exhaust/slow down light question

My best guess is your cat is breaking down. I'd highly suggest you take it off for a visual inspection.

 

Any loos of power?

 

Mine did that a couple times where the light came on briefly and went out just as quick. The engine sound changed during that brief period. Like you said, it went out quickly and I never had enough time to determine if I really had lost a bank. Eventually mine got worse over the course of a week, and the behavior eventually happened at idle where I went from 1k RPM down to around 750RPM. Idle was still smooth as glass but was just lower because it was dragging the other side of the engine. SDL for bank 1-4 was on indicating I was running on the 5-8 bank only. My car is a 95 2.7 so I have two SDLs. As soon as I revved the engine a little, the light went out and I got the bank back and the idle returned to normal. Upon closer inspection, my cat ECU for my 1-4 bank was original based on the date code while my 5-8 side was the newer cat ECU that had green potting material. As luck would have it, this happened the day of the BREXIT vote so I was able to get a favorable exchange rate ordering a new OEM cat ECU from Eurospares who has these in stock pretty cheap. Installed the new CAT ECU on the 1-4 side and a couple hundred miles later in all conditions, good as new. Normally, I would have done more troubleshooting on the cat ECUs and the thermocouples to determine exactly which part to replace before ordering anything, but after learning that the 1-4 bank CAT ECU had black potting, had a 1995 date code, and this is a common failure item on the F355 and 360, I decided to just replace the cat ECU. I also already knew my cats were good because I had my engine out earlier this year and inspected them. If you suspect the cat ECU to be part or all of the problem, there is a lot of good information on how to troubleshoot already written on FChat if you do a little searching. As Dave said above, if your thermocouples and cat ECUs check out as working correctly, it could be your cat media breaking down. Good luck.

 

I am pretty sure you had a bank shut down in conjunction with the SDL. It sounds droning and it was quick you may not have even noticed the half power of the engine.

I had this happen to me when my thermocouple was intermittently shorting. I was able to isolate the issue to the thermocouple by diagnosing the voltage outputs of the ECUs. As was said above it may be a bad SDECU also.

I would suspect a failing component in the SDL system. Shoot me an email if you'd like some help in diagnosing it.

 

Not too big into guessing...Some basic diagnostics as outlined above will send you in the right direction. John's question is pivotal; did you lose power? I'd start there. Dr. Bob has a wealth of knowledge.

 

Did you wash the car before driving?

 

A note from experience. You need to know what happened when. Did SDL come on first and then the engine go off song, or did the engine go off song first, then the SDL come on? Big difference. The OP seems to be saying the engine went off song first. If the engine when off song first it is possible that a couple of cylinders lost spark causing raw fuel to be dumped into the exhaust resulting in cat actually over heating. An ignition coil can fail intermittently, and engine will come back to full song and SDL will go out.

But be careful. The SDL doesn't actually function as many have stated here. . Read the WSM carefully. This is not fully addressed in the owner's manual. Flashing means exhaust gases are hot, 1724*F, slow down. Solid means they are hotter, 1796*F, and you should stop driving. If you continue to drive and the exhaust gases increase in temperature even further, to 1868*F, then the fuel to the problem bank will be cut off.

And if you have metal core 200 cell, metallic core cats there is a possibility that you could have damaged the cats even if you stop as soon as possible (and I mean 15-30 seconds) if the SDL comes on solid. It seems those temperatures are set for ceramic core cats which can handle higher temps than metallic cores. Ask me how I know. Oh, and there was no CEL during all thing nonsense, just engine farts and SDL.

[edit] Without going into detail, yes, after a little cool down and starting to drive again, SLD started flashing a second time, then engine, with SLD still flashing, came back full song and the SDL went out. Got home no problem. Next day started diagnostics. Started car all was fine. (???) Waited over night and tried again. Engine off song. A spark tester quickly revealed that the 1-4 coil was toast, no spark to two cylinders. Fortunately I decided to look at the cat through a bore scope. Was kind of a mess. Luckily I was able to clean out the slag and still had about 2/3 of the core remaining. I'll find out next year if it gets through emissions.

