according to the stats, 17/22 should be the gas mileage for a q, but recently, i filled up the tank to a full and only got 225 miles before the "low gas" light appeared.
what can one do to improve this?
poor gas mileage on 92q, advice needed
LAQ - try doing a search under "fuel economy" - I too suffer the same poor MPG when in town. I (actually mostly my wife) get only around 10-12MPG. When I can afford to I will have Dadealus change out my O2 sensors. I'd gladly take the 2MPG increase if I can get it. Consequently a couple of weeks ago I took a trip up to San Fransisco and got nearly 22MPG! It kills me to hear that my uncle-in-law's C5 Corvette can get nearly 32MPG on the highway and he has nearly 80 more HP! He gets around 20-22 in town! If I could I think I'd drop in a LS1 into my Q and have more power and MPG.
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Just becauase an engine can produce more power doesn't mean you use the full power - in day to day driving, if you did you would be getting 4-5 mpg!
All engines of the same displacement and rpm get essentially the same fuel economy. Unfortunately 32 valve V8 must turn say 10% higher rpm 2000 vs 1800 to generate enough torque to cruise [due to gulping hole the extra valve creates]----slows down air intake speed.
Think of the 32V as a 10% larger engine than it really is compared to a US old design 16valve V8.
California owners must understand that the Q loses 10% economy because of the oxygenated fuels you are supplied with............it was designed to run on 1989 GASOLINE not the product they currently sell and call gasoline.
O2 sensors primarily affect closed loop economy [steady speeds [50-74.999 mph]......acceleration/city economy is a function of your right foot.
Put a data logger on TPS: It will look like you are playing a bass drum in a rock band...up down, up down, up down in the city.
Put a C5 engine in a 1000 pound heavier car in front of an AT and you won't know it's there......the extra 100HP will be totally consummed by the extra weight.......each 100 pounds needs 10 HP Extra to equalize acceleration.
All engines of the same displacement and rpm get essentially the same fuel economy. Unfortunately 32 valve V8 must turn say 10% higher rpm 2000 vs 1800 to generate enough torque to cruise [due to gulping hole the extra valve creates]----slows down air intake speed.
Think of the 32V as a 10% larger engine than it really is compared to a US old design 16valve V8.
California owners must understand that the Q loses 10% economy because of the oxygenated fuels you are supplied with............it was designed to run on 1989 GASOLINE not the product they currently sell and call gasoline.
O2 sensors primarily affect closed loop economy [steady speeds [50-74.999 mph]......acceleration/city economy is a function of your right foot.
Put a data logger on TPS: It will look like you are playing a bass drum in a rock band...up down, up down, up down in the city.
Put a C5 engine in a 1000 pound heavier car in front of an AT and you won't know it's there......the extra 100HP will be totally consummed by the extra weight.......each 100 pounds needs 10 HP Extra to equalize acceleration.
Depending on driving style and conditions, 10-12 mpg sounds pretty reasonable to me. My car gets EPA mileage figures, but only when it's warmed up enough to get into closed-loop mode. A week of cool temps, cold motor, and short trips, and I net only 10mpg.
You might check your thermostat. Some of the plastic breaks down, allows part-flow when cold, and the motor gets up to closed-loop temp very slowly.
Anything that would cause ping would cause the ECU to back off ignition timing, causing poor performance and mileage. Plugged EGR, lower-octane gas, carbon deposits in the cylinder . . .
If your low mileage turns out "normal," ask yourself how your fuel cost compares to your overall cost-of-ownership. I would argue that the cost of fuel is a minor expense if you're driving less than 30,000 a year. Unless you're delivering pizza, that would probably mean lots of interstate, where your average should be over 20. My fixed costs (insurance, depreciation, tax, tag), plus repairs, have come to $8 a day over the past two years. I would have to drive 80-100 miles a day before fuel was more than 50% of my historic operating costs, and I'd still be spending only $40 a week for gas.
You might check your thermostat. Some of the plastic breaks down, allows part-flow when cold, and the motor gets up to closed-loop temp very slowly.
Anything that would cause ping would cause the ECU to back off ignition timing, causing poor performance and mileage. Plugged EGR, lower-octane gas, carbon deposits in the cylinder . . .
