A couple issues with my new-to-me F355

I was just having a little fun with you Ian. My point is simply that when you turn on the ignition and the relay closes, their is 12V applied to all the injectors. And if you measure the voltage at either terminal of the injector, both terminals will be at 12V. Thus, there is no potential difference across the injector, no current, and no power. Only when on terminal of the injector is grounded will electrons flow creating a current, thus power. Thus, if the ECU does not ground the injectors for one bank it would be cutting off power. So the wording in the manual is correct. Miro's word salad is irrelevant.

(Hadn't read your 2nd response.)

 

It would seem to be highly suspect that the system would be designed to shut down spark and not fuel. You would still be dumping raw fuel into an over heated cat which would ignite and make the situation worse. Additionally, doing so would result in cylinder wash which could result in scored cylinders and destroy the engine. And for what it's worth, 2.7s crack headers as well.

 

That’s the whole point of the SDL s on both motonic systems with the post CAT thermometer/ sensor . It’s not designed as such to work as you say ^ .
It’s when there’s a fault ( from what ever Eg a dodgy HT lead , plug or ignition coil ) that initially leads to poor or zero spark , more unburnt fuel getting through to the headers and later the CATs .

Idea is the temp increase is detected by the CAT ECUs .

It’s the execution that differs between the 2.7/5.2

Assuming it’s fully functioning in both banks the 2.7 via the fuel relay ( because there are two opposed to one ) can receive a signal from the main engine ECU s which there are two , one for each bank and shuts it down the affected bank .

With the 5.2 there’s only one ECU , one fuel relay ( I think L happy to stand corrected ) running the show so it doesn’t default to bank shut down otherwise it’s a show stopper .

Instead like the 2.7 theSDL flutters as the temp rises , then permanently stays on .Idea is the driver obeys the manual and stops and flat beds it to a service centre.
In reality some remove the bulbs , other owners remove the CAT ECU sensors and retro fit that voltage signal sender to fool the engine ECU that the exhaust ECU is detecting the correct parameters from its post cat the Technistrada gadet in post #7 ^ .
Some remove the CAT s all together , others do a mix and match retro fitting the exhaust ECU gear to test pipes with different thermocouples etc etc .

The whole Ferrari post CAT thermocouple measurement is a legacy of the F40 development, the turbo 2.85 V8 traversale which was developed alongside the 348 and Mondial T which is a detuned version of the same arrangement . Transversale , the T in Mondial and t in 348 world meaning the transverse driveshaft arrangement, not the engine or gearbox .

As said any overheat of the working , stress working functioning 2.7 leads to a bank shutdown if there’s overfuelling from faulty spark .
5.2 came along with increasing emissions regulations for and the advent of OB11 diagnostics .
Ferrari dispensed with separate bank management went from twin MAF sensors , one for each bank on the 2.7 s to a single unit for both banks on the 5.2 , so if there a issues with the MAF ( separate issue to loosing spark ) it’s can’t shut down the affected bank because it can’t tell being a single unit which bank is the bogey .So there are scenarios where by over enriching occurs and the thing keeps running haemorrhaging fuel into the 355 headers . But if it was a 2.7 it would be bank shut down .

Hence in certain situations with the 355 5.2 s you get over enrichment and the CAT ECU s if fully functional suppose to pick this up and the driver who supposed to have read the manual supposed to pull up when the SDL illuminates for more than [ insert time ] seconds .

As said chronic over enrichment / over fuelling = cracked headers and hot glowing cats with internal fires.

In theory with a F40 with CAT s and 348 running motronic 2.7. with a fully functioning system to headers are spared the overheat bcz the bank shuts down .

2.7 s have SDL s which flutter and stay on with the bank shut down ….it’s like driving 1/2 power no surprise there !

The first 355 s circa 95/ 96 we’re 2,7 s.

 

*For both systems it’s common for components to go bad .
Water ingress of the CAT ECU s getting under the potting compound , faulty connections ( corrosion) , duff thermocouple(s) .Even failed dash bulbs ….that’s why they flash up momentarily at start up .

Hence the suggestion to buy a $10 IR thermometer. When not “if “ the SDL illuminates check yourself the CAT temp s .

Which is why folks on here are asking to op to check first with his SDL saga .

 

Pay attention.

Let's assume for the sake of discussion that one side of a coil on one bank fails, say bank 1 The result would be loss of spark on two cylinder since this is s wasted spark ignition. Thus raw fuel/air mixture from the two fail cylinders enters the cat where it ignites, over heating the cat and setting off the SDL. To prevent further damage we agree that on a 2.7 car fuel is cut off to bank 1. This prevent additional fuel.air mixture from entering the cat. Thus, the cat will /should cool down.

