it wont start after that.

ItalianJoe1

Agreed, start here. Heat soak can cause a variety of issues, a simple voltage drop test will rule out half the system in one pass and tell you which area to check next.

marcellomax

Thank you guys for your input much appreciated will keep you posted.

marcellomax

OK here we go, it is the ECM, when it gets hot it quits why would they put it on top of the engine i have noooo idea. just as simple as that.

ItalianJoe1

It's there for ease of assembly, the whole engine and harness in dropped into the car in one shot, so they don't have to route many harness around, just plug in the body side harness to the M/E and off you go.

The new E/S63 have water cooling for the M/E as it would get baked on top of the engine. The GT it's over in the fender area to avoid that.

Rudeney

They used to put the ECU's in the e-box (SAM/fuse panel housing) over by the fender. That created the need for a longer wiring harness to go from there to all the engine sensors and actuator circuits. Not only that, being closed up in the e-box, things would get very hot. On top of the engine, built into a heat sink, and sitting between the air intake ports, it actually stays "somewhat" cool. MBZ has literally built tens of millions of engines with the ECU mounted on top like this with no failures. I think yours must just have been the result of a singular defect, not a systematic flaw.

EDIT: Oh, and before replacing the ECU, I might would disconnect the wiring harnesses and give everything a good shot of contact cleaner. Although they do use seals on the connectors, they are in a harsh environment and could still have some small amounts of moisture or dust work in there.

marcellomax

Holly Smokes, so they replace the whole ECM and guess what it still did it. well after they kept it for another 5 days turned out the Tranny Neutral safety switch on the valve body was the problem now all is good.

Rudeney

Interesting. Was the linkage just slightly off and then heat causing it be misaligned enough not to be in neutral?