If your low mileage turns out "normal," ask yourself how your fuel cost compares to your overall cost-of-ownership. I would argue that the cost of fuel is a minor expense if you're driving less than 30,000 a year. Unless you're delivering pizza, that would probably mean lots of interstate, where your average should be over 20. My fixed costs (insurance, depreciation, tax, tag), plus repairs, have come to $8 a day over the past two years. I would have to drive 80-100 miles a day before fuel was more than 50% of my historic operating costs, and I'd still be spending only $40 a week for gas.
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greg_atlanta
- Posts: 1111
- Joined: Tue Jul 23, 2002 4:37 pm
- Car: 2008 G35 Journey Sedan, silver/black (no sunroof), 1992 Q45 (in a past life)
I've always averaged 15 mpg in mixed city & 80 mph interstate driving... but it's improved to 17 mpg lately ('92 Q). I think the injector cleaning and intake cleaning helped, but my right foot is a little lighter than it used to be (seeing more cops around helps in that department).
LAQ: sounds your car needs to spend some quality time with a qualified mechanic. It's amazing what the car can do with some TLC.
LAQ: sounds your car needs to spend some quality time with a qualified mechanic. It's amazing what the car can do with some TLC.
i think my driving style is normal, yes, sometimes i open it up and frankly, often, but 10 mpg has to improve.
the car runs excellent though, once warmed up, it gets super quiet. oh, another thing i heard was some sort of a metal, shrill, type of sound under the engine. kinda of like the sound of q engine when turned off, and it is cooling down, you hear that interval sound in beats.
does this make sense to anyone?
the car runs excellent though, once warmed up, it gets super quiet. oh, another thing i heard was some sort of a metal, shrill, type of sound under the engine. kinda of like the sound of q engine when turned off, and it is cooling down, you hear that interval sound in beats.
does this make sense to anyone?
What I hear while my car cools down is all the heat shields "ticking" about once/second. Is that similar to the sound you hear?
If it's a clackity sound while the motor is running, you're probably hearing HLA (hydraulic lash adjuster) noise. In extreme cases, it sounds like a diesel. Excessive HLA noise is usually the result of insufficient oil-change habits.
Light HLA noise that disappears in the first few minutes is acceptable. Let's hope you're not talking about rod knock!
Back to mileage, are you saying that your car gets 10 even *after* it's warmed up? Yes, I would wonder about that, but 10 seems to be about "normal" for lots of open-loop cold-engine mileage.
If you're not getting warmup in 5 miles or so, be sure to replace that thermostat.
If it's a clackity sound while the motor is running, you're probably hearing HLA (hydraulic lash adjuster) noise. In extreme cases, it sounds like a diesel. Excessive HLA noise is usually the result of insufficient oil-change habits.
Light HLA noise that disappears in the first few minutes is acceptable. Let's hope you're not talking about rod knock!
Back to mileage, are you saying that your car gets 10 even *after* it's warmed up? Yes, I would wonder about that, but 10 seems to be about "normal" for lots of open-loop cold-engine mileage.
If you're not getting warmup in 5 miles or so, be sure to replace that thermostat.
If it's a clackity sound while the motor is running, you're probably hearing HLA (hydraulic lash adjuster) noise. In extreme cases, it sounds like a diesel. Excessive HLA noise is usually the result of insufficient oil-change habits.
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landtodd,the clackity sound is the right way to describe it. sometimes i hear it and most of the times i do not. the oil has been changed every 2500 according to previous owner, and right now it is see-through clean. what does HLA's exact function?
back to mileage, im just saying that i warm up the car every time and it was a mixture of surface and freeway drivin', a full tank barely got me 225 miles in total.
i had a 560 sel mbz that got better mileage than the q, i think, but you know what, i love driving q.
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landtodd,the clackity sound is the right way to describe it. sometimes i hear it and most of the times i do not. the oil has been changed every 2500 according to previous owner, and right now it is see-through clean. what does HLA's exact function?
back to mileage, im just saying that i warm up the car every time and it was a mixture of surface and freeway drivin', a full tank barely got me 225 miles in total.
i had a 560 sel mbz that got better mileage than the q, i think, but you know what, i love driving q.
