Fuel Efficiency Drastically Decreasing - Land Rover Forums : Land Rover and Range Rover Forum
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post #1 of 38 (permalink) Old 12-10-2018, 04:13 PM Thread Starter
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Fuel Efficiency Drastically Decreasing

Discovery Series II, 2002
I replaced my front and rear 02 sensors and my secondary air injection pump in October of this year in order to pass emissions. Prior to this replacement I was getting poor but tolerable gas mileage, about 260-280 miles to a full tank. I figured this was due to an inaccurate air/fuel mix and had the mechanic run a smoke test but it came back negative and they had no further suggestions or advice on the issue (surprise).
The next full tank after my 02 sensor replacement registered at 215 miles on empty. The next couple fill ups were only a half tank and those registered between 80 and 90 on empty ... I know a half tank test isn't too accurate though.
I read a post here that talked about the throttle position sensor. After reading about this and the throttle body, I'm thinking the sensor could be failing on me. Any thoughts on this?
My gas pedal has been sticking the last month when I press on it and only responds to a hard push, this usually disappears after the car is warmed up. Throttle body issues? If this was already discussed please let me know which thread the information is under.

Thank you for your time and input, my once annoying yet tolerable gas mileage is now intolerable and I would really like to get this figured out!
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post #2 of 38 (permalink) Old 12-10-2018, 06:37 PM
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That is pretty poor mileage.

What brand O2 sensors did you install?
Any other fault codes or warning lights?
What climate do you live in?

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post #3 of 38 (permalink) Old 12-10-2018, 08:25 PM
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What is the mileage or km on your Land Rover? Is the check engine light on? What state do you live in ?
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post #4 of 38 (permalink) Old 12-12-2018, 03:51 AM
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Definitley clean out your throttle body for the sticking gas pedal. It could be gummed up inside. Also clean out your IAC motor at the same time.

Another thought... your MAF sensor might be going bad. I'd hate for you to throw good money at a part and it doesn't solve your fuel economy problems.

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- 2001 Discovery 2 SE (NAS LHD) “MYRTLE”, 110K miles, 4.0L V8, NGK Iridium IX plugs, PCV mod, 180* T-stat, Hayden fan clutch/Dorman fan, removed TBH, SAI modded K&N filter, Safari Gard steel guards, Warn XD9000i winch, KO2 265/75R16 on steel rims, EBC rotors/Akebono pads, +2” TF lift & LEDs
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post #5 of 38 (permalink) Old 12-13-2018, 10:02 AM Thread Starter
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Thanks for your reply! I bought the 02 sensors from Atlantic British, part number is MKH100920SKA. I threw the boxes away and there is no brand listed on the invoice. :/ Mileage is 141,000. I live in Idaho, winters are typically mild but every now and then we'll get a lot of snow and very cold temperatures. It's a dry climate, summers aren't too hot either capping out around 105 degrees Fahrenheit in the summer for just a few weeks.
The check engine light is on but I haven't taken it in to see what the fault codes are, it happened so quickly after fixing it I wanted to wait a little while. Maybe never a good idea?
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post #6 of 38 (permalink) Old 12-13-2018, 10:24 AM Thread Starter
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Originally Posted by JUKE179r View Post
Definitley clean out your throttle body for the sticking gas pedal. It could be gummed up inside. Also clean out your IAC motor at the same time.

Another thought... your MAF sensor might be going bad. I'd hate for you to throw good money at a part and it doesn't solve your fuel economy problems.
I'll definitely get those cleaned out, or do it myself if I can. Thank you for the suggestions! I'll do some research, I love learning about new parts!
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post #7 of 38 (permalink) Old 12-13-2018, 11:55 AM
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I'll definitely get those cleaned out, or do it myself if I can. Thank you for the suggestions! I'll do some research, I love learning about new parts!
It's very easy and straight forward - you can do this yourself.