Now, you stated that on a 5.2 can not shut off fuel to one bank, but rather that it cuts off spark:

If that were the case there would now be 4 cylinders dumping unburnt fuel/air mixture into an already over heated cat, making the situation worse and possibly causing severe damage or fire.

If fact, in a 5.2 car, like a 2.7 car, it is still the fuel that is cut off as clearly stated in the owner's manual for a 5.2 car, as shown b fromelow the manual from a 98 model year car.

Image Unavailable, Please Login The manual goes on to say you should stop immediately.


Headers failing is a separate issue and is due to inadequate design and heat cycling, and is common on all model year cars

 

Badly worded on my initial posts later clarified.Meant if spark was to be inadequate and the injector still squirting fuel leading to u burnt fuel passing through. I did clarify this and apologies if you didn’t see this .

The single MAF means if there’s a fault with that the 5.2 can’t differentiate which bank is @ fault if there’s a MAF issue leading to overfueling .
It can’t shut a bank individually and my tech told me they crack manifolds (ALL end up with aftermarket) and set fire to OEM cats .
It’s reluctant to shut the whole engine down , as that’ entering potential accident law suit territory = safety . If your link to the drivers owner manual is correct already called out as ambiguous ^, then by the time it does kill the injectors it’s far too late .

The 2.7 is the other way a bit trigger happy with the cylinder bank shutting down, the exhaust ECU sends a signal to pin 52 on the engine management unit …..this triggers that bank only shutdown hence the ultra rare header cracking .You can still proceed on one bank it’s not a show stopper .

That’s not to say 348 s + F 40 s Mondial T s and early 2.7 355s can’t crack headers if the system has been unplugged / removed .A common hack to nuisance intermittent SDL s .

Unplugging the 5.2 without the techno Starda voltage signal results in permanent warning lights illuminated .

There is a difference between the way the 2.7 and 5.2 deal with shut downs and the 5,2 s is more risky by a country mile hence all the headers cracking , decat threads, and SDL threads on here .

Headers crack on 5.2 s because of a basically the driver ignores the SDL and the effected bank isn’t shut down until it’s too late .Any shut down of the whole engine is too late . That’s the crucial difference.
Or the exhaust ECU system has been disabled during the modding ,with aftermarket headers and de CAT ing maybe dash lights bulbs removed as well , or any combination of hacks away from OEM .

How many 5.2 are still running OEM headers ?
Compare that to 2.7 s ? .

Tech told me OEM internal CAT fires are common on 5.2 s for the reasons hopefully explained.

Anyhow I suspect the OP reading all this is motivated to investigate and fix his intermittent SDL s , his new to him 5,2 car .
So we both are helping him .

 

Since a certain assembly number, 2.7 355’s only have one fuel relay, so again, I don’t think bank shut down is achieved via relays.

You keep saying that the 5.2 is different in the way it handles SD’s, but I can’t see how it can be for the reasons I’ve given. On both the 2.7 and 5.2, you can’t use the existing relays to shut down a bank. Only the left ECU on a later model 2.7 controls the single fuel pump relay. On 2.7’s and 5.2’s, you will lose your SD and CEL warnings if you shut down the injector relay. The wiring diagrams show this. If you see a flashing SDL, then it stops flashing and the bank shuts down via an injector relay with no SDL how would you know to stop driving?
Bank shut down must be done via direct injector control.

The text of the 5.2 WSM manual tells you to stop driving if you get a steady SLOW DOWN light, so clearly the 5.2 can shut down one bank despite only despite having one ECU, one fuel relay and one injector relay.

Either your highly experienced tech is wrong or you’ve misunderstood him. My highly experienced Ferrari-trained tech is sometimes wrong or has gaps in his knowledge.

 

We will have to park this here . Iam only telegraphing some of the technical difference between the 2.7 / 5.2 he told me that he thinks leads to excess 5.2 header cracking and CAT fires .

He’s doesn’t see this with 2.7 s .
40 yrs F car Marenello trained etc etc .

But I do concede there’s a chance how ever remote I miss understood.

Edit EU / U.K. spec vehicles . Maybe US ( predominately on here ) are subtly different??

 

I don't see how having one MAF is relevant to shutting down the bank. There are two temp sensors and cat ecu's (one for each side) so the ecu will know which side is having the issue and the ECU controls each injector (via ground trigger), so will be able to shut down the injectors on that bank. The MAF has nothing to do with it. The only benefit the early 2.7 would have is it could also shut down the fuel pump on the offending side, which would be beneficial in the case of a leaky injector I guess, but that's about it.

