OMG! 21.75-21.65 MPG on SF Trip!

[tkd_q45]

As you all know, I've been whinning about poor MPG with our 92Q. Well I just got back from a trip up to San Fransisco (from LA - went to the peace rally but that's another thread all together!) and I averaged over 21MPG both ways (mostly 65-80MPH). I don't know how much of it had to do with driving at night in foggy/moist air. I did notice that as soon as I did any urban driving the fuel gauge dropped like a lead balloon. Fortunately I did very little in town driving. I'll see how the next tank or two does (now that we are back home) but I think my MPG will be back down to 10-11. Any thoughts on what's up with my car?

[PalmerWMD]

I think your hiway milage is very good.That <should > mean the engine is ok, but for comparison:

My first gen Q's usually get 13mpg in town thats with kinda spirited driving.My best in town mpg is usually 14-15mpg my worst 11 mpg.

Thses numbers have held for all my Q's, keep in mind that I tend to drive kinda hard ( At least 3-5 WOT runs per week, 100 +mph at least a couple of times per week)

Fred...

[PalmerWMD]

milage related questions:

How recent is your fuel filter? OEM?Plugs?Injetcors original?

A poor MAF connection cna also cause bad consumption and loss of power.But u dont have any powerloss right?

Do u do a lot of idling?Tell us more about the local drving conditions for your car.

Fred..

[Q45tech]

Mileage in closed loop is just a simple function of throttle position times speed...........80 mph vs 60 mph will use close to 33% more fuel per minute/hour etc...........actually any speed above 74.999 mph [2500 rpm] will be worse proportionately because you have entered the performance range where the mixture gets a little richer to protect the engine.

To assure best city mileage accelerate VERY VERY SLOWLY so that the rpms never exceed 2500 rpm in each gear.

You can burn an entire tank [22.5 gallons] in less than 1 hour at 6,000 rpm......6 mpg @ 150 mph

[infinitinut]

You can burn an entire tank [22.5 gallons] in less than 1 hour at 6,000 rpm......6 mpg @ 150 mph

Jeez, Dennis! It took me a little longer than that from Ozona, Texas, to Ft Stockton, Texas, but the speeds were up around there, most of the time. Limped into FT S. on fumes, though! Last trip out in March used normal velocities, keeping out of the triple digits.....most of the time! Now, from Mountainair, NM, up to Santa Rosa and I-40 interchange, on deserted 2 lane roads, triple digit speeds were the rule of thumb for a couple of hours. A NM native told me that there is a state law which forbids the issuance of a speeding ticket on rural roads!

[Q45tech]

10.0 millisecs x possible 16.6 millisecs = 60% open timeEach injector can flow 35 lbs per hour x 8= 280 lbs x opening time,280 x 0.6 [open time]= 168 pounds/6.2 lbs per gallon= 27 gallons in one hour.

Not sure the engine would survive if you burned this much fuel in one hour only possible if you hold 6,000 rpm and above for the entire hour. For sure the oil would need changing every hour of use!

At idle the 650 rpm is only [11%] of 6,000 and the open time is [2.2 millisecs [22%] at reduced 34 psi {12.5% less flow].....0.11 x 0.22 x 0.875 =0.021175 or times 27 gallons is = 0.57 gallons per hour at idle and roughly 2.5 gallons per hour at 60 mph ac on level road proper tire inflation correct alignment.

From 0.6 to 2.5 to 27 gallons per hour is controlled exclusively by your right foot.

Even a slight acceleration [without a down shift] doubles the fuel consumption, a downshift quadruples it at the start and if carried thru till 6,000 rpm cuts it by 90%.................easy to see why some drivers get 12-13 mpg around town vs 17 mpg in controlled tests.

Warmup from cold takes up to 10 minutes and idle may be 1300 rpm at start so fuel flow averages 50% [?? something close counting the start] more than warm idle so a cold first start warm up for 10 minutes in park might use 0.15 gallons............based on 6 days per week that would be less than a gallon per week to get the engine/transmission happy before driving away! So much for wasting fuel by warming up the car!

