Stage 3 - Control misc. devices


Most problems solved by now:

- 2 broken ignition wires

- 1 broken VEMS GND wire (hope it didn't kill anything inside)

- 1 broken WBO2 connection wire

- loss of fuel pressure

(It was not me who assembled/wired this car together... grrr)


Engine and VEMS is living again in another chassis.

Spent a half day of "mapping it right", but it can't be any better, finally we ended up with the config we started. With a ~30% improvement of req fuel because lambda values showed it necessary.

Main problem was unstable idle; loadsite pointer draws big ellipses in the VE table. Frequent stalling after backing off the throttle. Throttle reaction was horrible. Response is very late (0.5-1sec), and first it's become very lean (>1.5 lambda) . After that when falled back to idle, it was very rich (0.7x lambda) and stuttering for 10-20secs and then goes back to normal idle. It was reproducible. Played around with acc enrichment which values (or dimensions at least) are totally messed up in current megatune. Behavior changed slightly but problems remained.

Background info: current owner claims the car was running fine(?) the first day they started, and after that they poured injector cleaner into it and the next day it was hardly drivable at all. What can be caused by injector cleaner? -They removed all 6 injectors and flowed back to clean after that. (Some of them was somewhat blocked), -no change to problems.

Other suspect is misfire or problematic injectors. It's hard to detect a high-cam-duration 6cyl engine when a cylinder is not running fine. Any diagnostic methods? (Read the plugs is not the way -needs to remove the turbo)


Installed a PowerFlyback? because the ECU will go to another car using lowZ injectors. While it remained in the original High-Z config (injector PWM=100% and time to activate = 25.5 msec). Lambda went crazy:

Or even remapping was not really successfull. (Took away a lot in VE-table, still it was very rich, all-in-all lambda didn't follow VE-table changes; probably the well-known symptom of controlling injectors the bad way.)

Are you sure it's connected ? Yes.

If you apply 12V through a 22 Ohm resistor (the resistor is important!):

Voltage should drop to appr 6V.




Engine speed output is routed from Motronic 'ECU (55 pin) connector' pin 6 and signal goes to instrument cluster pin A7.

NEWS 2005.11.04:

Just tried the simple way and gave the tacho the signal of ignition and it's working more or less.

(Actually it gets fix +12V through a 10KOhm resistor (pullup) and that's going towards to the ignition pin of GenBoard through a diode)

+12V - - - - -10KOhm- - - - -tacho_signal- - - -|>|- - -ign.driver

So it's working but I see a bit lower RPM values on the tacho than the LCD shows. (maybe 10-20% lower, haven't tested much)

What can be wrong?

-Will look after voltage near the gauge, that can cause interesting reads also, I think.

However, with the tach output (since it's a freq-out signal, asyncron from the real ignition) it's possible to tune frequency.

- Wow, nice new feature I didn't know of :) Now I'm trying to figure out how it works. In actuators.c I see I can multiple value of engine.rpm_period by powers of 2 only. Multiplication of period gives me division of frequency. I'd like to multiple crank frequency by 3 or more likely by 3.3 . How can I do that?

The whole tach_out configuration is curently (1.0.23) sloppy:

 if(config.tach_divider == 0 || config.tach_divider == 1) {
                        // divide period by to 2 get freqout of rpm Hz
                        rpm_p = rpm_p >> 1;
                } else {
                        rpm_p = rpm_p << (config.tach_divider-2);

Something like scale16_4_clamped() in multitooth.c would do. Proposal for better utilization of config.tach_divider:

But 3 + 5 would do just as fine, *(32/64 .. 63/64) should be perfect for fine-tuning.

So we need to swap the code with a more sophisticated one. Please note that shifting (division with powers of 2) is not enough, for the 6 cyl engine I need to div by 3, and for a 5 cyl one rpm has to be divided by 2.5. Tricky.

Fuel Consumption Gauge

As what comes to controlling fuel consumption gauge, it seems that inside instrument cluster has some kind of adaptation module, which is engine type specific (size, number of cylinders etc.) - somehow it derives consumption from above mentioned tachometer signal and/or following two signals;

Don't know for sure, but 'Fuel rate output' signal might be some kind of pulses per second or pwm signal ? Someone could measure ?

Hope these help ?

I'm affraid we are talking about different motronic versions. Autodata catalog says that motronic pin 29 is ignition signal TO motronic. I can confirm that, since car was not running on motronic until I connected back that pin. Pin 32 is "throttle position control module" which might be some "cruise control" system. I'm not sure. I think my motronic didn't know the car's speed since my speedometer is fine without it :) (So signal from differential goes to the speedometer directly?)

Instead, maybe the instrument panel calculates fuel consumption based on fuel rate signal and speed?

Actually I only miss my tachometer, fuel cons. was inaccurate for ages (different size injectors and fuel pressure :)

Thanks however, and I still seeking tachometer signal specifications. No one using factory tachometer? I guess I have to wire back motronic to measure somehow :(

(or by phone# 1-2209238 in the evening)