Calling on Motronic experts: IC information

[ischmitz]

Originally Posted by AlexTRD

Hello, hoping to revive this thread to resolve a fueling issue on my 88' 924s. The ground side of the injector circuit (pins 14 & 15 @ DME connector) is getting about 10.5v when the DME is supplied power. The harness is good, and this problem still persists when I power the DME on a workbench. I tested the rbdt65a transistor and it seems to be functioning. Pins 14 & 15 seem to be giving the same exact voltage coming from pin 10 of the 0127 IC. Is the IC supposed to be supplying voltage here? Pin 10 on the IC also branches off to a couple capacitors, so I'm thinking either one of those have failed, or its the 0127 IC. I can find no info on this damned chip, so if anyone knows what the function of pin 10 is that would help immensely, thank you.

First off the injector output of the DME is a current sink. As such measuring the voltage of these pins without a load connected has little meaning.

In other words you need to connect a load (the injectors, or a resistor with the other side hooked up to +12V). When the DME wants to turn the injector on it will turn on the transistor T402 through the driver IC. The IC is a custom Bosch peak&hold driver. It measures the current through the load and switches to a hold mode after a set time has elapsed. This is to drive the low-impedance injectors wired in parallel on the 924. Pin 10 in the current-sense input and tells the IC how much current is going through the injectors. This information is used to regulate the current in the hold phase of the injector cycle.

What is the issue you are having? Are the injectors always on and dumping fuel or are they not working at all? If none of the above I'd look elsewhere.

Ingo

[rick-l]

I would guess that Pin 10 is one of the inputs to a differential amplifier that measures the injector current across R409 along with R404, C405, R405 and C407

+1 on not measuring the floating input

This is my guess at how it works. They went to a lot of trouble to rapidly close the injector discharging through the 47 Volt zenner. The design was probably dropped as being over engineered and too costly

Originally Posted by rick-l

This is what I was thinking.

• RED T402-on +12 V on top of coil, ground on bottom CHARGE
• GREEN T404-on T402-off +12volts on both sides of coil HOLD Energy in coil decays only due to resistance in coil and driver
• BLUE T402-off T404-off Pin 1 totem pole output at ground. +12 on top of coil, +47 on bottom CLOSE INJECTOR , collapse field

Just a guess at how it works

[AlexTRD]

Thanks for the quick responses. They are dumping fuel, the car won't start. It has been sitting for about 13 years, and fueling is my last issue. If back the adjustment screw on the airflow meter all the way lean, the car putters and tries to start.

[AlexTRD]

OK, so I'm not entirely sure what I did, but it's running again. I tried to clean up the boards on the DME after probing around, as there were a couple rusty spots, and slapped it back together. I'm not complaining though lol, thanks again for the quick responses.

[Jonny H]

In the UK, you can pick up Motronic units from cheaper GM cars for very little money. E.g. A 'Vauxhall CalIbra' has a near identical ECU. There was a guy over here who had one running on a 3.2 Carrera. it ran terribly with the wrong maps but you can bet the chips are the same.

[Tippy]

Originally Posted by Jonny H

In the UK, you can pick up Motronic units from cheaper GM cars for very little money. E.g. A 'Vauxhall CalIbra' has a near identical ECU. There was a guy over here who had one running on a 3.2 Carrera. it ran terribly with the wrong maps but you can bet the chips are the same.

Really?

[Jonny H]

Yep, have a read:

ECU woes, the continuing tale of the poorly 3.2 - Ignition - Impact Bumpers

[AlexTRD]

From what I understand, the s400 0127 IC is exclusive to Porsche for control of fueling, hence why it would run poorly to use the DME from another manufacturer. We have a ton of old BMW 3 series floating around parts yards here that use a similar DME

[AlexTRD]

I guess, if you had an EPROM flasher you could switch it over

[rick-l]

Originally Posted by AlexTRD

OK, so I'm not entirely sure what I did, but it's running again. I tried to clean up the boards on the DME after probing around, as there were a couple rusty spots, and slapped it back together. I'm not complaining though lol, thanks again for the quick responses.

I bet the injectors were stuck from sitting so long.

[hardtailer]

Hello Pelicanites!
I'm pulling up this thread as it describes to a large extent what i'm observing and I therefore would like to tap into your collective expertise regarding the Bosch ML3.1 of my BMW M3 E30 to repair its Motronic, which I damaged due to a short circuit while measuring with an oscilloscope, whilst the engine was generally running reliably apart from lean mixture at partial load, which had a mechanical cause in the form of leaks in the intake tract as I found out afterwards...

Anyway, since the short circuit, the ignition spark is absent; the fuel injectors inject, but possibly continuously, as the engine is flooded after unusually few revolutions.
Engine runs fine with another motronic when I swap to that immediately after, it just requires full throttle to clear the unburnt fuel.

In an initial repair attempt, I replaced T505 with a BC548C, as I thought I noticed visible damage. However, that didn't help and the replaced tested fine out of circuit.

In the meantime, I found the circuit diagrams on here, checked the diodes and transistors (using the diode check on the DMM), and all showed a forward voltage drop of 0.5 to 0.6V with no short circuit.
However, that is not to say I have overlooked something...

I also replaced the 12V to 5V voltage regulator and restored the trace to the 12V supply with a wire, as both were broken. Unfortunately, that hasn't resolved the issue either.
I don't see any further damage and I've re-soldered the usual suspects, meaning the semiconductors in TO-220 and TO-3 packages prior to this mishap and it has been reliable up until my shorting it.

