why is my web service/stored procedure truncating my insert values to one char?

I'm using jquery ajax to send values to my .net web service which in turn sends those values to a stored procedure. The problem i'm having is that no matter what values I send to the web service, they get inserted into my DB as one char. e.g. "test" becomes "t".

None of my receiving tables columns have a max value set of 1. Using firebug for Firefox I have confirmed that my ajax method is indeed posting the intended values to the web service.

Web Service:

 [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 = "开发者_运维百科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();

            }
        }

    }

Stored Procedure

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

The parameters of your stored procedure, particularly those with type varchar should be declared with lengths that match their columns defined in the table. For example: @Make varchar(50)=null.

Because VARCHAR is one character. Set it to VARCHAR(MAX) till you know what size you really want, replacing MAX with the size you need.

specify the varchar length of each field in your stored proc, eg @Make varchar(50) = null