Ok so heres the issue I'm having,on a full tank I'm getting up to 140 miles i have No codes except for the intermittent speedo which i'll fix sooner or later.there was a member Crusher that gave me a few things to check on and they all checked out fine even swapped out the new oem maf to the old oem one that i cleaned.the only other issue i can see is i have a higher idle speed after warmup its around 800-900rpm and a slight engine vibration.the knock sensor is a new oem part and harness and all the o2's are also new.erg tube has also been cleaned when i changed plugs and coils.

I'll take any suggestions at this point!just point and ill test,fix or replace it if it will make the issue better

1997 Maxima
A/T from i30
324k on it

 

idle speed is too high. Bring it down to 700 rpm which is stock idle speed for our 4th gen maxima's. Unlplug the tps sensor and start the car and then adjust the adjust the idle speed from the iacv. If you see the black screw in the picture, that is where your idle screw should. It should be in that position.

 

Bad O2 sensors, the upstream ones, can effect gas mileage. I know you said you changed them but my question is - did you have the poor gas mileage before you changed the O2 sensors?

 

This issue just started about a month ago.

 

Idle speed was fine before issue started the adjustment was not changed so there should be no reason to mess with it.

 

Check your fuses. There's a fuse under the hood which is a 7.5 fuse labeled ECCS and if u take it out it will give u that high idle that you have and that fuse also controls emission functions and gas mpg.

 

Calculate MPG the right way.
140 miles to a tank would mean your burning more then double the fuel.
If that truly were the case you'd be leaving a trail of black smoke behind you, that is if it would run without choking itself out.

 

I drive the same route 6 days a week 22.6 miles round trip so its easy to calculate.

 

The miles part may be easy to calculate, but the gallons part? Nope. Just look at the fuel gage. Does the halfway mark mean exactly half a tank, or does it mean "half a tank, pretty much"?

 

Filled up today from exact E line light not on 16.88 gal to a little over F line.

 

Calculate mpgs
1) when you're empty, fill up full
2) reset trip
3) drive until you need gas again aka empty
4) look at the pump/receipt for how many gallons you filled up.
5) divide the number of miles from your trip by number of gallons

 

Um thats what i posted and its a average of 5 weeks

 

Btw knowing the mpg is not helping me fix the problem so doing that is Null and Void! The symptoms have been posted so turning this into a MPG & I got this many miles on a tank of gas does not help the situation! Basics is there is a problem i fill up 1x a week drive +/- 140 miles tank empty we do NOT need to know miles per gallon its irrelevant!

 

Incorrect

Correct

 

Relax. They're just making sure you're not one of those people that think their gas mileage is bad, but when calculated properly, it's not nearly as bad as it seems.

If you're consistently putting 16+ gallons of gas in your max, and you're consistently only getting 140 miles to the tank, then yes you have a serious problem. You're getting about 8.75mpg.

Check for a stuck caliper in the rear which will cause major rolling resistance.
Check your fuel filter
Check to make sure the diagnostic screw on the ECU is where it should be, and not turned
Bad injector(s). One or more is leaking badly
Check and clean/replace air filter

Based on your extremely horrible mpg's, I have my money on injector(s).

 

Finally some common sense answer.are injectors a normal high failure item? Filters all get changed every 3k. Rear calipers just changed in october and ps e brake cable.

 

At 324,000 miles, I'd definitely say your injectors could seriously be the culprit.

I had two leaking injectors and my Max has 230,000 miles...

 

Leaking injectors would cause FP to drop at the rails correct? So i could hook a gauge upto it and watch?

 

Thats actually what popped into my mind after reading his post. I had a stuck injector on my old car but it was stuck shut so cylinder 1 on my car would not fire at all. it can be annoying hunting these problems down especially with no CEL code.

 

So should i just replace all 6? I have a spare set from a 2003 maxima if they will fit and if the answer is yes without modification ill just put them in tomorrow instead of the hassle of testing and elimination of the potential defective one.

 

they won't fit.

 

Well there goes that morning project!

 

yea as nealoc said its a no-no. the 5th gens on up use top feed injectors, 4th gens on down use sidefeeds. Now converting your rail to top feeds might be worthwhile because top feeds>>>>>>sidefeeds but you might aswell do a whole 00VI swap while your at it.

What i would honestly do is go swipe a set of injectors and rail from a JY and try them. See what happens. Thats what i did on my old 4th gen DD and it worked out pretty well.