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Q: Runs fine when cold- after 1/2 hour or so , spits and sputters then quits

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4 cylinder 2.4litre engine - problem started end of june when outside temp went above 95 and high humidity, girlfriend was borrowing it and at 1st issue was very intermittent now all the time, replaced cam sensor, last winter replaced crank sensor + radiator + starter, plugs / wires. took it to mechanic prior because it was surging, swapped coil packs , same issue. - he cleaned throttle body/ MAF. I removed thermostat and runs a little longer before dying - when it starts going the rpms go up, check engine light comes on, rpms drop then sputters and dies. will not start again until cools off. did cold compression test, all cylinders at 147. The engine sounds like a diesel with a lot of lifter noise although it always did since i bought it last october, took out primary o2 sensor to check for exhaust blockage(cat. converter plugged?), would that be a large enough leak to check?

My car has 12100 miles.
My car has an automatic transmission.

A: Hi and thanks for contacting YourMechanic. ...

Hi and thanks for contacting YourMechanic. To me this symptom sounds like three different problems that could be happening.

One problem is that the Engine Gas Recirculation valve (EGR valve) could be stuck open. This will cause the exhaust gases to enter the combustion chamber when the engine is cold. This causes the engine to heat up to quickly making the engine diesel and not burn the fuel correctly.

The second way is that the catalytic converter could be plugged. This will cause too much back pressure on the exhaust system making the cylinder too hot. When the engine gets too hot, it tends to diesel, which is burning the fuel at random times causing the engine to slow down.

The third way is for the Mass Air Flow sensor (MAF) to fail and needs to be replaced. The MAF sensor tells the computer how much air is entering the engine. When the MAF sensor fails, the computer defaults to high volume of air when there is actually low volume of air and demands full fuel. This heats up the engine too hot causing the engine to diesel and die off.

I would recommend replacing the MAF and rechecking. Then replace EGR valve. If you can put something over the exhaust with the engine running and it produces pressure, then the catalytic converter is okay. If not, then you need to replace the catalytic converter.

If you performed all tasks and still need help, you can contact a professional, preferably a YourMechanic professional to help you diagnose your stalling issue and repair your Mitsubishi.

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