98 I30. very poor mileage at 60-70mph

[infii30owner]

Hi

am first owner of my 98 I30. used to give very good mileage but off late its horrendously low! on highways its giving like 20mpg (used to give 28-30 before) and it pulls very sluggishly. i can feel some sort of push back or something when i give it gas. what could it be?

1. bad coils or spark plugs? (i put in brand new ngk platinum 2 years ago. cleaned MAF sensor with MAF spray)
2. loss of compression?
3. cat converter?
4. fuel injectors? ( i tried 4 fuel system cleaners like BG44k, techron, moc, redline...no change in performance or mileage. i took it to a local mechanic who are into repairing european cars etc. he says proper, not the $10 can, ful injector cleaning should restore the power.)

It used to very smooth car...

any other tests i could do myself to find the issue (like check on fluids, clean something)? there is no check engine light.

thanks

[handz1000]

i barley get 18-19 mixed city and highway miles on my 98 i30 with 91+ ...would love to know what it could be also ,so im subscribing..also i dont think its out of the norm these cars are not that great on gas ...but if you clocked at one point of getting 28-30 Hw then wow thats pretty dam good. since consumer reports says 19-22 or so and people usually get 18-22 tops that i know of...would love to hear some responses

[infii30owner]

the sticker says 28-32 on highway and i used to get 28 easily when it was highway only. and it was 22 in the city. now its like 21 on highway or city. it has 150k miles on it, that is roughly 11k miles per year. so its not heavily used car or whatever.

[johntom240]

seafoam is your answer, find a vacuum line coming off of your brake booster, split the can into 3 equal plastic cups. suck 1 cup through the vacuum line as your buddy revs ur engine 2 about 2k so it dusnt bog an die. wen the cup is just about empty shut the engine for 5-10 mins, then you should have a nice smoke show and put the other cup in ur gas tank, and if your iol change is due put it in the oil fill and let it warm and immediatly change ur oil. the first method proves most effective, its worth a shot , only 9 bucks aanywhere it really is a miracle ina can sometimes

[infii30owner]

hi..i tried seafoam just before i had bg44k and techron (maybe a month ago). but i emptied half of it in tank and other half where engine oil goes. i could try the way you suggested. have to see if i could do it. sounds like its worth giving it a shot.

[infii30owner]

how do i upload an image here? i just took a pic inside the hood of my car near brake drum. want to make sure i pull right end of right hose before i pour seafoam in hope car starts after this procedure!

is this safe by the way? is this some short term fix that will require me to do it again and again. i could repeat it once an year or whatever.

i see some posts asking people to do an oil change or change spark plugs right after this procedure. is that true?

[infii30owner]

https://picasaweb.google.com/1131372333 ... directlink

pl see image in above album.

should i unclip the "U" shaped hose at the end that is going into that box (behind yellow cap). not at the top but bottom. will see if i can put some markings.

[tigersharkdude]

is your car A/T or M/T? If A/T you are only getting about 2mpg less than what was stated for A/T cars, combined with 13+ years of wear and tear, the MPG is normal

Is your CEL on? if so, check the codes

[NutriaforBreakfast]

Check air cleaner-make sure you cant see holes in the filter
Clean throttle body with electronic cleaner
Clean the MAF sensor with high quality electronic cleaner
Check the EGR system esp the EGR valve to see if its sticking
Clean carbon from Idle Air control valve
Check and see if PCV valve is clogged
Look and see if EGR tube attached to back of intake manifold plenum is clogged
Your (3) O2 sensors might be getting old-I replaced mine at 150,000 miles
Generally speaking there might be a lot of carbon but seafoam cant dig it out sometimes
like it needs to be

[infii30owner]

Mine is At/T. No CEL Codes. I should have my window sticker from Infiniti that shows EPA estimates. If I find it I'll upload it here. How did you upload that pic tigersharkdude?

After reading some more on seafoam, I decided to let the mechanic guy do some thorough cleaning. He said he ordered some cleaning liquid.

Will request him to check on EGR tube and O2 sensors.

I saw another thread by someone with exact same issue. Car is a drag now..used to be silky smooth before

[infii30owner]

here is image of sticker from my i30.

https://picasaweb.google.com/1131372333 ... ober132011



you can see that listed or avg mpg is 28. it gave highway mpg range as 23-33.

[handz1000]

$42 of 91 premium got me 203 miles

i have 2 cel codes for o2 sensors need to replace both soon

[infii30owner]

thats about 10 gallons of gas. so its 20mpg.

my car has no CEL. it had knock sensor and coil misfire codes in 2009. no CEL since i replaced all coils.

the mechanic said he'll clean fuel injectors with bg44k and do another round of checks. am suspecting EGR pipe block or something. i hope this cleaning he is going to do over weekend would fix this car once and for all.