With the DME removed from the car and 12V applied to pins 18 and 35, and ground to 17 and 19, I measure at pin:
1: +0.6V
9: +4.9V
14, 15: +0.6V rising over several minutes to +10.4V
20: +1.3V rising to +3.5V
all relative to ground.
Only pin 9 of these shows correct voltage.

How can I track down the defective part? I have a single-channel signal generator to emulate a speed signal (the S14 engine has 116 teeth on the starter gear, different from the 911) but unfortunately, I currently have no way to emulate the signal from the reference mark sensor.
Is it true that after the first or only recognition of the reference mark, the Motronic could fundamentally do without this signal, as it calculates the ignition timing based on the pulses in the speed signal?

Thank you in advance for your support!

P.S. As a first contribution in this first post of mine w.r.t. the Opel/vauxhall motronic 0261200376 mentioned above in post #28 is NOT an alternative to the ML3.1 as it has 55 pins and therefore is not a ML3.1 but most probably a M1.3 using a 60-2 crank wheel.
I reckon the motronic referenced to in post 28 had only the lid of that Opel/Vauxhall...

[ischmitz]

Can you post a picture of the unit in question and explain what you shorted?

[hardtailer]

Unfortunately I cannot remember exactly were/what I shorted as it was about 2 years ago but it was on the PCB to which the 35 pin socket is attached.






The pads and tracks for the dc/dc convertor Unfortunately didn't survive the replacement and were substituted by the grey wires.
New spring clamp rivets will be fitted or I'll replace therm with screws and nuts.

The yellow arrow marks the spot where the +12V track burnt away.

[ischmitz]

Ah - that is very close to the 3.2 Porsche DME. Same Bosch 0127 peak&hold driver scheme for the injectors, likely with a different current sense resistor. Same flywheel decoder and ICV driver and same ignition driver. Just different inputs into the ADC because of the water-cooling and a different chip.

Does the DME show brain activity when you turn the ignition to RUN in the car. The ICV needs to vibrate. If that’s a yes the next step is to find out if the flywheel sensors put the DME into run mode. Check for fuel pulses when cranking or are the fuel injectors wide-open?

For bench testing purposes you need both the speed and reference signals to simulate the flywheel turning and then use an oscilloscope to confirm the 8051 MCU puts out spark and fuel pulses. After that it’s troubleshooting the analog portion to see if the fuel and spark signals are property generated to the outputs.

[hardtailer]

Thank you for your quick response, Ingo!
I was hoping that amongst others you would chime in 😀.

I am not where the car is but I can emulate RUN on the bench easily, however only without connecting an ICV, unfortunately.
Attached the scope views of the outputs to pin 33 and 34 and for reference, to ground.





I expect no buzzing ICV when less than 10mV is put out to it.

[ischmitz]

The ICV outputs are current sinks and measuring a voltage has little meaning unless you had a pullup resistor to Vbat hooked up to both outputs.

However, the fact that you see a signal with a frequency around 100 Hz might indicate that the MCU is generating a signal train. If that is the case it'll confirm the MCU is alive and running code. The ICV signal also serves the watchdog and makes sure the MCU doesn't get reset. Check the reset pin to confirm it is steady.

Next, once the flywheel decoder sees the flywheel signals it will transition into run mode where the MCU will issue pulses to the ignition and fuel output stages. That is the next step to confirm

[mysocal911]

This BMW DME ECM is basically identical to the Porsche 911 3.2, with exception of the EPROM (now a junk "performance" chip).
The way to begin troubleshooting, is to monitor the data & address I/Os of the microprocessor (uP).
You need to check pin 9 (reset) of the uP for ground, and all the data/address lines of the 8K EPROM.
The 8 bit latch circuit (S702) is critical for ADC & EPROM data to the uP.

It's simple to generate the speed & reference signal by using a sine wave generator & a pulse generator to initially to develop TDC.
If the S105 chip, RPM/TDC discriminator, is damaged, there are none available unless you find another DME ECM.
This also the case for 0127 (injector IC). All the other ICs, e.g. same ADC as the 911's, are available.

Don't waste efforts on the analog board until the uP & support ICs are running. You obvious need to have a good +5V supply
to the digital board. The analog board is simple to troubleshoot!

[hardtailer]

Thanks for chiming in too, Loren.

I have solid 5V power supply to the digital board.
I used the 1 channel function generator as input to s100 first to pin 4 and 7 and then to 2 and 3. Outputs from 8 and 10 respectively looked different from the input signals and from that I guess that s100 is not damaged.
Am I right in thinking so?

Pin 9 on the uC is not steady to ground but keeps showing a square wave going high. I take it that means it keeps resetting due to not seeing both rpm and reference signal simultaneously.

I will only able to continue work on this after I get a pulse generator, which will be next week at the earliest and will then continue checking the digital board as well as putting it in the car to check icv buzzing as well as check if the injectors are pulsing during start.

I'll update as soon as I've got new results.

Thanks again for your input guys!
Bernie

[ischmitz]

If pin 9 of the MCU keeps getting reset signals the watchdog circuit isn’t served by the ICV signal. That has nothing to do with flywheel pulses and needs to get fixed before attempting to put the MCU into run mode to generate fuel and spark signals.

[hardtailer]

Thanks for the pointer. I'll remember to check that first, once with the car.