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1994LS First MPG Check

3K views 22 replies 9 participants last post by  SLATZ 
#1 ·
I got 18.8 mpg on a 159 mi. trip, virtually all interstate/turnpike driving at 65-85 mph (using 91 octane no lead). My previous, somewhat less precise test gave me 21 mpg on the same drive. I know that different gas pumps can be a variable on a short mileage test.
The car runs great, but I think my fuel consumption is a bit high.
I'm looking for specific adjustments and other checks rather than anecdotes.
Thanks!
 
#3 · (Edited)
No stories, but I recommend some simple stuff, using good clean ignition plugs (I use the NGK BKR6EIX Iridium), clean injectors (use something such as Techron once in a while), clean ignition multi-connection plugs (under the air filter) sealed with dielectric paste, clean general electrical connections under the hood, functional (not high mileage tired) oxygen sensor.

Difficult to figure accurate mileage from only 160 miles. I try to use several fillings, and a GPS mileage reading, or use a correction factor for the car odometer. I would guess 24-25 mpg might be closer if all is well and clean, and a steady-state speed, although under some circumstances one might see as high as 28 based on my experiences. You might be surprised just how often one is on and off the gas pedal even when the drive is thought to be steady-state, thus sucking up more gas than you thought.

Not much to adjust on these cars. Others may have other suggestions.
 
#4 ·
Interesting, if it's running a little fat that could do it. Any specs for testing? I have no manuals for this car as it's a fairly new to me. I've put 4K on it so far and like it!
It has a little "flat spot"-can't describe it any other way- on deceleration. It would be a TPS adjustment on a 12V. Is it the same deal on a 24V?
The cold weather and a full garage have conspired to make this a low priority, but it's time.
Thanks!
 
#5 · (Edited)
Del-
You replied while I was typing-I'm senior slow.
I'll check all of the stuff you suggested. The GPS was in the GTV to check speedometer accuracy. I need to improve my data. I haven't used the Techron even though I have it on hand (maybe for the Milano).
As for the heavy foot, fuel economy is not my first priority but I want things to be right.
I'm going to pursue this because I'm finding this car and engine to be very cool.
 
#6 ·
if you get 21 or 22 on a long steady trip, with the 'low ethanol' blend (I can't recall if that's summer or winter blend here in CA) you are doing alright. I have broken 23 mpg one time barely on a stretch in central valley at 85 mph for about 200 miles. Around town here I barely get 19 -- on either car, but did hit 20.6 going 90 miles each way at about 75 mph about 4 weeks ago on the freeway

High value target (assuming timing is spot-on) is air filter then O2 sensor (check its output or if >80K miles might just be worth a swapola, its a 'maintenance item' they say), check the temp sensor resistance hot and cold (take it out, measure against room temp, and dip into a pot of boiling water, take readings, compare to chart in service manual), then we get into the more involved stuff like compression, etc.
 
#7 ·
Goats-
This engine isn't even close to the more involved stuff, so I think I'm going for the 02 sensor replace and temp sensor test. Since I can do the temp sensor test tomorrow, what readings am I looking for?
I bought this car from a long time AROC friend shortly before he died and want it to be right and haul ***!
 
#8 ·
page 561 of the 94 electronics manual shows the nonlinear response

roughly

0C = 1150 ohms
40C = 700 ohms
100C = 150 ohms

ie ice water 1150 ohms, boiling water 150 ohms roughly roughly

if running rich values will be higher than what I show above I think
 
#9 ·
Kinda depends how much of that trip you did at 80-85. These graphs illustrate the decline of mileage with increase in speed & increase in air resistance, so if ca. 50-55 mph equals the highest efficiency in terms of mpg (100%), at 80 mph that drops to 70%. So maybe your 21 mpg isn't so bad.
 

