348 running on one bank

one of the possibles is a bad MAF or the connector going to them, you may want to swap them over

 

Fuel pump gone bad.

 

Place your hand near your exhaust headers, you will feel the heat differance between the bank that is not running and the bank that is. Might even notice a little different exhaust note too but its pretty well balanced in the mufflers so i'd stick with the temperature test

 

The difference between running fine when cold but not when hot (with no warning lights) is usually the cold start circuitry (extra air valve, ignoring the MAFs, ignoring the O2 sensors, etc.).

That's usually the difference, but not always. Could be a fuel pressure issue (e.g. dying fuel pump, clogged fuel filter, bad fuel injector, etc.) or a dying alternator/battery, etc.

So you're going to have to dig a bit to narrow down the problem. First, do you see both "SLOW DOWN" lights illuminated when the dash lights do their self-test right at start-up? You need to insure that one of those bulbs isn't out.

Second, what is your resistance between the outermost male pins (#1 and #6) on the two MAF cables?

The screwdriver in the picture below is turning the MAF screw. To the right of the screwdriver is the black MAF cable. With the engine OFF, remove that cable and put an ohmeter to the far left and far right male pins. Note the resistance value for both MAFs (one on each side of the engine).
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Your not getting any lights on, CELs or slow downs,? are they working when you turn on the ignition?(not starting or running). Even if you are not getting lights on you might check the codes in the ECUs to what if any errors are stored. If all of that is ok I might check the fuel presure too as husker is saying. If its anything to do with the ECUs the lights should come on since its running that poorly. Regards, Vern

 

Doesn't matter, just make sure that the engine is OFF!

 

That bit of info is helpful, you disconnected the thermo probes but not the ECUs that the probes connect to correct? Try disconnecting the over temp probe ECU on the offending bank. I would guess its the temp ECU that causing the problem. Regards, Vern

 

Those are great resistance numbers.

If you already know which bank is not running, then I'd suggest moving the MAFs; swapping the left side MAF with the right side, (with careful attention to direction of airflow).

In this manner you could test to see if the non-running engine bank switches sides when hot again...potentially indicating a bad MAF on the side that doesn't have hot headers.

Also, based upon how you described the "SLOW DOWN" lights, I would not suggest swapping sides with the exhaust ecus. Nor would I recommend disconnecting or spoofing them. Your description seems to rule them out.

 

It's common for failing ignition parts to stop working when warm. Check the coil and ignition module by swapping sides to see if the failure changes sides as well. Start with the ignition module (right by the coil).

 

When was the last time your fuel filters were changed? If they haven't been changed in a while you may want to do that.

 

I had the same problem and after few minutes of driving one bank slow down, and also after the 40 000 Km maintenance where every thinks were checked and prior the mechanic was informed about this trouble.
I tested on my laboratory both thermocouples and ECU
The K thermocouple where calibrated and they are ok
a) If the thermocouples are disconected no light
b) The cat ECU are operating as following: between 0 to 940 C nothing
between 940 to 960 C the light to flicker ;between 960 to 980 C the light in continuous on and at 980 C the bank is shut down.

All the test where oK but the problem was still there. Because I was sure that it not due to the over heating because no light, no flicker light , I drove disconecting one untill I found which side was going wrong.
To verify if it was the line or the ECU I swapped the ECU ( very easy using tool 7 mm) and the problem change of side.

After I performed Xray on the ECU and I found that one welding was not good during to manufacturing and I suppose during driving with the vibration gives false information (send 12 volts to the 2.7 ECU)

I changed for 300 euros and the problem is closed

 

Marc, that's good to know because without your firsthand experience I would have ruled out the cat ecus due to the exhaust ecu schematic showing the *same* wire going to each SLOW DOWN light as to the Motronic 2.7 A/F ecu.

Now I'm wondering if I misread the schematic or if it is a misprint.

Because if you read the schematic like that, a bank would only be deliberately shut down by the A/F ecu if the exhaust ecu also lit the SLOW DOWN light. Sounds like that's not the real case, though.

 

Now don't take this the wrong way but Geez ND how many times do you have to have this explained to you about how the temp probes and the related ECUs work and how they relate to malfunctioning and shutting down cylinder banks when there is nothing wrong, ie; over heating cat. This is probably the no. 1 gremlin on the 348 and 355s. Do a search on the topic its been discussed a million times and you have been involved with most of them. This is probably what is wrong with mab 53's car, the ECUs not the probes and not the air flow meters.

 

Vern, you may be quite right on this one. If his SLOW DOWN light was lit, that's the direction that I would have gone, too.

Reading the exhaust ecu schematic, however, combined with no SLOW DOWN light, led me in a different direction this time. Perhaps the schematic was misprinted, or maybe I just read it wrong.

Can't win them all.

 

Where did you find the schematic?(just the one in wiring diagram in WSM). I wish there was a fix for those damn things everybody seems to have problems with them. I finally(after pulling my hair out) had just removed them from my 348 and watched engine functions close and never had another problem in 30,000 miles. Regards, Vern

 

Just the external schematic from the WSM, sorry. I don't have the exhaust ecu's internal schematic, however, it wouldn't be too difficult to design from scratch or to sketch the existing circuit with an ecu disassembled (isn't FBB doing this?).

I like the safety angle of having exhaust cat temp monitors...to me...just me, mind you...I'd rather disconnect the one fuel-shutoff pin at the A/F ECU rather than remove the whole SLOW DOWN warning circuit (i.e. keep the safety lights, remove the engine shutdown potential hassles).

 

Cat ECU's evidently with age on them are trash. The backside epoxy that was there to seal the unit seperates from the outside shell...moisture gets in & causes the $600+ part to code. I wish someone had a source to open them, fix & reseal. I tried to find & after several "nope" replies I gave up looking. If anyone knows who can service them lemme know. Disconnected the one side since light stayed on from the second the key was turned on (cold) I have 2 onboard halon nozzles in the engine compartment for protection

 

The reason I had not done that or worried much about it was in all the years of driving and working on cat equiped cars I have never had a cat meltdown. Also if the engine was running poorly, in most cases, you would have a CEL come on via one of the ECU sensors producing an out of perameter signal to tell you there is a problem ie; too lean of a mixture or timing being incorrect etc.
In all of the research I have done I can not find the reason why Ferrari uses the system(anyone know?), I mean I understand its perceived merits, did they have a problem at one time? Nobody else in the auto industry, that I'm aware of, uses it. How many times do you here about cats overheating, I know it happens but it is so rare and alot of those are caused by old cats that are plugged. If I didn't know better I would think it's a preplanned way for Ferrari to make money, like crap headers, cats and engine out belt services etc. I don't avocate pulling them out its just what I do since I feel comfortable with preventive maintanace that I do on my cars. regards, vern

 

The 348 engine is symmetrical, for one thing, with a limp-home mode that may have been a first at that time (though Caddy had a different approach to doing something similar with the Northstar).

If you are in the limp-home mode, you've got 4 cylinders running...and the exhaust ECU sensors will signal to shut down the fuel that would otherwise be going to the 4 non-running cylinders, yes?

Or say that you've got a failed spark plug wire, spark plug, or coil...fuel is being dumped into a hot Cat...seems like a good idea to me to have a temp monitor on said cat.

Now, with all of that said, my own personal preference would be an optional manual switch so that the driver could optionally decide to shut off fuel to 4 cylinders based upon an exhaust/cat temperature (or SLOW DOWN dummy light). The automatic fuel shutoff is bound to be the root of most complaints against this part of the safety system, so that's the part that I'd change if any.