 

The SDL system is firstly a safety system. It is uniquely designed to detect and protect you and your car from overheated exhaust components. Firstly you need to determine if your cats are truly hot. If they are, then the fix is completely different than SDL components


Go to your local auto parts retailer and spend $20 on an infrared temp gun. Let your car warm up to full temp and shoot your headers and cats and see if you actually have a hot cat that is tripping the system. If the temps are triggering the SDL them further engine diagnostics are needed.

If the SDL is solid, then that Is a bank shut down situation as opposed to a blinking SDL. Hopefully it is just a SDL component issue which can be fairly easily diagnosed

 

Paul, John's post has very valuable information. Unfortunately "guessing" at the finite possibilities is pretty normal on a forum discussion with not being in the car and experiencing what you did.

The system is pretty simple and only a few components to check out. You will figure it out with the folks here willing to help compared to some techs that offer little help other than criticism of the support of members here.

 

To me, this sound more like there is a problem with the engine that is resulting is the SDL if the problem persists long enough. And my guess would be ignition related. But it's impossible to tell without proper diagnosis. That it seems intermittent is always a problem.

 

Bob, please read my second post carefully. A solid SDL does not automatically mean shut down. There are 3 distinct temperatures: "Slow Down", "Stop Driving!!!", and "Why the eff are you still driving on 4 cylinders you effing idiot?" Or, at least, that's my interpretation.

 

Yes John. Solid will trigger a bank shut down with some duration and repetition parameters. I have read that WSM part as well and I think that possibly that stuff may represent all of the excess componetry on the SDECU board compared to the simplicity of the EGT board.

My experience with a solid SDL on watching it real time with a DVOM was due to an intermittent short creating voltage spikes in the SDECU that sometimes would just go solid and go away and sometimes shut down a bank. The shut down was most likely as a result of meeting the parameters outlined in the WSM.

Because those incidental spikes are random in a component short situation it may be impossible to diagnose using those parameters as data points

 

My 95 did this on and off for several years. I thought fuel pump, relays, coils. It was random.
Turned out it was cat ecu. I was constantly changing plugs from running on 4 cylinders. I removed both cat ecu several years ago and car has never run better. Not suggesting you run without ecu but it works for me.
Do other cars have this where you have cat ecu?

 

To further add to what John is saying, allow me to please describe the system a bit in case you don't already know some of this. Some has been said by others and all credit due.

The SDL is a Catalytic protection system. That is it's whole purpose - to protect the CAT from overheating and burning up (which then would render it's function useless for emissions).

The system has the following parts:

- Thermocouple connected to each CAT and one after the bypass valve for 96+ and up years (5.2 Motronic)

- Thermocouple ECU, often referred to as a TCU (electronic control unit) (original units where black potted, newer units are green potted)

- Wires connecting it all and to the main Motronic ECU(s)

Many times within this system you have a failure of the TCU (most common), Wiring, or Thermocouple. Proper diagnostics will yield the failed component. There are simple ways to do this diagnostics and more elaborate.

I have experienced exactly what John had referenced - a solid SDL with no bank shut down. So, it's clear as he stated that a certain temperature must been seen to go into limp mode - a solid SDL does not mean you hit that threshold.

Please take an SDL serious as an overheated CAT can lead to fire. That said, if you get any SDL upon a cold start, you can be certain you have a problem with the system and the fault is not likely real.

You can purchase new OEM parts from many sources, I buy most of mine from a couple dealers that are sponsors here and I get genuine OEM parts. If you wish to save a few bucks on these parts and take advantage to BREXIT, you can get then from Eurospares:

TCU: $194.31 Ferrari 360 Challenge Stradale - Exhaust System : Page 019 | Order Online Eurospares

Thermocouple: $151.88 Ferrari 355 (5.2 Motronic) - Exhaust System: Page 016 | Order Online Eurospares

Now, if the SDL is real, a number of possibilities can be causing that. If that is the case, it's also probable you may have damaged or had a damaged CAT and visual inspection may be required - if nothing more, for peace of mind.
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To add to what Dave said, mine eventually would go into limp mode when car is cold so I knew that it was a system failure and not a hot cat. Dave do other cars have this system which seems primitive? Do the cats get hot from raw fuel into the cat from failed ignition or injectors?

