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  <xs:element id="psix_OperatingLeaseAssetsAndLiabilitiesLesseeAbstract" abstract="true" name="OperatingLeaseAssetsAndLiabilitiesLesseeAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="psix_FinanceLeaseAssetsAndLiabilitiesLesseeAbstract" abstract="true" name="FinanceLeaseAssetsAndLiabilitiesLesseeAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="psix_MastPowertrainV.TheCompanyMember" abstract="true" name="MastPowertrainV.TheCompanyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_GaryWinemasterVersusTheCompanyMember" abstract="true" name="GaryWinemasterVersusTheCompanyMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_NumberOfOutstandingLettersOfCredit" abstract="false" name="NumberOfOutstandingLettersOfCredit" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardAverageFairMarketValuePerCommonShareThresholdTradingDays" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAverageFairMarketValuePerCommonShareThresholdTradingDays" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRightsNumberOfInstallments" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRightsNumberOfInstallments" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedVestingInvoluntaryTerminationPeriodFollowingChangeInControl" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedVestingInvoluntaryTerminationPeriodFollowingChangeInControl" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="psix_ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementPaymentPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardSettlementPaymentPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="psix_SWIECMember" abstract="true" name="SWIECMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_MORAgreementFeeMember" abstract="true" name="MORAgreementFeeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="psix_LongTermPurchaseCommitmentMinimumTargetPeriodForRenewal" abstract="false" name="LongTermPurchaseCommitmentMinimumTargetPeriodForRenewal" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="psix_OtherCommitmentFeeAsAPercentageOfGrossRevenue" abstract="false" name="OtherCommitmentFeeAsAPercentageOfGrossRevenue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
</xs:schema>
