92Q getting only 10-11MPG in town!

[tkd_q45]

Hi all,

I have a 92 Q45 with 105K. I'm getting crap gas milage. I posted some months ago and Q45 Tech suggested checking my thermostat and that maybe it had gone bad and my ECU was running in "cold engine" mode (if I remember correctly). Anyhow I did have the thermostat checked out. Tech told me it was just fine. In fact the mechanic (went to Beverly Hills Infinity) said that everything on my car checked out. So I'm really at a loss. Any suggestions? Anyone know a good Q mechanic in the LA area?

Thanks,Tom

[PalmerWMD]

Well it IS summer..

A possibility is that your coolant is running warm so the ECU will run the engine rich to protect it=results in reduced milage.

(Having said that I often have week were I run 12mpg in town if I use my leadfoot more than usual, my car gets 22mpg on hiway though)

Is your radiator still original?When was the last time your coolant was flushed?Are you running a mix thats too thick for summer (recommend running no more than 30% antifreeze tops in summer)

Also, are your oxygen sensors original?

Fred...

[crubio]

Try changing the breather element (air fiter). I had the same problem with poor gas milage. Replaced the filter and It really helped a lot.

good luck

crubio

[greg_atlanta]

See if the dealer offers an intake cleaning or injector cleaning.

Also, see if you can find BG 44K injector cleaner and use that several times, preferabley on long trips where the engine stays hot for a while.

Replace the air filter if it's anything other than bright pink.

Just because dealer says it's "OK" doesn't mean its running at peak performance.

Have heard good things about a shop in San Diego if that's not too far out of the way: http://www.jerrytucker.net

Might be worthwhile for a good independent to have a look.

I get about 15 mpg in my '92 Q, drive pretty hard. A lot of 80-90 mph interstate travel around town, though. May be lower if I was all stop and go traffic all the time.

[DAEDALUS]

I live in SoCal too, and it has not been that hot down here. 11mpg is downright awful. New O2 sensors might show a small improvement, maybe 3mpg. Is it possible the poor mileage is from a combination of factors? Did you have the temp sensors checked as well?

[landtodd]

If you do short drives, the engine won't warm up enough to go into closed-loop mode, which happens after 8-10 minutes of operation. When I abuse my poor Q and do nothing but short trips (all open-loop mode), I get 10-11 mpg. One 20-mile trip on a tank, and it shoots up to 13-14.

The EPA rating was just 16mpg city. You may have some room for improvement, but 16 mpg city is about tops.

[Q45tech]

"The EPA rating was just 16mpg city. You may have some room for improvement, but 16 mpg city is about tops."

The Q uses 0.85 gallons per hour at 750 idle in park and roughly 0.95 gallons per hour at idle in gear and 1.1 gallons with AC on standing still to make the 12-14 HP necessary to just stay running.

Unforunately California gas is lower in Btu compared to non oxygenated so it takes more to create the same HP.

14.5 mpg with easy acceleration might be closer to the truth then subtract some for idling time.

City according to EPA is a typical US city with little traffic and few red lights mild acceleration!http://www.epa.gov/otaq/labda.htmhttp:/ ... aq/mpg.htm

[Q45tech]

Guess I should point out that from idle [1 gallon per hour to 60 mph cruise at 2.5 gallons per hour, to 150 mph at 25 gallons per hour 6 mpg ......is all controlled by the accelerator pedal.

Acceleration uses a lot of fuel since even mild sets the injector opening at 2-3 times the constant 60 mph and WOT is 5-6 times.

4 sprays per rpm and a minuscle drop at idle to {{21 pounds [3.5 gallons] per hour}} are possible from each injector.

In the 3,000 sprays per hour at idle to 24,000 sprays per hour at 6,000 rpm is a wide variance....8 x 8.8= 70 times broken down by tenths or 700 possible outcomes directly controlled by your foot.Assuming the engine is functioning reasonably correct, 100- 200 units of the outcome might be controlled by the ecu the rest is up to driver.

[landtodd]

Acceleration is the most "fuelish" thing you can do, short of syphoning your fuel into someone else's car. It takes probably less than 30 hp to keep the Q rolling along at 60 mph, but it takes 300 hp to make me smile.

