456 wont start. Need help troubleshooting.

Colby- Sure sounds like the immobilizer is armed, but sounds like you tried that already by disarming.

 

Colby- I would not think so.

 

Start with the basics - check for spark and then fuel -

It is suspect that both banks are failing, so it would seem that is something that controls both (alarm related most probably)

 

Colby- There are roll-over shut off valves on both the 2.7 and 5.2 456s, but darned if I see where the reset switch is. Usually under the carpet in front of the driver's seat, I thought.

 

Very strange - I do not know if there are reset switches. I have not found it on mine.

 

Taz, I think the rollover shutoffs are mechanical only devices that seal off the tank/lines to prevent fuel leakage in the event the car has turned over. I wouldn't think one of those would be interfering.

Colby, I don't know if your car has an inertia switch, but if it does, I would think that the system designers would have put it downstream of the fuel pumps' fuses/relays, so even if you had tripped the switch, you "should" still have voltage at the fuel pumps' fuses, (but not the relays, unless the car is running).

The reason why you won't see voltage after the relays is because most EFI cars will only run the pump(s) for 1-2 seconds when the key is first turned on, to pressurise the system and purge air, then they won't turn the pumps back on until the RPM sensor is satisfied that the car is cranking (or sometimes not until the engine has actually fired).

I know that for the 550, the Motronic logic is to "fire" the pumps for 1-2 seconds on initial key on, however if you don't proceed with starting the car, and instead turn the key off, the next time you turn the key on, the pumps will not fire for the 1-2 seconds. Ferrari/Motronic figures the system should already be pressurised from the last "false" start.

I would do this:

1. First check for voltage before/after the fuel pump fuses (not the relays) with the ignition on (not the start position, but run position)

2. Next check for voltage leaving the relays going out to the injectors (key in same position). This checks that the ECU is generally happy, there are no conditions existing that would prohibit a start attempt, and it has activated a master relay to provide power to the injectors.

If you have voltage at both those points, then I would suspect an inertia switch has tripped and you'll need to locate & reset it.

Perhaps Brian or someone else who knows the 456 will jump in with additional advise.

 

Colby- No, when you start her, the LED should be lit for 6 seconds after you go to ON (II), and then go off, providing the immobilizer and alarm have been disarmed.

 

As Taz said, that alarm LED should go out after six seconds. It's telling you that the internal battery is failing on the alarm system. I've had this on my 550 in the past, however it did not prevent me from starting the car.

Regardless of the alarm/immobiliser, I think it's odd that you don't even have voltage at the fuel pump fuses. To me, this indicates a problem upstream.

Did you happen to check for injector voltage? I would think that if the alarm/immobiliser system isn't happy, it would probably keep the Motronics from energising the fuel injector relays as well as the fuel pump relays, but I'd think there would still be power at the fuses.

I see from the fuse/relay board description on page L30 of the 456 GT WSM, there's a relay "S" which controls "key operated services", some of which are injectors, fuel pumps, and many other circuits. It's possible this relay is acting dodgy?

Maybe someone with the actual 456 GT electrical schematics and wiring diagrams can trace the power flow further upstream and offer some suggestions where the power is being interrupted.

 

Not a silly question at all, particularly if the relay output terminates on that fuse/relay "mother board" instead of going out into the engine bay.

If it's the injector relays you're trying to test, you should be able to find which cable exits the board and which termination is for the injector power. The cable diagrams in the WSM for the 456 look to be pretty good (much better than our 550's).

But that "S" relay output probably terminates on the mother board, so rather than fighting with it to see if it's got voltage and is working, I'd probably just swap it out with another equally rated relay and see if that does anything and/or the problem moves. You could, of course, remove the relay and probe its socket with your DVM to see if the coil terminals are getting voltage, but that won't tell you if the relay's contacts are corroded or otherwise not making contact.

 

Colby, see the "S" relay in the pics below:
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To the best of my knowledge all the V12s have the inertia sw near the battery. On the M (not sure about GT) a tripped inertia switch turns on the 4 way flashers.

 

Did you try starting the while supplying voltage to the fuse for the pumps? If that is the case then you should be getting fuel...meaning spark is failing.

But it is strange that you are having issues with both fuel and spark...eliminate one at a time.

Can you have someone check for spark while you crank it? Ground a spark plug (ideally with a large clamp) and start.

 

Even with pumps on, that doesn't necessarily mean the injectors will work. To fire, they first need a constant +12 from the ECU's master relay, then timed pulses to earth from the ECU.

So with key on, I'd check for the constant +12 at the injectors - this is easy to do - just pop off any injector connector and see if one or the other terminals has +12 wrt ground/engine block. If the injectors don't have +12 with key on, then the Motronics aren't happy for some reason.

Ditto for the coilpacks - check terminal #4 in the harness connector that mates to one of the coilpacks and see if you have +12 there with key on. Again, no +12 means an unhappy ECU.

If you don't find +12 at either of those points, and you already know your fuel pumps are locked out, it's really starting to sound like it might be an immobiliser issue or that "S" relay isn't getting its turnon signal from the key switch.

BTW I spoke with another early 456 GT owner and he's pretty sure his car doesn't have an inertia switch. (Told him where it was on our 550's and later 456M's and he reported it's not there on his car.)

 

Stick a long screw driver against you ear and against the injector. If it goes click, click,click when the motor is being cranked The injectors are working.

Crack a fuel line just a bit and have someone crank the motor for just a second. If fuel spurts out you have fuel.


Put a timing light on a spark plug wire and see if it gets a signal.

 

Hi all. I know this is an old thread, but was there ever a resolution? I am going through the exact same situation. No Injector or ignition coil pulse.