328 only running on cyl. 5-8

Hello,

kind of happy that I found this great source of knowledge. As you can see, this is my first post. I am from Europe (Germany to be more specific), so please excuse if my English is not the best. As said in the title, there have a problem with my 328 (EU-Version, no Cat).

The problem occurred after the car was standing for approx. 6 month in the garage (heated, no temperatures below 10° C, no humidity).

On starting the engine will only run on cylinder 5-8. cylinder 1-4 are dead, apart from a small “glitch”: Repeatable every approx. 4 seconds there will be 1 misfire on cyl. 5-8 and at the same time 1 successful fire on cyl. 1-4. Even if this is my first Ferrari I am quite familiar with cars and ignition systems, so here is what I have done so far:

1. Checked the primary power supply on Terminal 15 during starting attempt => OK
2. Switched the complete coil packs (Terminal 15, 4, and 1 as well as the ignition module connector) => Symptoms stayed the same. Conclusion was that the coil packs are both OK.
3. Dismounted the distributor caps and switched the cables on the distributor cap (1<=>4, 2<=>3) and switched the distributor caps and the distributor rotor. => Symptoms stayed the same, repeated test 1,
symptoms also stayed the same Conclusion was that on the high voltage side everything is ok.
4. I DO NOT RECOMMEND TO THIS BECAUSE THE IGNITION TIMING WILL BE FLAWED, but nevertheless I did: From the original wiring I switched the complete coil packs APART from Terminal 4. On the starting
attempt cyl. 1-4 tried immediately to fire, though it was clearly noticeable that the timing was wrong (as it should be because cyl. 1-4 are fired with the 5-8 timing). So I aborted.


Conclusion so far is, that the signal to the ignition module for cyl. 1-4 to interrupt the mass contact of terminal 1 to induce the high voltage seems to be missing. So there is either something wrong with the ECU (Microplex) or with the cabling from the ECU to the ignition module of cyl. 1-4. Checked the cabling by measuring the resistance => No faults found.

At the moment I still have a little hope the TDC and/or angular speed sensor (ordered both new and waiting for the delivery now) is/are flawed and therefore the ECU behaves strange.

Otherwise last guess would be the ECU.

So my questions are:
Did any of you ever had/heard of a similar problem?
Any other ideas what might be the cause?
Has anyone an idea about the signals (actually there are two cables from the ECU to each ignition module) from the ECU? I think basically the ignition module should be a thyristor (and some “gizmo” stuff around) which is controlled by the ECU to interrupt the mass contact of terminal 1 of the coil at the right moment to induce the high voltage. Any idea how to “tell the thyristor to break the mass contact”, e.g. to simulate the “fire signal” from the ECU?


Any help is much appreciated,

Thanks for reading and regards,

Dirk

 

Wow, that was fast. Thank´s a lot.

I will follow the test procedures described in the Bulletin this evening. I guess the 25-pin interconnector just makes it easier to access the different pins, or is this interconnector necessary because of some built-in resistors / cross connections?

 

Again, thank you Steve.

Just back from my garage: Seems to be the ECU. According to the bulletin the Microplex output to 1/4 and 5/8 bank should both be 2,8-3,5V. Actuallly my output to bank 1/4 is 0,06V (rising to 0,25 when every 4 sec. the 1 successful firing appears) and output to bank 5/8 is 1.8V (still running though) and dropping down to 0,6V every 4 sec. when the 1 misfire happens.

So guess i have to get a new ECU or get my ECU reworked.

Strange, this thing looks quite solid and i heard it is normally quite rugged. But who knows...

(Still hoping that maybe someone shows up like "Hey, I had exactly the same problem, it was ..... (with "....." not being the ECU) but probably will not happen)

Regards,

Dirk

 

Just a feedback to close this.

It has been the ECU. Steve helped a lot with the bulletin. To add a little bit, the measurement with a DMM is more or less a workaround. I used a scope on the signal and in fact it is a square wave blocking the transistor/thyristor of the ignition module, frequency of course depends on revolution speed. Actually on the working bank (cyl. 5-8) high voltage was only 2,1V, nevertheless it was working fine. Bad bank (cyl. 1-4) had a flatline.

The repeatable firing on the bad bank was not induced by the ECU. Guess it is some kind of coil protection inside the ignition module which blocks the transistor/thyristor after a certain time to prevent the primary coil from being toasted.


Regards,

Dirk

 

Sorry for bumping up, but @Steve:

No need to be sorry, actually I am quite happy now. Thought about posting earlier, but wanted to wait until everything is done. So I have a new (used one, therefore not too expensive) ECU, car is running fine as ever and the best part is: Because of the troubles with the ignition and the other cars I have from the 80ties (which, as I told my wife, might have similar problems in the future) I could convince my better half that a Bear Pace 200 (Motortester and wastegas analyzer) is a good investment. Finally got one on ebay for 350 Euro (approx. 450 $). Only had to replace the oxygen sensor (60 Euro / 75$) and the thing is working like new. I always dreamed of having a real motortester. That thing is a blast. (Scoping primary/secondary voltage, checking compression of each cylinder by the power consumption during starting, has a 2 channel scope, complete wastegas analysis (CO/CO2/O2, HC), you name it and it does it. Wish I would have had it way back in time, it would have saved me sooooo much work. I don´t know about the States, but in Germany this stuff got really cheap.

Anyhow, really happy now and thanks again for your help,

Dirk