Itinerant Air-Cooled

Ok it seems like it should be easy to test an ecu on the bench.
I can simulate the input trigger with a spare coil, dizz and spark plug..and watch the output pins for grounding action. Question is, at what pin does the ECU get its running power to run the circuitry ? Any ideas welcome...
Most of the pins are associated with auxiliary gadgetry...so it must be fairly simple to set up a test rack to make sure its doing its switching function.
Thx

depending on the year the schematic with pins is about page 40

https://www.thesamba.com/vw/archives/ma ... Manual.pdf

Thanks.

Per AFC manual...get Pressure Up, Ign Off, Remove harness, jumper Ground (16,17) to Ign pins 14,15,32,33
Then turn Ign ON. I did this and injectors spray nicely into their collector cups. So that part of system works fine

dingo wrote: ↑

Tue May 16, 2017 10:57 am

Question is, at what pin does the ECU get its running power to run the circuitry ?

#10, straight from the double relay.
Colin

Every Ohms measuremen checks out fine within spec. The system is intact and no shorts. Volts measurements check out too, with the exception of Pin4, which does no live up to the 'Min 9.5V while cranking'. Pin 4 seems dedicated toTTS and CSV, so im not sure if this is perinent.
This leads back to my initial issue with the starter. Replaced bushing, starter and cables...things got better but not great.

ok finally got a flicker at the injector......
voltage at batt 12.5v...with IGN ON, voltage at Igniion lead is 12.15 v.....when connected to coil+ drops to 10.75v, tho i do hear he relay click

so volt drop at ign sw ? or bad relay contacts ?

... jumped Batt+ directly to coil+..and took the following readings.
IGN ON
Batt 12.39 v pin 10 12.33
88b 12.33, 88a 12.33v

Ign ON, AFM flap open (fuel pump running)
86b 12.17v
pin 20 12.18

Ign ON, starter engaged
86 9.5 v
pin #4 9.5 V
(for both of these, dips down to 8.5 v as starter runs)

* prior to addressing he f.i. , i had replaced the starter with a 'reman' and replaced the starter bushing...altho engine turned by hand freely..the starter always seemed sluggish..or intermittantly sluggish

Volt drop tests :
using remote pushbutton starter, from B+ terminal to starter+ bolt, it drops .4 - .5v
from B- terminal to starter case, it drops .12 V
so internal or mechanical resistance to account for the 3v drop during cranking ?

The Coil+ wire loses all .5v at the ignition switch. With ign ON, incoming is 12.5 and ougoing is 12.1 at the switch. When wire Connected to coil+, it reads 10.75 V..and that returns to 12.0 when green dizz wire is pulled. Is this normal behavior ?

Coil + reads 12.10 with points open and 10.75 with points closed.

dingo wrote: ↑

Sat May 20, 2017 3:26 pm

Coil + reads 12.10 with points open and 10.75 with points closed.

Do you think the starter is pulling the system voltage down too far?
Colin

The normal procedure would be to measure voltage between battery POSTS with the starter off then cranking. If it still drops to 9.5 v have the battery checked. If is holds at 12V +/- then move to the battery TERMINALS and test again. Then between vehicle ground and 12V + POST. You will isolate the place the voltage is being lost. Once you do you can actually measure across where you are losing it and see it fall. For example, if you thing it is the ignition switch that is costing you coil voltage, measure the voltage across the ignition switch on and off. If the switch is at fault you will see the voltage drop across it. If a battery cable is bad for example, you will see the voltage drop across the ends of the cable. If the drop is say between the battery post and terminal you will see the voltage drop between those two points. Loss at any connector should be almost zero which would mean the meter sees no voltage. If it reads voltage between two points, that is the loss.

Volt drop from B+ to strater is rediced to acceptable 0.2 V

Batt : 12.45 v (drops to 10.2 during cranking)
Coil + 12.15
Pin 10 12.42 v (drops to 10.1 v while cranking)
All injectors get 12.42 on pos terminal
Pin 4, during cranking is a steady 9.25...which is below the spec 9.5...tho this pin feeds hermotime switch and cold start injector..so im not sure how or why that would affect injector grounding.

Starter spins freel;y now, but now i get NO flickering at injectors..i.e. No grounding

If you are between battery posts and not the clamp on terminals, and the voltage drops to 10.45 volts you need to check the battery. If it is 3 1/2 to 4/1 2 years old or older it Is probably worn out, sulfated or both.

Try turning the engine by hand a little. If it turns freely I would suspect a dead or discharged battery. If the engine is harder than normal to turn then it could pull the battery down but I would suspect a bad or discharged battery first.

Engine turns freely by hand. The batery is 'new'...some generic brand..i might have been on the shelf for years. , but it went from store to Bus. When cranlking, the volt drop is initially to 9v as the starter pauses, then as it gets momentum, the volts are steady at 10.2 or so

with charger plugged in and on 'engine start' mode,(about 13v or s) i get the flickering at the injector plug
I guess this Batt is Krap

As explained to me, this seems to be the case of a cell dropping out under load. It makes sense as each cell carries 2.1V and that is exactly what iam losing duri ng cranking