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Discussion Starter #1
The car starts, ticks over, pulls away smoothly,
comes up to temperature just as it should.
Gears change as they should.
No lights 0n the dash
The overhead display says there are no fault codes.
Brakes aren't binding

I got 15 to 17 mpg from last 2003 Overland.
Which I drove a fair bit harder / faster,

Have you any solutions please?
Beyond suggesting, "Drive it harder and faster." :)

Thanks.
 

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What engine? What year? What mileage? What engine maintenance has been done?

Even though the CEL hasn't illuminated, there still could be some stored or pending trouble codes.
Or another remote possibility is the instrument panel CEL bulb is burned out.
You really need to manually scan the PCM for any trouble codes.

If the mileage is that crappy, my first guess is that the engine is running in open loop for various reasons or the engine needs a long overdue tune up.
 

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Discussion Starter #3
What engine? What year? What mileage? What engine maintenance has been done?

Even though the CEL hasn't illuminated, there still could be some stored or pending trouble codes.
Or another remote possibility is the instrument panel CEL bulb is burned out.
You really need to manually scan the PCM for any trouble codes.

If the mileage is that crappy, my first guess is that the engine is running in open loop for various reasons or the engine needs a long overdue tune up.
Thanks :)

4.7 High Output.
75,000 miles.
Well maintained, as far as I can tell.

The overhead display says there are no faults.
The CEL light lights up when I switch on.

What do you mean by "Running in open loop please?"

What does a "Tune up" involve please?
I'm Old School, where tune-up means plugs and points.

Thanks,
 

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You really need to scan the PCM for hard, stored or pending trouble codes before diving into this deeper.
There might be a clue there or there might not be.
I see you're in the UK or is it Canada? Here in the US most major auto parts stores will scan the PCM for trouble codes free.

Basically 'open loop' means the PCM detected a serious engine fault and will not use engine sensor feedback for maximum performance and maximum gas mileage. In that situation the engine can also run richer and be noticeably sluggish.
Typically with a cold engine startup the PCM is in open loop with a richer fuel/air ratio until the engine is up to operating temperature which at that point it goes into closed loop.

There are so many things that can cause poor gas mileage other than a lead foot that the vehicle needs to be put on an engine data scanner at the dealership or trusted shop to troubleshoot.
At 75K miles some 'common' less serious things off the top of my head:
Spark plugs need changing
Clogged or bad catalytic converter
Bad O2 sensors
Clogged air filter
Throttle body needs cleaning
PCV valve (if applicable)
MAP sensor bad or dirty
And a bunch of other engine sensors one of which could be bad.
Bad fuel
Carbon buildup on the valves, heads, pistons etc.
Dirty fuel injectors

With these modern engines there's not much of a tune like the olden days.
Primarily changing spark plugs, air filter and if applicable with some engines; PCV valve, spark plug wires, fuel filter.

In addition have you tried using a fuel injector/carbon cleaner thats added to the fuel tank?
If not, i'd give that a try for at least a few gas tank fill ups and see what happens.
 

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Discussion Starter #5
Thank you very much Moparado.
I'm in the UK.

Thank you for explaining "Open loop"
very simply and very clearly.

Thank you also for your list of possible causes.

The mushroom headed sensor on the throttle body
is very dirty, so I daresay the throttle body is.
Does this point to a faulty PCV valve please?

The last one I took one off, I broke,
so I'm loath to take this one out
before I buy a replacement.

I will take your advice and add some cleaner to the fuel,
and to check / change the plugs.

Can I get the MAP sensor out without dismantling stuff please?
 

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Its great to hear from a Jeep owner the UK. Thinking it must be somewhat of a rarety there?

If your engine is a 4.7 inline six gas and not some diesel variant i have no clue as to what you mean by a mushroom sensor on the throttle body.
From what you described that could either be the MAP sensor or the Throttle Position Sensor (TPS).
The MAP sensor is located on the left side of the throttle body and could indeed if bad or dirty cause deteriorated engine performance and thus poor gas mileage.
The TPS is located on the rear of the throttle body and if bad can cause various engine symptoms.
When replacing the TPS its internal arm has to match up exactly with its mate in the throttle body.

The MAP sensor is very easy to replace, took me no longer than a few minutes to replace mine.
The TPS on the other hand can be a little more trickier to replace especially if its torx screws are seized.

I have a 4.0 inline six in my Jeep XJ. The 4.7 inline six is a later upgraded version due to its longer crank shaft stroke.
Here in th US, the 4.7 inline six is commonly called a stroker.

Can you explain in detail exactly where that mushroom sensor is located on the throttle body since the last one you replaced broke.
 

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Discussion Starter #7
Thanks Moparado :eek:)
I have a 4.7 V8

Grand Cherokees are also made in Europe.
An RHD "Yank-Tank", what could be finer?
Except perhaps, "Ham and eggs in Carolina?"

Many petrol ones were converted to LPG unfortunately.
Eroded valve seats are taking them off the road.
The diesel ones are getting rarer.faster as the engines go TU..

