456 GT RHS bank not working until hot

Did you try swapping injector relays to see if the issue changed to the other side? Clicking sounds don’t always mean the internal contacts are supplying power. I don’t have a wiring diagram for the CEL/SD lights, but on Ferraris of this era, the injector relays provide power to their respective CEL/SD lights and the respective L/R Motronic ECUs provide grounds for their lights when the key is turned on (after the ECUs run through a rapid self-test). I’m just puzzled why heat should affect this system though. I hope it’s not the circuit board in the relay panel that is heating up and making better contact. At least it will be easy to faultfind because you have a hard fault when the car is cold. I'm also puzzled why you have fuel pressure if it's an injector relay problem. Usually the injector relays provide power to the fuel pump relay coils. Are you checking fuel pressure when the car is cold?

Narrow band. I think the 360 was the first Ferrari to have wide band sensors.

The heater wiring should be relatively easy to check, although heaters on some Ferraris only operate when the fuel pump relay activates. It may be possible to jumper the pump relay, but pull the fuse for the fuel pump. That way, you may get O2 heater power with just the key turned on and no current drain from the pump running constantly. Heater wires on the O2 sensors are usually white (same colour)

I don't think the 2.7 has an inter-ECU link. The 5.2 does. The 5.2 does send coolant temperature and immobiliser unlock signals through an inter-ECU link. I do have a partial diagram for the LH bank on a 456GT 2.7 and it shows it has a coolant temperature sensor and no separate plug for inter-ECU wiring, so it's likely each bank has its own sensor.

 

Here's the diagram for the LH Bank... It's a work in progress.. Not sure of the inputs/outputs

https://www.dropbox.com/t/BJBcHjhw1A49kRg6

Understood, but the fuel pump relay coil gets its power from the injector relay on most cars with the Bosch 2.7 system. Then it's up to the ECU to provide a ground to the pump relay coil when the respective crank sensor senses engine (bank) rotation during cranking. Or does the 456 prime the fuel pump with just the key on?

OK, then there is probably nothing wrong with your injector relay or fuel pump relay. Not sure about your crank sensor until I know about the priming method on the 456 (non-M). If you jump power from the injector relay socket directly to the wiring, the pump may not activate if there is an internal wiring fault in the relay panel.

I have the feeling that bad O2 sensors or sensor heaters will just force the ECU into open loop mode, not kill a bank.

Anyway, check for power at the O2 heater fuse with the key on. If no volts, crank the engine. On the 456M, the fuel pump relay provides power to the respective O2 heater fuse (and the fuel pump fuse, of course) during cranking.

 

The relay panel internals should be fairly similar on the M and non-M 456.

Let me know if you need a wiring diagram.

 

Lots of data here, but all of it confusing...

I assume you mean an aftermarket immobiliser? Only the 5.2 has a factory immobiliser and it controls both ECUs and, as far as I know, the CEL/SD lights come on when you turn on the key irrespective of immobiliser status. Do you have factory black and red fobs?

I was starting to think you had an immobiliser issue, but why, if it only affects the RH bank, is the RH bank ok.

Not sure about the 2.7 car, but the 5.2 has a "one shot" priming circuit. It only works once when you turn on the key. Cycling the key or even the battery switch has no effect. Thereafter, the engine must be cranked (if not completely started) before the pump fires up again. Next time you turn on the key, it will prime again. The one shot system works irrespective of immobiliser status. The WSM for the 456 seems to be a little more vague when it comes to pump operation description.

The common is 12 volts power from the respective injector relay. Power should appear with the key on. The ECUs provide grounds to the coils (or coil powerpacks as applicable).

 

Interesting. I didn't realise.

By the way, are you in the USA?

I just saw this note for the CEL on a 5.2 456GT

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Of course, it's anyone's guess what the 2.7 does.

I'm trying to find out what's the easiest way to identify the 2.7 and 5.2. I see the coils have power packs on the 2.5. The ECU doesn't fire the coils directly. Of course, the 5.2 also has fobs.

I think I'm getting confused here. The topic title says the RH Bank isn't working, but...

So if the RH bank isn't working, then I would be leaning towards an immobiliser issue, given the behaviour of the dash lights on power up.

 

I know this happens on the 5.2 with the factory immobiliser. The Immobiliser ECU is wired to the RH ECU only. The RH ECU has to send a signal on CAN Bus to the LH ECU to wake up that. I have heard recently that someone else got their LH ECU to operate by disconnecting the RH ECU, but I can't remember which car it was. Anyway, the 456 2.7 doesn't seem to have a CAN Bus, but there are unidentified wires in the LH Bank wiring diagram.

Thanks for that. Recalibrating....

At least you have made some progress.

