为什么我的web服务/存储过程会将insert值截断为一个字符?

我使用jquery ajax将值发送到我的.net web服务,然后再将这些值发送到存储过程。我遇到的问题是,无论我向web服务发送什么值,它们都会作为一个字符插入到我的DB中。例如,“测试”变成“t”。

我的所有接收表列的最大值都不是1。使用Firefox的firebug,我已经确认我的ajax方法确实在向web服务发布预期的值。

Web服务:

 [WebMethod]
    public void InsertAllVehicles(string Make, string Model, string SubModel, decimal Liter, string Cylinder,string Fuel, string FuelDel, string Asp, string EngDesg)
    {

        using (SqlConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["localConnectionString"].ConnectionString))
        {
            using (SqlCommand comm = new SqlCommand())
            {
                conn.Open();
                comm.Connection = conn;
                comm.CommandType = CommandType.StoredProcedure;
                comm.CommandText = "Vehicle_InsertAll";
                if (Make.Length >=1)
                    comm.Parameters.AddWithValue("@Make", Make);
                if (Model.Length >=1)
                comm.Parameters.AddWithValue("@Model", Model);
                if (SubModel.Length >=1)
                comm.Parameters.AddWithValue("@SubModel", SubModel);
                if (Liter != 91)
                    comm.Parameters.AddWithValue("@Liter", Liter);
                if (Cylinder.Length >= 1)
                comm.Parameters.AddWithValue("@Cylinder", Cylinder);
                if (Fuel.Length >= 1)
                comm.Parameters.AddWithValue("@Fuel", Fuel);
                if (FuelDel.Length >= 1)
                comm.Parameters.AddWithValue("@FuelDel", FuelDel);
                if (Asp.Length >= 1)
                comm.Parameters.AddWithValue("@Asp", Asp);
                if (EngDesg.Length != 0)
                    comm.Parameters.AddWithValue("@EngDesg", EngDesg);
                comm.ExecuteNonQuery();
                conn.Close();

            }
        }

    }

存储过程

ALTER PROCEDURE dbo.Vehicle_InsertAll
    @Make  varchar = null,
    @Model  varchar = null,
    @SubModel varchar = null,
    @Liter decimal = null,
    @Cylinder varchar = null,
    @Fuel varchar = null,
    @FuelDel varchar = null,
    @Asp varchar = null,
    @EngDesg varchar = null
AS
IF @Make IS NOT NULL
BEGIN
    INSERT INTO VehicleMakes (VehicleMake) VALUES(@Make)
    END
    IF @Model IS NOT NULL
    BEGIN
    INSERT INTO VehicleModels (Name) VALUES(@Model)
    END
    IF @SubModel IS NOT NULL
    BEGIN
    INSERT INTO VehicleSubModels (Name) VALUES(@SubModel)
    END
    IF @Liter IS NOT NULL
    BEGIN
    INSERT INTO VehicleLiters (Liters) VALUES(@Liter)
    END
    IF @Cylinder IS NOT NULL
    BEGIN
    INSERT INTO VehicleCylinders (Cylinders) VALUES(@Cylinder)
    END
    IF @Fuel IS NOT NULL
    BEGIN
    INSERT INTO VehicleFuel (FuelType) VALUES (@Fuel)
    END
    IF @FuelDel IS NOT NULL
    BEGIN
    INSERT INTO VehicleFuelDelivery (Delivery) VALUES (@FuelDel)
    END
    IF @Asp IS NOT NULL
    BEGIN
    INSERT INTO VehicleAspiration (Asp) VALUES (@Asp)
    END
    IF @EngDesg IS NOT NULL
    BEGIN
    INSERT INTO VehicleEngDesg (Designation) VALUES (@EngDesg)
    END

    RETURN