Thermocouples, slow down lights, related CEL’s, and how to conquer them...

Just found this today and bookmarked it as my car has aftermarket cats and exhaust...the information here is pure gold.

 

Scott -

14 months after your initial post, I'm certain you've already capped the thermocouple bung. But for the sake of thread completeness, we now have a Gothspeed cap which is used in conjunction with their new Cat ECU "bypass" box.

The cap nut: 179278 CATALYST TEMP. ECU SIMULATOR - Ricambi America, Inc.

and the ECU: GS179278-SIM CATALYST TEMP. ECU SIMULATOR - Ricambi America, Inc.

All designed and manufactured by Fchat's very own, Gothspeed, in California.

 

Hi, hopefully you can help!

I am having the flashing (but not constantly on) Slow Down/CEL light problem.

I have fitted Fabspeed manifolds, connected to Larini de-cat pipes, connected to a Tubi sports exhaust box. All sounds incredible!!

My F355 is a 1997 UK RHD, 5.2 Motronic.

The de-cat pipes still have the pre & post sensors, along with the original thermocouples and OEM CAT Ecu's. I also have the original exhaust valve connected to the Tubi.

Would installing the above ECU replacements and completely removing the thermocouples solve my problems?

many thanks
Mark

 

The SDL system is an integral part of the Motronics. You have to either satisfy it with properly working components or fake it out with components designed to do just that.

As you don't have cats, you don't need thermocouples and you could use Goths bypass units to send a 1.5v or similar that will keep the main ecu happy and your sdl off. You may need an me at the BP location as well if you are getting CEL associated with it.

You would need to do a proper diagnosis of where the SDL and CEL are coming from and correct the component causing that issue or abandon the sdl system and go with the fake out method, replacing the SDECU with the fixed voltage units and capping the bungs for the thermocouples .

 

Similar to you, I have fabspeed headers and test pipes. To eliminate all the SDL issues, I have Jev's original thermocouple circuit that sends the correct voltage to the ECU (I believe Goth's is similar and works the same) and use fabspeed's 90 degree offset tubes for the rear O2 sensors to keep them out of the exhaust stream. These work perfectly and I have never had any issues with codes or SDL's since and never expect to.

SDL's are generated by malfunctioning cats. Since you have no cats, you need to use Goth's (or Jev's) circuit to send your ECU a corresponding signal for cats within a normally operating temperature range.

The second O2 sensor "sniffs" the exhaust stream to see if the cat is functioning correctly and "cleaning" the exhaust stream. Since you don't have them, in order to avoid codes, your rear O2 sensor needs to "sniff" a relatively clean exhaust. For this, you need to get it farther away from the exhaust stream by using a 90 degree bent pipe with a bung that accepts the O2 sensor.

 

Thank you for the above replies.

on the Fabspeed site there are 2 different O2 sensor spacers:

Universal O2 Spacers - Fabspeed Motorsport
Universal O2 Spacers with Catalytic Converters - Fabspeed Motorsport

with my set up and the decat pipes any suggestion which one i should order?
thanks
mark

 

The post cat sensors function is to determine cat efficiency using o2 levels. No cats, no need to determine efficiency of test pipes, so again you need to fake the Motronics out.

You would use the mini cat version in your set up to hopefully keep the CEL happy.

There is also another brand of mini cat made by Big Daddies Garage.

http://www.bigdaddiesgarage.com/mini-cat-cel-fix.html?gclid=COiluYrukdICFdqNswodWuoIVA

 

The post cat sensors function is to determine cat efficiency using o2 levels. No cats, no need to determine efficiency of test pipes, so again you need to fake the Motronics out.

You would use the mini cat version in your set up to hopefully keep the CEL happy.

There is also another brand of mini cat made by Big Daddy.

 

Any word on when a 348 Gothspeed solution will be available?

 

Nothing yet, but there's indeed hope.

I have a shipment of pieces which left the dark underworld of Gothspeed yesterday (due to arrive at Ricambi next week). Although I don't expect to see a 348 ECU in there, Goth never ceases to surprise me with things he'll toss into our shipments. It may not be safe to hold your breadth, but its o.k. to cross your fingers and hope!

Re-Imagined Ferrari Parts by Gothspeed - Ricambi America, Inc.


.

 

Thanks for the update! Will keep checking this space and your site.

 

I assume this would be the same for gutted cats?

I'm trying to understand the setup on my car (5.2 Euro-based). I couldn't figure out why my exhaust gasses were so eye wateringly acrid. When I purchased my car, I knew I had no cats in the bypass system (Mille Miglia exhaust system), but I have just discovered that I have post-cat extenders, so it looks like I have no main cats either (the cats, I assume, have been gutted).

Getting back on topic... When cats are "damaged" I understand that the temperatures go up. Is it because cat blockage causes the cats to heat up, or is it because the cat material blows through causing more hot exhaust gasses to contact the sensor.. or is it because the muffler becomes blocked with cat material causing more heat build up upstream? (or a combination of all 3?)

