Fuel economy Q

[jing]

I used to average roughly 450-500km per tank of gas, filling up usually around 50L each time which equals out to around 21-23.5mpg.

Now I average around 400km per tank.. or in other words, roughly 19mpg.

What can I do to increase my mpg back to what it was before?

Here's what's been done so far:
- reset timing to stock @ 15 degrees (it was advanced before, my mpg decreased AFTER it was set back to stock actually)
- replaced stock pump with walbro
- new nismo fpr @ stock fuel pressure
- new fuel filter
- new plugs gapped @ .032 (stock boost)

I should also mention that my driving style has not changed much, if at all since the decrease in fuel economy.

Specs:
Redtop SR
Splitfire coils
PBM cobra pipe
3" catback exhaust
3" test pipe
FMIC
HKS SSQV vented to air

[Jaketenpointo]

Maybe check for vaccuum leaks? change your O2 sensor?

Get a bicycle..... haha infinite miles per gallon.

[guitaraholic]

Maybe check for vaccuum leaks? change your O2 sensor?

Get a bicycle..... haha infinite miles per gallon.


Good advice, also check MAF connection, a leaky injector, fouled plugs, bad coils (though would run rough if that was the case).

[SlideWell]

incorporate an engine management system into your car, i.e. Apex-i Power FC, to tune your car for optimal gas mileage. if its tuned right you can get high 20's mpg with just under 400whp, thats what Justins S14 @ Position 1 in Port Orchard, WA car gets. He used to drive to Monroe from there, do an event, and come back with half a tank left.
low 20's is typical for city driving on a near stock SR depending how you are driving it and the landscape etc.

[guitaraholic]

Well, an engine management system will definatly help you don't "need" on to get good fuel economy. It's a little bit of a misnomer that you can either tune for power or fuel economy. True, things like HUGE injectors and sometimes a High Flow fuel pump can bring down fuel economy, but I still believe you can get good fuel economy on the stock ECU,, and here's how

The stock ECU (well with a daughtercard of some sort for bigger injectors, MAF, ect), has two modes, open and closed. During open loop (I hope I don't mix these up). The computer is checking signals from the MAF and O2 sensor, and probably a host of other sensors. It is trying to achieve the optimal A/F mixture at all times. This is usually as steady state driving conditions such as cruise. The computer doesn't care if you have a turbo that can put out 600whp (at least not at cruise). It just cares if you are running rich or lean.

On closed loop, (Full throttle, start up, and a few other conditions), the computer goes to the maps and doesn't care about A/F ratio. It does whatever is in the maps. It's at this time when you "tune" for power, and yes, you mileage will be horrible if you romp on it all the time. The more power you make the worse your mileage.

I have a 98 240sx w/ a 98 Sr20det engine with for now the stock T28. I have the usual bolt one (550cc injectors, Z32 MAf, chipped ECU, Walbro, FMIC, Full 3" exhaust) and I get 29-30mpg on the highway. In fact, I get over 30mpg if I am doing over 75 mph constantatly. I can't figure that one out except maybe I am driving where the engine works more effeciently. I can run up to 15psi of boost with no probs. So it makes plenty o' HP and still get civic-like mileage..

Hope that helps

[RHD95S14]

Well, an engine management system will definatly help you don't "need" on to get good fuelhttp://images.intellitxt.com/ast/adTypes/2_bing.gif (http://zilvia.net/f/#) economy. It's a little bit of a misnomer that you can either tune for power or fuel economy. True, things like HUGE injectors and sometimes a High Flow fuel pump can bring down fuel economy, but I still believe you can get good fuel economy on the stock ECU,, and here's how

The stock ECU (well with a daughtercard of some sort for bigger injectors, MAF, ect), has two modes, open and closed. During open loop (I hope I don't mix these up). The computer is checking signals from the MAF and O2 sensor, and probably a host of other sensors. It is trying to achieve the optimal A/F mixture at all times. This is usually as steady state driving conditions such as cruise. The computer doesn't care if you have a turbo (http://zilvia.net/f/#) that can put out 600whp (at least not at cruise). It just cares if you are running rich or lean.

On closed loop, (Full throttle, start up, and a few other conditions), the computer goes to the maps and doesn't care about A/F ratio. It does whatever is in the maps. It's at this time when you "tune" for power, and yes, you mileagehttp://images.intellitxt.com/ast/adTypes/2_bing.gif (http://zilvia.net/f/#) will be horrible if you romp on it all the time. The more power you make the worse your mileage.