 

Hi Bob - great data point!

Regarding other cars, I really don't know as aside from my former 95 vette, I've not worked on much non-355's stuff in a long time.

Fuel buring in the exhaust could certainly cause the over heat condition along with restrictions in the CAT such as a failing element or blockage. On a car with test pipes, I don't recall people mentioning this problem as the exhaust is not restrictive.

 

"I have experienced exactly what John had referenced - a solid SDL with no bank shut down. So, it's clear as he stated that a certain temperature must been seen to go into limp mode - a solid SDL does not mean you hit that threshold."

This is not true. You can go into limp mode with a faulty component with no overheated CAT. The trigger for the limp mode is a voltage reading, period. Said voltage spike can occur from design parameters or from component failure creating the spike.

As I said above, I observed this phenomenon in my vehicle with my SDECUs tapped and a DVOM driving around. Random voltage spikes that caused solid SDL and bank shut down on account of faulty , shorting thermocouple. On replacement of the properly diagnosed and indicated thermocouple the issue was resolved correctly.

The motronics responds to electronic signals, it doesn't care if they are real or faults, it reacts accordingly.

You may get bank shut down with a faulty component and normally operating exhaust parameters.

 

Of course, Bob. In my case, per your comment, I know my situation was from a faulty TCU and not real temperature - so your point is well taken.

The component faults have been an on going issue.....

 

I had this issue. Cat's were fine; but, pulled them anyway and replaced with test pipes. Pulled out the exhaust ECU's too. Replaced the O2 sensors as a precaution with the test pipes. No problems since, and more power. I get the reason for the system, but if the Cat's are gone, then the system is meaningless... The SDL's were probably due to bad exhaust ECU's but not 100% sure. Regardless, one new exhaust ECU cost more than everything I replaced.

 

Here is a video on my car of the intermittency that creates the SDL and bank shut downs on some occasions.

This was an issue with one of the aftermarket SDECU s that I have installed on my car. This is at idle but just prior to this video I had a bank shut down that was triggered by this problem.

This type of voltage spiking can occur from faulty thermocouples or SDECUs.

There was no overheated CAT in this example. It is strictly from faulty components. I have a bunch of SDECUs from various aftermarket sources that I am messing with and I just put a different one in an fixed this problem.

[ame]http://www.youtube.com/watch?v=_37B9PpiQWo[/ame]

FYI. The normal voltage reading on a warned up cat is around 2.0 volts. The spikes as you see in this vid create the problem.

The output/signal wire of the SDECU is tapped with a positap and allows you to view what the Motronics is seeing without any guessing. It is the same as having the coveted motronics breakout box but a poor mans version just for this parameter.

 

I agree that live data is a great tool for diagnostics. But, I would suggest another method of tapping the outputs, perhaps getting to the connector pins. I'm not a fan of piercing wire insulation as that may create a potential issue.

 

The point of that post and video was not to debate the relative merits or not of tapping outputs but to real time demonstrate the actual cause of SDL and bank shut downs as they occur.

To my knowledge no one has posted a real time video of what the root cause of these issues are. The WSM describes how the componentry is supposed to work but the reality is that it is prone to faults as seen in that video.

Those spikes will shut down a bank. They can come from faulty components. You can tap the output however you'd like, hat pin, positap, make a breakout box or connector, whatever.

If you don't know what the units are outputting you're just guessing.

 

Given many known component failures of the system, educated guesses can be applied to do so simple component tests and solve the problem. I've used the simple method twice with success.

I also recall loaning you a new TCU, Bob (twice) so you could try the same. Sometimes the issue may be deep and other times it's a surface problem found easily with some component swapping. Pretty standard in the diagnostic world.

I'm not discrediting your work or experience on this issue but others have valid experience also