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#10 · (Edited)
On our trip to Galveston several years ago in the loaded 94LS, we averaged about 25-26 mpg across the Rockies, down through Utah and into Col and New Mexico, then across Texas to College Station, before going to Galveston, and then back to Seattle. At one stretch going "downhill" from the Rockies toward Texas, the car averaged about 28 for a few hundred miles at about 75 mph. Otherwise, it was normally 25 mpg at 70-80 mph very steady state (lots of straight flat empty freeways). Washington, Idaho, and Oregon are worse because of the numerous hills and increased traffic, although, with Oregon and Washington being heavy speed enforcement States, the mileage should be a little better, having to hold the speed down just a little.

Not quite as good these days, as I think that at 100k miles, while the oxygen sensor clearly works, easily passing the smog checks, it might be getting a little tired for max mileage. I've always kept all connections cleaned and protected.

When I first bought the car, the mileage wasn't that great, and it had ignition hesitations/cutouts at speed which were getting to be a real pain, but cleaning the ignition connections under the air filter box, and using dielectric grease everywhere, completely cured the problem. It's been just great ever since.
 
#11 · (Edited)
28 mpg in a 24V LS? -- you mustve had that paint waxed to a T, drafting a semi, no slipstream resistance, and burning 95 octane with a 20 knot tailwind! Seriously, when my 5 speed was at 36K miles I couldn't get past 22 mpg on flat, straight CA freeways using cruise control and I honestly do not think any of the LS cars I have had could ever get north of 23.5 under any circumstances. I think the window sticker was 18/23? for the auto car and 17/24 for the 5 speed? Someone have an old winder sticker here?

http://www.alfabb.com/bb/forums/alfa-romeo-cars-sale-wanted/145971-wtt.html Del what is your mileage per gallon these days ?
 
#12 ·
Mines a different animal altogether being a four banger but food for thought...for other reasons I changed the CTS and later, the thermostat. I think my mileage readings stayed roughly the same, maybe went a wee bit down. Why? The crisper responses from the motor I get are more tempting. I think the mileage calculations need to happen over the course of a tank at least and better, 2 or 3 and not just steady state running. Ciao, chris
 
#13 · (Edited)
I have all the mileage and gallons used on the Texas trip recorded (as with all trips), and have checked them over and over. I did say it was downhill dropping down from the Rockies into Texas, quite an elevation drop at very steady state driving. Also might have had a tail wind, lol, but the many hundreds of miles recorded don't lie. I think that air density at sea level does make a big difference in increasing gas consumption compared to being a mile high.

Just checked the numbers again, and for the major portion of the trip down I averaged 25+ mpg, and several stretches were 26-27, and one stretch of several hundred miles was 28. We averaged 24.5 for the entire trip (6857 miles, 280 gal), from Seattle to Galveston and back to Austin and then El Paso, including city driving in those cities plus Houston and San Antonio, before heading back up through the National Parks in Arizona and Utah and then back to Seattle.

Checking other numbers, for the trip down to see you in San Diego and back, we averaged up to 26.9 at about 75-80 mph. One stretch in northern Cal was 26.9 down off the mountains, 26 from there to Roseville, east of Sacramento. From Roseville to Bakersfield, the car also got 26. Back up along Highway 1 along the winding Big Sur road from Santa Barbara to SF, we averaged 24.7. In SF and north up the coast, the mileage figure decreased as we pooped along in tourist traffic along 101 in Northern Cal and Oregon. Not good there, was probably 22-23, thus bringing the mileage down for the entire trip (2875 miles, 118 gal) to 24.2.

One thing to remember, I have the back of the car just a little higher than that of the 91S, the front being the same, so that the car is slightly nose down in attitude. My aero engr studies indicated that this was slightly better for reducing vehicle drag at speed, but maybe only several percent.

Nowadays I get 21-24 mpg around the Puget Sound area, sometimes slightly lower, depending on traffic and where I drive, 22.2 for the last 1900 miles of city driving, plus a dash down to Portland and back ~300 miles).
 
#15 ·
yep Del the numbers don't lie for sure! Were you running 15's or 16's (and what tire pressure?) and did you get miles driven by the odometer, GPS, or both, ? I wonder if maybe part of my car;s apparent low mpg is that it might be under-reporting odometer miles by 10%???
 
