Loss of power at highway speed and high fuel usage

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Loss of power at highway speed and high fuel usage

Postby Marchy on Wed Sep 01, 2021 12:52 pm

Gday team,
Slowly coming to terms with the new MN 2.5 but have come across my first slight issue I'm unable to rectify. And searching so far has not given me much if anything, but happy to be corrected there.

When driving at highway speeds all is happy in life, however if I back off for roadworks or the like there is a few moments of no power when applying right pedal again, time between backing off and accelerating doesn't seem to matter from 5 seconds to 30 seconds of coasting I have had this symptom. It's as if there is zero power, I even looked to see if it had stalled the first couple of times. After a few seconds (5-20)things come back and all is well. No codes thrown yet so no info there. It's almost as if it's not getting fuel, but if there was a supply or flow rate issue I would expect under load performance to be impacted.

Since buying I have given the manifold a clean out as it was very blocked, cleaned MAF sensor, removed battery multiple times, fitted provent, ran 2 batches of injector cleaner.
Today I pulled the SCV hoping I could polish like the one in my ML but it's the sealed version. Only thing I'm yet to change is fuel filter.

Primarily did all of the above to try and reduce fuel usage, as it was sitting around 13l/100 initially when purchased. It's down to around 11.5 around town now but oddly goes up to 12-12.5 on the highway. Can't help but think something is up due to the higher fuel usage on highway compared to around town.

2013 MN Auto
200k
245/70r16 and 265/70r16 no change to fuel usage
No bar work, no lift, no weight.

I'm pretty much out of ideas now, short of a dealer visit to see if they can pick anything up. Will do fuel filter first just so I can feel like I've done everything but don't see it making much difference.

Any suggestions?

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Re: Loss of power at highway speed and high fuel usage

Postby RHKTriton on Thu Sep 02, 2021 8:06 am

Hi Marchy.

I'd have a look at the turbo. VGTs are prone to crap flagging up the vane mech.

See if you can freely move the actuator lever end to end.

Didn't see that you'd cleaned the MAP sensor. Give this a clean with Sensor cleaner and check hoses and manifold port is clean.

If you SCV is original, I'd be inclined to replace that. Or at least run a higher strength injector cleaner through half tank of fuel.

Long term, 200 to 300mm 2 stroke oil per tank keeps things nice.
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Re: Loss of power at highway speed and high fuel usage

Postby Marchy on Thu Sep 02, 2021 2:37 pm

RHKTriton wrote:Hi Marchy.

I'd have a look at the turbo. VGTs are prone to crap flagging up the vane mech.

See if you can freely move the actuator lever end to end.

Didn't see that you'd cleaned the MAP sensor. Give this a clean with Sensor cleaner and check hoses and manifold port is clean.

If you SCV is original, I'd be inclined to replace that. Or at least run a higher strength injector cleaner through half tank of fuel.

Long term, 200 to 300mm 2 stroke oil per tank keeps things nice.
Will check out the VGT actuator, not something I'm familiar with yet. Just need to make sure it goes from end to end smoothly?

MAP sensor hose was blown out when I did the manifold clean and port is fine. Will give the sensor a hit next time. All hoses seem fine, have checked them multiple times trying to stop those annoying oil seeps from inlet pipework.

Have run injector cleaner through half tank, as well as the one where you run in from the fuel hoses direct to engine. Will add a SCV to the shopping list if things remain the same.

Might have put a dash of 2 stroke in the tank from first or second fill ;)

Thanks for your input.

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Re: Loss of power at highway speed and high fuel usage

Postby RHKTriton on Fri Sep 03, 2021 8:40 am

Problem with modern vehicles, loaded with computers, is they can be "emotional" and sometimes I reckon you'd need a Shrink to sort them out. lol.

Sometimes you can hop in and fire up with everything working great. Then the next run it seems just a little off.

Other things you could also check are the temperature sensors around the engine. Probably no effect in your case.

With the SCV, when Ive had mine apart, you'll see evidence of marks that look like solid particles have rolled around between the metal surfaces. It's possible that these may act like wedges and jam the plunger on their way through.
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Re: Loss of power at highway speed and high fuel usage

Postby Marchy on Fri Sep 03, 2021 9:53 am

RHKTriton wrote:Problem with modern vehicles, loaded with computers, is they can be "emotional" and sometimes I reckon you'd need a Shrink to sort them out. lol.

Sometimes you can hop in and fire up with everything working great. Then the next run it seems just a little off.

Other things you could also check are the temperature sensors around the engine. Probably no effect in your case.

With the SCV, when Ive had mine apart, you'll see evidence of marks that look like solid particles have rolled around between the metal surfaces. It's possible that these may act like wedges and jam the plunger on their way through.
Funny you mention the temp side of things. Had to duck up the folks place last night and noticed that the fan clutch was engaged most of the way, water temp on scangauge was 91-93°. Ambient temp was 25-27°. When slowing for road works im thinking that the extra load the fans put on the system when applying throttle from low rpm combined with a sluggish response from the transmission is giving me the "loss of power" I described above.

Coming home after the cool change came through the fans were not spinning as much water temp 87-89°, ambient down to ~10° and response was noticeably better.

Is the fan on these things ECU controlled or the normal fluid filled clutch hub setup? Running fans all the time could potentially cost a bit of fuel economy also I'd imagine.



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Re: Loss of power at highway speed and high fuel usage

Postby RHKTriton on Sat Sep 04, 2021 9:31 am

Just the viscous type. They do fail sometimes.

A locked up fan sucks a bit of power and being on the engine side of the transmission, the effect is magnified at the wheels.

On a similar example, I installed a solid flywheel when I replaced the clutch, which weighs about 5kg more than the one I took off. I notice a definite few seconds delay before the revs come on the boil.

Re temperature, have you checked the gap between the radiator and AC condenser? This can easily collect bugs and grass seeds.
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Re: Loss of power at highway speed and high fuel usage

Postby Marchy on Mon Jan 31, 2022 11:18 pm

So the thirsty gutless triton saga continues. Since last update I have flushed cooling system, SQL, replaced SCV and another SQL. Now it drives smoother and drinks more fuel. Prior to SCV I was in the 11's and whilst not thrilled was coming to terms with it. Now since SCV and SQL I'm back up around 13.5-14l/100ks. I still suspect the viscous hub might be running the fan far too much, water temp down around 85° at times and fan roaring constantly so will replace when I do next service, but not sure what has changed since SCV swap.

Another odd thing it now does since the first SQL is under reasonable acceleration it squeaks similar to a belt squeak but not as high pitched and very consistent coming from the fuel pump side of engine. I have checked hoses,belts and I'm fairly certain the noise is in the fuel system but as for where I have no idea, any ideas what may vocalising its dislike for life?

I even took it to a real mechanic for a once over and he seemed to think all was good in the world.

One day I will like this ute but it's making me work for it.


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Re: Loss of power at highway speed and high fuel usage

Postby DibbyDibbyDJ on Tue Feb 01, 2022 5:12 am

Marchy wrote:Another odd thing it now does since the first SQL is under reasonable acceleration it squeaks similar to a belt squeak but not as high pitched and very consistent coming from the fuel pump side of engine. I have checked hoses,belts and I'm fairly certain the noise is in the fuel system but as for where I have no idea, any ideas what may vocalising its dislike for life?






Sounds like you either have a leaking EGR pipe gasket, or it is slightly loose. They squeal like a loose belt if not right.

It will more likely be the one from the EGR valve to the cooler, as that is that squeals because of the boost pressure, but the one from the head to the cooler regularly come loose, but dont make as much noise, just dumping a bit of soot out around the flange to the head
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