Isn't it good to know that if you get stuck in winter immediately after a fill up that you might have 36-39 hours [idle fuel usage rate] before you freeze to death.

[bryq45]

You can burn an entire tank [22.5 gallons] in less than 1 hour at 6,000 rpm......6 mpg @ 150 mph

Is there an "optimal" speed that the Q should be travelling to get the highest MPG?I know city driving is the worst, and highway driving is significantly better fuel wise. But according to the above statement, there appears to be a point of MPG diminishing returns. What speed might that be around?

Another question: Fred asked " Do u do a lot of idling?Tell us more about the local drving conditions for your car."

How harmful is idling to a Q, or any car for that matter?My remote start on my car runs for about 13 or 14 minutes, then shuts off. Is that too much idling. HOw much is too much. Once i had a 'lady friend' in the car and the car idled for several (at least 3) hours. I KNOW that cant be good, but it only happened once.BRY

[Yengec]

I get on average 17.60 Miles per gallon on my 95 Q45. 60% highway driving and 40% city. I have not done any tune ups recently and I average around 85/mph on hwy and around 40-60/mph in the city

Most of the driving is down around Miami and Ft. Lauderdale area in hot humid sticky nasty ugly South Florida weather.

I'll post any changes should one ahappen after a soon to be coming tuneup.

But >21 on hwy is awesome.

Danny

[Q45tech]

"went to the peace rally but that's another thread all together!) and I averaged over 21MPG both ways (mostly 65-80MPH). "

How could you exceed the speed limit by even 0.1 mph and be for peace, as your excessive speed is causing your car to use more than it's fair share of Iraqi oil?.......what happened to the flower covered Beetles of the 60-70s.

Hopefully those that vote for peace will also vote for an ENFORCED national 55 mph speed limit [if you exceed it your car gets burned on the spot and you walk for a year] which will reduce our consumption by at least 15% and get us out of the mess were in!...........just joking but their are so many dichotomies in US culture.

[PalmerWMD]

1)Is there an "optimal" speed that the Q should be travelling to get the highest MPG?2)How harmful is idling to a Q, or any car for that matter?BRY

In my experience I would still get good milage around 75 mph.

Many members have remarked how mpg tolerant the Q is at higher speeds for example (From my previous Q's which were all w/ plugs under 30k):

A distillation of observign first gen Q45's in years of hiway drving ( I also meticilously(sp?) chekc my milage)

65-75: 22+ mpg (near constant, mostly even terrain)75-85: 20mpg85-95: 18mpg80-100 mph: 17mpg (mostly hi 80's but going upt o 100 on occasion)Very hard running most of it over of it over 100mph:14mpg

2) Not harmful in a wear and tear kinda sense, just realize deposits formed during combustion wont be burned out like they would in hard drving, so it might dirty your engine inside if u do it all the time.

So after a week of a lot of idling be sure to run it <real> hard for a couple min at least.

Fred...

[Q451990]

Long, long ago I took the Q to Key West. Three full sized guys and a bunch of luggage... I could almost tell how far I'd been by the fuel gauge... 100 miles per quarter tank. Averaged about 20MPG with CC set at 79 or 80. Probably got a little less on the seven mile bridge with my 110 MPH run... stupid, stupid, stupid Midnight and no headlights so the only thing that would have made me fish food would be a mechanical problem.

The Q always seems so happy on long trips... I think that's where it really shines.

Heath

[PalmerWMD]

seven mile bridge with my 110 MPH run... stupid, stupid, stupid Midnight and no headlights so the only thing that would have made me fish food would be a mechanical problem.Heath

Wow!

Fred...:bowdown

[EWT]

You can burn an entire tank [22.5 gallons] in less than 1 hour at 6,000 rpm......6 mpg @ 150 mph

I get between 4-5 mpg with my Supra on the racetrack. A guy with a 427 Shelby Cobra was complaining at the gas pumps that he only got 6 mpg. He was pretty surprised when I told him I had him "beat" with my 181 cid motor.

