348 ecu help please

Even if Motronics 2.5 has the same diagnostics functions as 2.7 it's still not going to provide easy answers a lot of the time. So you need to start thinking in terms of basic engine diagnostics.

Since you don't have an easy way to determine if one of the two banks is dead try the next easiest way. Disconnect the ignition module on one bank and try to start the car. If it doesn't even try to start reconnect that module, disconnect the other side, and see if it will start then. If you can get the car to start with one module disconnected I'll bet it'll probably run exactly as well as it does with both modules connected, in which case you will know that one bank is dead and you'll know which bank. It's not as quick as a non-contact pyrometer, but it should only take 10 minutes at most. And in case you haven't already checked and cleaned the ignition module connectors you might actually solve the problem just by fiddling with them since those and the MAF connectors Miroljub mentioned are probably the single most likely culprits if the root cause is indeed the rain.

Spend some time reading about the way early Motronics works. There's plenty in the archives and on the interweb. One thing you will find in the archives here is a great deal of discussion about electrical connectors and grounds. I don't think the 348 electrical system is any worse than on any other car of the period but the terminals themselves certainly are. Therefore, we have to pay particular attention to connections. One thing that really helps is using a good electrical cleaner, and eventually a good contact enhancer, on the terminals. I'd suggest getting a bottle or even two of DeOxit D100 cleaner and some DeOxit Gold for later. Treat the terminals of every connector you disconnect with D100 and let that work for a couple of weeks, reapplying every every time you get a chance. It's okay to drive the car during the process. After you've given the D100 plenty of time to work flush it out with some mild brake cleaner and dry the connectors well with canned air. Then apply a little DeOxit Gold to each contact to help keep them clean. Doing a good job of this to the engine bay connectors and to the grounds will cure a myriad of ills, especially intermittent problems.

Anyway, figure out if both banks are working and go from there. I'm just guessing based on your description that an entire bank is dead but it could be something else entirely.

Miroljub, in case you're reading this, the SDL boxes are just amplifiers for the thermocouple signals, right? In that case they couldn't be an issue here but if they use the thermocouple output as a trigger to switch another voltage source it's possible that a failure there could shut down that bank, assuming 2.5 even has that capability (and I'm not sure it does). Just trying to make certain that the SDL circuit isn't a consideration in the diagnostic process...

 

I know from personal experience the 2.5 can throw a solid SDL light and it doesn't shut anything down. I had a bad thermocouple that would throw the light even when starting the car cold (sometimes blinking, sometime solid) and it never affected the way the engine ran.

 

The TCU is basically an amplifier (100 times) of the small Thermocouple voltage. In the case of 348 2.7, the TCU does not send the (varying) amplified voltage to the ECU but operates as follows:

1. When the voltage from the ThC reaches the level equivalent to 900C temp, the TCU starts flashing the SDL

2. When the ThC voltage reaches the level equivalent to 940C, the TCU lights the SDL permanently

3. When the ThC voltage reaches the level equivalent to 980C, another circuit switches +12V (or 13V as the book says) to Pin 52 of the ECU and this shuts down the injectors on that side

So, all that the 348 2.7 ECU gets from the TCU is a switch-on of +12V to the ECU's pin 52 at the critical temperature (i.e. critical voltage from the ThC). When the TCU is disconnected, voltage on the ECU pin 52 is always zero so there is no possibility of ECU shut-down. If it is suspected that a TCU, due to some internal fault, sends +12V to the ECU pin 52 all the time and keeps it shut-down, disconnecting the TCU should allow the affected ECU to run.

 

Ant this is what I found out ant wrote earlier at http://www.ferrarichat.com/forum/348-355-sponsored-bradan/537300-348-sdecu-pinout-wiring-diagram-3.html:

Based on my quick look at the wiring diagrams, the 2.5 348-s have the following arrangements:

Non-cat version - no ThCU-s, SDL connected to the ECU; I believe the ECU lights the SDL up based on the engine temp as there are no Thermocouples on the exhaust.

Cat version - two ThCU-s with 4 pins (+2 separate pins for the Thermocouple); only 3 out of 4 used: +12V, ground and connection to the SDL; no link to the ECU so it appears no bank shutdown function, only Light SDL.

2.7 348-s came with ThCU-s with 6 pins (+2 separate pins for the Thermocouple) on both, Cat and Non-Cat, and had the additional bank shutdown function.

 

Awesome info, Joe & Miro. So since his is a 2.5 the OP shouldn't have to concern himself with the SDL "ECUs" during the diagnostic process.

The reason I asked is because I was thinking to suggest that he disconnect the SDL boxes during diagnostics, but then got to thinking that probably wasn't even necessary. Guess it isn't...

 

Very nice!

 

Another thing to check is the grounds on the upper center of the valve cover. There are some 6mm bolts. My car was mis-firing and the bolt fell onto the floor in front of my feet. Sure wish I could say it was my incredible diagnostic skill. FWIW



Jeff Pintler
89 348tb, 86tr, 99 360 3pdeal, 05 S-160 Bobcat