Fuel Economy
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elwesso
- Posts: 30810
- Joined: Sun Feb 23, 2003 4:52 pm
- Car: 94 Infiniti Q45t 5 spd
2007 BMW M Coupe
2007 Infiniti G35 S 6MT - Location: Indiana
- Contact:
Thanks a lot of the help.
One of these weekends when im at the shop, ill go through the throttle body and clean it out without taking it out. Eventuually i will take it to the dealer to get all this stuff done (plugs, coolant flush, plenum cleaning/tb cleaning, and other stuff) Is there anything else i should have them do while im there???
Back to my gas mileage, i was thinking it could be the o2 sensors or MAF, what do you think. Personally i dont think it is the MAF because it has a steady idle, but i dont know a whole lot about this engine. Let me know what you think
One of these weekends when im at the shop, ill go through the throttle body and clean it out without taking it out. Eventuually i will take it to the dealer to get all this stuff done (plugs, coolant flush, plenum cleaning/tb cleaning, and other stuff) Is there anything else i should have them do while im there???
Back to my gas mileage, i was thinking it could be the o2 sensors or MAF, what do you think. Personally i dont think it is the MAF because it has a steady idle, but i dont know a whole lot about this engine. Let me know what you think
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szh
- Posts: 15932
- Joined: Tue Jul 23, 2002 12:54 pm
- Car: 2018 Tesla Model 3.
Unfortunately, no longer a Nissan or Infiniti, but continuing here at NICO! - Location: San Jose, CA
Since fuel economy was the original question ...
On my 1995 Q, I have seen as high as 25 mpg (leisurely long highway trip - driving at a steady 65mph, on cruise control). That was only over two tankfuls, so the numbers are approximate.
I have also seen as low as 8-9mpg. That was on a sustained high-speed run over ten years ago. I was doing over 135mph for many hours - stopping often for gas!
In general, I do about 60 to 70 percent highway driving in my daily commute. At speeds usuall near 70-75mph with an occasional higher speed. I seem to get between 17 to 18mpg as an average. I try to use my cruise control a lot to try and keep as much of an even push on the throttle as I can - my own foot tends to push much too hard on the accelerator!
Z
I have also seen as low as 8-9mpg. That was on a sustained high-speed run over ten years ago. I was doing over 135mph for many hours - stopping often for gas!
In general, I do about 60 to 70 percent highway driving in my daily commute. At speeds usuall near 70-75mph with an occasional higher speed. I seem to get between 17 to 18mpg as an average. I try to use my cruise control a lot to try and keep as much of an even push on the throttle as I can - my own foot tends to push much too hard on the accelerator!
Z
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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
"(2) The highway fuel economy test is designated to simulate non-metropolitan driving with an average speed of 48.6 mph and a maximum speed of 60 mph. The cycle is 10.2 miles long with 0.2 stop per mile and consists of warmed-up vehicle operation on a chassis dynamometer through a specified driving cycle."http://www.smartpdf.com/40CFRP...1.HTM
Obviously the RPM at 48.6 mph [1800] vs 75 mph [2850] is 1.54 times greater so at minimum the miles per gallon will be significantly less for those who drive over 60 mph.
The above was written with G35 in mind [Q= 1620 rpm vs 2500].
No body ever asked the government to measure steady state 75 mph freeway MPG.
So every engine is optimized for 55 mph and to heck with what happens over that.
"(c) Steady state tests. Constant speed, road load tests may be conducted to help give insight into operational differences and exhaust emission and fuel economy changes due to a retrofit device. Speeds between 0 (engine idling) and 60 mpg will be investigated, with a time period at each speed long enough to ensure that engine operation has stabilized."http://www.smartpdf.com/40CFRP...3.HTM
Obviously the RPM at 48.6 mph [1800] vs 75 mph [2850] is 1.54 times greater so at minimum the miles per gallon will be significantly less for those who drive over 60 mph.
