[Diy_efi] Momomotronic lambda terror

Dana Scott turbo at mustangs.com
Sat Nov 20 15:52:00 GMT 2004

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.

----- 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

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