Poor Fuel Economy

Submitted: Tuesday, Dec 29, 2015 at 19:43
ThreadID: 131233 Views:4799 Replies:14 FollowUps:9
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Hi all, I have a 2005 2.9 Turbo Diesel (Intercooled) CRDi Hyundai Terracan. It has approx 250k on the clock, I have owned the car for approx 10 mths. My dilemma is that the fuel economy is getting worse. It was constantly getting 350-370Km to half tank (city driving). In the last 6 months the economy is now down to 270km at half tank. I use the recommended oil 10w30 (Penrite) have changed the fuel filter and oil filter. Tyres pressures are as per tyre placard. I know there are a lot of factors that affect fuel economy but in general I drive the same area and style since purchase. I am thinking maybe time to see if the in-let manifold is blocked? Any suggestions/recommendations are welcome.

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Reply By: Member - John - Tuesday, Dec 29, 2015 at 20:13

Tuesday, Dec 29, 2015 at 20:13
Gordon, have you checked the air filter?
John and Jan

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AnswerID: 594278

Follow Up By: Gordonk - Tuesday, Dec 29, 2015 at 20:33

Tuesday, Dec 29, 2015 at 20:33
Thanks for your reply John. Yer, sorry, missed that in my comments I have also changed the air filter too. No improvement to date in fact is getting worse.
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Reply By: Les - PK Ranger - Tuesday, Dec 29, 2015 at 20:32

Tuesday, Dec 29, 2015 at 20:32
Do check the air filter as suggested Gordon.

If the Terra has an EGR system and the usual PCV return, then yes you could have a choked up MAP sensor, which may affect the engine management.

I would do a bit of research, remove the MAF sensor (typically in the air filter housing) clean it and refit.
This usually only has a little dust on it, but check and spray with the cleaner up inside, you'll see fine wires, sometimes an insect can find their way in there.

Also take out the MAP sensor (in the inlet manifold) and clean this, usually all choked up with the tar like build up from the particulates from the EGR mixing with the oil mist recirculating via the PCV.

While the MAP is out, carefully dip a screwdriver in the hole and move around a bit on the inner walls, when you pull this out you will either see it reasonably clean, or caked with the same substance as the MAP sensor will likely be covered in.

Use CRC Sensor Clean spray, available from Super Cheap Auto and other such stores.
One can will clean the MAP and MAF quite a few times, best done every service, unless you block EGR and / or fit a catch can (either of these mods will remove one of the causes of the tar).

Don't wipe anything or touch with fingers, just use the spray and let it do the work.

If the screwdriver dip test seems to indicate the inlet manifold is significantly coated with that tar, then yes a manifold clean might be good to do, then make sure an EGR block and / or catch can is fitted to reduce this issue.

Do a google search for these 2 mods, plenty on the forums about them.
AnswerID: 594282

Follow Up By: Gordonk - Tuesday, Dec 29, 2015 at 20:36

Tuesday, Dec 29, 2015 at 20:36
Thanks Les, sounds like a very good start. Sounds a bit complicated but will give it a go. Thanks again.
FollowupID: 862640

Follow Up By: Les - PK Ranger - Tuesday, Dec 29, 2015 at 21:26

Tuesday, Dec 29, 2015 at 21:26
Not too difficult when you know where they are Gordon.
I just did a google search > hyundai terracan maf sensor hyundai terracan map sensor < lots of vids and forum type threads on this.
Here's a post of my DIY MAP / MAF clean . . . Ford PK Ranger MAP / MAF clean gives you an idea of what to look for / how to clean.
FollowupID: 862645

Reply By: KevL64 - Tuesday, Dec 29, 2015 at 21:52

Tuesday, Dec 29, 2015 at 21:52

"Tank" is not a unit of measurement.

Without actual litres of fuel added the distance is useless.
Have you considered perhaps your gauge may have developed a fault?
AnswerID: 594285

Follow Up By: wholehog - Tuesday, Dec 29, 2015 at 22:05

Tuesday, Dec 29, 2015 at 22:05
I'd agree. Do a more realistic fuel consumption testing to ascertain the kilometres per litre or litres per one hundred kilometres than your current 1/2 a tank on the gauge method. Try filling the vehicle fuel tank up each time and reset the tripmeter and get a few tanks to compare, you don't have to run it to empty, but fill it the same each time.
FollowupID: 862649

Follow Up By: Gordonk - Tuesday, Dec 29, 2015 at 22:10

Tuesday, Dec 29, 2015 at 22:10
Hi Kev, yes I agree just using the half way mark as a rough guide. However my first tank was
510 Km - 63 Lt used = 12.3 l/100.
340 Km - 44 Lt used = 12.9 l/100.
345 Km - 48 Lt used = 13.9 l/100.
285 Km - 42 Lt used = 14.9 l/100 and my last fill was
400 Km - 63 Lt used = 15.8 l/100.