The above was written with G35 in mind [Q= 1620 rpm vs 2500].
No body ever asked the government to measure steady state 75 mph freeway MPG.
So every engine is optimized for 55 mph and to heck with what happens over that.
"(c) Steady state tests. Constant speed, road load tests may be conducted to help give insight into operational differences and exhaust emission and fuel economy changes due to a retrofit device. Speeds between 0 (engine idling) and 60 mpg will be investigated, with a time period at each speed long enough to ensure that engine operation has stabilized."http://www.smartpdf.com/40CFRP...3.HTM
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Q451990
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- Car: 1990 Q45 - 118K, 2022 Toyota 4 Runner, 2004 Frontier M/T - 108K, 2012 Xterra (Mom's), 2023 Rogue (Inlaws)
- Location: Columbia, SC
- Contact:
elwesso,
Do you have a service manual? If so there's a procedure in there for reading ECU codes and also a check for O2 sensors. I'd say your best bet for better fuel economey is making sure that your O2 sensors are not sluggish, the plenum is clean, the throttle body is clean, and the injectors have been flushed. A clean engine is an efficient engine. And to echo another post... best case is to find a GOOD tech with the Consult that can work up a profile for you on the car. These guys are getting harder and harder to find with real-world Q experience.
Heath
Do you have a service manual? If so there's a procedure in there for reading ECU codes and also a check for O2 sensors. I'd say your best bet for better fuel economey is making sure that your O2 sensors are not sluggish, the plenum is clean, the throttle body is clean, and the injectors have been flushed. A clean engine is an efficient engine. And to echo another post... best case is to find a GOOD tech with the Consult that can work up a profile for you on the car. These guys are getting harder and harder to find with real-world Q experience.
Heath
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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 log and graph your injector open time vs mph steady in 5 mph increments from 55-85 mph..........Watch the time go from 2.2 to 4.0 to 6.0 to 11 [WOT] as you push on the accelerator more and more to change speeds...........add to that the 13% more fuel from acceleration enrichment.
Watch what happens when you turn AC on 2.2>2.5 minimum.......13.6% more fuel at 60 mph per second per minute per hour at the exact same speed just for AC between 2 and 2.5 mpg WORSE depending on ambient temperature.
Turn your headlights on bright or worse your AC fan on high or your rear defroster that's 0.4 to 0.85 HP more from alternator drag thats 5-7% more fuel required at the same 60 mph.
Watch the O2 cycle the steady state injector opening time 2.2....2.2,2.1,2.3,2.1,2.2.2.3 ...........+- 4.5% so that the average AF is 14.7:1
Guess I'll be forced to do it for you .
By the way the greatest most effective mileage improvement device is raw egg mounted so that the accelerator can't be mashed more than a third of its range..........maybe a massive spring for the last 2/3 of travel.............a 15...12... 10....8 cents per mile gauge.
Watch what happens when you turn AC on 2.2>2.5 minimum.......13.6% more fuel at 60 mph per second per minute per hour at the exact same speed just for AC between 2 and 2.5 mpg WORSE depending on ambient temperature.
Turn your headlights on bright or worse your AC fan on high or your rear defroster that's 0.4 to 0.85 HP more from alternator drag thats 5-7% more fuel required at the same 60 mph.
Watch the O2 cycle the steady state injector opening time 2.2....2.2,2.1,2.3,2.1,2.2.2.3 ...........+- 4.5% so that the average AF is 14.7:1
Guess I'll be forced to do it for you .
By the way the greatest most effective mileage improvement device is raw egg mounted so that the accelerator can't be mashed more than a third of its range..........maybe a massive spring for the last 2/3 of travel.............a 15...12... 10....8 cents per mile gauge.
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elwesso
- Posts: 30810
- Joined: Sun Feb 23, 2003 4:52 pm
- Car: 94 Infiniti Q45t 5 spd
2007 BMW M Coupe
2007 Infiniti G35 S 6MT - Location: Indiana
- Contact:
Heath, I dont havea service manual. I dont think i am going to purchase one right away, since i am going to buy an extended warranty.
