Bosch Mono-Jetronic

[Land Shark]

At 05:09 PM 1/31/96 GMT+0200, you wrote:

>I recently started looking at the FI system in my wife's Fiat Uno again,
>after it developed a flat spot on accellerating.
>
>The system consists of a single injector in the throttle body, an inlet air
>temp sensor, a throttle position sensor, a servo to control the throttle at
>idle (idle speed), a water temp sensor and a lambda sensor. And engine rpm
>info is sent to the system from the ignition computer.

 What .. NO MAP sensor .. and no AIR FLOW or AIRMASS sensor???

 are you SURE???

>Question 1: How? As I understand things, you need to know the load on the
>engine. How does this system find the load? Perplexing. The only thing I can
>think of is that the mixture is controlled by the closed loop system, even
>under acceleration etc. But would the lambda sensor be fast enough? Would a
>slow lambda sensor then cause a flat spot? Ooooh, my head hurts :-)

 Well, in most BOSCH systems .. load .. called Tl is measured like this ..

 Q(kg/hr)=f(Up/Uv)

 Tl=Q/(N*Ki)

 Ti=(Tl*[c1,c2,c3])+Cvolt

 Where Q is the airmass as a function of the incoming air sensor voltage
 on the air FLOW sensors it is an exp function .. on the AIRMASS Hot films,
 a bit more complicated ...

 Tl (load) is made from Q, n (rpm), and Ki, the injector flow constant

 From there .. Ti is formed by applying multiplicative lambda corrections
 to Tl and then adding the correction for battery voltage ..

 Ti, time for injection, is applied directly to the injector ...

>Question 2: This thing has a diagnostic port, to be read by a "Fiat
>something-or-other tester" which I obviously don't have. Seems to be
>three-wire. Anybody know what the protocol is likely to be? Peter? Should I
>put a scope on it and see what comes out? Should the ignition be on, or the
>engine running, when I do this?

 Check out ISO-9141 ... If you can get a jump of the internal EPROM, maybe we can
 figure it out ...

 Jim