 

I think Portofino is saying that if a 5.2 (single) MAF issue led to overfuelling on both banks resulting in overheating on both sides and there were legal requirements not to shut down both banks, the 5.2 couldn't be designed to do this. Having said that, minor differences in temperature sensing and other quantum effects would probably lead to one bank being shut down first, after which, it would be hard to get the engine to higher rpms making it less likely that the second bank would reach the shutdown point. Or maybe there is logic in the 5.2 which only allows the first bank to be shut down.

 

2,300-to-3,000 is the hardest RPM band for the ECU(s) to keep the mixture in the 'zone' and avoid SDLs.
4,000-to-8,500 is significantly easier by comparison.

Also note: The thermal control unit can go bad and randomly throw SDLs when there is not enough wrong to matter.
I have replaced several of these, but there is an analogue solution if you search.

 

I'm assuming here that overfuelling results in overheating. Wouldn't overfuelling trigger the O2 sensors to tell the ECU to reduce fuel flow to both banks?

 

We replaced a ****load of 2.7 manifolds. They were worse than 5.2s until they improved them.

 

Ignition is not cut. Fuel is .

 

There is nothing in the design of the car that allows that. If its losing ignotion it was not shut down, it was malfunctioning.

It would be lunacy in a modern car to shut off ignition and not fuel.

 

Not to mention the fuel blowing up the muffler and the EPA that would never allow it. Just not done.

 

Another fantasy. There was never any such thing.

 

Hes an idiot.

 

You have missed the boat here by miles. You have no idea. Sorry, despite your best effort you are helping no one. What you have done is spread a great deal of misinformation on a very well understood situation.

 

Wow. Someone actually read the book. How dare you speak truth.

 

Well, with a single MAF, if the MAF is at fault both banks will be affected equally. I wouldn't be a single bank problem. Additionally, if there is an MAF problem, both 2.7 and 5.2 have defaults programed into the ECU. These allow you to drive, but typically the car will not have much power, poor throttle response and wanting to stall at idle. If the system is working correctly and the MAF is trying to over fuel, the O2 sensors will take over and lean out the mixture. It won't (should not) generate an SDL.

Over fueling (rich running) is a very different issue than no spark. Over fueling with spark results in too little O2 in the exhaust. The pre cat O2 sensors will pick that up and lean out the mixture and there should not be and SDL generated. Also note that each bank as it's own O2 sensor thus the ECU can adjust the fuel supply to each bank independently whether it's a 2.7 or 5.2.

On the other hand, a no spark issue will result in unburnt air/fuel mixture in the exhaust. As a result, the O2 sensor will see too much O2 in the exhaust, think it's too lean, and actually add more fuel making the condition worse, potentially generating more heat in the exhaust/cats and turn on the SDL and the ECU will know which bank is at fault since both 2.7 and 5.2 have TCs for each bank after the cats. Both will know which bank to cut fuel from in the SDL case.

The point is that both 2.7 and 5.2 cars monitor both exhaust O2 levels and exhaust temperature for each bank and that everything is in one box (ECU) for a 5.2 car does not mean it doesn't know what bank is having a problem if the problem affects only one bank.

I also would disagree that 2.7 don't have header failures. Mine failed at about 30k miles. Contrary to what you are saying, it's been stated (don't know if it's true) that header failure is often due to the break up of the ceramic cats, restricting the exhaust, on early cars. Later cars are said to have metalic core cats and less prone to exhaust blockage and header over heating from blocked exhaust. Where the truth is on header failure I don't know, but they seem to fail frequently on both 2.7 and 5.2 cars.

 

Keeping in mind that the leaning has a limit (10% fuel flow?) and if this is exceeded, the CEL illuminates.

 

What I know form experience with my 2.7 car is that if the MAF goes wacko you get a CEL with MAF code and the ECU at some point goes into some type of default mode that allows you to drive but with the issues I stated: loss of power, poor throttle response, will tend to stall at idle. But no SDL.

 

@Portofino I have a 5.2 which has absolutely cut a bank when a faulty cat ECU erroneously indicated an overheating cat.

 

Also @Portofino The cat temp monitoring system is nothing to do with the MAF(s). Each cat has a thermocouple and cat ECU and the Motronic is able to identify which cat is overheating as it reads two separate inputs for cat temps. Single or dual MAF doesn't matter, both monitor each cat individually. On a 5.2, unplugging the cat ECU does indeed give a warning light, but it also prevents bank shutdown. You can even do this as a short term workaround for a failing cat ECU if you are sure that the warning light is erroneous.