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Old 11-30-2012, 12:12 PM   #1 (permalink)
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Question 2005 Low Mileage after Maintenance any Ideas


Okay I replaced the :
1)spark plugs
2)Both air filters engine and inside cabin a/c
3) water pump and upper and lower hose and new coolant
4)drive accesory belt
5)timing belt,roller tensioner bearing, idler bearing, hydraulic tensioner, cam seals, crank seal and water pump and gasket
6)I also cleaned the rear a/c filter

The car is running smooth as silk, no engine lights or anything, idle is smooth, starts very easly.

But on the trip the computer my mpg has dropped from a 22 to 17 mpg. The gas is at half a tank and it was full when I took it to the shop. The gas has not changed.

I have searched the web everywhere to find an answer and found none, because everything else mentions engine lights or roughness.

the only idea i have is about something I read about the computer going into a hard mode and reading sensors but I have no idea.
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Old 11-30-2012, 12:30 PM   #2 (permalink)
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After you have burned at least 3 tanks full (preferably 5) then do a manual check. A half a tank of the computer is probably not accurate. Then compare this to your last manual check to determine any difference.

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Old 11-30-2012, 01:34 PM   #3 (permalink)
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After you have burned at least 3 tanks full (preferably 5) then do a manual check. A half a tank of the computer is probably not accurate. Then compare this to your last manual check to determine any difference.
I agree completely. You need to calculate mileage over several tankfuls (you can do this for each tankful and then averaging them together). This eliminates variations like one tank being fuller than another. And you should calculate your mileage manually (using actual gallons along with your odometer readings), which should be more accurate than the readings calculated by the car's trip computer.

The maintenance you have done should all help. One other maintenance item, which I have seen recommended here on mdxers for improved mileage, is to clean the EGR valve and ports.

One final note. My 2004 MDX is well maintained (have done all of the above including the EGR cleaning), and my driving style is not overly aggressive. Mine gets 13-15 around town (mix of lots of local driving with some highway driving) and 18-20 on a long trip. These are actual numbers I've calculated, not based on the car's trip computer. I suspect the car's trip computer may overestimate mileage. Especially if you only look at it when you're cruising on the highway, which ignores your consumption when you're stopped and on local roads.

HTH
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Old 11-30-2012, 01:47 PM   #4 (permalink)
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Question agree but still do not understand

I agree the manual way is the exact way.
90% my drving is highway.

But I am curious as to why the change in the trip computers mpg.

The entire time I have owned the mdx it has read 22, and I constantly reset it, but it always goes back to 20 to 22.
I have never seen anything else.

Now after all the work yesterday it is stuck at 17. The driving conditions are the same. The only change is the maintenance.

I also understand things that were working can fail due to collateral damage when doing repairs, and also understand hard modes of computer systems.

Just trying to figure out the change in the trip computer thats all.
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Old 11-30-2012, 05:26 PM   #5 (permalink)
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Cool MPG is self correcting


Well I have done nothing to the vehicle since the low MPG yesterday, except to clean the Rear Cabin a/c blower screen this morning. It was totally covered in like a lint from a dryer, that no air could of passed through it. But as soon as it was cleaned the inside noise in the cabin was very quiet and lots of air flow. 1000% percent improvement.

The good news just drove to the airport and the trip MPG is self correcting and now showing 20mpg.

I am wondering if there is something happening with some of these major mx items is causing a hiccup in the electronic Trip computer that takes some time to workout!
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Old 11-30-2012, 06:21 PM   #6 (permalink)
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Maybe someone in the shop helped themselves to some gas.

Glad everything is back to normal.
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Old 11-30-2012, 08:00 PM   #7 (permalink)
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The trip computer showing 20-22mpg is more suspect than it showing 17. My trip computer has never matched my manual calculations. I calculate my mileage average for every tank fillup. Sometimes it's only off by .5mpg, and sometimes it's off by over 1.5mpg.
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Old 12-02-2012, 01:01 AM   #8 (permalink)
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I have found that my MDX is very sensitive to the types of gas you put in it. For example, Safeway's (or cheaper supermarket brands) unleaded is different from Sinclair's unleaded as I get different MPG. Premium fuel also gives my MDX a boost of about 2-3 mpg so all of this must be taken into account.
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Old 12-02-2012, 07:02 AM   #9 (permalink)
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I have found that my MDX is very sensitive to the types of gas you put in it. For example, Safeway's (or cheaper supermarket brands) unleaded is different from Sinclair's unleaded as I get different MPG. Premium fuel also gives my MDX a boost of about 2-3 mpg so all of this must be taken into account.
You are using instantaneous computer readings to get these figures. As noted above, these readings are not accurate.

Regardless, different brands of gas are not going to give that big of a difference in mpg.

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Old 12-02-2012, 11:11 AM   #10 (permalink)
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different brands of gas are not going to give that big of a difference in mpg.


I only use premium fuel (92 or 93 octane), and I calculate mileage for every tankful, as well as averages over three tankfuls. (Gotta love Excel!) I have never experienced any significant difference between brands of gas (and that includes major brands and off brands).
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Old 12-03-2012, 08:54 AM   #11 (permalink)
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[QUOTE=davejet;525765. The gas is at half a tank and it was full when I took it to the shop. The gas has not changed.[/QUOTE]



Shop may have disconnected the battery which can reset the trip mileage.
Could have been road tested, probably city driving cycle, which may explain the 1/2 tank change.
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