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**Exhibit 99.4**

 

**CERTIFICATION**

 

I, David R. Demers, certify that:

 

1           Ihave reviewed this annual report on Form 40-F/A of Westport Innovations Inc.;

 

2.          Basedon my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessaryto make the statements made, in light of the circumstances under which such statements were made, not misleading with respect tothe period covered by this report;

 

3.          Basedon my knowledge, the financial statements, and other financial information included in this report, fairly present in all materialrespects the financial condition, results of operations and cash flows of the issuer as of, and for, the periods presented in thisreport;

 

4.          Theissuer’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls andprocedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (asdefined in Exchange Act Rules 13a-15(f) and 15d-5(f) for the issuer and have:

 

(a)          Designedsuch disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision,to ensure that material information relating to the issuer, including its consolidated subsidiaries, is made known to us by otherswithin those entities, particularly during the period in which this report is being prepared;

 

(b)          Designedsuch internal control over financial reporting, or caused such internal control over financial reporting to be designed under oursupervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financialstatements for external purposes in accordance with generally accepted accounting principles;

 

(c)          Evaluated the effectiveness of the issuer’s disclosure controls and procedures and presented in this report our conclusionsabout the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based onsuch evaluation; and

 

(d)          Disclosedin this report any change in the issuer’s internal control over financial reporting that occurred during the period coveredby the annual report that has materially affected, or is reasonably likely to materially affect, the issuer’s internal controlover financial reporting; and

 

5.          Theissuer’s other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control overfinancial reporting, to the issuer’s auditors and the audit committee of the issuer’s board of directors (or personsperforming the equivalent functions):

 

(a)          Allsignificant deficiencies and material weaknesses in the design or operation of internal control over financial reporting whichare reasonably likely to adversely affect the issuer’s ability to record, process, summarize and report financial information;and

 

(b)          Anyfraud, whether or not material, that involves management or other employees who have a significant role in the issuer’s internalcontrol over financial reporting.