SDL/ECU's/Test Pipes...

I had similar problems with my 1990 348 ts. Disconnect the Cat ecu boxes (which are very problematic) and expensive. Disconnecting will not affect the engine running qualities and will likely solve your SDL issue. Cat ecu boxes are mounted on each sid of the rear shock towers.I believe new Cat ecu boxes are about $ 400 US each !

 

Agreed that replacing the converters with test pipes is probably the best option, mainly because converters drastically increase heat in the engine compartment, which leads to accelerated component failures and a higher risk of fire. They’re also rather restrictive, so you’ll see a definite increase in power.

What I would *not* do would be to disable the SDL setup while leaving the converters in place. The SDL system is there for a very good reason-- to prevent fires. Lots of Ferraris have burned over the years as a result of overheating converters.

There is a very good chance that your SDL woes stem from problematic thermocouples. I kept reading how the ECUs were the main problem but mine look to have been replaced and none of the potting is cracked. Fortunately, I saw a post by Drbob101 (I think that's his screen name) suggesting to someone else that thermocouples fail more often than people realize. Mine look fine and the car doesn't have many miles, but replacing one TC totally eliminated false SDLs on that bank. Still need to replace the other side, but I'm pretty sure the new TC will cure that bank's SDLs as well. So if you want to repair the system and assuming your exhaust "ECUs" look okay, I'd suggest pinging Drbob for some of his replacement TCs. He's very knowledgeable about the SDL system so check out his posts on the subject.

One more note-- there is a chance that there's something else wrong with your engine. The disparity in external converter temps suggests the possibility of an internal failure in one of the converters, or an injection problem on one bank (perhaps leading to an internal problem on that bank’s converter). Removing the converters will drastically reduce the risk of fire from an overheated exhaust, but it may also reduce the obvious symptoms of another problem. My suggestion would be to check your AFRs on both banks no matter what, just to make certain that you don't have a leaking injector or some other problem that will cause engine damage in the long term.

If it were my car I'd ditch the converters, but I'd sort out the SDL system and the engine management before doing so. That way I would know that the engine itself is safe and could then mothball all of the removed components with reasonably assurance that they could be reinstalled without issue if they were ever needed. In fact, that's *exactly* what I'm doing with my own car.

HTH.

 

Alternatively you could wire in the Aerospace Logic Catalytic Converter Instrument and ECU Controller (which is not cheap at $689) but is dead reliable, gives you a new gauge that allows you to not only see what the temps are but resolves the entire SDECU problem permanently.

Yes, I have one, I have used it, and it works great. No affiliation other than being a satisfied customer. Although I might be selling mine in the future when I finish with the install of the MS3-Pro as I will have individual runner EGT's. I might keep it though since it's an easy way to monitor each turbine inlet as well.

http://www.aerospacelogic.com/index.php?dispatch=products.view&product_id=220

Mark

 

I am pretty sure that they are no longer selling that product. FYI

 

It was listed on their website yesterday. Either way, I still have mine and it works well, so something similar or a used one is a good answer to the problem.

Sent from my SM-G920P using Tapatalk

 

If you contact them you'll find that they aren't available.

Cribbj posted something about that in the original thread concerning it.

There is a guy in the UK who has made a prototype, blue tooth enabled SDECU that can output the voltages to a phone app. Hopefully he will continue with that development and make it available.

 

If you have an issue with the TC or the sdecu that is triggering the SDL then that issue will also be there with test pipes. That's strictly an output voltage problem unrelated to cat temps.

If your issue is truly temp related then I don't know if the test pipes will change that.

 

If you remove the converters you can also remove the thermocouples & "ECU"s. They are only there to prevent damage from an overheating converter.

 

You can't remove them because there is a bias voltage in the output of 5v if you unplug them and it will throw sdl.

 

You need to have about 1.5v on the SDECU line to avoid the SDL lights. It's pretty simple to put a resistor in line to generate the correct voltage.

Mark

 

What are the error codes from the ECUs? Test pipes are a band aid for a symptom, you need to determine the cause.

Yes, you need to reconnect your sensors. The O2 sensors regulate your A/F in closed loop mode and the temp sensors are a safety mechanism to keep your car from overheating and potentially causing more damage.

 

Is that really the case with the 348? From what I've read here the 355 requires some trickery when eliminating the SDL circuit, but I believe the 348 is different and the "ECU"s can simply be disconnected or removed.

 

No, the SDECU circuit is a CAT protection circuit. Sure, you can remove CAT's but CAT's have a purpose. If you enjoy the smell and the guy behind you eyes burning, go for it.

