Fuel Pump Noise & Observed Mileage

squid · #1 (**permalink**) 12-24-2007, 10:48 PM

Thread moved here from "Fuel Requirement".

luvex35 · #2 (**permalink**) 06-21-2008, 04:27 PM

My apologies to the Forum. I was unable to start a new thread, not sure how to do it. I put this post under fuel. I just returned from Prime Infiniti of Hanover, MA. Had my first oil change 4,275 miles. I had them use the Mobil One synthetic, cost $98.00, won't need another oil change until 9,275 miles. They were unable to reprogram the passenger airbag for the recall, they will do it next service. They also mentioned that I will need to have the fuel pump replaced. If when starting your EX it makes a "groan" sound (only way I can describe it), it means there is an "issue" with the fuel pump. They replace it with a new re-programmed pump, no charge of course. There is no problem with pump other than the noise, new pump, no noise. Other than that, all is well, after many hand washes and high pressure laser touchless washes, no sunroof leaks.

spd56 · #3 (**permalink**) 07-03-2008, 07:06 PM

my fuel pump also made this groaning noise when starting, they replaced it and the only difference is my fuel average dropped with the new fuel pump.

spd56 · #4 (**permalink**) 07-03-2008, 07:32 PM

what kind of millage are you getting on your ex35. I am averaging 23 city/highway
if I drive 55mph I get 30-31 highway, at 65mph I get 26-28mpg at 75mph I get 24-26mpg
If I drive like a sports car and punch it, its pretty much 17-24 but driving with cruise control and coasting over breaking, I seem to average 23-28. I don't live in hilly terrain so that may help

luvex35 · #5 (**permalink**) 07-03-2008, 10:04 PM

Quote:

Originally Posted by spd56

my fuel pump also made this groaning noise when starting, they replaced it and the only difference is my fuel average dropped with the new fuel pump.

How much did your average drop? I'll take the groaning noise over a drop in economy. I don't get some of these numbers that are posted. I drive like an old lady and am only seeing an average of 20-21 mpg.

spd56 · #6 (**permalink**) 07-06-2008, 10:51 AM

not sure about your mileage, using 91 to 93 octane will increase your MPG by at least 2MPG
My avg local/highway is 23.6 when I only do city driving I have been as low as 20-21mpg
I find the highway can be 26-30 depending on speed. My pump change there was a notice in mpg but may take awhile for the computer to average out new driving habbits

DalRock · #7 (**permalink**) 07-18-2008, 02:40 PM

I have 7k on my EX and have been very happy with the MPG. Fortunately, the majority of the miles I drive are highway miles. I also do not have significant hills in D/FW. I am averaging overall 25.5 mpg. I have not had to replace my fuel pump so I can't comment on before/after a new pump.

I always believed that a higher octane would increase your mpg too. I have witnessed that a lower octane gas has not affected my mpg. The car will run better (when accelerating to warp speed) on higher octane's but mpg were not an obvious improvement. I am and have been using 87 octane the last 10 times and have not lost any mpg. In fact, the best mpg I recorded was 27 and it was with 87 octane. I imagine traffic was good to me during that week.
My driving habits have extremely affected my mpg though. It is amazing how bad your mpg can be with this Station Wagon/Race Car. (on a side note, is it "effected" or "affected"?)

I do wonder though, the first 3 months I was using 93 octane, when it was a newer vehicle. I then switched to the lower octane after 3 months (after the break in period). I wonder if the new car break in period limited my mpg? This should be answered by someone who knows more about cars.

Anyway, there is my MPG Diary.

squid · #8 (**permalink**) 07-18-2008, 11:00 PM

Hi all, not a EX owner yet but I do have some knowledge. New vehicles do historically get better MPG after about 10,000 miles after all the moving parts loosen up. As for Octane I posted this a few years ago on a Nissan Titan forum but the info is still true today.

Quote:

Last night while I was out making my rounds, my 20 year old nephew called to ask me some questions about his 1976 Camaro I gave him when he graduated High school. (Yeah, uncle Squid is cool.)
Anyway, it seemed that as he put it some POS Honda ricer smoked him? I asked him how the Honda could be a POS if he had lost? He ignored me as expected. (Sometimes Uncle Squid shows his age.)
What he was looking for was some information on how to make the venerable Chevy 350 a little more potent. As we were talking I noted some misconceptions he had concerning some very basic aspects of internal combustion engines that I thought I?d share with all of you.

Octane
Plain and simple, octane is simply a measure of fuel-detonation resistance.The higher the number, the less prone the fuel is to detonation.
Detonation is the un-uniform ignition of the air/fuel mixture in the combustion chamber. Normally, the combustion flame front originates from the spark center. When detonation occurs, the charge is lit at not only the spark center, but also from hot spots caused by build up from carbon deposits within the combustion chamber. This causes an uneven flame front, resulting in a sudden rise in combustion pressures, which can damage a piston on the power stroke.

What's even worse than detonation is what's called pre-ignition, which occurs when the air/fuel mixture (Charge) unintentionally lights off without a spark. This usually means the event occurs toward the end of the compression stroke when charge temperatures and pressures are still rising. With pre-ignition, the sudden change in charge pressure from premature ignition as the piston is still moving up is equivalent to taking a hammer and beating it on top of your pistons. The sound is very similar, just like a ping.

Higher octane fuels are especially helpful to boosted or high-compression performance engines, along with older engines. With boost or a high-compression ratio, the air-fuel charge is compressed to higher pressures, which makes it more susceptible to detonation. Older engines with carbon deposits built up in the combustion chamber also benefit from high-octane fuels as the added space occupied by the deposits also effectively increases the compression ratio.

Now this is where it gets fun.
Today?s engines, like the VK56DE in our Titan and the Infinity QX56 control detonation with knock sensors that retard the spark timing at the onset of knock. Retarding spark timing or richening the air/fuel mixture to reduce knock ultimately robs power. This is why an increase in octane increases horsepower. Since the engine's knock threshold is effectively raised with higher octane fuels, spark timing is not retarded. This allows combustion and charge expansion to occur so that more force is put into the power stroke. Bottom line: Higher octane fuel only helps you make more power if your engine is at the verge of detonation (whether you know it or not).

In the case of my nephews Camaro with the H.E.I 350 (No ECU or Knock Sensors) a higher octane fuel won't help. But with the Titan you can gain the extra 10 HP that the QX56 gains by using Premium fuel.

Comments and additions are expected and appreciated.

dividedhighw · #9 (**permalink**) 07-19-2008, 07:53 PM

Awesome, squid!

A great analysis that puts fuel-related discussions in perspective.

So, since higher octane fuel gives a little better power, I deduce that one should also expect a slight mileage improvement (as long as your right foot isn't too "squirt-happy").

Where I live however (Ontario, Canada), 91 octane gas is about 9 to 10% more expensive. This leads me to conclude that unless the mileage improvement is in that same range (or better), it would still be more economical to run with regular 87 gas, no? (BTW, I'm assuming here that the engine computer will adjust sufficiently so there's no detonation and fuel still burns as "cleanly".)

I'm just wondering because I'm experimenting with my first tank of regular and although I notice a little less power, I'm finding the engine less "surgey" (if that's a word!) and less prone to kicking down too far when accelerating from a highway on-ramp, for example.

donesber · #10 (**permalink**) 07-20-2008, 01:42 PM

Hi

I'm a newbe, but have had the same questions about octane and fuel economy. I have about 9200km on my EX and have tried both hi and lo octane with inconclusive results. I plan a long trip in august and will try to keep good records to see if hi octane is worth the extra $ in better fuel economy.

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