456 GT RHS bank not working until hot

Hi all, I have spent considerable time searching through the forum and i have found a heap of info on problems similar to mine and i have tried all things i came across but still no siccess in finding my fault.
some info.

I believe my 96 456 GT is fitted with the twin motronic 2.7.
Fuel pressure on both banks is 3.5 bar at idle and 4 bar without vacuum
Both banks have ignition and spark plugs are firing
Both injector relays are clicking
No engine check lights, no slow down lights
TPS resistance measurements are within spec
Swapped MAF left to right, no difference.
Unplugged CAT ecus and also swapped left to right, no change
Voltage from the CAT ecu to the motronic at engine start is 0.7V per side

Here is the scenario.
When the engine is cold, it fires up right away with no issues. Sometime just a little low on Idle RPM for 5 seconds but then it rights itself. The engine runs on the RHS bank only (1-6 cylinder). It will run fine however in what feels like a limp mode or low power mode. At this point, unplugging MAF, TPS or injector from the RHS bank makes no difference at all to the idle. Once the engine warms up over 190 Farenheit, the RHS bank starts to gurgle to life. Once the bank is fully up and running, then disconnecting MAF, TPS or injector has an immidiate effect on the idle speed. This somewhat tells me that the Right bank ECU is off or incapacitated in the warm up phase.

When the engine is cold and expericencing the issue, both the Injector relays have clicked on but RHS bank does not work. Pulling RHS bank injector relay makes no difference. Once engine is hot and RHS bank is running, pulling the injector relay has a drastic effect to the engine running. This tells me that power does get to the relay. I feel its the ECU that is not in the position to "operate" or somethign is telling it not to operate. Is there a signal i can test?

If i am driving the car when cold, it has low power and even on ful lthrottle the RPM rises slowly like a limp mode. Once the engine temps get closer to the 190, the power comes on during throttle application, it nails you to the seat but then cuts out, and it can do that right up untill it is hot enough and the power stays on. Once it is on, it is very good. Once power is on, I have noticed that holding say 2nd gear and slowly bringing the RPM to 7000 RPM that the power, sound and vibrations are very good however at some point between 5-6000 RPM the CEL would blink and the power would cut at the same time the RPM needle would show a slight drop when the power cuts.

Other than that, the car performs very well once hot.

I hope the above was not too long but i wanted to try and clearly protray the problem as experienced and what i have tried so far. Any help would be greatly appreciated!

Few questions i have

Is there a link between the ECUs?
What can tell an ECU not to run without putting on the CEL?
Is the ECU relay for the RHS ECU the same as the LHS ECU? or is there a relay each?
Is the coolant temperature sensor signal shared for the 2 ECU? or is there 2 sensors?
Could the 02 sensor be faulty? ie the internal heater is not working therefore not sending a signal untill hot?
Is the O2 sensor narrow band or wide band?

 

I will add that i am aware of the crossflow intake, ie, LHS throttle is for the RHS bank.

Also, i dont believe that the RHS bank injectors are firing. I believe they are off during the warm up phase. If they were firing, after the 10 minutes there would be a heap of fuel in the exhaust and you would be able to smell it very strongly.

 

Thanks for the great response.

The 456 has separate injector and fuel pump relays.

I did swap the injector relays didnt make a difference.
Fuel pressure and flow was seen when engine was cold.


Thanks for the info on the ECU link. This helps further diagnostic.

Might try swapping O2 sensors left to right.

Will also jump the injector relay output straight to the out wire on the relay panel. This way i can isolate the panel.

 

My 456 does not seem to prime fuel pumps with the key on ignition. Unless it does it one time, the very first time following a period of inactivity?

When i had the gauge on, the car had already been started a few times. So the pressure only came when the car started cranking.

I notice that the RHS ECU is goverened by the immobilizer. When you put the key on ignition, the CEL lights are supposed to be on. They are if the immobilizer is disarmed. If it is armed, then the RHS bank CEL is off and comes on as soon as immobiliser is disarmed. LHS bank is on regardless.

Also worth noting that as the RHS bank fires the spark plugs, and there are no CEL, then this means the ECU is on and operational. It might just be that there is something wrong with the power connection to the injectors. I notice that each injector wire goes to the ECU, and the other to a common. Is that a common ground or positive?

 

The immobilizer is a ferrari dealer or ferrari option immobilizer with the little electronic key to insert for disarm. No remotes.

I think the fuel priming etc is ok as the rail had pressure.. im going to look down the path of injector power to that bank. I hope to find a missing link there as it would make the most sense.

I will also inveatigate the immobilizer as it may cut injectors. Perhaps the RHS bank is not being restored properly. Might be a faulty relay on the immobilizer?

 

I corrected the title yesterday. Must not have saved! Its def the LHS (cylinder 7-12)

My car is a UK delivered mode, as far as i can guess, non european models are based off US specs. Hence my gauges in Fahrenheit. I think my car is likely a US spec car.

 

Interesting fact, i thought about it firing on the RHS bank and the left being off.
So i took that option away. I unplugged the RHS bank ECU and started the car.. it fired with the LHS bank from cold so it can operate!

I then plugged the RHS ECU back in and now they are both working from cold...

If there is a link between the two.. it could be possible that the RHS ECU was telling the Left not to operate? Will see if it tells it to not operate going forward...

 

Thats great! Thanks for advising on the pins to check! I guess as it is now working, i will need to test this when it stops working again!

 

Been testing 4-5 times a day for 2 days. Still working.

 

Does anyone know what this one pin connect is used for? It is part of the ECU loom and is very close to each ECU plug. One per ECU.
They are both disconnected on my 456.
Are they meant to be disconnected?

I know there is a similar one in the padsenger footwell, that if connected, it will run a test sequence for the operation of the rear active spoiler. Am i correct in assuming this is to be left disconnected?
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Interesting.. i did notice a drop in Idle RPM when this was connected.
Maybe to tune the throttles minimum open position?

 

Yes they sort of have a small vibration sound, and you can feel them Vibrate if you touch them.

I wonder if the rear spoiler one is supposed to stay connected or disconnected?