Mine looked like they were ready for a change at 75k. The car was stock until 65k.

OP, change the plugs, use premium, rest ECU, and check to make sure the throttle body is opening all the way when at WOT.

 

My daughter bought a new Mazda CX-9 V6. The manual said to run premium, but she put in regular to save a few bucks. The cat system failed twice while it was under warranty, and the dealership siad it was the result of running regular fuel The dealership told her it would be $1800 if it went out again after the warranty expired, so she traded it for a Subaru Outback.

 

Yeah always use what the car recommends.

 

Doesn't surprise me. The ECU would have had to majorly retard the timing and dump fuel to keep the block from grenading, which in turn caused higher EGT's and roasted cats.

 

Do you know for a fact that the previous owner used only regular gas? That seems a pretty difficult determination to make without knowing the previous owner.

 

Whenever I buy a used car with basically unknown maintenance history I completely go through it.

New air filters, induction service, fuel injector service, compression check, new plugs, and change all fluids front to back. You could also send out an oil sample to check the internals.

Good luck

 

+1000000000000000000000

 

The last used vehicle I bought was a six-cylinder '90 Ford pickup with 19K miles on it in '92. I sold it in 2003 with 105K miles on it.

I never touched the drive train except for a fan belt replacement and routine oil and oil filter changes on the engine. When I sold it, the original air filter, radiator coolant, AT fluid, spark plugs, and rear end oil were still in it, and it was running and driving just fine.

I know the fellow I sold it to kept it for several years with no issues, so the truck obviously wasn't dying when I sold it.

Routine maintenance (with the exception of engine oil and filter) is highly overrated, but if it makes you feel good, have at it.

 

i reset the ecu and began running premium only.. there is still no difference is performance.. and to add more info.. The motor has a loud and audible ticking sound coming from the top of the motor.. the ticking speeds up as i step on the accelerator.. I fear that the ticking is 'rod knocking' or a stuck lifter...

I was hoping the ticking was because of the grade of gas... but even after running premium its still ticking... any ideas?

 

Those engines were freakin bullet-proof.

 

Im about a year late but whatever, Ive been doing my research and what ive understood is that becuase lower octane fuels have more burning resistance the engine thinks its burning when its not. Again im not expert (so if im wrong correct me) thats what i understood. and that the engine will start knocking when too much regular fuel is used. What does that mean? knocking???

 

Basically, the higher the octane the less knock you should experience. As others have said, different engines require different grades of fuel like regular, mid grade, or premium. Most cars run regular now I believe, but the higher end cars always are PREMIUM for a reason. Again, other people mentioned the ECU will cut back on timing to compensate for regular. To be honest, just run premium from now on. There's no going back in time to see if it's been ran on regular. Knocking is basically a knocking sound. Nothing to it, but that. It's just more pronounced and you will definitely hear it.