 

You're basically correct in your assumptions, except that there is certainly still the possibility of a fuel mixture problem even if both exhaust manifolds are the same temp. I'm not saying that's the case, but you'd be well served to check test the exhaust mixture to make certain.

The O2 sensors on the 348 are independent of the SDL circuit. They provide info to the engine management systems so they can "trim" the fuel/air mixture during part throttle conditions, based on real time feedback from the O2 sensors.

For the engine to run at its most efficient best you want the O2 sensor circuits to be fully functional. As stated earlier, the SDL circuits are in place to reduce the risks resulting from overheated converters. Two separate circuits with two separate purposes.

 

Exactly Mike. The sdl system is a stand alone warning circuit that has no effect on fuel trim.

In providing thermocouples I often have chats with guys in which they confuse their issues by throwing this and that bypass valve fault and 02 sensor problem with sdl.

Solving the sdl problem is indrpendent of engine management functions.

 

As best as I've been able to determine, there are two versions of the ECU's electronics (excluding differences in connectors over time) - the older version that operates by grounding the slow-down light circuit to turn on the dash SD light, and the newer version that outputs a range of voltages depending on cat temperature.

Steve Magnusson wrote the following in an earlier post (in thread, http://www.ferrarichat.com/forum/boxers-tr-m/394111-possible-cat-ecu-replacement.html):

All of the "before Motronic", cat-equipped F (so 1978 US 308 thru 1991 US TR) use the same warning light ECU system/strategy -- i.e., the warning light ECU grounds one side of the warning light bulb to turn it "on" when it thinks the cat is overheating."

So based on this, then it sounds like all the Motronic cars have the ECU that outputs a voltage, so removing them would require splicing in a small circuit to generate a voltage appropriate to normal cat operating temperatures.

Prices for replacements for the older-version ECU range from $700 to $1000 or so, while the newer version is about $300 or $400.

 

Not really. For example, you might have a leaky injector resulting in fuel igniting in the cat. That's why I mentioned the first thing is to pull your ECU codes to help determine the root cause.

How to pull the ECU codes:

Ferrari 348

 

Do some free diagnosis first before you start throwing parts at the problem:

1. Pull your ECU codes.
2. Disconnect your temp sensors and drive the car until it is fully warmed up and running in closed loop mode. Does it still go into limp mode? Then the temp sensors are not your problem, as when they are disconnected they do not disable one bank of the motor - they will only throw an ECU error code and slow down light.
3. Pull the hotter side cat off the car and shine a flashlight in both ends to see the condition of the catalytic matrix material. If there are dry crumbling pieces or "slag" (melted core) showing, it has been exposed to excessive heat. The cats are fairly easy to remove and don't require dis-assembly of any other components in the exhaust system.

If your cat is bad, you have to ask yourself why. It is because of something occurring further up the causal chain. A test pipe may alleviate the symptom but it does not address the cause.

For example, you might have a bad O2 sensor that reports the bank is running lean and the ECU drives it into a maximum rich condition trying to compensate, and winds up damaging your cat. Start with the simple stuff.

 

IIRC, higher MAF resistance = leaner. It's possible that the right bank had been running rich and someone tried to lean it out, but it's also possible that it was adjusted that way from the factory because that was what was needed to attain the correct fuel mixture. Or, the resistance might have drifted over time. Were the original plugs in the MAFs or had they already been removed?

The O2 sensors generate voltage and will not change the resistance of the MAFs.

The only way to know if your engine is tuned correctly is to *measure* the air/fuel ratio on each bank. This is particularly important in a case such as yours, when you don't know what caused the converter to fail. For example, the converter matrix could have been damaged by a leaking injector, which will cause internal engine damage over time. It is also important to measure the AFRs after removing the converters, to ensure that that the engine is not running too lean.

Simpy adjusting the MAFs to spec in NO WAY ensures that the fuel mixtures are now correct. In fact, it would not have guarantied correct mixtures if the car was brand new-- that was simply the original spec used to start the car initially, so that the AFMs could be adjusted to the correct spec based on actual measurements. There is no safe shortcut here-- you need to measure the mixture to find out what's going on, even if you remove the converters. You can either have a shop do it or you can purchase/borrow a WBO2 setup, but not doing it at all means that at best your engine will almost certainly not be tuned optimally, and at worst means that it is sustaining expensive internal damage.

 

try O2 sensor extenders as well. I had a similar problem. once I install the extenders the sensors read more clearly. instantly the engine ran much better.
the rough idle occurred when I installed the test pipes. typically the port for the O2 sensor on most test pipes don't allow enough clearance for the sensor to read quick enough.
also try the 1" extention. no need to get a 90 degree or anything fancy as long as its SS.