blacks92seAuto

i usually get about 16-19 mpg 100% city driving. My car is running good and everything to tune-up has been done within the last year. My last tank I got 13mpg....and I figured maybe i drove it hard too much. But now that I toped her off with a full tank, I have gone about 25 miles and it is already almost at the 3/4 line. usually when I go 25miles its barely below the F line....anyone help me out on what it could be? car doesn't stutter or have any problems starting or idling...the only thing I could think of is a knock sensor, but would this cause a 3-5mpg decrease? what else could it be?

Golden Ice

well..to get the obvious out of the way...check the air filter?

blacks92seAuto

how could an air filter drop mileage from 3-5mpg over a few days?

Wiking

If bunch of squirrels decide to s hit in... (Smbdy here had a squirrel family munching off wires, and his fault story developed during the wEek.)

KS problem might be intermittent, as stuck calipers(did u use handbrake?) or whatever...

Filling a tank and/or gauge -measurement style has 10% error margin, how u drive means 50% of your mpg etcetc.

internetautomar

iTrader: (30)

if your air filter gets plugged it does affect your gas mileage.
also where/when you buy your gas has been shown to affect it as well.
the knock sensor by itself will not affect your mileage, it's the need to push the pedal farther to achieve the same power that causes the mileage decrease (my theory).

I'd start by giving the car a thorough looking through to see what if anything is awry.
Brakes move freely?
tires at recommended pressure?
Air filter Clean?
all plugs look good?
all injectors functioning?
alignment?
tires in good condition?
axle boots torn?
I think you get the hint

blacks92seAuto

OK, to get the dumb obvious out the way first. I have 17" tires 225/50/17 and the max pressure is 51 PSI...I havent checked them lately but I usually fill them up to 35psi warm...What is the reccommended pressure for best mileage on aftermarket tires? I have remanufactured front calipers, new pads, and new rotors. They should not be sticking at all...all tho I found a small groove on my front right rotor, and I think there is still a lil *** rock inbetween the pad and rotor cause it does squeal when applying the brake.
And after this kid hit me in december I had all wheels realigned. The spark plugs I replaced with NGK plugs from automart maybe 8 months ago, and I got a ngk o2 sensor from him as well.
I did do something stupid when I was cleaning my air filter a few weeks ago, but if it was a problem it should of showed up the last 2 weeks as well. But anyways, I cleaned my air filter with an air pressure tank, AFTER I did this, I found out its not smart to do because its compresed oily air. So would my air filter even tho it looks clean, could it be screwed up? And I fill up with shell Vpower. Once it stops raining Ill pull the spark plugs and check the condition.

Wiking

- 100psi is best for mpg? Use still recommendations. I suppose tire walls got that info. Its load/speed dependent: over 100mph needs more pressure...
- plug wires, cap: http://www.cardomain.com/memberpage/748507/12
...or then NOT if u have VE.

- disconnected groundings playIng?
- Air filter has no effect but in drop of max power. No problem with press air: still max airflow reduction cuts top pwr and oily paper filter is not best. - Broken filter fibers may have bad effect on MAF hot resistor (dunno really, heard this).

- Yes, pull plugs and check against ngk web page fault chart
- KS. Check ALL other sensors also. http://www.cardomain.com/memberpage/748507/9

RRJohn

Maybe a hole in your tank or filler tube letting the gas slosh out?

Golden Ice

If I understood you correctly, you said a plugged air filter wont affect mileage...but, when I changed the air filter in my Riviera, it went from getting 3 mpg (50-55 miles per tank with an 18 gal tank) to 9 mpg (150-175 miles per tank). Before I changed the filter, I ran about 5 full tanks before I got discusted with it and had the filter special ordered, and i've run atleast 10 tanks since. I've not let the air filter on the max get discustingly plugged, but I can't see it NOT making a comparable difference, in spite of there being a 30 year difference in the age of the cars.

Of course I may have misunderstood what you were saying..

915spd

hard driving maybe? o2 sensor? or was this in the tune up? air filter. it made a difference in my max. sometimes there's just crap gas out there.

Wiking

Part 1.
- If system works as it should, MAF detects 'how much' air goes to engine. ECU injects fuel based on measured air volume. Always same percentage%, not more, not less.

- ECU does not check filter or its condition.

- Now it really does not matter how the airflow to engine is regulated (Note: when engine warm; O2 in control). Usually regulation is done with throttle. Lets assume throttle is now totally open, and we have adjustable element, today renamed: FILTER. Nobody would know the difference... not ECU, not any body...


