Do any of the 348 guys here have a pinout or car wiring diagram for 348s that would show the 6 conductors used on the 348 SDECU? 355/360 has 3 used pins. 12V, ground and signal. I am interested in what the other three in the 348 part are for. Thank you
Are these of any help ? Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
That shows the sdecu having 4 conductors excluding the TC leads. The one I have in my hand has 6 plus the TC (2). Does anyone have a clue what these leads in the 348 sdecu do?
Bob, the units on my '91 have 6 pins for the harness connector as well. I intend to try to figure out what each does when I get a chance. Just need to come up with a safe way, non-invasive method of tapping into each lead so I can check voltage under various conditions. I'm in the midst of doing a bunch of work on the car but will try to get to it soon. In the meantime I'd welcome any suggestions on how to best create physical access for measurements. Ideally, I'd like to place a short "T" interconnect between the box and the harness that provides a separate connector from which to measure voltage during actual operation. Are plugs and sockets that are compatible with the OE wiring readily available?
Mike, I'd suggest making a breakout box (or connector). I have a similar device for biasing guitar amps after installing new tubes..
That's exactly what I'm envisioning. I just don't know if the connectors are readily available, but I haven't looked yet. Hoping the doc knows and can save me some effort...
Mike, I have the outputs signal lines on my 355 tapped with positaps that I have been using to test and plot the voltages, etc. They are easy to apply and work well. The pin on them is very small and if you are concerned about it after removal you could always shrink a piece of tubing on that area. You could also back probe the connector as well. I recently acquired a logging, blue tooth enabled DVOM which is very cool and eliminates having to have to leads run into the cockpit when testing while driving. I was hoping to come up with an easy way for 348 guys to use 355 or goths new sdecu by just mating the connectors properly. The six leads throws a monkey wrench into that idea though. All of the connectors are readily available. You could build your own break out connector for that 6 wire plug as well using a male and a female and some wire. You could tap the leads between the two extra connectors or crimp an extar conductor on each pin and have it pig tailed out of the housing.
Bob, I know Positaps have worked for you and I'm not starting a debate, I just want to say I'm in favor of other methods that do not pierce wire insulation as I don't think that is the best approach give the environment these wires are in within the engine bay.
Agreed. I will not be piercing the insulation, even with the tiny DVM probes intended for the purpose. Bob, if you could point me to the connectors I would appreciate it.
MIke I am pretty sure they are metripack 150 although it appears that the back end may have been redesigned because the images I see of them don't look exactly like what I have in my hand. Joe at Motorcycle Terminals, Connectors, and Wiring Accessories is going to get me a 6 way male and female housing and I'll see if they work. Stay tuned.
Just a note, on the wiring diagrams in post 2 the sdecu are for the 2.5 motronic system not the 2.7. Ricambi also shows that the earlier 2.5 system was a 4 pin connector where as the later 2.7 sdecu was a 6 pin connector. It also shows 2 different part numbers 142581 and 141037.
I have marked-up the wiring diagrams for both, the 348 and 355 exhaust ECU-s. The 348 diagram is for 2.7 but I don't know whether the 355 one is 2.7 or 5.2. It does not look easy to wire-in the 355 ECU to the 348 because, in the case of 348, there is one signal to the main ECU and the SDL is controlled directly by the exhaust ECU whereas, in the case of 355, the exhaust ECU sends 2 signals to the main ECU and, I guess, the main ECU triggers the SDL (could not find the SDL on the diagram). Image Unavailable, Please Login Image Unavailable, Please Login
That's what I surmised given the number of leads on the 2.7 348 compared to the 355. 355s use the same SDECU for 2.7 and 5.0. There are only three conductors , 12v, ground and a single signal wire that goes to the main ecu. The sdl and bank shut down etc. come from the main ecu. This may explain something regarding the design of the 355 SDECU. If you look at the board in there it has a ton of components. The output is only a single voltage amplified of the thermocouple. I've often wondered what all that stuff was for as I have installed simple off the shelf voltage amplifiers that do the job and have minimal componentry on them. Maybe viscovini just used the same board in the 355/360 units and all the extra stuff was left over from 348? This seems to be a dead end for the idea of using the 355 units on 348s. To bad. I did send Goth a note on this and as he designed a 355 replacement, maybe he could do the 348 as well.
