QuestionI recently took my 2003 Mitsubishi Galant ES 4 cyl into the shop due to a "Service Engine Soon" light that appeared. The car has about 95,000 miles and I assume needed some maintenance, even though the only problem I noticed was some vibration upon braking.
Regarding the service light, they pulled a code for the engine computer. The code was P0135 - a fault code for the Bank 1/Sensor 1 Oxygen Sensor Heater Circuit Failure. I then asked them to perform a 100,000 mile Maintenance Check.
The shop recommended the following and I agreed for them to do it: Replace the Bank 1/Sensor 1 oxygen sensor - Replace valve cover gasket and spark plug tube seals - Replace spark plugs and ignition wires with insulator boots - Resurface both front brank rotors, clean and lubricate the caliper slides - Clean and adjust rear brake shoes - Replace timing belt and balance shaft belt, idler pulley and timing belt roller pulley - Replace timing belt hydraulic tensioner pulley and balance shaft tensioner pulley, Replace water pump with a new one and replace the alternator belt and the power steering / AC belt.
$1,500 later, the Galant runs noticeably different, mostly in a positive manner. The problem occurs when I accelerate out of first and second gear. The engine / acceleration noise is noticeably louder than before the repairs. The engine revs louder moving from first to second gear, then again louder moving out of second into cruising. It sounds like the engine is working harder than is required in reaching cruising speed. Once in cruising speed, the engine noise is acceptable, but not as quiet as before all of these repairs.
I had the shop take a drive with me to listen. Unfortunately, the mechanic was not familiar with how the car sounded before the repair and could not distinguish a difference in noise. I left the car and they checked out everything, coming to the conclusion that the car was okay and that the repairs themselves are causing the difference in acceleration noise.
Still, something about this noise just doesn't seem right. I appreciate any help you may have to offer, Philip. Thanks!
AnswerI would like to ask if this service was done at a Mitsubishi dealership or another service shop?
I believe the recommendation for the "90k service" was the right thing to do... ie: timing belt, tensioners/pulleys, belts, plugs, gaskets, wires, water pump, etc. This "Preventative Maintenance" package that you just got done will save you from having future problems. The resurfacing of the rotors should have resolved any vibration you had under braking.
The oxygen sensor replacement was good too as they are usually only good for about 100k miles... sometimes less and sometimes more. Bank 1/sensor 1 gets the hottest and also the most use. It is most prone to failure. The code P0135 does not always mean that the oxygen sensor is bad... it means that that sensor provided the ECU with data that was out of "normal" range. It was a good idea to replace it, though, at 95k miles.
Now, the engine noise. It is common for the engine to be a bit louder after the service and a bit more responsive, as well. The timing belt at 100k miles, as opposed to a new one, is going to be stretched out( a little loose). Also, the hydraulic tensioner that maintains the tension on timing belt as it stretches will also lose some of its rigidity. The combination of these nice new parts being installed will cause the valves to "pop" crisply open and shut and would account for louder sound from the engine at mid-range RPM's 3500 - 5000. It will, in time, quiet down once the new belts stretch in.
If you notice excessive noise and vibration at low RPM's, there is the possibility that the small inner timing belt is a bit off causing the balance shaft to be out of sync with the crankshaft. This can cause excess engine noise and vibration. The timing marks on the pulleys for the inner timing belt are well marked and it would have had to of been a careless mistake for that to happen. The balance shafts' main purpose is to smooth the engine at low RPM's and make it easier to take off with 5-speed and engaging the torque converter in Automatics. I believe that if this were the case the noise would be more noticeable at idle and low RPM's... but it is possible.
So does it seem to idle OK? Smooth, steadily at about 800 (+/-100) rpm? Your steering wheel doesn't visibly shake does it? Let me know and we can go from there. I'll help you the best that I can.
Philip
