1997 Max SE, auto, pure stock, 123k miles, bought it at 108k miles

(1) 3 month ago, did major tune up (ail filter, fuel filter, transmission fluid, throttle body clean, drain coolant, 4x brakes, spark plugs, drive belt x 2, CV boots x 2)

(2) Just changed front O2 sensors x 2 (bosch from Autozone), knock sensor (ebay), KYB struts and shocks (w/struts and shock mounting kits).

***all work done by a mechanic, a friend’s friend***

Now the problem…it used to get 20mpg after I did (1), and now after (2), I got about 16-17mpg. Other forum says it supposes to increase by 3-4mpg and car pulls a bit harder, especially in the 3 rpm range.

I “think” the car accelerate a bit faster at low rpm, that’s about it.

Also front left suspension squeaks on bouncy road, could it be the spring isolator or bad installation on the left front?

I can't figure out why mpg DECREASE instead of INCREASE...


PS. never reset ECU after (1) and (2)

 

tires are a big thing, if you're tires are junk your mileage will be crappy. did you ever change the pcv valve? not saying that would make a significant difference but it's part of the tune up and real cheap and easy.

i'd either have the mechanic that did your work check out the squeaky struts. i have gr2s and they squeak sometimes over certain bumps but nothing major. did you put on dust boots? maybe they were hiding the noise before and shredding so he didn't reinstall them?

have you been driving it harder since the tune up looking for performance increases or driving habits the same? goodluck figuring it out!

 

I'm a shade tree mechanic but here are my comments.

I don't see where the shocks and struts would impact mileage at all. Make sure the tires are inflated correctly. As to the O2 sensors, try changing the one in the tail pipe. That way you will have them all new. Did you make sure the KS was tight and plugged in correctly? It is located in a diffucult place to get your hand into. I changed mine in May and it was tough. Reset the ECU.

One more thing...drive slower.....

 

PCV valve didn't changed, no rear dust boots but its the front left suspension that squeaks anyways

Could the bosch O2 already went bad or bad installation since i use bosch and needed split wires? Or the ks was installed incorrectly.

Would a bad installation on 02 trigger any codes?

By the way, what is the exact correct way to reset ECU on 97 Max? Or should I jsut drive it and let it get adjusted by itself.

 

i am by no means an expert on the knock sensor, but im pretty sure it takes a few weeks after you change one in order for the ecu to recognize it.. driving habbits can play a role too, along with what kind of miles your comparing them too.. around town or highway ya know. another thing you should really look into doing is having the tubes for the egr valve cleaned. this made a big difference in my milage.. i do almost all highway driving, and was averaging 300 miles to a tank.. after i had them cleaned i average about 365 now.

if you figuring out your mpg, you really shouldnt go by your fuel gauge. fill up your tank, top it off and set your trip odomoter. go through the tank, and fill up and top off again.. write down how much gas your car took and how many miles you got from that. then do your math.

the only thing i can tell you about investing $1,000 into the car is - you better get use to it..