When the Motronic ECU senses a problem, does it simply put on the Slow Down light, or does it modify the engine behaviour? When the Slow Down light is triggered, does the ECU also send a signal out to the Check Engine light (illuminating both lights) or does just one light illuminate? Does it also log a fault in the ECU? Does the logged fault then trigger a Check Engine light at a later stage?

Thanks,
Cheers.

 

A flashing SDL is based on a certain temp reading and a solid SDL is another (higher) with a bank shutdown. It's all listed in the WSM, Ian.

 

Ooops (*^ ^*) .... back to the books.

(EDIT) I've just found it in the Owners Handbook, too. I'm just wondering what has been done to my car to prevent bank shutdown or do gutted cats never raise the temperatures high enough for bank shutdown (just a flashing CEL)? My CEL and SDLs have been completely disabled with a jack@ss ([PO] wiring modification on the binnacle.

Thanks, Dave
Cheers
Ian.

 

Ian likely your cats are all gutted and your wiring is faking the signal.

Gutted cats will not heat up because no extra back prssure your car if not running correctly will just run with excess fuel. Not likely to run lean but could happen.

The things I know about that have and could cause. Sdl and bank shutdowns were faulty coil, bad sparkplug wires, faulty fuel injector as a few examples.

Its because of this that I like the system as designed but your car has to be working properly or it will trigger the light.

My car has tubi mufflers, a capristo twin valve, with hyperflow main cats. It does not throw cel very oftain less than once every two to five years.

R cently it has ben the longest about 4 years. I think I have it sorted finally.

 

You need to do a lot of reading and then replace components if they are missing.

Please not the euro cars are a little differant but the manual shows you.

Although some have chosen to bypass, and I almost did I do think it is better to fix it properly then no more problems.

I like it b cause it has helped me find other problems quicker and gives me piece of mind.

 

As Dave has said when cats get too hot it will shutdown that half of the engine. This was what happned to mine when a coil malfunctioned on 1 cylinder and then when it cooled off everything worked fine again until it git too hot again.

 

On a 5.2 there is only one SDL unlike 2 on a 2.7. There are OBD codes for cat temps that will trigger CEL after the required number of cycles by the OBD system.

But, an initial SDL will not throw a CEL until those parameters have been met. If you did an OBD scan , you might have a pending code for the 5.2 single sdl though.

 

Thanks, Grant... I'll keep an eye on it.

lol.. I've been deciphering the manuals 16 hours a day these past few weeks and still struggling... Anyway, I've restored the instrument wiring to original... and will probably refit the binnacle tomorrow and pray that the CEL or SDL lights don't come on. However, I'm hoping because the cats are (most likely) gutted, I won't get an SDL.

About getting the car back to original... I might refit some main cats at some point (if the SD illuminates... and my neighbours' complaints about the "volume" get too bad ).

I wired up an adaptor lead for an OBD2 reader when I first bought the car... I might even get the chance to use it )))

Thanks, guys.
Cheers
Ian.

 

Bob from another post I think Ians car was throwing both because of a jumpered setup in the instrument binnacle from a previous owner who chose to fake it out to likely sell th car or not fix the problem.

It was jumpered to throw the sdl at start up but then never come on again no matter what was happening.

 

Just to clarify. The PO (or one of them) had rewired the binnacle lights so that both lights would come on with the ignition key in "RUN" (prior to start) like the normal confidence check, but neither light would illuminate if there was an actual problem.

I see how you could wire up the binnacle to not illuminate a particular light, but he chose to stop both illuminating. I don't know why he chose to hide the CEL light, as he already had O2 extenders (on gutted cats).

Cheers
Ian

 

Hi Jevs
I enjoyed reading your threads and how you got round the thermocouple problems. I have an F355 Spider UK RHD 1997, the last time I drove the car I worked the engine hard and the car went in to safe mode. This has happened once before a few years ago, I drove it home, and when the car cooled down it previously reset itself. On this occasion it did not reset. I have replaced the two thermocoules for new ones. I had a local mechanic round with an OBD2 reader and he connected it to the Motronic 5.2 ECU 3 pin connector and he said all the pistons were firing ok and he could see the CAT sensors working, but the car is still down on power as if it were still in safe mode.
My guess that this is a fuel problem on the left bank, could this be the ECU has regulated the fuel system, which may need to be reset. Is there a way around this without taking it to a Ferrari dealer, which may have a more appropriate OBD2 reader? The car starts well from cold, but you can tell it still doesn't run correctly/down on power, and getting popping noises from the left side of the exhaust when the car warms up. I have checked all the fuel injectors and they work fine..
The mechanic says we can have another look when the car is back on the road as its off the road for the winter months.
Any comments or suggestions would be welcomed.
Thanks

 

Phil, would you like to start a new message thread for this one (since you've eliminated the thermocouples as a possible cause) and we'll take it from there.

Cheers
Ian

P.S. A basic OBD2 reader should list the faults logged in the ECU. If the mechanic didn't see any, then you'll have to go back to engine basics: Fuel, air and ignition. Fortunately, there is a ton of cheap engine diagnostic tools on the market these days.

 

As stated above as long as your possitive its not the thermo ecu

If its spark a missfire should show up and since you said its good i would check fuel