 

Thinking more on the immobiliser:

As you said both injector relays click, I would assume that the immobiliser cuts power downstream of the relays. Since the ECUs control their respective relays, I would also assume that battery and key power are not removed from the ECUs. The immobiliser might be intercepting the power from the LH Bank injector relay outside the relay panel. Assuming the layout of the relay panel is the same as the 456M's, I would be looking for an immobiliser relay on the wire coming from relay panel plug G pin 5 (or 4) or plug J pin 11 (or 10).

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Sorry the labelling is upside down. The top image is from the 456M which has a different relay panel orientation, the but same relay/fuse numbers.

The wiring may look more aftermarket than typical Ferrari.

 

The plug is shown in the only wiring diagram I have for that engine (same wire colours... black/blue and black). It is labelled as "connector for excluding idle control". Joining the plugs puts a ground on pin 42 of the ECU.

Since both of yours are disconnected, I assume joining the plug excludes idle control rather than enables it. Perhaps it is used when tuning the engine? (overriding the idle air controller).

 

That's what I was thinking. Do your idle air controllers make a distinctive noise with the key on? Perhaps they stop making noises if you hook up those plugs.

 

Disconnected.

So did you try connecting the test plugs to see if the vibration stopped? I probably wouldn't do it with the engine running in case it messes up your idle parameters/fuel mixtures.

 

@LP13 I don't mean to hijack this thread, but it's the most recent discussion of this type of issue.

I've got a 1994 456 GT with a lot of similar symptoms as of this afternoon: half the engine is running, no warning lights, no "cool down 1–6" type lights, the fuel system 'clicks' are clicking. The difference is that the 'off' side doesn't come on at temperature, and there's a strong smell of gasoline that the car doesn't normally have.

I feel ignorant, but between the owners manual and the forums, I've lost track of how "left-hand side" and "right-hand side" (much less cylinders 1–6 and 7–12) of the engine are referenced, but I have a left-hand drive car, and the passenger-side exhaust manifold is hot and the driver-side exhaust manifold is distressingly cool after driving. I realize that the details of which side isn't behaving isn't critical, but I figured I'd include it.

I'm in the US, but it's a European model with a kph speedometer. I'm honestly not sure if there was an immobilizer on very early 456s like mine, but if there was one, it's been deleted because the car has always been (to me), just a turn the key and go situation.

All that to say, just making sure: you sorted out* your issue by disconnecting the ECU from the "good" side, started the car successfully with only the "bad" side ECU present, then after reconnecting the "good" side, it's been working again?

*not wishing you (or me) bad luck, but I picked up your tone above of the hopeful but concerned aspect of how just unplugging it may have solved it. I had a similar issue (among many others) about a year ago, and did a much-needed, huge electrical system overhaul with a remanufactured fuseboard and all that, and it had been behaving impeccably in this area… until this afternoon.

For me, both today and when I had the issues a year ago before the fuseboard replacement, if the car has been off for a while (a few minutes), it seems like it starts on all cylinders, then after less than a minute, it shuts off half the engine. I can feel the "pep" of the full engine the first time I accelerate from a stop, but that's it.

I'm currently doing the ECU reset process here, but with "at least 30 minutes with the battery disconnected" being "overnight." This process had worked before in the past, prior to the large electrical work, but the half-engine issue would eventually come back. I'm not sure that process isn't effectively snakeoil, but it's something to try as I really think the issue is somewhere in the ECUs.

Like, I said, not meaning to hijack a thread, just trying to keep similar discussions consolidated for easier searching. Hope yours continues to behave!

cc: @Aerosurfer

 

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LHD car = driver on the left side of the car (although you wouldn't know it by asking AI). Right bank = cylinders 1~6. Left bank = cylinders 7~12.

These V12's are cross-flow engines, so the air intakes are on the opposite side to where combustion takes place. So if you were to squirt starter fluid in the right hand intake, you are feeding cyclinders 7~12 (left bank).

So the left hand side exhaust (7~12) is cool. The problem could be anything... coil pack, ignition power module, ECU, Motronic relay, fuel pump, crank sensor, etc.

First we have to know if your Check Engine Light/s and Slow Down Light/s are working. Do they come on with the key? Euro models may not have light bulbs fitted to these warning lights, so that makes fault-finding harder.

Anyway, you can always swap over components to see if the issue swaps sides. First check fuses

e.g. fuse 17 (Left Motronic ECU cyl. 7~12). Use a multimeter to check for continuity rather than checking it visually.

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Check left hand fuel pump fuse 19.
Try swapping fuel pump relays R (left side) & T (right side). Check that the relay socket pins are tight and the pins are free from corrosion.
Try swapping the Injector relays U (left side) and Q (right side).

Unfortunately, this is a slow process. If you are good with a multimeter, you can check voltages at relays and fuses and skip various steps. Note that, typically, fuel pump relays will only get power with the engine cranking/running.

Save this wiring diagram to your desktop PC or laptop for use later:

https://www.dropbox.com/t/0zkJJ2txmGnJXCDG