#16 ·
This thread is timely. I've been getting disappointing gas mileage (~17 mpg) for the past couple of months from my '91 164S. Even accounting for cold winter temperatures and a fair amount of stop-and-go driving/short trips I believe this is 2-3 mpg below what the car should be getting. I replaced the O2 sensor this past summer so it shouldn't be the problem, though I plan to check it anyway. Pretty sure I'm running rich based on exhaust smell and reports by friends following me that I'm putting out puffs of black smoke during up- and downshifts.

To make matters worse, my Check Engine light doesn't work (again! even though it was fixed by DiFatta's mechanic a year ago -- the 'fix' lasted all of a week) so I can't use it to read engine fault codes.

****ed modern engines.........

Good advice above, I will check temp sensor, air filter, plugs, injector and other connectors, O2 sensor.
 
#18 ·
Del you made me think of something last night later after I read this. You were running 16's and the odometer and speedo were quite close to referee method (GPS)? Typically would we not expect the odo and speedo to under-report by about 7%?

IF it didn't ; then perhaps my odo's may be UNDERREPORTING by 7 % or so, which would bring my 19-20 is mpg up to 20 - 21 mpg without doing a thing!

If that's the case, then my 23.5 ends up at 25 ish.

???
 
#19 · (Edited)
I think my 91S is off by about 4+%, also with 16's but a different brand of tire. When the S speedo reads 80, the car is doing about 76-77 or so according to the mile markers by the side of the road and the GPS. The LS is a lot closer than that.

Also, the tire temps/pressures of the S are not as high generally as the LS, I'm sure, because the daily driver S sees hardly any high speed hot day freeway miles at all as the LS does, the LS being our trip car. I usually run lower pressures (~29-30 psi) in the S anyway because of the rougher pavements of our cities, since I also run the S in the stiffer "sport" setting 98% of the time.

The LS, I usually start out cold at 32-33 psi for a trip, the car being loaded with 2 people and lots of luggage, cooler, full tank of gas, etc. I'm sure the pressure climbs considerably higher after steady state higher speed conditions are achieved on a hot day. Plus I basically tend to feathertouch the gas pedal to maintain a steady speed, trying to be super smooth (unless there is a winding road to be found, lol, and no, I don't use the cruise control, don't like it).

I guess I would say that I have probably accidentally(?) optimized the LS for the driving we do in it, while the driving you guys do is maybe/probably more normal like I do in the "daily driver" S. It gets lousier mileage by about 5-6 mpg (cold store trips, lots of lower (heavy throttle) gears, etc).
 
#20 ·
Since I started this thread a year ago, I've done a a bunch of work (t-belt, coil packs, plugs, ignition modules, etc.) The car is running perfectly.
I just completed an 881 GPS mi. drive for an Alfa club weekend near St. Louis.
My average for the trip was 25.6 mpg. I even got 27.6 mpg on one tank, using ethanol free 93 octane, 100% highway at 70-75 mph. I probably even had a tail wind on that leg!
 
#21 ·
that's pretty good. My 4 gets steady around 30 and at times 33 on the hwy. RC Mostro? I'll not go there :) caio jc
 
#22 · (Edited)
...I'm looking for specific adjustments and other checks rather than anecdotes...
Place a rolled up face towel under the accelerator pedal

Seriously though, the first thing to do is verify the accuracy (or inaccuracy) of the odometer with a second source because without doing that you are working with numbers that you have no proof are correct. I wouldn't put a lot of faith in the Alfa instrument being very accurate from my own experience.

Once that is accomplished and you can get accurate data there are a number of factors that can affect mileage. I was getting about 16 on my Land Rover and because it has OBD2 I was able to run an app on my phone called Torque which allowed me to monitor in real time my average and instantaneous mileage. It was the instantaneous figure that allowed me to modify my driving style and increase my average to almost 22. Contrary to what you might think I didn't do it by slowing down, in fact slowing down can be the worst thing. What you want to do is keep the momentum up and drive as smoothly as you can, keeping your speed up on grades and coasting when possible. Using cruise control is not a good way to improve mileage unless you are on completely flat ground and even then may not be as good as you can do it manually.

Edit: jeeze, just realized this thread is a year old. I hate it when that happens
 
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