Slowdown, et al.

???? According to my WSM you have them backwards, unless the 2.7 for the 348 is different than for the f355.

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See post #16

 

Interesting. This is from the 2.7 348 WSM:
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It is possible that, for the 2.7 355, the code assignments are different. On my 2.7 348, when I disconnected the Exhaust ECUs, I straight away got ("silent") codes 4121.

 

Yes, I think we have a typo in one of the one of manuals. 348 and F355 codes side by side. They are all the same but 4121 and 4122????

Anyway, the OP said he was getting a flashing SDL, so I would assume the cat ECUs are connected. But what is causing the CEL to flash? I know that when I first got my 355 the CEL would occasionally flash but there was never a code. Replacing the O2 sensor for that side corrected it. My theory (LOL) is that STFT went to max when I hit the throttle and the cel would flash, then STFT would drop back into the normal range and it would go out, but that's just a theory.

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I think so but tha

 

Just a thought, but I had a similar issue (SDL, CEL, cut power) etc.
I initially thought water in the cat ECU's.
Turned out to be a (very) dirty crank angle sensor.

 

Both could be correct. It is possible that the 355 uses a different code number for "Cat Temp Too High" because it has a different high temp signal going to the engine ECU than what the 348 has. At too high Cat Temp:

348: The Exhaust ECU switches on +12V to pin 52 of the engine ECU.

355: The Exhaust ECU sends about 3.9 V to the engine ECU. I do not know to which Pin, Ian? (3.9 V is the 100 times amplified Thermocouple voltage of 39 mV which it produces at 940C/1720F critical point of the EGT).

 

Ian's diagrams show cat ecu connected to pins 11 and 44. I guess I could disconnect one of the cat ECUs on my car and see what code it throws. Don't know if I want to do that.

 

I had completely forgotten that the F355 2.7 and 5.2 cat ECUs have different wiring. The F355 2.7 seems to have two power wires on the 4-pin plug going to the ECU. Orange and Pink/Black are the power wires, Black the earth and Violet/White the temperature signal.

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The right bank has a green power wire on pin 1 (A).

The 5.2 only uses 3 wires.

 

I notice that, on 2.7 355, pin "D" of the Cat ECU goes to pin 12 of the LEFT engine ECU and to pin 11 of the RIGHT engine ECU (diagram below). The engine ECU pin 12 supplies power to the TPS which is probably 5V. The question is whether pin "D" of the Cat ECU should go to pin 11, or to pin 12, on both engine ECUs ? Pin 11 is not used in the case of 2.7 348 and a general Motronic 2.7 ECU pinout that I have shows that pin 11 is for "Signal, Knock Sensor".

A Cat ECU getting 5V on its pin "D" does not make much sense to me as the Cat ECUs are powered by 12V on their pins "A".

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Pin 12 is also used on the RH ECU. If you look really closely, you will see a faint angled dash to pin 12...

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That still doesn't explain why the TCU gets 2 power sources.

 

I see this post says there is no "trace" on pin 4 (D) of the Thermocouple ECU on the 2.7

https://www.ferrarichat.com/forum/posts/145063021/

Does no trace exclude no voltage? @wbt

 

Yes, I remember that post. Wayne said about pin 4 (pin D) "as far as I can trace with a scope" where "trace" actually means "test" with a scope. His conclusion that this pin is unused (in normal operation) means that he could not detect anything on the pin D link to the engine ECU, even with a scope which is many times more sensitive than a digital multimeter. This is a bit of a mystery and suggests that the Cat ECU pin D may actually be connected to pin 11 of both engine ECUs; if connected to pin 12, the scope would have detected +5V there.

 

We just need a volunteer to pull their car to pieces.

 

Actually, I found this. LH ECU 2.7... Nothing on pin 11

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Are there two wires squeezed into one hole? One looks green/yellow, not pink/black for both.

 

This is the right side for the 2.7 that I have from Ian. Pin A goes to a splice that say "power from steering column in run" (12V). B goes to ground, C goes to pin 44, D to pin11. Pin 12 is power for the TPS (5V?).