So as you can see the economy is getting worse. These figures are over roughly 8 months of driving. These are just some of the figures but you get the picture.
Not sure if my calculations are correct the formulae used is
Km divided by Lt = ?
100 divided by ?
FollowupID: 862650

Follow Up By: Les - PK Ranger - Wednesday, Dec 30, 2015 at 00:07

Wednesday, Dec 30, 2015 at 00:07
When I fill up, every time, I log it in a notebook.
Around town I'll typically be top off main tank to get an accurate figure.
Lets say I put in 110lt, and odo reads 980km.
You take lts used (110) and dived by 'hundreds of km' (9.8) = 11.22 lt / 100km.
FollowupID: 862654

Reply By: swampy - Wednesday, Dec 30, 2015 at 00:39

Wednesday, Dec 30, 2015 at 00:39
clean egr system
including maf sensors etc , chemically clean inlet manifold
do a compression check
do a leakdown check
Remove injectors and have spray pattern and volumes checked
varation of around upto 3ltr per hundred can be driving style

AnswerID: 594289

Reply By: Member - Duncan W (WA) - Wednesday, Dec 30, 2015 at 13:50

Wednesday, Dec 30, 2015 at 13:50
Gordon have you posted your question on the Terracan Forum. The Forum has been running since 2005 so plenty of info available.

I'm sure the question has been asked plenty of times. I have the V6 so my consumption has always been abysmal.


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AnswerID: 594303

Reply By: The Bantam - Wednesday, Dec 30, 2015 at 14:04

Wednesday, Dec 30, 2015 at 14:04
Inaddition to all of the above.

Remember that diesels ...... pretty much all diesels object to being babied and run short.

Give it some fresh oil and a new filter and give it a flogging.

Get it out and give it a good run on the highway, at least 4 hours at highway speeds prefereably with some long hill range pulls.

Diesels take a long time to get properly warmed up, and low fuel, air, oil and exhaust flows don't allow them the clean themselves out of soot build up.

AnswerID: 594305

Reply By: Ron N - Wednesday, Dec 30, 2015 at 14:44

Wednesday, Dec 30, 2015 at 14:44
Gordon, at 250,000 kms, the engine would be rated as "well worn". Have you replaced/overhauled any fuel injection components in recent years?
The Hyundai 2.9L engine is actually made by Kia, and it uses computer-controlled, lean-burn, common rail injection, along with a turbocharger, and air-to-air intercooling. It's a high-tech engine.

With all CR fuel systems, the injectors are critical items and wear out first, due to the enormous pressures they have to handle - the needle valve in the tip starts to not seal as it should, resulting in fuel dribble.
The multiple orifices in the injector tip commonly get clogged with carbon, resulting in poor fuel atomisation.
In general, CR fuel system injectors should be cleaned on a regular basis, as they are critical items,, and very prone to poor performance caused by carbon buildup.

The second component that suffers from wear, and reduced performance due to carbon buildup, is the turbocharger.
You can check turbo performance easily enough with a simple boost gauge, which displays the manifold boost pressure and which will alert you to low levels of boost.

The other area that can affect fuel economy in a diesel, is air supply, so it pays to ensure that the air supply isn't restricted.

If your vehicle uses EGR as an emission control device, it pays to regularly inspect the EGR system for clogging, which is common in EGR systems, and which leads to reduced performance and poor fuel economy.

Lastly, you need to check the intercooler for cracking, which results in the turbo-boosted air supply being lost to the atmosphere.
The result is the same as having a defective turbo - the engine isn't getting the air it should, manifold boost pressure is low, and both fuel economy and power levels will suffer.

Cheers, Ron.
AnswerID: 594306

Reply By: Member - Kirk L - Wednesday, Dec 30, 2015 at 15:10

Wednesday, Dec 30, 2015 at 15:10
I agree with Les. First check air flow sensor near air filter. I would almost bet this is it. Clean with spray as said. 5 minute job. This will also affect the l/100 km reading on your dash if you are using this as a guide.
AnswerID: 594310

