Mitsubishi Montero & Montero Sport This sport utility vehicle offers more size than the other Mitsubishi SUVs, but manages to keep a sporty look and comfortable feel, unlike many larger SUVs.

Lean Combustion

Old 05-04-2019, 10:34 PM
Bremboy71's Avatar
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Join Date: Oct 2018
Posts: 9
Default Lean Combustion

Hello wonderful people.

I have a situation here that is bothering me, I have 2003 Montero sport 3.0 and it has been presenting some issues that i cant resolve. I have looked at the Workshop manual and i just would like a second opinion. My Montero was doing some odd things as it would shift everything ok but when in Fourth gear and you would step on the gas it would it looks that it would lower the rpm befor if would kick up strength to rebound. I looked at the scanner and i replaced the upstream and downstream O2 sensor and i could notice a white residue which gave me a indication of a lean combustion. As the downstream was not giving me the correct numbers on the scope. But the problem persistes and im not sure if this coule be the spark plugs but they are not that old to fail. Would love some feedback.

Thank you all
Old 05-07-2019, 11:06 PM
Senior Member
Join Date: Oct 2004
Location: Washington State
Posts: 1,311

It is possible that your fuel pump is not outputting enough fuel (tired pump or plugged filter/injectors) to maintain proper fuel/air ratio. Your description of bogging down when you step on gas (wide ope throttle) might be a clue to that. If you can read live data stream to confirm this would be great. Check your Long Term fuel trims (to see if they are in a high positive territory) and your Short Term fuel trims when you give it gas (if they climb up from idle levels). Post back, then we can try for solutions depending on results.
Old 05-12-2019, 01:17 PM
Bremboy71's Avatar
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Thread Starter
Join Date: Oct 2018
Posts: 9

Awesome Thank you so much. I changed the filter and pump. I thought it would have been the Downstream sensor that was giving the wrong info but the problem persists. Will look into your idea. You this a Fuel Pressure Regulator could also be the case?
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