456 will not start when engine is hot need urgent help

Most cars use a crank sensor to coordinate the timing at start up. Maybe this is the problem.

 

heat creates resistance. It could be the battery itself, or the cables to the battery.

otherwise i would suspect ignition ( crank sensors as mentioned) or fuel pressure.

But i dont know much about something as modern as a 456.

good luck.

 

456's have had connector problems and you may have something that is making good contact when it is cold, but loses contact when heated. Dave Helms of Scuderia Rampante is producing gold connector kits which help on the connector issues.

http://www.scuderiarampanteinnovations.com/solutions.html#gold

For other things that may be causing the problem, an SD1 should be able to diagnose the problem. Temperature sensing problems are an obvious potential cause, and that could be a connector problem or a sensor problem. The water temperature sensors are under the intake manifold on the 456 and I am not sure you can reach them without removing the intake manifold to see if they are making good contact. 33 and 39 below.

Intake manifolds have also tended to loosen over time in in the late V12 cars. You might check and make sure the intake manifold bolts are correctly torqued. If somewhat loose, you may have good vacuum when cold and a vacuum leak when hot, and that could make hot starting more difficult. As near as I can tell, the torque on the 24 or so nuts holding down the intake manifold is only 9.8 Nm. Any pros who know the torque for sure, let us know.

Is your car a 95 (Motronic 2.7) or a later car (Motronic 5.2)? May help someone who knows more than I do.

Taz
Terry Phillips
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if its a 2.7, pls reset the ECUs by turning off the battery switch for about 30 minutes. Then start the car as suggested in the manual to reset the computers . then drive and see if problem persists. if not, your car is "learning" information that is making it send the wrong mixture or timing during a warm start. AGree with TAZ the intake manifold gasket and vacuum leak may be part of the problem.

 

I have a similar problem so I'd be interested in your solution - although mine always starts, it still needs to be started twice in your "half-warm" condition. Perhaps it's nothing, or perhaps a slight leak from an injector or a loss of fuel pressure after shutdown in one of the FI rails on mine.

First easy check for you: fuel pressure regulators (number 12 in the picture). Modern fuels are aggressive on the membranes inside of these.
I replaced both the FPRs since one was leaking after a period of standstill. They're very expensive but Rockauto.com has imitation ones that fit 100%, or PM me privately for a different solution. It could be yours has worse starting problems than mine if one of the fuel pressure regulators is leaking. Fuel keeps on leaking out after shutdown until the pressure in the rail has worn off, putting in about 50-100cc of fuel in the plenum, flooding the engine on that side. To check, take off the black covers on the plenum and pull off the tiny vacuum hoses (14) on the front side of the regulators, preferably when running or just after it has been running. If any fuel comes out of the regulator, it is bad and needs replacing. Check and report
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Here is a little better image. Ricambi's images are higher res than Eurospare's.

Taz
Terry Phillips
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please tell us the answer when the car is fixed. I have the same problem.

 

Bundas, how are your FPR's, have you checked them?

 

I find myself without time enough to think about my toys. No employees at this time. I will follow this thread with interest, thanks

 

if elettrical and eletronic is ok, it can be valve clearance too tight!!
saluti, filippo

 

You had a starting issue with your 456 and received some helpful advice from the forum. Did you ever resolve the issue? If so could you please share the results for the rest of us with similar issues?
Gary

 

His last post was in 2016 It's unlikely he's monitoring the forum.