A method (45) for determining the total pressure in a cylinder (P.sub.cyl) of an engine as a function of the angular position (crk) of a crankshaft (14) and from a quantity of fuel to be injected in possibly several injections, includes: determining the pressure in the cylinder when there is no combustion, the pressure being called the pressure without combustion (P.sub.cyl.sub._.sub.m), determining, for each injection (inj.sub.i), a curve of sub-variation of pressure (P.sub.comb.sub._.sub.i) caused by the combustion of the fuel quantity injected during the such injection (inj.sub.i), the shape of the curve being estimated as a function of the quantity of fuel to be injected (MF.sub.i) and of the angular position for start of injection (SOI.sub.i) of the corresponding injection, determining the total pressure in the cylinder (P.sub.cyl) by adding together the pressure without combustion (P.sub.cyl.sub._.sub.m) and the pressures given by the pressure sub-variation curves (P.sub.comb.sub._.sub.i) of each injection (inj.sub.i).

A processing circuit is provided which includes at least an integrator circuit which uses a reference voltage set to have a predetermined magnitude as an operation reference and which integrates a detection signal so as to convert the detection signal into a voltage waveform and a base voltage adjustment circuit which is connected between an input terminal and an output terminal of the integrator circuit and which adjusts the magnitude of a base voltage that is a potential when the detection signal in an output signal output from the integrator circuit is not present. As another form, a processing circuit can be adopted which includes at least one or more amplifier circuits which amplify an output signal from an integrator circuit and a base voltage adjustment circuit which is connected between a supply portion of a reference voltage fed to the amplifier circuit and an input terminal of at least one of the amplifier circuits and which adjusts the magnitude of a base voltage that is a potential when a detection signal in an output signal output from the amplifier circuit is not present.

A processing circuit is provided which includes at least an integrator circuit which uses a reference voltage set to have a predetermined magnitude as an operation reference and which integrates a detection signal so as to convert the detection signal into a voltage waveform and a base voltage adjustment circuit which is connected between an input terminal and an output terminal of the integrator circuit and which adjusts the magnitude of a base voltage that is a potential when the detection signal in an output signal output from the integrator circuit is not present. As another form, a processing circuit can be adopted which includes at least one or more amplifier circuits which amplify an output signal from an integrator circuit and a base voltage adjustment circuit which is connected between a supply portion of a reference voltage fed to the amplifier circuit and an input terminal of at least one of the amplifier circuits and which adjusts the magnitude of a base voltage that is a potential when a detection signal in an output signal output from the amplifier circuit is not present.

A processing circuit is provided which includes at least an integrator circuit which uses a reference voltage set to have a predetermined magnitude as an operation reference and which integrates a detection signal so as to convert the detection signal into a voltage waveform and a base voltage adjustment circuit which is connected between an input terminal and an output terminal of the integrator circuit and which adjusts the magnitude of a base voltage that is a potential when the detection signal in an output signal output from the integrator circuit is not present. As another form, a processing circuit can be adopted which includes at least one or more amplifier circuits which amplify an output signal from an integrator circuit and a base voltage adjustment circuit which is connected between a supply portion of a reference voltage fed to the amplifier circuit and an input terminal of at least one of the amplifier circuits and which adjusts the magnitude of a base voltage that is a potential when a detection signal in an output signal output from the amplifier circuit is not present.

A processing circuit is provided which includes at least an integrator circuit which uses a reference voltage set to have a predetermined magnitude as an operation reference and which integrates a detection signal so as to convert the detection signal into a voltage waveform and a base voltage adjustment circuit which is connected between an input terminal and an output terminal of the integrator circuit and which adjusts the magnitude of a base voltage that is a potential when the detection signal in an output signal output from the integrator circuit is not present. As another form, a processing circuit can be adopted which includes at least one or more amplifier circuits which amplify an output signal from an integrator circuit and a base voltage adjustment circuit which is connected between a supply portion of a reference voltage fed to the amplifier circuit and an input terminal of at least one of the amplifier circuits and which adjusts the magnitude of a base voltage that is a potential when a detection signal in an output signal output from the amplifier circuit is not present.