I always wonder how so people in this forum get better mileage than I do. I’ve seen as high as 22mpg mentioned on a post. These are my last 4 fill ups mainly doing urban driving with the first one getting some highway miles and the last one driving a lot in 3rd gear instead of drive.

217.6 miles 18.759 gal 11.6 mpg151.8 miles 14.327 gal 10.6 mpg110.4 miles 10.278 gal 10.74 mpg155.2 miles 16.197 gal 9.58 mpg

I don’t get it. I don’t push the car around town. Some days my car doesn’t see 4000 rpms. The only time I push it is on the highway with some open road, which you don’t see much in NJ. I’ve had service done including plugs and o2 sensors. Don’t get me wrong. I know the Q is a econobox. I know the Q sucks up gas, but these numbers are crappy.

What year what mileage - TCS/ACTIVE? Use any oil between 3,750 mile changes? Thermostat last changed when [coolant temp sensor]; MAF clean and operating correctly? Cats not melted and clogged [back pressure test] Dyno Jet test results? Fuel type? Conventional or oxygenated?

As you can see impossible to diagnose mpg without the car and some serious time and money.

At least try a highway run to get an idea of true performance. Warm up car, fill it up, reset odometer, immediately get on the highway and cruise for a couple hundred miles, fill-up immediately after you get off highway and calculate mileage. Hopefully you have near stock rolling diameter tires.

Those numbers arent bad at all. In the real world I get 11-13mpg city and 16-18mpg highway. Old knock sensors, o2 sensors, bad MAF connector, old plugs. Probably halfass gas too.

Q45tech wrote:What year what mileage - TCS/ACTIVE? Use any oil between 3,750 mile changes? Thermostat last changed when [coolant temp sensor]; MAF clean and operating correctly? Cats not melted and clogged [back pressure test] Dyno Jet test results? Fuel type? Conventional or oxygenated?

As you can see impossible to diagnose mpg without the car and some serious time and money.

1995 Q45 Standard with TCS about 75000 miles. Doesn't burn oil much. Thermostat changed, I don't know. MAF cleaned when I did service as far as working properly, my Q was hooked up to a consult. Can that tell if it's working fine? The cats, beside the two house cats that I have at home, if there was something wrong with the cats, would the dealer said something. Dyno Jet test, what's that? I don't think it's ever been done. Fuel type, Sunoco 94 or Mobil Super 93. I get it in New Jersey. I don't know if they oxygenate the gas here but I'm sure you know, Dennis. So what your saying as far as the time and money that it will cost me to find out my problem is "Stop your bellyaching and pay for the gas."

maxnix wrote:At least try a highway run to get an idea of true performance. Warm up car, fill it up, reset odometer, immediately get on the highway and cruise for a couple hundred miles, fill-up immediately after you get off highway and calculate mileage. Hopefully you have near stock rolling diameter tires.

Yea, my tires are stock size. Next time I go to my weekend home, about 100 miles, I will do that. I think the last time I did, I probably got about 15 mpg, so we'll see what it will do the next time.

louiegz wrote:1995 Q45 Standard with TCS about 75000 miles. Doesn't burn oil much.

Yea, my tires are stock size. Next time I go to my weekend home, about 100 miles, I will do that. I think the last time I did, I probably got about 15 mpg, so we'll see what it will do the next time.

Then something(s) is(are) seriously wrong. I would start with cleaning the intake path. How's the air filter? Lots of posts as it is a DIY job that requires more care and time than for which you would want to pay a dealer.

Assume the fuel filter is <12K miles new? And the injectors are clean?

If you don't do it, might have the dealer resistance check the KS.
Modified by maxnix at 11:53 AM 9/14/2004

I've had everything else done. The fuel filter was changed in April when I changed the Fuel pump. I changed the air filter and the dealer cleaned the intake and the injecter were cleaned. The only thing that still original is the KS. That's all part of the plenum stuff, isnt it. Might have to wait for next year. I've spent way too much this year on the Q. I still have to get 2 PS hoses replaced and tie rod boots. Wouldn't a consult pick up bad KS? That was done at the last service.

Dealers are not good at accurate fine diagnosis of mpg. No codes doesn't mean optimum operation just that the sensor are generating a signal that is close to normal.

