SDECU

If by skipping you mean a misfire then you may have a legitimate SDL. Does the "skipping" occur first and then the SDL comes on? If so it sound like you are getting raw fuel in a cat and that causes it to over heat with resulting SDL. A blinking SDL is not the cause of the skipping, but the result.

 

If you interchange the Left and Right SDECUs, does the SDL switch to the other bank?

If you have cats, you don't want to use a dummy SDECU, but if you just want to use one temporarily for faultfinding, you can get one from Technistrada for less than $100

https://technistrada.com/dummy-load-sdl-bypass---not-for-installation-into-vehicles-equipped-with-catalytic-converters

They also have cheap thermocouples and SDECUs

Or... you could stick a 1.5volt battery across the SDECU plug pins:

https://www.ferrarichat.com/forum/posts/148714133/

You're not going to do anything by disconnecting the SDECU.

If you get an SDL before the car has even warmed up, then it will probably be an SDECU or thermocouple issue.

 

To add to my post. If you unplugged the SDECU it would be expected that the SDL would come on solid as it would be a failure mode. That it kept skipping still sounds to me like a legitimate misfire problem.

Again, need more details. Does the skipping start before the SDL comes on?

 

If you totally lost a crank sensor, yes a cel. But intermittent, not necessarily.

I had a similar problem on my car years ago. Intermittent miss, and SDL. Turned out to be a bad coil pack and I was loosing to 2 cylinders. Still got hot enough to damage a metallic core cat.

I don't think you would smell fuel as it would be burnt up in the cats. I never smelled anything.

 

I can only tell you what the manual says, which you probably know. Flashing SDL is warning, no fuel cut off. Solid SDL is possible cat damage and fuel cut off.

I really don't know exactly what would happen if you just disconnect the SDECU. Never tried it.

In my case I never had a fuel cut off but with metal core cats it got hot enough to do damage.

 

I have the same issue and the Technistada bypass didn't worked for me but still, it's a cheap attempt so I'm not complaining.

My auto electrician is building me a couple of new ECU cats and he told me he fixed the problem to one of his customers with exactly the same issue / exhaust setup (dekat). He's based in Modena and worked for Ferrari back in the days (he was involved in the making of the F355 ) so I'm quite confident to fix this problem in a few weeks when my new ECUs arrive.

 

Can't say. I've always replaced both coil and module since they are both cheap and not worth the time to diagnosis which is the problem, particularly when the problem is intermittent.

But from everything you have stated the SDL appears to be legitimate and it appears the problem is ignition. Rule out plugs and high tension leads and it leaves coil, module, crank sensor, ECU or possible bad connection/broken wire.

 

1. Get yourself a laser thermometer that can read a high range of temperature
2. When the car starts throwing flashing SDL, pull over, get out and measure the cat converter temperatures. Compare left to right to see which one is high, or maybe both.
3. You cannot simply unplug the Thermal ECU. Its output goes to 5V and the car will shut down the one bank. It does not shut down one individual cylinder. It shuts down all four cylinders.

If you have a digital voltmeter, you can splice to the output of the T ECU and see if the voltage spikes up when there is a flashing light and if the voltage corresponds to the higher cat. This may involve permanently attaching wires to the module and leaving the wires someplace accessible.

If your SD ECU is of the black type, it's time to replace them.

 

355 crank sensor is Bosch #0261210126. Google search. They are cheap. But I would guess not the problem. https://www.amazon.com/stores/page/041B22D8-ACF5-45B2-9E39-A8295E2C766B/search?ingress=0&visitId=cb9a8413-8ee9-43b5-844e-2fc307ec450f&terms=0261210126

 

Just adding on. if the crank sensor was the problem you would lose an entire bank, not just have some skipping.

 

I just don't know. Problem is, as always, it's intermittent. It's like you need one of these, Image Unavailable, Please Login
so when you are driving around and it starts to skip you can stop and quickly test for spark on each cylinder, if if keeps skipping long enough.

 

WOW.... If this is the case, we probably have a thousand questions for him. For example:

Can the exhaust bypass cat ECU generate a SDL on a 5.2 car?
What is the logic for exhaust bypass system CELs (inside the Motronic ECU)? We've tried to simulate the exhaust bypass SDECU signal by simulating all possible SDECU output voltages, but we still get CELs.
Is the Motronic ECU comparing open and closed exhaust bypass temperatures or just one of these? Is the Motronic ECU logic using the exhaust bypass "open" command to know when to measure temperature? Does the logic compare main cat temperatures?
We don't know what all the 355 codes mean for the 5.2, especially relating to the exhaust bypass system.

If the Technistrada cheap solution didn't help you with your main (de-) cats, then playing around with SDECUs will not help. You either have a wiring issue between the SDECU and the Motronic ECU, a Motronic ECU issue or the issue is not with the main cats.

 

Hi John,

To be clear, I had 2 separate issues several years apart. The first was while driving I had a loss of power, off sounding exhaust and an immediate SDL. Having read about SDLECU failures here I figured that was what it was. (It turned out to be a legitimate SDL.) Since I was on a highway, before I could pull off to stop the (200 cell metal core) cat over heated enough to be slightly damaged (but I did not know that at the time). I let things cool down and continued on my way home stopping when the SLD would come on. After about 3 or 4 cool downs the engine come back to full power and I drove home w/o further incident. Seems a lot like your case. The next day I started looking for the problem and ultimately the car started running on less that 8 cylinders. That's when i tested spark and found no spark on 2 cylinder. I replaced the coil and ignition module and that fixed the problem. About a year later I had the same problem and replaced the same coil again under warranty. That ended that problem for good. There was no CEL involved. This situation seem most closely related to yours, but who knows.

The second problem was the breaking up at 4k. It seems unrelated to your problem. This happened while driving and anytime I hit 4k RPM in any gear it was like I hit a rev limiter. The (1-4) CEL would flash on and then off sometimes but there was never a SDL. I drove home keeping it under 4k. I check codes when I got home but found none. I started checking things, crank sensor resistance, wiring harness continuity between main ECU and crank sensor, replaced crank sensor,... Nothing seemed wrong and nothing fixed it. Then I took the car out and ran it up and down the street, breaking up, until the CEL came on. I immediately stopped and check the codes w/o shutting off the engine, and found the crank sensor code for (1-4). (As you know, on a 2.7 car you get the crank sensor code when the engine is off so it was important to let it keep running.) I when back and started checking the wires again and and by tugging on them I found the signal wire in the harness had broken internally right at the crimp in the connector as shown in the image below. The back part of the crimp goes over the insulation so it was holding the wire in place but by tugging on it, the insulation stretched indicating that the wire was broken inside. All I can figure is that under 4k there was contact but at 4k some resonant vibration cause the wire to make and break contact and the result was the rev limiter effect. Cut and crimp a new pin and all was good.


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Yes, the harness wires at the crank senor connector pins.