excessive maintainence, low fuel economy

[IvoryJ30t]

im not compaining about the cars fuel economy, i just cant understand how other people get 20+ mpg in city driving.

just short of 100K miles. 95 maxima

within the last year- tiresfuel filterplugs [ngk copper every 12k]all O2 sensorscoolant temp sensorair intake temp sensorcleaned MAFrebuilt axleshoses, coolantBG chemicals every 12k [44k, isc, aisc]cleaned and siliconed [grease] harness connectors-coils, injectors, maf, iats, cps, tps, and ground points.

a whopping 16 mpg in city driving.

i did the work for the hell of it. the only failures ive had were a bad rear o2, and a starter. i get nissan parts real cheap with no tax.

im just amazed how some people ignore everything besides oil changes, and get great gas mileage.

[sicride]

either A) you drive like a loon, or B) you have a problem my friend. I see no air filter change though it seems as though something like that was just left out of the list. How bout a distributor cap? How does the car behave power supply wise? Obviously to get that kind of mileage there is either a hard driving condition, tons of sitting in traffic with the A/C on, or a lack of power at some point. 20mpg on a VG30DE should be No Problem.

[IvoryJ30t]

air filter changed every 6 months [OEM]

oil/filter every 3k miles [5w30 GTX]

trans flush 10k ago.

tires @ 34 psi

i do drive like a maniac, but my girlfiend gets the 16 mpg, i can get it into the low 14's

if you open my throttle plate, you can see the metal of the intake manifold [perfectly clean]

1 yr old battery, alternator healty, 0 ohms between block and negative battery terminal.

the car has no running issues, no stumbling, stalling, hesitation, ect...

COP ignition, no distributor.

i hardly use the AC, and its a VQ30DE, RE4F04A [4AT]

[rogoman]

If the thermostat is old, it may not be regulating the coolant temperature properly, so if the temperature is on the cold side, the ECU will run a richer mixture all the time which will hurt the MPG.

If you do a lot of stop/start short trips, it will hurt the MPG. Make a lot of long trips on a tank full to see what your highway MPG is; should be between 25 - 30.

[IvoryJ30t]

thermostat replaced with hoses/coolant.

ive replaced so many things trying to make it perfect, that ive forgotten alot of them.

i suspect the MAF.

[IvoryJ30t]

i always reset the trip odometer when i fill up, and i always go to my usual exxon station.

if i drive VERY gently, ill get 18 mpg.

"normal" driving gets about 16 mpg

i would say the average city/highway split is 85/15

i get about 25-26 mpg on constant highway use. [trips]

im not sure if something is wrong, or if it's just in my head.
Modified by IvoryJ30t at 7:31 PM 7/7/2006

[rogoman]

I've got a 91 240sx with an auto transmission and I average in the low 20's city driving; around in the high 20's highway driving.

You might try other brands of gas. Some brands seem to burn faster then others.

I've found out that during the winter months, the refineries put in a fast-burn additive into their gasoline in the interest of reducing emissions.

[NISTECH]

Take a look at your perking brake cables on the rear calipers. Pull up the brake handle a few times then release it and go look at the pivots on the rear calipers and make sure both pivots are sitting on there stops. If they are not you are dragging the rear brakes. The rear brake cables on the A32 had issues and there was actually a TSB to replace the cables and rear pad hardware to resolve the dragging brake issue.

[IvoryJ30t]

nistech- when you brought up the parking brakes, i thought that may have been the problem. however, the brakes disengage fully, and i can roll the car back and forth on level ground.

i say that, because when i last did the rear brakes, the pistons were difficult to turn back in.

since the ban on MTBE, sunoco no longer sells 94 in NY. that was my previous normal fuel.

now im stuck with 10% ethanol crap exxonmobil 93

[NISTECH]

Do the inspection on the return pivots exactly how I said. They do return about aaa 50% of the time but its that other 50% they dont. Inspecting them like I mentioned is the best way to do it, maybe do it 3 or 4 times to be sure its all good. Regaurdless of the MTBE ban your fuel milage is lower then it should be. Besides every one else would be getting lower fuel milage too as it is a nation wide ban on that stuff.

Something else you could do is get a consult hooked up to the car and moniter your Alpha% and see if it confirms an engine problem. If your alpha is running anywhere from 94% and LOWER you are running rich and confirms its an engine problem and not brakes or chassis related.

[IvoryJ30t]

i was considering bringing it to nissan for a consult scan and power balance test.

the snap-on OBDII scanner we have gives me a gm/s reading on the airflow, but i dont have the conversion table/graph to compare to.

it also reads out the ltft/stft.

last time i connected the scanner, i saw bank 2 had a much higher trim value than bank 1, and the alpha% had very slow reaction on bank 2.

that made me change the O2 sensors [NTK sensors]

i have not made any current [within last few months] readings with the scanner.

also- yesterday, i took a new meter readings-12.8 v battery14.08v running0.6 ohms from block to negative battery terminal

im going to have to ohm from the O2 sensor harness and the MAF harness to the ECU terminal.

[IvoryJ30t]

the fsm has a very small example of the MAF flow in gm/s. would you happen to know of a bigger/more detailed example?

if i can get around to it today, im going to do the O2 sensor monitor test with ecu diagnostic test mode 2. to make sure theres activity.

[IvoryJ30t]

so, performed the O2 monitor test.

both sides tested, at idle, 2k rpm no load, and light load driving.

both O2 passes the 2k rpm no load test [ about 15 flashes in 10 seconds]

there was activity during cruising/light load

however, at idle, the light would cycle, but after a short time, stay either on or off. the FSM says a steady state light [on or off] indicates open loop.shouldnt the car stay in closed loop during idle?

[NISTECH]

You never moniter O2's at idle the cars will tend to lock either rich or lean at idle. The unwritten operation of the earlier OBDII systems is that the ECM will find the best idle quality and hold it so it is not unusual for it to hold a light on or off at idle. That is why most nissan tests are at 2k rpms. I am not real familier with all the available moniters on aftermarket scan tools but if you can pull up alpha% on it by all means do it and see what kinda alpha your running at 2k rpms and even idle for the hell of it. Response to change with alpha is not real important its what it is at that is. Spec on it is 91 -109% but anything holding below 94% is a sign of a problem.

[IvoryJ30t]

2k rpm no load for 1 minute-

st alpha% bounced between 99 and 100 for both banks.

both O2 cycling rapidly

I also did a power balance test- each cylinder bottomed out at 700 from 750 in about the same amount of time. the change in engine feel was very even across cylinders. not really sure how that works.

i dont know if the results of that are worth anything without a graph.

i dont have a printer for the snap-on mt2500 [using consult port adapter, not OBDII port]
Modified by IvoryJ30t at 9:33 PM 7/10/2006

[NISTECH]

Your alpha looks good. You really should start looking at chassis drag.

[IvoryJ30t]

could it be the 100k trans?

it doesnt slip, fluid still bright. [flush 10k ago]

but it feels a little lazy compared to new transmissions.

i killed a new bmw 325 last night, trying to cut me off at a stop light, so i know the trans is putting power down.

[NISTECH]

i killed a new bmw 325 last night, trying to cut me off at a stop light, so i know the trans is putting power down.

How often does this occur? I think we may have found the problem with your fuel milage concerns...lol

Seriously , yes the trans can play a part but I lean toward the probably not side on that. I was more thinking wheel bearings, brakes, tires and such.