Attn: 3.2 engine tuning gurus help????

[captainlewis]

I hope I am not wearing out my welcome with so many posts, but some have you have helped me fix almost every problem on my 1985 Carerra.

174,000 miles on Engine

current status:

Idles great
good power
great compression
50lbs of lio pressure 3200 rpm
200 degree oil temp never to hot
1 qt of oil burn every 1400 miles

work in the last 2 weeks

replace spark plugs with bosch 7s had 5s (ht range)
replace cap & rotor
replace fuel filter
techron fuel treatment
fuel pressure & regulator tests to spec
02 sensor test to spec
valve adjustment
replace head temp sensor 2 wire update
clean K & N air filter
new DME relay
full throttle switch tests to specs
oil & filter change
test for vacuum leaks
california smog test (technician stated running very clean
no djustments necessary

Not done

spark plug wires, I tested resistanceare pliable look oem
no spraks in the dark

no out of car injector service

LOW FUEL MILEAGE 22 MPG AT 72 MPH WITH CRUISE ON FLAT RUNS[
EVERYONE SAY TO LOW A MILEAGE FOR CAR AND MY 1984 TARGA GOT 27
OPEN TO SUGGESTIONS QUESTIONS ETC. THANK YOU jl

[stlrj]

It isn't always the engine. Alignment can make a huge difference. If you have too much toe in or out, your mileage goes out the window.

I have two cars that have the driver information display for instantaneous gas mileage, a 99 Dodge Intrepid and 99 Grand Caravan. I've been experimenting with the toe on both cars and, without a doubt, the slightest misadjustment does make a huge difference.

[kodioneill]

how are you checking your mpg ?

[captainlewis]

200 mile runs full to full gas station near freeway no traffic flat run. JL

[kodioneill]

what type tires and sizes are you running? is the o2 sensor plugged in? and how old is it?

[911st]

Long shot but check for brake pad drag. Get an inferred temp gage and hit each of your wheel centers with it after a cruse (or put your hand on each). The stock rubber lines can swell and retain pressure in the caliper or a piston may just be hanging up. You might start by jacking the car up and spinning the wheels

Some times the O2 can get lazy. They still output correct voltage but they do not react as fast as they should.

There is a Ca smog jumper under the drivers seat. It is a brown wire. Pluged in is supposed to make the car run leaner. Do not know if this will effect things.

Changes in wheels from light weight 15 Fuchs to 17" cast rims can effect MPG some to.

[captainlewis]

O2 sensor plugged in sensor is new, stock size tires 205 55 16 front rear 225 50 16, thank you jl

[kodioneill]

my 82 has 130,00 and the rear brake lines were plugged. so as the previous poster said check for brake hang up.

just to note my 85 carrera has 15 inch rims.

[Targa Me]

It sounds like you've done all the right things to your engine. Along with the alignment make sure you're tires are properly inflated.
FYI: Here's how I check my mileage.
Fill up tank until the nose clicks off on its own.
Set the odometer to Zero.
Don't fill up again until you are near the empty.
Fill up tank and note the gallons.
Note the miles on the odometer.
Divide the miles by the gallons filled.
Ex: 430 miles divided by 16 gallons = 26.875 mpg.

[tshih]

with today's fuel having 10% ethanol by volume and that alone means about 10% less mileage per gallon due to the energy content in ethanol is less than an equivalent of gasoline (octane), 22 mpg instead of 27mpg is not too low. Also try the same test at 60 mph runs and see what the mileage is. If it goes up then it is aerodynamic drag that is lowering your mileage.

[burgermeister]

Sounds normal to me. That's about the mileage I get.

EPA rates them at 16/23 ( www.fueleconomy.gov ) using the current rating scheme. I have never exceeded the EPA highway mileage on any vehicle, at least not since driving through Ohio during their peak revenue enhancement years (aka late 80's) going a steady 55.

[captainlewis]

Burgermeister, You are probably right, I am beginning to think I am chasing the mileage ghost. When I had my 84 carrera gas was real gas. I am going to send my dme control Unit to Steve Wong for a bench test and have one of his chips installed as I heard that this mod make them run a little crisper I might gain some mileage then. I am anal by nature, hence porsche technical freak, I really dont care about the expense, I would love to have enough time on my hands to go broke from the expense of driving this car. Thank you for your input. JL

[m110]

Captain lewis

I get similar mileage, maybe a little more if I was to do a flat, constant speed run, but rarely past 26mpg.

The engine's lowest full load specific consumption is 187 g/hp/hour at 2600 rpm which is about where you're at 76mph in 5th.

I'll bet if you dyno'd your engine you'd find it was a little off the mark after all these years. I also noticed a mph increase running without a cat which I surmise is from a slightly clogged but functioning cat. Ride height, weight, tire rolling resistance, altitude, temperature, driving style and how long it has been since you passed a snarky Subaru or M3 all have a bearing as well.

[burgermeister]

2600 RPM at 76MPH in 5th? Surely that's not stock gearing. 3100-ish is more like it I think.

[m110]

Originally Posted by burgermeister

2600 RPM at 76MPH in 5th? Surely that's not stock gearing. 3100-ish is more like it I think.

Yes, it was a big "about". My apologies.
My G50.01 gear chart with 215/60-15 tires has 2600rpm at about 62mph and 76mph at 3200rpm. Still both in the relatively efficient range for cruising although I think there still is a difference in consumption.

[captainlewis]

Had Steve Wong bench test DME controll and install SW stock chip. Mileage before 21 hwy mileage after 21 hwy same test long run over same road cruise on 72 mph. I love the chip and the new found performance but I ams still hunting for a solution no so much to get higher mileage but to cure my curiosity of what I have missed, I have checked for brakes hanging up, any info appreciated, thanks JL

[Mark Dia Gruppe]

You mentioned you got 200 miles out of 16 gallons, but you said you're getting 21mpg. Wouldn't that be 12.5 mpg? 200 miles divided by 16 = 12.5 mpg. If you're getting that kind of gas mileage, then yes, something is definitely wrong.

[stlrj]

You might also consider the fact that the 911 gas tank has an inverted bowl inside the spare that is either filled with air or gasoline or some combination of both that makes it almost impossible to make an accurate reading on your re-fill.

As long as we're getting totally anal about this, we might as well take everything into consideration and not assume anything.

Of course, the assumption is that the amount of air trapped inside the bubble would remain fairly constant, but I wouldn't bet my life on it, as even the slightest discrepancy would influence your calculations dramatically.


Cheers,

Joe
74 911 w/86 3.2 conversion

[captainlewis]

thanks for the input. I fill the car at the exact same station the exact same pump parked at exactly the same spot when I refill, as an update retested intake manifolds for vacuum leaks disconnected the o2 sensor and idle speed controll valve, and it surged at idle will do the intake manifold gaskets and go from there, JL

[stlrj]

Originally Posted by captainlewis

... but I ams still hunting for a solution no so much to get higher mileage but to cure my curiosity of what I have missed, I have checked for brakes hanging up, any info appreciated, thanks JL

Tire pressure. I like to keep mine at 40 psi on all corners.

Different tires have different rolling resistance. Do you know if the tires you have are rated for rolling resistance?

Alignment still needs to be addressed.

Do you know what your no load AFR is at 3200 rpm?