13D Filing: King Luther Capital Management Corp and CECO Environmental Corp (CECE)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

CECO
Environmental Corp.

(Name of Issuer)

Common Stock, $0.01 par value

(Title of Class of Securities)

125141101

(CUSIP Number)

Jacob D. Smith

Principal, General Counsel & CCO

Luther King Capital Management Corporation

301 Commerce Street, Suite 1600

Fort Worth, Texas 76102

(817) 332-3235

(Name,
Address and Telephone Number of Persons Authorized to Receive Notices and Communications)

October 13, 2017

(Date of Event which Requires Filing of this Statement)

If the filing person has
previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Sections 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Section 13d-7 for
other parties to whom copies are to be sent.

*	The remainder of this cover page shall be filled out for a reporting persons initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be
deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act
(however, see the Notes).

Persons who response to the collection of information contained in this form are not required to respond unless the form
displays a currently valid OMB control number.