EXHIBIT 10.4

FIRST AMENDMENT TO PLEDGE AGREEMENT

This FIRST AMENDMENT TO PLEDGE AGREEMENT (this “Amendment”), dated as of
November 6, 2007, is made and given by each of the undersigned (collectively,
the “Pledgors” and individually, each a “Pledgor”), in favor of WB QT, LLC, a
Delaware limited liability company, as agent for the lenders (the “Lenders”)
from time to time party to the Credit Agreement defined below (in such capacity,
the “Secured Party”).

RECITALS

A. Each Pledgor executed in favor of the Secured Party, for the benefit of the
Lenders, the Pledge Agreement dated as of January 31, 2007 (the “Pledge
Agreement”) pursuant to which each Pledgor pledged and granted to the Secured
Party, for the benefit of the Lenders, a security interest in the shares of
stock, ownership interests and assignable partnership interests described in and
appearing opposite the applicable Pledgor’s name in Part I of Schedule I to the
Pledge Agreement.

B. The Pledge Agreement relates to certain indebtedness incurred by Quantum Fuel
Systems Technologies Worldwide, Inc., a Delaware corporation (the “Borrower”)
pursuant to that certain Credit Agreement, dated as of January 31, 2007, among
the Borrower, the Lenders, and the Secured Party, as amended by a First
Amendment to Credit Agreement dated as of September 13, 2007, and as amended by
a Second Amendment to Credit Agreement dated concurrently herewith (as so
amended, the “Credit Agreement”).

C. Tecstar Automotive Group, Inc. (“Tecstar”) will execute a promissory note in
favor of Whitebox Advisors, L.P. in the original principal amount of $5,000,000
(the “Note”), and the Secured Party and the Pledgors desire to amend the Pledge
Agreement to secure the obligations of Tecstar under the Note.

AGREEMENT

NOW, THEREFORE, in consideration of the premises and of the mutual covenants and
agreements herein contained, it is agreed as follows:

1. Defined Terms. Capitalized terms used in this Amendment which are defined in
the Pledge Agreement shall have the same meanings as defined therein, unless
otherwise defined herein.

2. Amendment of Obligations. The definition of “Obligations” contained in
Section 1(a) of the Pledge Agreement is hereby amended in its entirety to read
as follows:

“Obligations” shall mean (a) all indebtedness, liabilities and obligations of
each Pledgor to the Secured Party or any Lender of every kind, nature or
description under the

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Credit Agreement, including the Borrower’s obligations on any promissory note or
notes under the Credit Agreement and any note or notes hereafter issued in
substitution or replacement thereof, and any other Loan Document (as defined in
the Credit Agreement), (b) any and all indebtedness, liabilities and obligations
of any Pledgor to the Secured Party or any Lender of every kind, nature and
description under any Guaranty and any other guaranty or guaranties executed and
delivered by such Pledgor in favor of the Secured Party, (c) all liabilities of
each Pledgor under this Agreement, and (d) solely with respect to Tecstar
Automotive Group, Inc. (“Tecstar”), all indebtedness, liabilities and
obligations of Tecstar to WB QT, LLC of every kind, nature or description
including without limitation under the promissory note executed by Tecstar in
favor of the Secured Party dated as of November 6, 2007 in the original
principal amount of $5,000,000, including Tecstar’s obligations on any
promissory note or notes issued in substitution or replacement thereof, in all
of the foregoing cases whether due or to become due, and whether now existing or
hereafter arising or incurred.

3. Effectiveness. This Amendment shall be effective as of the date first above
written upon the complete execution and delivery (whether by facsimile or
otherwise) thereof.

4. Affirmation of Pledge Agreement. The Secured Party and each Pledgor each
acknowledge and affirm that the Pledge Agreement, as amended hereby, is hereby
ratified and confirmed in all respects and all terms, conditions and provisions
of the Pledge Agreement, except as amended by this Amendment, shall remain
unmodified and in full force and effect. All references in any document or
instrument to the Pledge Agreement are hereby amended and shall refer to the
Pledge Agreement as amended hereby.

5. Successors. This Amendment shall be binding upon each Pledgor, the Secured
Party and their respective successors and assigns, and shall inure to the
benefit of each Pledgor, the Secured Party and the successors and assigns of the
Secured Party.

6. Counterparts. This Amendment may be executed in several counterparts as
deemed necessary or convenient, each of which, when so executed, shall be deemed
an original, provided that all such counterparts shall be regarded as one and
the same document, and any party to this Amendment may execute any such
agreement by executing a counterpart of such agreement.

7. Governing Law. THIS AMENDMENT SHALL BE GOVERNED BY THE INTERNAL LAWS OF THE
STATE OF MINNESOTA, WITHOUT GIVING EFFECT TO CONFLICT OF LAW PRINCIPLES THEREOF.

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IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly
executed as of the date first written above.

 

WB QT, LLC, as Agent By:   /s/ Andrew J. Redleaf Name:   Andrew J. Redleaf Its:
  Director - CEO

 

TECSTAR AUTOMOTIVE GROUP, INC. By:   /s/ Kenneth R. Lombardo Name:   Kenneth R.
Lombardo Title:   Secretary

 

WHEEL TO WHEEL, LLC By:   /s/ Kenneth R. Lombardo Name:   Kenneth R. Lombardo
Title:   Secretary

 

S-1

[Signature Page to First Amendment to Pledge Agreement]

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TECSTAR PARTNERS, LLC By:   /s/ Kenneth R. Lombardo Name:   Kenneth R. Lombardo
Title:   Secretary

 

S-2

[Signature Page to First Amendment to Pledge Agreement]