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On the LHS diagraM, A = power (12v), B = earth, C=44, D = 12(?). But the TPS also goes to pin 12 for power. Doesn't make sense for both A (12V) and D (5V?) TO be connected to the cat ECU.

Anyway, this thread is completely hijacked at this point. I'm sticking with an ignition problem as the initial cause.

 

Looks like an old diagram... I think I made some amendments after seeing the photo above a few months ago.

RH
https://www.dropbox.com/t/gsAsyzVj5fbFS1Uv

LH
https://www.dropbox.com/t/wYBoovwhhEupdyEo

 

Yes, from 2021. Thanks for posting the updates. But why are the cat ECUs connected to both the ignition and the engine ECU for power? Ignition is 12V, ECU 5V(?).

 

The thread is not really hijacked but we just branched a bit to the 355 because you brought in the 355 fault code table (which is not applicable in the case of the Lucas's 348). Anyhow, we should not eliminate faulty Cat ECU(s) until Lucas lets us know whether his Cat ECUs have been disconnected or, if the Cat ECUs are connected, lets us know what happens if he disconnects them.

Considering the presence of code 4121 (both sides) I would not ignore the Cat ECUs but perform the checks I mentioned above as they would easily eliminate (or confirm) problem with the Cat ECUs before digging into something else. And it is a very well known fact that these 348 Cat ECUs fail regularly.

 

I hear you, but in the OP's first post he states that the first thing the car does change tone and is lose power. The SDL is secondary. When I questioned him about this he reaffirmed that the SDL and CEL don't come on until after loss of power. I had a similar experience in my 355. Turned out to be an ignition problem, intermittent coil failure. I don't know how a coil fails intermittently, but replacing the coil fixed the problem permanently. Put the old cat ECU back and it's been fine for years now.

In any case it's odd that 4121 comes on for both sides. And if that does mean the cat ECUs are disconnected, wouldn't the SDL be on all the time, and how would it effect the engine intermittently? Makes me wonder if one or both of those codes are old. I would clear all the codes and see what happens.

Like I said, I'd get one of the pen spark testers like I posted in post 9 and as soon as the car started doing this I'd stop and check the spark to each cylinder. Then either way, that's a done deal, fix it or move on.

 

Classic Coach just finished an extensive restoration of you car. Let them diagnose the fault you're getting and rectify it. Rocco will help you in this matter.

 

If a Cat ECU is disconnected, it will cause code 4121 but the SDL will not be lit because, on the 348, it is the Cat ECU that lights the SDL, not the engine ECU or anything else.

I earlier asked Lucas to check whether his Cat ECUs are maybe disconnected but I just realised that my question was not relevant taking into account that he gets the SDL (not sure if he said one or both).

Lucas, do both of your SDLs light-up for some 2-3 sec. at ignition switched to "on"?

 

Going a bit into the memory banks here, but I did not measure any signal or 12/5v level or otherwise on that pin. Didn't seem to be tied to ground either. I can't recall if I tested on the right or left side. My assumption from this test was it was designed into the wiring loom early then they took a different software route in the motronic during development. Later cars have nothing connected to that pin.

 

Going back to this, since it's only on 1-4 I still think that the codes may be old and should be erased and then see if they come back. But it still sounds like an ignition problem that results in raw fuel in the cat of bank #1. It's just very similar to my experience with my 355. In my case the one high flow cat was actually damaged a little before I could pull over. Yet I do not recall every getting any code related to high temps or otherwise. After a couple of stops to let things cool down I was able to drive home, about 40 miles, with no further incidences that day, no misfiring. When I started the car the next morning it immediately started missing and that's when I found the lose of spark.

Anyway, the OP hasn't check in since Sunday so maybe he found the problem.

 

Follow up- my mechanic happened to be in town (shout out to Scott at Rosso) and he pulled the plugs. Drivers side dry, passengers side wet. We’re going to replace the coils, plugs, and leads and also test the fuel pressure when it’s in his shop next week.