[Q45tech]

In the closed loop range [50-74.9999 mph] the injectors are using the same 2.2 millisecond opening time [to create the 14.7 AF that the cats need to be efficient]. SO mileage is DIRECTLY AND ABSOLUTELY PROPORTIONAL to rpm so 75/50=50% 60/50= 20% difference if you get 27 mpg at 50 mph 24.3 mpg at 60 mph[held absolutely stable on say a dyno or flat track] you would get 20.25 mpg at 74.9 mph.

Unfortunately the BSFC varies slightly in that at 50 mph [1665 rpm] the engine is operating at the ragged edge of producing enough torque to be efficient...........My guess is that back in 1987-88 when they were designing things they chose 55 mph as the optimum point but that would vary with altitude and temperature.So 55-60 mph is the best point.

Engines could be made to run leaner [lean burn] but that would be outside the range of the cats to correct it.

http://www.circletrack.com/tec...lass/h ... harticles/

http;//www.splorg.org/~b/me107b/engine/body.doc http://www.thirdgen.org/newdes...shtml

"BSFC" how much fuel it takes to make a HP is a great thing to search on.

[landtodd]

EPA was 16/22 for gen-1 Q45.

[tkd_q45]

Thanks for all the feedback. My wife does not have the best of driving habits, but even if I'm doing the driving in town mileage still stays around 10-11 MPG. Maybe that's what I'm stuck with and should learn to live with it. It just pains me to know that I COULD be getting up to 14-15 mpg and that would make a major difference in our fuel bill.

To answer Plamerwinds questions:

milage related questions:

How recent is your fuel filter?OEM?-yes-

Plugs?

-plugs should be pretty fresh (that is if the dealer actually put them in!)

Injetcors original?

- only two have been replace

A poor MAF connection cna also cause bad consumption and loss of power.But u dont have any powerloss right?

- no loss of power - at least not noticable

Do u do a lot of idling?- in town, yes -

Tell us more about the local drving conditions for your car.

I live in West Hollywood (part of the "west end" of Los Angeles) OUR TRAFFIC SUCKS!!!!!!

[maxnix]

Quote »I live in West Hollywood (part of the "west end" of Los Angeles) OUR TRAFFIC SUCKS!!!!!![/quote] Idling can destroy MPG because your are burning fuel and not going anywhere. Think how you can travel ~45mph at only 1500 RPM, less than 1000 RPM more than idle.

Take the car on a nice road trip of 150-200 miles, starting with a full tank. Choose a route you can cruise a pretty much constant velocity. When you arrive at your destination, immediately fill your tank and calculate your highway mileage. If you are not going over 80 mph or doing a lot of WOT passing, you should be around 20-22 mpg. Repeat fill ups whenever your driving regimen changes and record mpg. Using the highway constant cruise mpg as a baseline, you can tell pretty well if something is wrong with your car; that is, if it is driver, environmental factors or mechanical condition affecting mileage.

[pnanda16]

so much for the 1st gens ,my 2nd gen 97 Q gives me 18-20 in mixed city (40% city, 60% freeway) driving and about 23 in long trips. Long trips include a mostly 75-80 range with occassional tripple digits ( just for the passing or kicks ). The absolute worst I have ever seen on my car is 16/17mpg.

Quick question on the overdrive button.In city driving (lessn than 40mph), I turn off the overdrive option. With overdrive on, at 45mph, my RPM is about 1400. Isn't that too low? I remember dennis mentioning that too low RPM is going to be harmful for the transmission, as transmission the oil pressure is directly related to the engine RPM and the cooling is not proper at higher speeds if the RPM is low.

Also, how durable is this overdrive switch? I think I use it about 5 to 10 times a day (@_@)!! by durable, I mean the switch itself. Also, how bad is it for the transmission mechanism?

[PalmerWMD]

staying out of OD is not bad for the transmission at all.

Actually its good to prevent transmission and engine lugging.In town I always stay out of OD but in "3" (first gens dont have a switch you just take it from "d" to "3" to disengage OD).Plus u have more immediate power.In my 91 Q I only went to D over 65mph

your consumption will worsen a bit, but I think its a fair tradeoff.

As for the mechanical switch itself i cant say, how long it will hold up, but I am sure a competent independent could replace it for not excessive $$.