I do a WOT every week or so. I am going to put in some injector cleaner next fillup, so we'll see if that helps. Thanks for your help. Is there anything else i could do that can be done without having specific knowhow??
I do a WOT every week or so. I am going to put in some injector cleaner next fillup, so we'll see if that helps. Thanks for your help. Is there anything else i could do that can be done without having specific knowhow??
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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)
elwesso wrote:Is there anything else i could do that can be done without having specific knowhow??
Given all the issues discussed so far, the consensus is that it's time for professional help. The internet does have its limitations.
Plan on having a qualified tech spend 2-3 hours fully diagnosing the car.
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Q45tech
- Moderator
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- 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
How are you going to get it in there? The car won't run with the intake hose to MAF off and if you try feeding it in the air duct, it will run down hill towards the MAF [hot wire explosion possible].
Cleaning the TB is hard, how do you get the rear of the plate perfect without brushes and lots of rags and special TB cleaner .............carb cleaner is too volitile needs to soak.
Throwing in some [off the shelf] injector cleaner won't do much to clean a dirty injector, it will keep one clean after a rail flush if used prior to every 90 day oil change. Guess if you used it [BG44k] 4 times per year from brand new you could defer a rail flush for a few years.
Cleaning the TB is hard, how do you get the rear of the plate perfect without brushes and lots of rags and special TB cleaner .............carb cleaner is too volitile needs to soak.
Throwing in some [off the shelf] injector cleaner won't do much to clean a dirty injector, it will keep one clean after a rail flush if used prior to every 90 day oil change. Guess if you used it [BG44k] 4 times per year from brand new you could defer a rail flush for a few years.
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elwesso
- Posts: 30810
- Joined: Sun Feb 23, 2003 4:52 pm
- Car: 94 Infiniti Q45t 5 spd
2007 BMW M Coupe
2007 Infiniti G35 S 6MT - Location: Indiana
- Contact:
Rail flush..... Can this be done at any shop, or something that can only be done at Infiniti??
Thanks a lot for all your help, and it looks like i am just going to have to bite the bullet, since unless i want to spend some real money getting the thing cleaned out.
Would the injector cleaner work better if you used it in higher concentrations, like putting a bottle in with 1/2 tank instead of a full tank, or would that harm the system.
Thanks a lot for all your help, and it looks like i am just going to have to bite the bullet, since unless i want to spend some real money getting the thing cleaned out.
Would the injector cleaner work better if you used it in higher concentrations, like putting a bottle in with 1/2 tank instead of a full tank, or would that harm the system.
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elwesso
- Posts: 30810
- Joined: Sun Feb 23, 2003 4:52 pm
- Car: 94 Infiniti Q45t 5 spd
2007 BMW M Coupe
2007 Infiniti G35 S 6MT - Location: Indiana
- Contact:
Next time I have it serviced ill ask them about it. For the mean time, I added some injector cleaner. The way I see it, if it doesnt damage anything and i get 1-3 more MPG, it was worth my $6.
Another thing..... I have a leaky valve cover gasket. It isnt too bad, it just smells a little just after it has been shut off (and the smallest little amout of smoke when you turn it off). I felt the valve cover on both sides, and it seems that there is a little (not much) oil underneath it. Is this something that should be done promptly, or can wait. Also, what would be the protocol on fixing this. Since it is at an early stage, could some gasket expander be used??
Another thing..... I have a leaky valve cover gasket. It isnt too bad, it just smells a little just after it has been shut off (and the smallest little amout of smoke when you turn it off). I felt the valve cover on both sides, and it seems that there is a little (not much) oil underneath it. Is this something that should be done promptly, or can wait. Also, what would be the protocol on fixing this. Since it is at an early stage, could some gasket expander be used??