Reply By: Keir & Marg - Wednesday, Dec 30, 2015 at 15:33

Wednesday, Dec 30, 2015 at 15:33
Try googling Terracan EGR to see the multitude of posts related to the EGR and the build-up of sludge and soot in the inlet manifold which progressively blocks the inlet causing really bad fuel economy. In addition, if you have picked up water in the fuel, it's likely that your unit injectors are damaged. We had a combination of both these issues in our common-rail DID Pajero which went from averaging 11.7L/100km to 16L/100km between 150,00km and 200,000km. The inlet manifold was badly coked up and the injectors needed replacing. It cost about $5k to sort out the problem (but that included an additional filter to collect any water and sound an alarm) and the vehicle drives like new; we regularly get sub 10L/100km unloaded on a trip (that's close to 30mpg in old money) and usually about 14L/100km when towing 1.3 tonne of van.
AnswerID: 594312

Reply By: Member - Trouper (NSW) - Wednesday, Dec 30, 2015 at 15:34

Wednesday, Dec 30, 2015 at 15:34
Worth thinking about having the valves checked and adjusted if necessary. I noticed a loss of power and more fuel usage per Km over a 10 month period. I had the injectors and valves done and now I'm back to my 12lt/100km. Admittedly it was a 2000, Troopy 1HZ dinasour with 260k on it but it fixed my problem. Worth a thought after you have checked all those other modern sensor thingies.
AnswerID: 594313

Follow Up By: Ron N - Wednesday, Dec 30, 2015 at 17:36

Wednesday, Dec 30, 2015 at 17:36
Trouper is right - not many people do regular valve adjustments today - but a valve adjustment can provide a substantial difference in performance if the engine is high kms, and hasn't had a valve adjustment for a long time, or if ever.

Cheers, Ron.
FollowupID: 862694

Reply By: Gordonk - Wednesday, Dec 30, 2015 at 21:59

Wednesday, Dec 30, 2015 at 21:59
Thanks everyone for your comments and sound advice. I will definitely start with the simple items such as cleaning all the sensors mentioned, (I bought some CRC cleaner today) and progressively work through to the bigger (more expensive) items as required. I value your advice and appreciate your contributions, experience and especially your valuable time.

Cheers, Gordo
AnswerID: 594333

Follow Up By: Les - PK Ranger - Wednesday, Dec 30, 2015 at 23:27

Wednesday, Dec 30, 2015 at 23:27
Good luck with fixing the issue Gordo, do the screwdriver dip test when the MAP is out, not point taking off the manifold unless it looks like it needs doing.
After the MAP / MAF clean, I would take the EGR off and ensure that is operating / clean, though if it was not opening / closing properly, a CEL / code should be coming up (P0401 insufficient EGR flow or P0402 excessive EGR flow are common if not opening / closing respectively).
FollowupID: 862717

Reply By: Member - Kirk L - Thursday, Dec 31, 2015 at 13:13

Thursday, Dec 31, 2015 at 13:13
Let us know how you go Gordon.
AnswerID: 594365

Follow Up By: Gordonk - Thursday, Dec 31, 2015 at 21:49

Thursday, Dec 31, 2015 at 21:49
Will do Kirk, received plenty of good advice, will start with the basics and go forward from there till I get my original economy back. Filled the tank today, my economy test revealed 16.6L/100 so it is definitely getting worse.
FollowupID: 862757

Reply By: Frank P (NSW) - Friday, Jan 01, 2016 at 10:10

Friday, Jan 01, 2016 at 10:10
HNY Gordonk,

If you go to the trouble and expense of getting your Terracan's intake system thoroughly cleaned out, I suggest you install an oil catch can in the crankcase breather system to prevent, or at least greatly retard the choking of the system with cooked oil mist.

Mann-Hummel is a highly respected brand - you would need the 200 model, I think. I got a kit for my BT50 from Western Filters but they don't list one for the Terracan.

The kit is nothing too special, just hoses, hose reducers and fittings as well as the can itself. If you get a can you could then get what you need to suit your vehicle from a place like Pirtek.

In 25,000 km in my BT50 my can has trapped about 100ml of oil and kept it out of the intake system. Oil that would otherwise have clogged MAP and MAF sensors and the intercooler and, after EGR injection, turned to half-cooked gunk in the inlet manifold.

My vehicle is new so for warranty considerations I cannot consider blocking or bypassing the EGR system. That may be an option for you but you would need vehicle-specific advice on that.

Also, be aware that a properly fitted catch can that keeps the crankcase breather system closed is legal, but blocking or defeating the EGR system is not - though it is better for your engine.


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AnswerID: 594390

Reply By: Batt's - Wednesday, Jan 06, 2016 at 14:18

Wednesday, Jan 06, 2016 at 14:18
Adding extra weight to the vehicle over time like accessories etc everything adds up and not pumping up the tyres correctly to suit the extra weight will also increase your fuel consumption.
AnswerID: 594541

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