The mushroom sensor is a Throttle Position Sensor.
Sounds like I'd better clean it, thanks :)
Have you any advice on cleaning them please?

I think the MAP sensor is in the valley
deep down somewhere inaccessible
between the air con pump and the alternator.
I need a skyhook to get high enough to see clearly.
The picture in the parts book is somewhat vague.

I broke the PCV valve when I took it off.
I have a new Mopar one on it's way :0
 

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Discussion Starter #8
Correction.

The mushroom shaped doodah is the motor air idle control.
The position sensor was clean.
 

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Thats the Idle Air Control valve (IAC).
It needs to be cleaned i'd say every 30K to 50K or so miles depending on the quality and/or condition of the air filter in addition to dusty environments and if the engine is burning a significant amount of oil.
It controls the amount of air flow into the throttle body primarily at idle.
I cleaned my IAC a few times and then replaced it with a new Mopar IAC as a PM item.

If you're 100% sure the IAC is ok then you might want to clean the MAP sensor.
IMPORTANT! Only use a MAP cleaner solvent designed for that purpose.
Otherwise if say if a carb cleaner is used it will destroy the sensitive sensor element in the MAP.
Very easy to replace.

Keep in mind these inline six engines are gas guzzlers right out of the factory one of the reasons they don't use them anymore although 11mpg is definitely on the low side.
Good luck and if you solve the gas mileage problem give us an update.
 

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Some really simple things to increase fuel mileage are:
Are you driving 4 WD all the time?
Replace air filter
"Smoke Test" for vacuum leaks
"Clean" Catalytic converter
Change plugs and wires

Be careful spraying some sensors down with regular carb cleaner. It can remove some protective coatings.
 

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Discussion Starter #11
Some really simple things to increase fuel mileage are:
Are you driving 4 WD all the time? Most of the time Guts
Replace air filter I've replaced the filter thanks
"Smoke Test" for vacuum leaks Will do :)
"Clean" Catalytic converter Thanks, I'll get that cleaned as soon as I can get back on the road..
Change plugs and wires Thanks, will do.

Be careful spraying some sensors down with regular carb cleaner. It can remove some protective coatings. Thanks, I will be very careful. Your postage costs are so high, postage costs more then new parts,
I have a further problem,
Can you help with it please?

I broke a stud / bolt that holds the oil fill tube on.
There's a bit more than a 1/4" sticking out.

I've used a lot of freeze release,
and a special stud removing doodah.

All I've done so far is strip the threads off the stud.
So, now I have an 11/64 stud :(

I'm waiting for a smaller doodah.
Like this 1/4"Drive Impact Stud Extractor T&E tools new 8544 | eBay
 

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I have had mixed results with stud extractors. The style I have had a bit better luck with are spiral extractors. I make a dimple in the center of the broken bolt with a punch to center the drill bit. Drill on slow speed and keep steady pressure on when the bit is turning. Use lots of oil to keep the drill bit cool. If you're super lucky, the broken bolt may come out with the drill.

Tap the spiral extractor in the hole with a hammer and use a tap wrench to hold the extractor as you back it out. Sometimes I've used an open end wrench to turn the extractor as I tap on it with a hammer.

Good luck!

Hanson Screw Extractor Set 5 Piece
 

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Discussion Starter #13
Thanks Guts :)

Drilling the stud brings a whole mare's nest of problems.
The stud is quite low down at the front of the engine,
not far behind the radiator.

I think the cost of the job would write the car off.
It took me about 2 years to find the car.
Most of our V8s were converted to LPG
with all the valve erosion problems.

I'm pinning my hope on the chuck type extractor for the moment.

Have you any idea for persuading the block
to release it's grip on the stud please.

I've tried paraffin, normal releasing oil,
freeze release gloop, and tapping the end of the stud.
I've even heated the block with a steamer
before using freeze release on it.
So far, there's no sign of the block
loosing it's grip on the stud. :(:(:(
 

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Might not be of any help now but for future reference use a reverse drill bit to make the initial hole for the easy out or stud extractor.
A couple times in the past just drilling the hole with a reverse drill bit removed the broken bolts with no need for the extractor.

OP, don't know what your exact situation is but be careful not to drill past the stud and into the block.
If there's enough of the stud protruding and you can get a welder in there some have had success welding a bolt head to the stud. This solution is not for everyone especially for an inexperienced welder and every situation.

If there's enough of the broken bolt/stud protruding, heating it with a MAP torch worked for me in the past.

If all else fails:
One other possible solution is to leave the broken stud and if possible re-engineer the dipstick mounting bracket position so it bolts up to another nearby bolt on the engine.
This is what i would seriously consider at the point you're at.

Again i don't your exact situation or how confined the work space is.
 

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Chuck extractors have a tendency to mangle what's left of the bolt beyond hope, proceed carefully.

In your limited work space, try using a right angle drill. You may be able to rent one. You only need one big enough to hold small bit. Have you talked with any local mechanics? They encounter broken bolts daily. They will likely have a cutting torch to apply enough to make a difference. Heating the engine block with a steamer will not get it hot enough and may have forced water past the threads creating more rust where you don't want it.

