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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8609
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Mitsubishi Galant ES: My 1999 Galant ES with 2.4 liter fails

Customer Question

My 1999 Galant ES with 2.4 liter fails smog. I changed the plugs, Cleaned the throttle body set idle to 700, Changed air filter changed oil. Had Error code PO125 Replaced temp sensor, Flushed coolant system new Thermostat checked in hot water Opens. Timing at idle too high 10°. fails 15 and 25 MPH test.
15MPH HC Max 54 I get 149, CO 0.50 Max I get 3.99
25MPH HC Max 37 I get 147, CO Max 0.47 I get 3.92
I need a suggestion as to what to fix.
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.
Hi, The high HC content is an indication of unburned fuel in the exhaust. This means your top suspects are going to be:Ignition componentsIgnition timingVacuum leaksLow compressionThose are your key areas of interest if you are not getting any other trouble codes (like individual cylinder misfires, catalyst failures, etc).With the plugs new and no fault codes that would indicate a coil issue etc, I would start by checking your compression and making sure you have adequate compression in each cylinder. Specified compression is 185 psi per cylinder, and no more than 14 psi variance per cylinder. Technically the engine will run as low as 140 psi as long as all cylinders are even, however the lower the compression gets, the higher your HC numbers will get.If the compression is within agreeable range, I would next check for vacuum leaks. This is best done with the engine idling and spraying around the intake and all hoses with brake cleaner.... if a leak is found, it will draw in the extra fuel and affect the idle.It is worth noting that this model is very common to have the intake manifold crack along the weld right behind the throttle body, so check that area for leaks first.If no leaks are found, then I would resort to checking the timing belt alignment. If the belt is off a tooth it will cause abnormal air intake resulting in over fueling and as such high HC, as well it will cause the ignition timing to read high at idle as well.