I wouldn't worry too much about that though, and drive the car as befits your traffic situation.

Fred...

[Chaz98Q45t]

Palmerwmd - sory to hear about the March eta for your Q.My friend has 1995 740I that never drives in overdrive unless he's cruising...I've tried it a few times, definitely more low end power, I guess Im gonna try it for a while to see how I like it and the MPG difference...

[PalmerWMD]

Also, Often trannies go from OD to 3 back to OD back to 3 all the time in some types of traffic

So when u keep it out of OD in town, you will save on the total number of shifts per given trip/week/month/year.And that is <definetly> good for the transmission.

Fred...

[Q45tech]

The 97 with its 3.694 diff vs the 90-96 [3.538] is 4.3% higher but the smaller engine displaces 9% less so in theory the 97 should get 4.7% better highway mileage at the exact same speed and load.

If it does get 1.0000000000 mpg better as hoped I would be surprised --- maybe half that amount in real world conditions.

Around town [the 94-01 Q] have the same 1st, 2nd, 3rd, 4th gear ratios in transmission] so weight might be a factor.

But I would be surprised if a 97-01 saves more than $50 per year [@15k/yr] in gas compared to a 94-96 or even a 90-93.

But if this occurred over all 16 milllion new cars sold a 1mpg saving would be a Billion dollars at retail.

[OLU40]

Yeah Bry. I have automatic start that runs preprogrammed for about 12mins. I notice that at times that the fuel drops a little. Traffic in NY is a *****. Long distance even at speed I get almost 400 miles to the tank.

[natsoundup]

I haven't checked my mileage in a while... always used to get 20.5 on the highway...

I did a run from Greenville, SC to Jasper GA and back yesterday....couldn't quite do it on a tank of gas ( I didn't want to push it)

20.3 mpg was the average

I was happy because going down there I averaged 75...coming back I was probably averaged in the low 80's. I think a cop gave me a break.... I was doing 85 before I saw him....slowed to about 78..... I just held my breath....

90Q 149k miles...... plugs changed at 113k... BG44k probably at about 140k or so...

[BadQ45t]

I don't know about not being able to tell the difference between 1st gen and 2nd gen gas mileage. It seems like I always get a flat 20 MPG in my 97' but I've yet to see better than 16-17 in my 92. It could be age related but I get a little better cruising range with my smaller gas tank in the 97 than I can in the 92.

[Chaz98Q45t]

I just replaced my plugs at 54k miles - actually one of my friends who's a mecahnic did t at his house this weekend - I asked him about the O/D button and driving around town. He agrees - that taking it out of O/D while drving around town will help lower the #'s of shifts and thus help the transmission in the long run. He mentioned that it is a pain to remember keep switching...I've tried it the last few days and I like it. Hopefully will see 250k miles on my Q.

[Q45tech]

Well the transmission is only designed [rated] to last 100,000 full shift cycles [1,2,3,4..4,3,2,1] how many do you do per mile/day?

By the way highway mileage is most affected by tire type, inflation, and alignment...too much toe, too much camber can easily lower things by 10%.............the difference between a running pressure of 40 psi and 32 psi can be more than 5%....brake /bearing drag and the temperature/type of ATF and diff fluilds another 1-3%.................sluggish O2 [slow to switch] can increase fuel usage up to 10% usually 4-5% [1mpg worse].Oxygenated fuels will decrease mileage by a minimum of 5% [1 mpg].

Easy to see how a 60/120k car can get 15% [2-3 mpg] worse than a brand new one on the same stretch of road.........all those unattended to things add up!

By the way just turning on AC increases the injector duration by 0.3-0.35 millisecs 2.5/2.2=up to 14-16% more [2-3 mpg less] fuel in the 55-74.999 mph range just for AC............which is not considered in EPA test...........as AC is a luxury remember!

I'll bet owners are checking MPG with AC ON no wonder their mileage is so poor!

Atlanta to Tampa the Q constantly [19 trips] gets 24-24.5 mph [depending on temperature] at the speed limit no AC takes 20.0 gallons +- 0.5 to go 484 miles [always fill up at same two stations].