I have a 98 240sx w/ a 98 Sr20det engine (http://zilvia.net/f/#) with for now the stock T28. I have the usual bolt one (550cc injectors, Z32 MAf, chipped ECU, Walbro, FMIC, Full 3" exhaust) and I get 29-30mpg on the highway. In fact, I get over 30mpg if I am doing over 75 mph constantatly. I can't figure that one out except maybe I am driving where the engine works more effeciently. I can run up to 15psi of boost with no probs. So it makes plenty o' HP and still get civic-like mileage..

Hope that helps

Good information but you did switch the names around.

Closed loop would be the first paragraph, and open loop would be the second.

[joe3180]

I have a 98 240sx w/ a 98 Sr20det engine with for now the stock T28. I have the usual bolt one (550cc injectors, Z32 MAf, chipped ECU, Walbro, FMIC, Full 3" exhaust) and I get 29-30mpg on the highway. In fact, I get over 30mpg if I am doing over 75 mph constantatly. I can't figure that one out except maybe I am driving where the engine works more effeciently. I can run up to 15psi of boost with no probs. So it makes plenty o' HP and still get civic-like mileage..

Hope that helps

i have the same setup but on an 89 240sx. and i get the same mpg has he does...28-30 highway. its great. before i installed the maf, inj, front mount, t28 turbo, clutch and tuned the ecu, i had all stock except the exh and fuel pump and was getting crappy mpg like 17-20. i dont know what exactly i did to change it but im happy with the result. im also boosting 15 time to time. i was thinking it was the tune that did it but there is no way for me to really figure it out very easy so im not going to and just enjoy. hope it helps in someway.

[steve shadows]

Honestly the best way to really really GET THE MOST out of your fuel economy is to take full control of your fuel and ignition maps

I suggest investing in a Power FC L Jetro unit.

Then reducing the fuel injector time on the low load cell portions of the map by 15% in every cell up to 4K rpms and eveywhere below load cells half way up the map. This should yield cruising AFRs of around 14.8-15.0 and also more low end torque.

Also I have found that the factory OEM Timing maps are WAY too advanced on the low load cell portions of the map, unless you are running about 100+ octane.

This may be due to the quality and octane suggested in Japan.

What you really need is about - 10 degrees less timing in every cell of the map to get the most efficient driveability and fuel economy as well as torque out of the SR 20det

Not 41 degrees of timing but 21 degrees of timing...dead serious

[Def]

First of all, get rid of that vented BOV and get a proper bypass valve vented back to your intake pipe.

Secondly, try replacing the O2 sensor, that is probably the change(more than likely your driving or gas blend has just changed).

[dawagarage]

i dont know anything about all the plethora of technical knowledge that these guys are sharing with you, however...
there are common things that anyone with any car can do, such as:
-weight reduction. not necessarily strip down your car, but remove useless things that sit in your car.. heavy wheels, because of the whole rotational mass thing, play a part in gas mileage, as well as braking, etc.... shit, even adjusting the tire pressure in your car can affect your fuel economy.
-weight reduction pt 2: do you yourself need to lose weight? im not poking fun here, this is an honest question.
-but the biggest thing you can do to positively affect your fuel econ is to adjust your driving habits. if you were to google 'how to improve gas mileage' or something like that, almost every legit site will say the same thing. but we drive these cars for fun so im sure that neither you, me nor almost anyone else on zilvia is willing to do that. but thats the answer to your question. how about cruise control? if you have it, try to use it as much as possible. one thing i see a lot of people do is to continue to accelerate to a red light? whats the point? as soon as i see a red light, i shift into neutral...
-keep your maintenance up to date, keep things fresh. such as all your fluid changes, to decrease friction, change your spark plugs, blah blah blah. use top tier gas, to keep your engine cleaner. top tier gasoline isnt a scam/scheme.
-but yeah. on your daily drives, be lighter on your go pedal.

[Ceepo]

I just checked my gas mileage

Sr20det Redtop(3000 or so since rebuild)
FMIC
Megan Elbow
Megan DP
Buddy Club Spec 2
Stock Boost
Stock FPR
Walbro 255
HKS bov, Not vented

I get an average of 24(in town) and 28-30(highway) i about shit my pants when i figured those number because my back bumper is black as hell...

[jing]

Picked up another O2 sensor for cheap, guess I'll throw that in and see how far a tank takes me and report back!

[markapple0507]

ya sound good ^^^^ let us know. also where'd you get it and what price? im asking cause im kinda in the same predicament and figured i would give the sensor a try but i an they're expensive