poor gas mileage on 98 I30

[infii30owner]

Hi

I have 98 I30. first owner. my i30 has 145k miles on it. in the last year or so its been giving less miles per g than before. what could be the reason?

i did replace all ignition coils, ngk spark plugs, knock sensor (got this one from nissan dealer) almost 2 years ago. also replaced air filter, cleaned MAF as suggested by user loystock in this forum. am also trying fuel injection cleaner redline now to see if it helps. i always keep tire pressure at 30psi.

could it be drive belts or o2 sensor? i have no SES light. however i do hear a knock whenever car accelerates from say 10 to 20 (more like during automatic gear change)

now i'm seeing about 22mpg on mixed highway (70%)/local. used to get 22mpg in city before and 28 on hwy. i always used premium (91 octane) or highest octane as recommended.

don't usually take this to dealer for oil changes or regular services as they rip off with unnecessary charges.

thanks

[loystock]

Looks like you have done the right things but I'm worried about the knocking. You may have a failing knock sensor but unfortunately, P0325 (KS problem) does not turn on the CEL.You better take you car to Autozone and the likes for free diagnostic. If you have a DVM, check the KS resistance is @ 550K-ohms (550-620K-ohms)

[infii30owner]

thanks loystock.

don't have DVM. getting that KS and putting it back is not that easy. let me see if anyone can run free diagnostic. if i can find one trusted mechanic, i'd rather pay him something reasonable and let him tune this car. just don't trust dealers...if i can get that mileage back i won't mind paying few $$$s to someone since i could use this car for another 50-75k miles easily.

[tigersharkdude]

Not trying to be rude or anything BUT really?!?!?

Only 22mpg mixed..originally said the car was going to get ~19 city/25 highway

my car gets around 15 city/25 highway..I dont complain as its been worse. My car has gotten as low as ~12 city and 18 highway

[infii30owner]

i am not kidding. i still have original window sticker that says 22 in city and 28 (max 32) on highway. i did see close to 30 just 2 years ago when i drove down from reno to san francisco. my highway/local mix used to be around 25. with gas prices so high have to pay attention to these matters

[tigersharkdude]

Just throwing it out there...Ive had two of these cars, and have a bunch of friends that drive A32's. Most of them tell me they get between 15-18 city. These cars are NOT known for having great gas mileage. I have never seen 350 from a tank of 100% city driving. ~16 gallon tank @ 300miles.... is only 18.75mpg. <<Thats normal for me.

[loystock]

Mileage also depends on driving habits and condition of engine-transmission (assuming no 'sticky' brakes). My sons drive the I30s and both of them are not lead-footed so mileage on both cars are close to factory spec. But these guys are not consistent in tracking mileage. I do track the Q45 and my average mileage for the last 11 years is - city=13-14MPG; highway=20-21MPG; combined=16-18MPG. Now that CHP is strictly enforcing speed limits, in my commute, I seldom go over 85 so my latest mileage has improved - combined is more towards 18MPG and I even get 22MPG on highway.

[infii30owner]

i agree. i rarely go over 70. not braking a lot. ramping up gradually etc. highway mileage coming down from 27 to 22 is quite a bit. hence the concern. think i even had transmission fluid flush a year or so ago.

[infii30owner]

loystock,

as you suggested i still suspect my coils and nothing else like as others here and elsewhere suggested (check for clogged EGR pipe, fuel pressure, clogged converter etc). i also saw a post on amazon that someone had improved mileage and power once they replaced all 6 coils from same manufacturer.

what i observed is one of the rear coils (one close to driver) is not exact length as others. i can still feel the knock at 10mph and 30mph. don't know if knock or missing is right word. there is no SES light. is there any way to tell what is the right coil length. does the spec say that? part number seems to be correct.

don't want to spend close to $900 on 6 coils from dealer and find out that mine were equally good or only one of them is bad.

wish i could swap my coils with OEM nissan coils from someone and see if issue goes away. i hope to see mileage and power gain. its down on those both bow.

[Maxbumpo]

Have you seen this thread?

easy-and-foolproof-coil-test-t230317.ht ... oil%20test

[infii30owner]

thanks. am going to try this.

plus i'm going to throw in techron 20oz fuel injection cleaner. from what it says about product, maybe that will cure the knocking/pinging and restore power.