F355 Limp Mode

Ha
d the same issue recently after a track day at Road America, mechanic at Lake Forest says alternator belt had become loose and some various bolts need to be replaced, $1700 damage to my pocket book.

 

Check you ECU's for the cats, I am telling you mine got wet and holy **** car died on me

 

You need to look at the SDECU ad phrogs said. It sounds as if you are getting a bank shutdown as a result of that system. You may have a hot cat or a malfunctioning SDL system.

 

Eric did it backfire at all first or just drop the bank?

 

Does it still have the cat ecu's? Exact same problem happened to my car (intermittent limp mode), it was the passenger cat ecu. I have test pipes so unplugged both and no problems since.

 

How do you unplug cat ecu?

 

Maybe losing one of the crank sensors? Try to determine if a bank is dropping out.

 

I think it's a tcu

 

You have three SDECU. There are two connections on them. A four position plug and a two position plug. The 4 wire one is the one that goes to the ecu. If you want to dc your sdl system unplug it.

Good luck. I think it's foolish

 

They're in the rear corners near the taillights in the side, just unplug the wire that runs to the main ecus.

Challenge cars (and other 2.7 cars) just have two, one for each side. 5.2's have three.

 

Not if you don't have cats, then it can only throw a false alarm.

 

Bob
I've never tried it on the 5.2 system but i would think if you DC that it would go into limp mode?

 

Runs perfectly fine disconected.

Thermocuple or the main plug that goes to the ecu.

Unplug and it will run just fine. The slow down light Will flash in this configuration.

 

Disconnecting the thermocouple only works if the cat ecu isn't bad. In my case, it didn't even throw a sdl when I unplugged the thermocouple and stayed in limp mode. When I unplugged the cat ecu the sdl light came on and it went out of limp mode.

 

Thanks
Good to know.

 

When I bench tested all this stuff if you dc the Tc the SDECU would output 5v which should trigger a sdl or bank shutdown. I have taps on my SDECU outputs now and if I unplug the harness connector I get 5v on the signal line ( bias voltage)

I don't understand how those that dc everything don't get sdl or bank shutdowns. The only way to completely understand this is to tap the outputs of these cd systems and see what the motronics.

 

I'm asking for the purpose of diagnosing not putting a bandaid on a bullet wound. I appreciate your concern and I agree with you.

 

Bob when i unplug my 99 it goes straight to solid sdl and bank shutdown.

 

The 2.7 system operates differently. If you unplug them, the sdl light comes on but no limp mode. Both of my sdl lights are on, but as I have no cats,the cat ecu's were monitoring nothing. If the exhaust temp ever got hot enough to trip an sdl light without cats, I'd probably already be running around the back of the car with a fire extinguisher.

 

That's how it should respond. The 5v bias should look to the motronics as a overheated cat. Limp mode is triggered at around 3v

 

I didn't know 2.7 operated differently than 5.2. Thank you