Injectors -- "a lively crew of gremlins making power for me." LOL -- a 911 driver who cares becomes adept at sorting out "good" noises and "bad" noises. Wonderful diagnostic tool for the developed ear. I was looking for a 911 when I got my Q. Haven't completely abandoned the idea . . . the last one we had was a brute. In a good way.
Me, I've never heard a Q's injectors over the sound of the motor that I know of. A mechanic's stethescope would help sort out injector and HLA noises in short order. Injectors are a plausible source of the noise, but I have no experience.
Little details aside, HLA corresponds pretty closely to the hydraulic lifter in an OHV design. It's called a different name in the OHC design. It's a similarly constructed piece that serves at least one of the same functions. A noisy HLA is about the same thing as a "sticky lifter" from the old days. Not much to worry about unless the noise is excessive or remains loud after warmup.
The remedy is iffy, and gets iff-ier as the HLA gets stickier. There's often not enough oil flow through the HLA for *any* solvent to disolve the sticky varnish in just one session. Or two, or maybe five. If it's a noisy HLA, I think it's most likely something to live with until the motor expires of something else, like valve seals, which sadly, aren't economical to repair. (You'd be surprised such a simple piece can spell doom for the motor -- it's wild. More reason to keep up with oil changes!) You could replace HLAs, but that would be prohibitively expensive, involving as it does removing the cams and timing chains.
I suggest the lightest synthetic oil in the recommended range, and a few oil flushes with BG Quick Clean, hope for the best. That's what I'm about to do with both of mine.
I'm glad your car has a good oil-change history. Nice to hear that the oil is so clear. Maybe the noise *is* injectors? Any indication of whether he used mineral oil or synthetic? Synthetics tend to leave much less varnish.
" warm up the car every time and it was a mixture of surface and freeway drivin', a full tank barely got me 225 miles in total."
Yup, I would investigate that kind of mileage with a warm motor. You're right -- something could be amiss. I wouldn't be terribly concerned, but I would want to know that everything was working right.
Thought: the O2 sensors are electrically heated during warmup. You might check that circuit. Overall, really bad O2 sensors (they fail gradually) will penalize you about 2 mpg on the highway after warmup.
Static timing is a possiblity. The timing chain stretches to a point with mileage and will cause ignition timing to back off by 1 or 2 degrees in 100K miles. In the other direction, too-far advanced timing will cause ping and make the ECU back off the timing. Because the ECU backs off in *chunks*, it's best not to have timing on the ragged edge. Better a couple of degrees away from optimal than have the ECU dropping chunks off and gradually adding them back.
Oh, but wait -- you have emission tests, 91 octane, and oxygenated fuel in LA, right? Gas less than 92/93 octane can cause ping/retard/reduced mileage. Oxygenated fuels carry a mileage penalty. As always, Dennis' observation, this time about "1989 gas," is well taken.
As for another possible source of ping/retard/reduced mileage, it's common for the EGR passages to be *completely* full of carbon. Easy enough to rod out. I may be wrong, but I think your CA emission inspection tests only idle emissions. An idle test won't catch a malfunctioning or clogged EGR, because the EGR functions only at part-throttle cruise. Combine a clogged EGR with an ECU that watches the knock sensors like a hawk, and that could be the whole problem right there. Even if it's not the whole problem, I'll bet your car would benefit from having the EGR lines and passages cleaned out.
"i had a 560 sel mbz that got better mileage than the q, i think, but you know what, i love driving q."
The only car in recent memory I would like to trade back to was a positively brilliant '98 MB E430, but the depreciation would eat me alive at $15 - $25 a day. (The Q depreciates about $2.50 - $3.00 a day.) The Benz, even 6 years and 140,000 miles younger, just isn't 10x better than the Q. Gas is such a small part of the overall cost-of-ownership.
Me, I've never heard a Q's injectors over the sound of the motor that I know of. A mechanic's stethescope would help sort out injector and HLA noises in short order. Injectors are a plausible source of the noise, but I have no experience.
Little details aside, HLA corresponds pretty closely to the hydraulic lifter in an OHV design. It's called a different name in the OHC design. It's a similarly constructed piece that serves at least one of the same functions. A noisy HLA is about the same thing as a "sticky lifter" from the old days. Not much to worry about unless the noise is excessive or remains loud after warmup.
