[Diy_efi] Momomotronic lambda terror

mbelloli at speedymotorsports.com mbelloli at speedymotorsports.com
Sun Nov 21 00:33:33 GMT 2004

     I would agree with Dana. Many times I've seen these kind of readings
from a lamda sensor.  Well This is what You'd see if you were looking
at it like the computer does, using a scan tool.  An open ground to
the EGO sensor will end up leaving nothing but the signal originated
from the computer on the signal line.  It will appear to switch back
and fourth dramatically, because the voltage is sitting right on the
threshold of rich/lean reading.  In fact the computer is not getting
any input from the EGO at all because the circuit is not completed to
ground in the computer.  A reall good way to test this is take the
signal wire leading to the lamda sensor and with the key on engine
off, hold that wire in one hand while touch the positive and negative
battery terminals of the battery with a finger of the other hand. 
Use yourself as the tool.  And watch the lamda gauge you have.  It
should be very clearly moving to full rich, and to full ean reading. 
If not the path to ground path is missing.

Good Luck,


> My guess is that you have lost a ground connection somewhere.
> I would also do a check on the lambda readout. A pot across a 1.5V battery
> should work well as a test input.
> -Dana
> ----- Original Message -----
> Subject: [Diy_efi] Momomotronic lambda terror
>> Hi all,
>> i drive a '92 Volkswagen Polo. This car is equipped with a Bosch
>> Monomotronic, it is not OBD2 compliant. Since three weeks, I have
>> trouble
>> with that car and can't find a solution. This is why I ask here for some
>> assistance.
>> Symptoms:
>> I use a lambda display (the LED knight rider solution). The engine is
>> running much to rich. When I drive with constant speed and then switch
>> to
>> idle (e.g. when stopping in front of a traffic light), the engine
>> immediately runs rich (0.9 V) and stays there for at least 20 seconds,
>> sometimes even for one minute. This also happens when I use fuel cut-off
>> before running idle. I checked that to make sure that the EGO does not
>> measure some gases left in the exhaust pipe.
>> When driving with constant speed and revs, the lamda readout is quite
>> strange in my opinion. Former drivings with lamda display connected
>> showed
>> a
>> very well controlling engine, i.e. the light moved to rich, stayed there
>> (exactly one LED on), then moved to lean, stayed there (exactly one LED
>> on),
>> and so on. Now, the changes between lean and rich are performed much
>> faster,
>> and furthermore, the LEDs flicker like crazy. Even being at the rich or
>> lean
>> point where the engine stays for approx. 1 second, 2 or 3 LEDs on the
>> lean/rich end of the scale are flickering.
>> This flicker happens even when performing the movement from rich to lean
>> or
>> vice versa. It deteriorates when I accellerate (preventing the engine
>> from
>> WOT enrichment, of course). I already saw the LEDs flicker so much that
>> the
>> visual effect was as if 8 LEDs were on.
>> On the other hand, both fuel cut-off and WOT enrichment work correctly.
>> This drives me crazy, esp. because in few cases, the engine tends to
>> stall
>> when running idle.
>> I've already
>> - cleaned throttle plate potentiometer
>> - changed coolant temperature sensor
>> - checked air temperature sensor
>> - changed EGO sensor
>> - changed ECU
>> - cleared ECU's adaption values
>> - read DTC via Volkswagen protocol (no DTC were found)
>> - performed actor tests via Volkswagen protocol (everything worked fine)
>> - checked injector
>> So far, so bad, because now I have no further ideas, and that is why I
>> ask
>> on this list for any suggestions what to do. Has anyone had such a
>> bl**dy
>> behaviour of a Monomotronic euqipped car?
>> Thanks for any help,
>> Jens Knickmeyer
> _______________________________________________
> diy_efi mailing list
> diy_efi at diy-efi.org
> http://lists.diy-efi.org/mailman/listinfo/diy_efi

diy_efi mailing list
diy_efi at diy-efi.org

More information about the Diy_efi mailing list