(G) Bosch Mono Jetronic

Dear All,

Could anybody tell me how this kind of Fuel Injection System works ? and how to tune for the best result ?. My Uno using this kind of Fuel Injection System, and I need some information for setting Idle and Idle Pre-Warming.

Many Thanks,

Hendro. N

AIUI...

This is a very basic system which is trying to mimic a twin choke carburettor.


The quantity of fuel injected is determined by the following:

throttle position (there are two tracks on the potentiometer - one to correspond with each of the "chokes": the second one doesn't come into play until the throttle is part open.)

engine speed

inlet air temperature

coolant temperature

lambda sensor voltage (when warmed up)


The idle speed is adjusted automatically (using the stepper motor on the butterfly valve) under the control of the ECU.

When you turn the key to ignition on, just prior to a cold start, you may hear the stepper motor open the throttle a bit - you may even see the pedal go down a bit, if the cable is tight.


There isn't anything you can set: if it's all working as intended the ECU will take a stab at an ammount of fuel to inject, and if the engine is warm and the lambda sensor is switching, the ECU will correct this guess to maintain the correct gas mixture into the catalyser (on average).

When cold (ATS and CTS the same value, and no lambda switching) the ECU will juggle throttle position and fuel to give a slightly fast tickover.


On the mono-jetronic the ignition is totally separate from the injection (so no MAP sensor), but there is the vacuum advance to the distributor ot advance the spark on light throttle.

Check the advance cartridge - it fails and you get very flat performance and poor economy.


Give it a really heavy dose of injector cleaner, and a full set of clean filters, including the fuel filter.


That's about it - anyone else care to add, or contradict anything??


John H

Dear John,

Thank you very much, I'm very grateful. Now I have a little knowledge of Mono Jetronic Fuel Injection System.

I also got information that resetting ECU could be done for having best performance.

As I noticed, my Uno have a problem with Throttle Position Sensor, or you said Potentiometer. Could you inform me whether it could be replace by new sensor, or I should buy the whole Carb/Injec body ?
do you have any idea how much does it cost ?

Thank you and best regards,

Hendro. N

AFAIK

The Mono-jetronic can be reset by disconnecting the battery for a few minutes.
Do it while the engine is hot, and restart without touching the accelerator - it will start to "learn" the settings it needs.

If you search this site you may well find the instructions a bit more fully detailed. Might be on the Panda section.

I believe the official line is that the potentiometers (2 of them) are factory set on the throttle body, but ISTR Enzo found some details for setting it up from scratch.

The FIAT cost of a new throttle body probably exceeds the value of the car[:0]

There have been one or two recently on Ebay - went for about 26UKP - but I wouldn't bet on seeing another one.


Best of luck.


John H