The remedy is iffy, and gets iff-ier as the HLA gets stickier. There's often not enough oil flow through the HLA for *any* solvent to disolve the sticky varnish in just one session. Or two, or maybe five. If it's a noisy HLA, I think it's most likely something to live with until the motor expires of something else, like valve seals, which sadly, aren't economical to repair. (You'd be surprised such a simple piece can spell doom for the motor -- it's wild. More reason to keep up with oil changes!) You could replace HLAs, but that would be prohibitively expensive, involving as it does removing the cams and timing chains.
I suggest the lightest synthetic oil in the recommended range, and a few oil flushes with BG Quick Clean, hope for the best. That's what I'm about to do with both of mine.
I'm glad your car has a good oil-change history. Nice to hear that the oil is so clear. Maybe the noise *is* injectors? Any indication of whether he used mineral oil or synthetic? Synthetics tend to leave much less varnish.
" warm up the car every time and it was a mixture of surface and freeway drivin', a full tank barely got me 225 miles in total."
Yup, I would investigate that kind of mileage with a warm motor. You're right -- something could be amiss. I wouldn't be terribly concerned, but I would want to know that everything was working right.
Thought: the O2 sensors are electrically heated during warmup. You might check that circuit. Overall, really bad O2 sensors (they fail gradually) will penalize you about 2 mpg on the highway after warmup.
Static timing is a possiblity. The timing chain stretches to a point with mileage and will cause ignition timing to back off by 1 or 2 degrees in 100K miles. In the other direction, too-far advanced timing will cause ping and make the ECU back off the timing. Because the ECU backs off in *chunks*, it's best not to have timing on the ragged edge. Better a couple of degrees away from optimal than have the ECU dropping chunks off and gradually adding them back.
Oh, but wait -- you have emission tests, 91 octane, and oxygenated fuel in LA, right? Gas less than 92/93 octane can cause ping/retard/reduced mileage. Oxygenated fuels carry a mileage penalty. As always, Dennis' observation, this time about "1989 gas," is well taken.
As for another possible source of ping/retard/reduced mileage, it's common for the EGR passages to be *completely* full of carbon. Easy enough to rod out. I may be wrong, but I think your CA emission inspection tests only idle emissions. An idle test won't catch a malfunctioning or clogged EGR, because the EGR functions only at part-throttle cruise. Combine a clogged EGR with an ECU that watches the knock sensors like a hawk, and that could be the whole problem right there. Even if it's not the whole problem, I'll bet your car would benefit from having the EGR lines and passages cleaned out.
"i had a 560 sel mbz that got better mileage than the q, i think, but you know what, i love driving q."
The only car in recent memory I would like to trade back to was a positively brilliant '98 MB E430, but the depreciation would eat me alive at $15 - $25 a day. (The Q depreciates about $2.50 - $3.00 a day.) The Benz, even 6 years and 140,000 miles younger, just isn't 10x better than the Q. Gas is such a small part of the overall cost-of-ownership.
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BadQ45t
- Posts: 3255
- Joined: Fri Jul 26, 2002 7:54 am
- Car: '21 Nissan Leaf SL Plus (wife's car)
'05 Nissan X-Terra S 4x4
'97 Infiniti Q45t SOLD! Miss the old girl
'84 Nissan 300ZX (Original Owner)
'16 Mercedes Benz S550e V8 Power & 35 MPG - Location: Half Moon Bay, CA
Back to the gas mileage, you're certainly not getting what you should be. I've been driving my 92 almost full-time the last three or four weeks and I get 300 before I see any low gas light. Today I was at 275 when I dropped 16 gallons in and topped off too. You need to do some of the suggested maintanance ASAP.
wow, landtodd, thats hell of a coverage.
appreciate it, will try those recommended updates.
and maxnix, you are right, i should be getting at least 300.
i am planning a drive on highway only next time, to las vegas.i should make it in one tank, but somehow i doubt it, i will probably run out of juice at the state line.
we will see.
appreciate it, will try those recommended updates.
and maxnix, you are right, i should be getting at least 300.
i am planning a drive on highway only next time, to las vegas.i should make it in one tank, but somehow i doubt it, i will probably run out of juice at the state line.
we will see.