Low Miliage

03-18-2007, 11:14 PM
99 Honda Passport 2WD

Review the following,

Air Filter was just changed.

I was having the EGR valve error code issues, I cleaned the EGR pipe, and Check Engine light went off ages ago, so I assume the EGR is clean to a extent.

Before I upgraded sound system's 250w amp, 2 12in subs, 400 max power x2 = 800w.

Before I got new tires, nothing special just needed new tires, almost 100% sure there same size and tread.

Before I fixed my fuel guage (I think, could be wrong) it may have been ok after this. HOWEVER, when the fuel guage was fixed the fuel pump now has problems starting the car, Ive been told its a bad fuel regulator sensor.

Alternator and Battery are Ok.

No Check Engine Light.


My miliage is down to 13mpg, this was at 110miles with 30 of that being city driving and the rest highway. So if im not mistaken this is considerably low. So thats basically 14mpg on highway?

My previous miliage was 14-16 city, and 18-20 highway.

I listen to my music almost all the time, and not to be shy, with the subs hitting hard. :evillol:

I read the FAQ, and it mentioned a possible bad battery or alt. Could the fact that my subs are on all the time using enough juice (to effect the idle of the engine) cause lower gas miliage?

Also, Jiffy Lube, recommended it was time for a Fuel Injector Clean. Ive gone at least 18-20K since ive owned this vehicle for 1 year. And it hasn't been done.

My Mechanic is going to replace spark plugs on tuesday. Anything I should recommend him to look at?:screwy:


03-19-2007, 11:34 AM
how many miles on he truck?

If you have over 100k i may be worth changing out the O2 sensors that are infront of the cats.

03-19-2007, 12:03 PM
130K, car runs great, idles like nothing else ive ever seen. 250rpm smooth!

03-19-2007, 05:57 PM
have you tried disconnecting all that sound stuff and see what happens, since you see to thing that may be your problem ?


03-19-2007, 10:34 PM
I recently changed my O2 sensors and my mileage recovered from 14 to 17 mpg. My 3.2L was at 158K or so.

03-19-2007, 11:23 PM
Any idea how much the O2 sensors cost? My friend is gonna put 6 new spark plugs.

Just a couple notes,

I did 100 or so highway with power drive and got 16mpg, w/ subs on.
Then I did a 100 or so highway miles, and got 13mpg without power drive.
And then today I did 100 or so highway w/ out subs and with power drive on, and got 16mpg.

So I think the subs don't make any difference.

However power drive added at least 1-2mpg. Interesting.

Ill find out if the spark plugs do the job on wensday when I make another highway drive.

03-19-2007, 11:49 PM
Check this thread. I was actually down to 12 mpg before I swapped the sensors. http://www.automotiveforums.com/vbulletin/showthread.php?t=652127

03-21-2007, 11:44 AM
Well, ive changed the two o2 sensors after the cats, and flushed the fuel injectors, and also replaced all 6 spark plugs.

Lets hope for the best. Im gonna do 40 highway miles today when I travel to my girlfriends house. Will update later tonight.

*crosses fingers*

03-21-2007, 06:18 PM
Post cat sensor only lets you know if the cat is doing its job. It's the precat sensors which have more to do with A/F mixture, fuel efficiency.

03-21-2007, 10:49 PM
Well, I had 67 miles tonight, 30 of which is city and 37 of which is highway, my fill up avg is 18.7mpg so assumeing im getting 16-17 city and 20-21 highway, 16+21 = 37 / 2 = 18.5mpg So by this it means my gas miliage isback to normal I assume!

Im still gonna replace the back o2 sensors.

Ill update more later on once I can confirm again tommarrow night.

03-21-2007, 11:39 PM
Klownicle, thanks for all the feedback...
when you get it all where you are sure that its all right again, can you do another mpg test like you did with powerdrive on vs. powerdrive off...? it'd be interesting to see if that holds up...



03-22-2007, 11:15 AM
Ah. I misunderstood. I thought you changed the post cat sensors...

03-22-2007, 11:37 AM
I changed the o2 sensors after the cats.

I will keep you guys updated with powerdrive vs no power drive.

03-28-2007, 12:12 PM
After doing some testing my miliage for highway is 20-22, and my city is 16-17.

And power drive unfortunatly killing any rumor. Does nto safe me gas. I got at least 4mpg less using it.

Oh well thanks for your help guys.

03-28-2007, 12:47 PM
So you picked up 1-2 MPG. not bad. That will pay for itself quickly with gas prices around 3 bucks a gallon. I'll add this thread to the FAQ's.

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