What a car. 12 mpg seems really good, but my perspective is skewed. My last daily driver was a 500 cid '72 Eldo convertible that got 6 mpg city at best, estimated 2-3 cold. It could manage 10-12 mpg at cruise, but it ran on regular.

Hey! There's something I don't remember anyone asking -- you *are* running 93 octane, aren't you? Anything less, and the knock sensors cause the timing to back off with concurrent reduction in mileage. Hard on the cooling system, too, as a greater percentage of the energy in the fuel is rejected as heat.

[ardvarkus]

to 150 mph at 25 gallons per hour or 6 mpg

Dang, no wonder I need to get gas on each trip into the SF Bay area!

Adam

[BadQ45t]

The entire state of California is now only 91 octane, that's the best they offer. LA and SoCal used to offer a high of 92 and the Bay area only got 91 but now it is statewide.

I wonder if the older Q's suffer due to the lower octane? My dad's 92' gets about 14 city and 18 highway....I get a solid 20 MPG mixed driving and 24 on the highway if I keep it under 85mph.

[tkd_q45]

Thanks for all the info/insights guys! I just returned from a long weekend in San Diego. Going down in heavy Friday afternoon traffic I averaged a whopping (for me)17.9MPG! Things opened up once I hit San Juan Capistrano (just north of San Diego for those of you not familiar with the area. On the way back it looked as if I was getting in the 20MPG range until I hit traffic in Orange County.

Maintainace wise everything has been pretty much kept on top of -IE air filter, fuel filter, cooling system etc. I haven' t yet replaced the O2 sensors. Is this something that my local/average mechanic can do or do I need to go to the dealer?

Anyhow I was told that the 91 premium ocatane fuel in CA is due to the abundance of those of us who need premium (not enough hi-test to meet the demand so it must be "watered down"). I think I heard this on NPR. That plus the oxignation of our fuel I heard hurts performance in every way. I find this fuel issue so ironic in a place where there are so many really nice premium fuel burning vehicles.

[DAEDALUS]

Glad your mileage isn't quite so bad. 20mpg is pretty good. Any ol' mechanic should be able to replace the sensors, but it's a pretty easy job if you want to save $60. The only difficult thing is access. They sit in the exhaust manifolds just below the engine. Sensor socket is about $10 from PepBoys (or borrow one from them), and a flex head ratchet should be enough to get up there from the bottom to get them out. Economically, I think they should more than pay for themselves. Let's say they last for 60,000 miles, and over that time, assume they add an average of 1.5mpg to your mileage. Let's also assume 18mpg before replacement. Then let's assume an average cost of $1.70/gal of gas. Thus w/o sensors, you'll pay $5,667 for gas over the next 60k. With new sensors, you'll pay $5230. They cost about $100 for the pair (or $200 for near-identical factory units). Kind of like quadrupling your money in 3-5 years. Not bad!

[DenverQ]

What is the part # for the O2 sensors? and who makes he stock ones?

[Q45tech]

With CA Premium now in the $2.35 range and average traffic mileage down to 15-16-17 [with ethanol oxygenate]........extreme maintenace, synthetic oil, ATF, diff fluids, tire inflation, precision rotor trueing [to avoid any pad drag], etc, etc.

MAKE economic sense........or finding a 2,000 pound 2 liter manual econo car.

It won't get nasty till over $3 per gallon this Summer.

LOTS of difference between a rural Kansas city [16 mpg] and a CA MEGALOPLIS.

[VimyJ]

Octane is added to prevent knock. Relative levels of octane should meet fuel performace requirements of manufacturers in different geographic areas that require different blends for emission purposes.

In Illinois, we have up to 10% ethanol added. Georgia has almost pure gasoline. I get 22-23 mpg here but going through GA I got ~24.5 Dever premium gas octane levels are around 89 because of the altitude. Octane levels are not really performance enhancers but rather detonation stablizers. A higher octane like racing 100 octane allows for maximum timing advance for more power but this too is a relative function of the detonation point of the fuel not "more powerful" gas. At least this is how I understand it.

[VimyJ]

And to think some people were calling me an alarmist a couple of months ago when I started a thread in the "General Chat" area about $3 gas.