The use of paraffin may prevent others penetrating oils from getting where they need to go. Try using a release oil with phosphoric acid. Phosphoric acid is the ingredient in Coca-cola that eats rust. You will need to use the liquid type, gels and paste are for surface rust. Penetrating and release oils need time, a day at least, to work.
 

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Discussion Starter #16
[QUOT
Chuck extractors have a tendency to mangle what's left of the bolt beyond hope, proceed carefully. As I found out Guts:(

In your limited work space, try using a right angle drill. You may be able to rent one. You only need one big enough to hold small bit. Thanks I have thought about getting a guide made to fit in the hole in the oil fill tube / funnel. But I'm sat on my Khyber while I scratch it., my Khyber.
Have you talked with any local mechanics? No, I'm in a very vulnerable group courtesy of age and infirmity, I keep way from people.
They encounter broken bolts daily. True. the other side of that coin is that they earn money when they break a customer's stud.
They will likely have a cutting torch to apply enough to make a difference. True, I may have to invest in some oxygen, and modify my torch to get in there,. Have you any experience with induction heaters please. Small neat, and no risk. If what they say in the ad is true.

Heating the engine block with a steamer will not get it hot enough and may have forced water past the threads creating more rust where you don't want it. "True" he agreed through pursed lips :)

The use of paraffin may prevent others penetrating oils from getting where they need to go.
Induction Heater.jpg
Try using a release oil with phosphoric acid. Phosphoric acid is the ingredient in Coca-cola that eats rust. Aluminium oxide rather than rust.
You will need to use the liquid type, gels and paste are for surface rust. Penetrating and release oils need time, a day at least, to work. It's several days since I used penetrating oil.
The wretched stud still seems tighter than a duck's Khyber
Note, Khyber is the shortened version of rhyming slang prefered by true Cockneys.
The full version is Khyber Pass.
I'll leave it with you :)
 

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It sounds like you are determined to take the longest, hardest and the most convoluted route through the Khyber Pass.

Induction heating is a cute idea. However you actually want to heat the block not the stud. You heat the block because when metal is heated it expands. Even 0.125 mm of expansion can be enough room to get the stud out. When you heat the stud and expand it, you eliminate any possible clearance and just make the bolt softer and easier to mangle.

With a mix of an aluminum block, steel studs and road salt/sea air, you get dissimilar metal corrosion. Your parts are now likely welded together on a molecular level. Good luck with that.

Mechanics encounter broken studs when customers bring 18 year old, corroded, clapped-out heaps of junk and expect them to be repaired at a discount. I have a broken exhaust stud, from the factory, on my truck, should I avoid the dealership?

Moparado's suggestion of welding a new stud to what's left may be your only option. However, I think you should do the local mechanic a big favor and avoid him. Had you used induction heating on the nut in the first place, you could have avoided snapping It off, Instead of blaming your mechanic...
 

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Discussion Starter #18
It sounds like you are determined to take the longest, hardest and the most convoluted route through the Khyber Pass.
Thanks Guts, you gave me a great chuckle there :)

Induction heating is a cute idea. Perhaps
However you actually want to heat the block not the stud. You heat the block because when metal is heated it expands. Where you spoke of using a cutting torch, did you mean use it to heat the block or the stud please?
Even 0.125 mm of expansion can be enough room to get the stud out. True. The other side of the coin is that if you heat the stud, then the stud expands faster than the block crushing the crud jamming it in the block. When you heat the stud and expand it, you eliminate any possible clearance and just make the bolt softer and easier to mangle. True, that's what's keeping me listening to other folks opines

With a mix of an aluminum block, steel studs and road salt/sea air, you get dissimilar metal corrosion. Your parts are now likely welded together on a molecular level. Good luck with that. Thanks :eek:)

Mechanics encounter broken studs when customers bring 18 year old, corroded, clapped-out heaps of junk and expect them to be repaired at a discount. Oh dear :-(
I have a broken exhaust stud, from the factory, on my truck, should I avoid the dealership? Probably not, they should do it for free under the guarantee.

Moparado's suggestion of welding a new stud to what's left may be your only option. However, I think you should do the local mechanic a big favor and avoid him. The local mechanic and I have been friends for more than 30 years. He did part of his training with me.
Had you used induction heating on the nut in the first place, The thing we both assume to be a nut wasn't a nut. It was part of the stud. The stud was threaded on either side of the what looked like a nut.
The stud held a plastic doofer on the ally block.
heating it was not a sensible idea.
Oil Fill Screw.jpg

you could have avoided snapping It off, Very true :(
Instead of blaming your mechanic I am the man who you call "your mechanic." I absolutely definitely blame me.
I must admit, I feel a little miffed with Mopar.
Their parts diagram didn't give me the information I needed.
Nor did they tell me they'd turned the stud out of a carrot :)

The screws, which came with a similar amount of torque
are only 8.8.
There was plenty of corrosion around them
judging by the white crud that came out
when I chased the threads in the block.
 
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