I found that there are two connections to the main ECU (as mentioned in my earlier post). Image Unavailable, Please Login
There are 4 ports on that connector but only three are used. One is 12v one is ground and one is the signal wire. Image Unavailable, Please Login
That's interesting. So the connections of the exhaust ECU-s are (colours as on the attached diagrams): 355: 1. Green: +12V 2. Black: Ground 3. Violet: Main ECU Pin 44 4. Pink: Not used 348: 1. Green: +12V 2. Orange: +12V 3. Black: Ground 4. Brown: Ground 5. Violet: Main ECU Pin 52 6. Dark Green: SDL bulb The 348 exhaust ECU has two pins to +12V and two pins to the ground so these 4 connections are easy (equivalent to the two 355's connections 1. and 2.). The violet wire must be the signal to the main ECU (pin 44 on 355, pin 52 on 348). I guess the pin numbers are different because the 348's ECU is 2.7 and the 355's is 5.2. If the signal coming from the 355 Exh.ECU is the same as that from the 348 Exh.ECU, then the 355 unit should work on the 348. However, we are left with the wire 6. of the 348 Exh.ECU which lights the SDL bulb. I wonder if the "not used" wire 4. (pink) of the 355 Exh.ECU actually has the function of lighting the SDL bulb. If so, then it can be connected to the 348's SDL line (dark green). A bench test comparison of the two Exh.ECU-s would be required to verify both, whether the lighting of the SDL bulb (signal from the 355 unit's Pink wire and signal from the 348's Dark Green wire) occurs at the same threshold (thermocouple temperature) for both and whether the voltages coming out of the Violet wires are similar. Image Unavailable, Please Login Image Unavailable, Please Login
Does anyone know at what temperature (or thermocouple voltage) the SDLs are supposed to be actuated? I'm guessing that the components within the control units drift over time, causing the SDL to illuminate even when the temperature is below the designated threshold. So we can't use an old control unit to determine the intended point of SDL actuation. BTW, thanks for the highlighted diagrams, Miroljub. Nice work.
I just determined that the diagram I showed for the 355's Exh.ECU connections is actually for the 355 with 2.7 ECU, same as the 348's. So, it seems that the arrangement is: 348's Exh.ECU Violet wire (signal) connects to Pin 52, Pin 44 is not used 355's Exh.ECU Violet wire (signal) connects to Pin 44, Pin 52 is not used It appears that, in the case of the 348's old Exh.ECU, its signal goes to Pin 52 and that, in the case of the 355's newer Exh.ECU, its signal goes to Pin 44. So, a 355's Exh.ECU may work fine on a 348 if its signal wire (Violet on my diagram, Violet/White actually) is just connected to the free pin 44 and Pin 52 left unconnected. Activation of the SDL still remains a question of whether the unused 4th wire (Pink on my diagram, Pink/Black actually) of the 355's Exh.ECU is for the activation of the SDL.
Here's a post from a prior extensive thread on the SDECU that FBB started. John (cribbj) did this work. Image Unavailable, Please Login
On a 5.0 355, there is no fourth, pink wire in the harness loom at the SDECU junction. As I said above, there are 4 posts on the connector on the SDECU. Possibly that fourth post which is not used in 5.0 355s, carries the SDL voltage? In that case then connecting it to the sdl wire that you identified in the 348 may do it. I will set up a bench test of the 355 SDECU and see if there is an output on that 4th post at the sdl trigger temps. Can someone with a 2.7 355 (MY 1995) take a pic of the car harness connection at the SDECU as I did above for 5.0 and post it please. I am interested to see if there are 4 wires being used in 2.7 355s.
My '95 2.7 has 4 wires. I have run the cat control unit and thermocouple on a scope right up to temp. As far as I trace on the scope the 4th wire is floating or at least doesn't output any signal with a red hot termocouple. Slow down light easily defeated by placing a 2.5v signal onto the signal wire on the main engine ECU harness. Main ECU signal wire appears to have a 100K ohm weak pull up to the 5v rail, I have series circuited a 1k resistor and 2.5v reference (LM336-2.5) between grnd and signal. For $1 parts I have forever solved my slow down lights headaches. FYI I run test pipes so don't have a risk of overheating.
Great info. Thank you. So a 2.7 355 only uses one signal wire like 5.0 even though they have a fourth wire. This doesn't help the cause of possibly using the more simple 355 SDECU for 348s. It would seem the additional outputs are necessary in that version of 2.7 models.
Perhaps the signal wire of the 355's TCU, going to Pin 44 of the 355's 2.7 ECU, will keep the 348's 2.7 ECU "happy" when connected to its Pin 44 instead of the Pin 52 used by the old TCU. However, there will be no early SDL warning. This could be solved by a separate small circuit, monitoring the TCU's signal output, to switch the SDL bulb on at certain threshold.
