Weird SDL issue tonight on a 95 2.7... Any ideas?

Could be one of many serious things, of course, but simplest to check and most likely cause end up being one and the same: Cat ECU might be bad.

There are many posts on here about troubleshooting this, but what's worked for me is to start by swapping the two ECUs (L & R) and see whether the error (if it happens ever again) "jumps" to the other bank magically. If so, you have a faulty (worn out / heat cycled) Cat ECU.

Hope that helps. I'm no mechanic but this is one issue I've read my share on so hope I send you down the right path.

 

(btw - for completeness, the "no power" mode is a limp home mode where the bank that the cat ECU thinks is bad shuts off, so you run on 4 cyl. feels terrible and sounds terrible).

 

Had exact same thing on my 95 . Was cat ecu. Just disconnect from the harness and see if it goes away.

 

I had similar symptoms. thermocoupler was bad.

But don't guess, it's easy enough to pull the ECU codes from the car.

 

Had the same thing recently. Turned out to be the cat ECU, which is a common failure on these cars. There has been a lot written about this topic and how to troubleshoot cat ECU vs. thermocouple failure vs. something more serious. Take a look at the potting material on your cat ECUs. The newer units have green potting where the old units have black potting. If either of yours are the older black units, you're probably on borrowed time. Eurospares has OEM cat ECUs and TCs in stock fairly cheap due to the current favorable exchange rate since Brexit. Good luck.

 

Brian summarized this perfectly. And, plenty of threads on this topic - you probably don't even need to search - just look down the page

 

Remove the side covers in your engine bay. Shine a flashlight under your main ECUs and look for a small rectangular box under each main ECU that has two connections in to it. That is your cat ECU on each side. One connection goes to the main ECU just above it; the other connection goes to the thermocouple for that bank of the engine. There are two threaded studs that go through each cat ECU with a nut to hold the part in place. Before removing anything, you can shine a light in there and look for black or olive green potting on the face of the ECU that you'll be looking at. Green means it's been replaced already; black means it's original or been replaced a long time ago. My 5-8 bank was green with a date code a couple years old. My 1-4 bank was black with a 1995 date code. My issue started like yours-Only happened once then fine for a couple weeks. Then it started happening again and again. Please read all the other threads about troubleshooting this properly as you don't want to just swap parts. Mine is a 95 2.7 like yours, and it's easier to troubleshoot than the 5.2 cars beacause we have two main ECUs and therefore two slow down lights. if this is happening when the cats aren't hot enough to legitimately throw the SDL, chances are it's either the cat ECU or TC for that side/bank. If it's happening after the car and cat are thoroughly warmed up especially after some spirited driving, the problem could me much more serious meaning thorough and methodical troubleshooting is warranted.

 

This sound like it could be more than a cat TCU/TC problem. One thing, if there is raw fuel getting into the cat it only take second for things to get hot. You're not talking about exhaust temp, you are talking about flame temp of fuel burning in the cats. Things go bad fast.

 

Loss of ignition on a couple of cylinders. You said tone changed, then flashing SDL and loss of power. Flashing SDL won't cut off fuel so loss of power could be a result of loss on ignition and un-burnt mixture in cat. Not saying this it the problem, but I had the same symptoms a couple of weeks ago, right down to coming back to full power and SLD going off. Drove home 50 miles with no additional problem. Turned out to be an intermittent failure of the 1-4 bank coil pack. Took several starts over several days to get the failure again and diagnose lack of spark. Again, I'm not suggesting this is your problem, but symptoms are similar. Coil packs are cheap and commonly available. Google search Bosch 0221503407

 

I also had the same as John but the 5-8 bank, faulty ignition. It was pretty obvious with the smell of fuel on mine.
Mine turned out, after I bought a coil pack, to be the ignition wire comming from the main ecu which tells the coil to fire.

 

http://www.ferrarichat.com/forum/144820960-post4.html

 

Just unplug the cat ecu. You don't have to remove it from the rear of the computer. One on each side. See if the problem goes away. I had the exact problem onmy 95. It would happen out of the blue sometimes while driving other times after just starting the car so you know the cats can't be overheating. Notorious for failing it really is a stupid system. Simple fix. Do it before you foul plugs.

 

The SD system won't necessarily throw a code. If you don't have a solid CEL, you may not have any stored codes. OBDII has pending codes, I don't believe OBDI does.

As a test, you can try that but if you do have cats, I would not recommend removing the SDL system or disabling it. Find the problem and fix it. Also, I think you will get a SDL at start up if you unplug as a min voltage is not seen (perhaps that's only 5.2)

FWIW, in the garage now and just replaced a black potted TCU with new green from Eurospares.

 

You can unplug on the 95. I've run mine unplugged for 10000mi and car has not had one problem. I am not saying you should run unplugged for anything more than a test, but for me these ecu and thermocouples are such a problem I prefer to go without the system. I don't think Ferrari had much confidence either in their cats or management system so had to build in a safety system.

 

Do you have cats or only test pipes? Do you get SDL's at start up?

 

Get yourself a DVOM and tap the outputs or back probe the connectors and find out what is really going on with the SDECUs without guessing.

The SDECUs serve a purpose in our cars. You really want the system working properly. An overheated cat or exhaust can be dangerous and thus the reason Ferrari built them into out card.

The diagnosis is easy with the correct methodology. Get the proper tools and is be happy to guide you through it.

 

I've got Hyperflow cats and no SDL. When these things go bad on the road, it is downright dangerous. Mine started acting up at 70 mph on a crowded interstate highway. The car just went dead. It would not rev ,lost power, almost got rear ended by a semi when my car suddenly slowed down to a crawl. Could not muster enough power to get to the side of the road. After a few minutes of coasting in the middle lane of the highway, power came back on and could drive home. I thought it was fuel pump relay or the pump or coils. This would happen off and on for a few years. Sometimes going away for 2-3000 miles then comeback again. It was only after I disconnected the ecu that the problem went away. I will never connect them again. I think the spark on these cars are weak and if you foul a plug you loose a two cylinders, raw fuel gets into cat and they overheat. I have programmable computers so I run good fuel mixtures. These 95s run rich and that is why they run a different plug then other years. I've had my car for 16 years and 60000 miles soI feel I can tell if car is running right by seat of the pants.

 

Bob, you always recommend tapping outputs - please explain how this will tell you if you have a bad TCU verse thermocouple. Are you tapping the thermocouple separate from the TCU? And if you are, on a 2.7 it would mean 4 taps, a 5.2 6 taps.

I just don't understand the advantage of this compared to some component swapping.

 

You tap or back probe the output of the SDECU. This is where the motronics gets its information from that triggers the SDL.

By doing this you know immediately if you have found the problem and where it is originating from and if you have fixed it correctly.