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post #8 of 38 (permalink) Old 12-14-2018, 07:38 AM
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Are you warming up your truck before you drive it? How long? What code do you have? Do you smell any fuel? Are you sure you've properly tightened your gas cap, how old is the gas cap? How does the truck idle, run? The 260-280 mileage range on a full tank doesn't seem that bad to me if you are doing city driving, in snow and warming up the truck before driving. When I lived in kansas I would take a pretty big hit on my economy every winter.
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post #9 of 38 (permalink) Old 12-16-2018, 09:01 AM
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MAF was a drastic decreaser for my disco
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post #10 of 38 (permalink) Old 12-16-2018, 03:34 PM
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I think warming up the truck like people used to do normally back in the old days is the best thing for these trucks.
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post #11 of 38 (permalink) Old 12-18-2018, 09:03 AM Thread Starter
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I always warm up the engine before driving it when it's cold, depending on how cold about 5-7 minutes. It idles pretty low at about 750 rpms and I never smell any fuel.
The gas cap is always on good and tight and I just replaced it last winter. I remember my gas mileage decreased a couple winters ago when we had a ton of snow and I let my car run for about 10 minutes before driving but my new mpg range is such a sudden and drastic change I didn't think it could be that.
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post #12 of 38 (permalink) Old 12-18-2018, 09:40 PM
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I think warming up the truck like people used to do normally back in the old days is the best thing for these trucks.
Yeah, that's valid for those who didnt bother to read at least the vehicle owner's handbook, which IMO is a matter of common sense

OWNER'S HANDBOOK
Publication No LRL 0322ENX
08.2000 Discovery Series II - 2nd Edition (page 95)

My friends call me Fery

2000 Discovery Td5 ES manual

Hawkeye v.6, Nanocom EVO,
VDM UCANDAS, oscilloscope


if you think my english is peculiar it means you didnt hear my japanese

ALL MY ADVICES ARE BASED ON MY OWN KNOWLEDGE AND MY WAY OF UNDERSTANDING THE DESCRIPTION AND OPERATION OF SYSTEMS... I'M NOT A LAND ROVER TRAINED SPECIALIST JUST AN ADDICTED ENTHUSIAST.
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post #13 of 38 (permalink) Old 12-18-2018, 11:57 PM
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Yeah, that's valid for those who didnt bother to read at least the vehicle owner's handbook, which IMO is a matter of common sense

OWNER'S HANDBOOK
Publication No LRL 0322ENX
08.2000 Discovery Series II - 2nd Edition (page 95)

I'm confident the book is wrong on this. Common sense says "warm up the engine first" not turn the key and drive it like you stole it. From what I understand this engine is based on an old 1960's Buick engine design. Back in those days people warmed up the engine first.

Book got it wrong on fluids types, coolant, spark plugs, radiator replacement.....
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post #14 of 38 (permalink) Old 12-18-2018, 11:59 PM
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The second sentence contradicts the first sentence.

I always let mine warm up and when it goes past blue I drive it.
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post #15 of 38 (permalink) Old 12-19-2018, 12:10 AM
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Originally Posted by WLADiscoII99 View Post
I'm confident the book is wrong on this. Common sense says "warm up the engine first" not turn the key and drive it like you stole it. From what I understand this engine is based on an old 1960's Buick engine design. Back in those days people warmed up the engine first.

Book got it wrong on fluids types, coolant, spark plugs, radiator replacement.....
They say to drive it carefully untill it's up to temp not like it was stolen ... at idle from cold start the oil will hardly reach the top end of the engine so that will wear out faster.... though i can't contradict such an expert like you, nor can the vehicle's builders who dont know what fluids or parts are good for it
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My friends call me Fery

2000 Discovery Td5 ES manual

Hawkeye v.6, Nanocom EVO,
VDM UCANDAS, oscilloscope


if you think my english is peculiar it means you didnt hear my japanese

ALL MY ADVICES ARE BASED ON MY OWN KNOWLEDGE AND MY WAY OF UNDERSTANDING THE DESCRIPTION AND OPERATION OF SYSTEMS... I'M NOT A LAND ROVER TRAINED SPECIALIST JUST AN ADDICTED ENTHUSIAST.
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