The MAF is the trickiest part as it almost directly control injector opening.

For example if the steady state 60 mph cruise causes a 2.4 millisec inj open time.................a 10% extra rich signal would only be 2.52 milisecs.As the first 1.2 millisecs in the time for the pintle to fully open:2.2 minus 1.2= only a real 1.2 of fuel flow, so 10% more is 0.12 ..........2.4>2.52 millisecs .............20% too rich would be 2.64 millisecs,

Acceleration can easily be 4-6 millisecs and WOT 10-11 millisecs.............5-10 times more fuel is used per second in accelerating than cruising.

The best most accurate way is to use a Consult and look for tiny changes way beyond what techs are used too.

Something is causing the fuel to burn: either you foot or an inaccurate signal.

Q45tech wrote:
Something is causing the fuel to burn: either you foot or an inaccurate signal.

Great quote there.....

Anywho, let me tell you from personal experience what helped me most...

- Using BG44k with half tank on a road trip (city miles with BG44k=worthless)- Setting my base timing perfect at about 15-17* BTDC- Replacing my o2 sensors...

All the other things (KS, intake cleanliness, Tstat, and so on) will help if they are really bad.. This past winter I was getting the same MPG as you... The last month of my Q I was getting a SOLID 15-16 MPG, all city driving, hardly enough time to warm up, and liberal use of the throttle...

Bad KS would be detected by the consult... Or at least if they look at the calculated timing at idle it should say 15*BTDC, if its lower then something is retarding...

KS didnt really help mileage that much, maybe a little..... I remember a post by dennis that said something to the affect that, if one Q gets 22mpg and the other gets 24 mpg, you start by doing a rail flush, then check timing, o2 sensors, and so forth...

In summary, i would highly recommend you throw some new o2s in there...

that doesn't sound that bad to me. if i do short trips with lots of WOT runs,,,,,i'm looking at 10mpg to 13mpg everytime. when i took a 250 mile trip to ocean city maryland i averaged around 18-19 mpg, and that was averaging around 80mph! seems to me, for the Q to get the best mpg,,,you need a very long highway trip,,,,nothing in jersey fits that bill!!!!!

Jeff, I still think your a bit off..

IVe seen 22mpg pre-o2 sensors, and almost 25 (24.something) doing the same speeds...

elwesso wrote:IVe seen 22mpg pre-o2 sensors, and almost 25 (24.something) doing the same speeds...

I had them replaced in May. This is what was done to my Q. http://nico.zeroforum.com/zerothread?id=64194

My mpg didn't improve any bit.

Another thing to check is idle fuel pressure. It should be 34 psi at idle and progressively increase to 43.4 psi as you open the throttle towards WOT as the plenum [pressure differential drops----less vacuum].

Not having the vacuum hose on the fuel pressure regulator will always maintain 43.4 psi even at idle and light cruise .......this alone could decrease mpg by some factor [14% at most - probably half to a third that] as the O2 can eventually signal up to 20% doward correction.

Q45tech wrote:Another thing to check is idle fuel pressure. It should be 34 psi at idle and progressively increase to 43.4 psi as you open the throttle towards WOT as the plenum [pressure differential drops----less vacuum].

Not having the vacuum hose on the fuel pressure regulator will always maintain 43.4 psi even at idle and light cruise .......this alone could decrease mpg by some factor [14% at most - probably half to a third that] as the O2 can eventually signal up to 20% doward correction.

How do you check the fuel pressure and what do you use to check this? How about this vacume hose to the fuel pressure regulator? How can I see that I have this? Is this easy to check?

Never mind. I saw it in the FSM.

1995 Q45: Temp gauge used to come up to just about the middle when engine at full temp. Now it only climbs to a little past the bottom hash mark, maybe 1/4". When cold, before starting, the gauge is below the bottom hash mark, maybe 1/4". Outside temps are cool now so the heater is needed. After starting and driving for a couple of minutes I push the ECON button on the dashboard, and set temp to 85 degrees. Within 5-10 minutes the inside of the car is WARM to HOT. (Nice) Then I back the temp down to a comfortable level. QUESTION: Is my thermostat or temp sending unit bad?