Slow down light...legit at start?

Hi all! I've recently acquired a four-post lift, and with it, lost any excuses to continue to let my 355 languish in the garage. I'm in the midst of replacing most/all of the brake parts due to gunk, and while I wait for parts to come in (and back), I wanted to work on the SDL. Background:

* It's a 5.2 6-speed.
* The light has flashed since I bought the car two years ago.
* Due to bad brakes and the until-recently inability to fix them, I have only driven the car one mile in that time (literally around the block). I did start the engine several times, but I know my ownership experience will be more expensive because of all the sitting around.
* I have replaced all three ECUs and all three* thermocouples with Technistrada parts. I cleared the codes (P1445, P1448, P1449) and started the car.

The slow down light was only out for about three seconds, then began flashing again. Two of the codes returned. The exhaust was a bit smelly, but the gasoline is obviously quite old (PO must've put stabilizer in it), plus I don't know what the normal smell is. I have a belt service kit I bought from Ricambi, which also includes plugs and a fuel filter. Recommendations appreciated!

If this is likely to go away with a routine engine service, is engine-in or engine-out recommended? I can't drop it through the lift, but I do have jacks and stands as well.

* I have not yet been able to get the center/bypass thermocouple screwed in because there's stuff in the way and I haven't had time to remove it yet. But the other two are screwed in and all three ECUs have electrical connections to the new thermocouples.

 

I had a similar issue with SD flashing randomly upon start up, but in ‘94 348. Sometimes unplugging and replugging the Exhaust ECU will help. But, I can confirm that the car does not like old gas, stabilizer or not. I believe you can siphon old gas out and replace wifh new gas. Worth a try. It could help.

 

Each of the ECU feeds a single voltage line to the car ECU. What you should do now is to hook up a volt meter to these lines at start up and see which one is causing you problem. For the SDL to flash, one of those lines must be at an elevated voltage (normal is 0.5V, elevated is something much higher like 1.5V). Since you already changed all three TCU and all three thermocouples, chances are your wiring harness has a problem if you have multiple CEL code. Possibly a ground wire is broken.

The 5.2 355 should not be extremely smelly when it is running cold at start up. If it continues to be smelly, your cat converters are probably burnt through. Which will also cause several more CELs.

As for the engine out on a 4 post lift, there has been several threads describing in detail how to remove the engine from a 348/355 on a four post lift. Search and you will find it.

 

SDL will flash when the signal from the TCU to the ECU reaches 3.75 volt (EGT at 1650 F). If any of the left and right Thermocouples has bad connection to its TCU, it will cause SDL flash, soon followed by the bank shut-down. I also believe that poor connection of the TCU to the ECU will cause SDL flash.

To test the new TCU-s and Thermocouples, the bypass thermocouple should also be screwed-in otherwise it will probably cause a fault code being at ambient temperature.

 

Thanks for these details! Will get my voltmeter out and check it!

This is concerning. Hopefully it's somehow not that...

Thanks! I did find it, and it looks pretty straightforward. So I guess you're saying it's worth doing the full engine out rather than just removing the fuel tank and doing the belts from there?

 

How soon will it shut the bank down? Are we talking immediately, or a minute? Because of the brake situation when I got it, I've never driven this car at full power. And no with no brakes at all (until this weekend, hopefully), I can basically only listen to hear things like this.

Makes sense; will do!

 

The SDL will flash as a warning. If the cat temperature continues to climb, it will be solid. If you continue to drive it, in about 15 minutes the bank will be shut down.

As for engine out service, that is what I do ... take the engine out.

 

Excellent on both points! Thanks for the clear advice!

 

I have gutted cats on my car and I get a intermittent slow down light on start up.
It would also flicker a lot at times

I know mine is a electrical issue somewhere on the car as I tested all of my ecus and thermocouples with my multimeter and a torch and bench tested all of them, 2 sets plus spare ecus I have purchased and no issues on the bench. So I am going to have to trouble shoot more but as of now I bypassed it.