Part 2.
The power that injection engine gives out, is directly proportional to air volume. The more restricted intake, the less power. [simplification]. So if FILTER lets less air in, less fuel is injected, less power. So if more air in, more fuel is automatically injected, more power.


Part 3.
Cold engine is different story, then ECU controls by assumption AND Throttle position info. Injected amount is fixed; based on throttle position, not air volume. Now if air volume is half, injection amount is double. Result is blk smoke... On cold engine is no checkup how the burning process went, no feedback to ECU from O2.


I know Riviera is in France, nice beach... Maxima, in my garage.

Golden Ice

Well, I haven't studied fuel injected engines in depth..I know with my '63 buick riviera (nothing FRENCH about it aside from the name similarity...thankfully nothing more) and my '84 GMC both get lousy gas mileage with dirty air filters (carbed), and my mothers '91 s-10 blazer got worse mileage and ran like crap with a fairly dirty air filter (throttle body injected), so I have to assume there can't be a major difference in the detrimental effects of having a dirty air filter, whether its carbed, TBI, or EFI. the engine doesn't run right with a dirty air filter, one way or another.

I suppose I'm if the air filter is clean anyway..although I can't see it hurting any to put a new one in since the old one got blasted with compressed air, which CAN damage the filter medium and let dirt through that it would have otherwise filtered. A $5 air filter is cheap insurance.

blacks92seAuto

well i just started workin on pullin the plugs....first one i pulled... looks all brown/orange with a hint of a black...and it smells like fuel.....leaking injector? car does not run rough or anything

nelledge

iTrader: (6)

Check the coils while you are in there. I've had coils go bad without significant change in engine feel. Any signs of cracks or brittleness? Eh. Just an idea.

blacks92seAuto

front 3 injectors OHM out ok at 10.9....I omhd my knock sensor and it was 562...when my ohmeter was set at 2000k....does that mean it ohm at 562k ohms? it would only pick up ohms from my knock sensor when it was set at its highest, 2000k

blacks92seAuto

Its a jdm ve motor I put in a year ago. it has 8 month old ngk plat plugs from automart, and it has 8month old o2 sensor....full warpspeed exhaust 1 year old, ASP pulley 6months old, CAI 1 year old, reman front brake calipers, new rotors, pads, new rims/tires, fresh alignment, I have the adv. timing by moving the cam position sensor or whatever....ground kit... last summer I went through ALL of the wire connections, cleaned and reconnected. took me a few hours........I changed the fuel filter 1 year ago...since then I have done maybe 6 treatments of seafoam and run some chevron fuel system cleaner through........exhaust doesnt blow black or anything, and doesnt seem to smell like fuel.......

The only thing I can think of...is I recently had a car alarm/ remote start installed last week, and thats when my mileage dropped....but wtf would it have anything to do with my mileage?

sry was just listing things some of you are asking me.....the front 3 injectors ohm at 10.9 .....I think the knock sensor is ok, it ohm at 562k (562 on 2000k mode I think im right but i have no clue) I dont know what could be the problem...
Last week I did put some Isoheat stuff(absorbs water and moisture from gas tank) and I put in 1 bottle of chevron fuel system cleaner in...both on a fuel tank...could this maybe of eaten my injector seals up or something causing them to leak? I do have an extra fuel line with 6 known working injectors on it...I just dont want to swap it if its not the problem.

Wiking

Filter should have taken off all dirt that possibly was released. Cannot figure anything spoiling six injectors at once. ECU is the ctrl point for all those, that may go bad anytime...

Its important that each injector, coilpack primary/secondary -windings are about equal.

KS may give right reading, still be bad. Only way is to use bypass - and/or (go to stealership and) have it tested with tester while engine running =get actual ECU response and ign timing checked.

blacks92seAuto

I looked over your sight again Wiking, and I noticed that you put your 2x 500k ohm resistors in ....did you run those parrallel or in a series? and why didn't you just sue a 1,000k omh resistor? you said you now get 30mpg on the highway...what did you get before this KS bypass?

And what kind of resistor should I look for, I was told that they have different watts, or volts or something is different between kinds of resistors.

I am taking my car to my friend mechanic and he is going to hook it up to his computer and mess around with it, If he doesn't find a leaking injector, or something else wrong, then Im going to throw a resistor in place of my knock sensor to see if that fixes the problem, and if it does it looks like ill be pulling allot of stuff off my car for a little **** sensor.

BTW my gas mileage still sucks...Im at 67 miles on the trip, and gauge is just barely above half a tank....so im guessing im only going to get 150miles on this tank, give or take....I usually get at least 200miles on a full tank before i need to think about refilling...