No Power at high revs

[the_mog]

Hi All,

My Navara D40 2.5DC AUTO is giving me grey hairs:

The symptoms are as follows...

At high revs (4500+) it seems that there is a loss of power,
if i accelerate normally say 50% throttle then everything is fine, it changes gears at around 2800RPM

If i drive hard from first gear, then it changes at 5000RPM to 2nd however it goes like a rocket until 4500RPM then sort of gets sluggish.

From 2nd to 3rd and up it really battles to get up to speed when the throttle is 100%.

if i play with the throttle, and keep the revs down i manage to get 160km/h easily and can maintain that speed.

The following has been done in an attempt to repair the vehicle:

Gearbox totally rebuilt
Turbo Totally rebuilt and recored
EGR cleaned (it was full of $..T
Turbo vacuum hoses all replaces

I have a Delphi Diagnostic tool that can measure pretty much everything.

No OBDii Errors on the engine
P1815 is the only error on the Gearbox (I had a look in the manual but have no idea what that error could be)

I had a look at the Intake Manifold Pressure and on acceleration and it rises from 110KPA to 220KPA when driving hard then suddenly drops down to 180KPA at 4500Rpm

If you need anymore info, please don't hesitate to ask

Thanks

Kenny

 

[happy john]

At 4500-5000 there is no power it drops off rapidly in a diesel. There is just no need to rev it like that to get it going, your better off with a petrol if that's your driving style. Have a look at some dyno charts for your car, note how above 3500 the power drops. Time to change gears...

 

[Mordecai]

At 4500-5000 there is no power it drops off rapidly in a diesel. There is just no need to rev it like that to get it going, your better off with a petrol if that's your driving style. Have a look at some dyno charts for your car, note how above 3500 the power drops. Time to change gears...

Shit mate, like happy man said try changing gear at 3000rpm, diesel engines work on low revs and torque. lol lol

 

[308bever]

it`s a diesel mate! buy a skyline if you want to race it (((-;

 

[happy john]

Kenny, the fault code you are getting relates to comunication between the tcm and the ecu. It has to do with the tcm and manual mode. Perhaps that is why you have the erratic running and the fact that the auto is holding it up to redline without changing. I would of though if you sink the boot in it would change well before 4500rpm.
Cheers

 

[the_mog]

Thanks all,

I hear what you say re: driving like a maniac, but this ususaaly happens when overtaking,

Kenny, the fault code you are getting relates to comunication between the tcm and the ecu. It has to do with the tcm and manual mode. Perhaps that is why you have the erratic running and the fact that the auto is holding it up to redline without changing. I would of though if you sink the boot in it would change well before 4500rpm.
Cheers

@happy John,

Do you have any advice on where to start looking for this fault?

Kenny

 

[happy john]

Sorry mate, I'd not have a clue where to start looking apart from a loose harness or something when you had the box rebuilt.
Cheers

 

[jonney]

stop speeding [ 160 kph ] overtaking. keep on over reving this engine and you will break it.

 

[happy john]

He is in South Africa, they must have some form of Autobarn

 

[jonney]

OH i see John, maybe a turbo Porsche would go better. i don,t think the navaras were designed to be fast cars.

 

[Old.Tony]

Apart from the fact that it's not really a race car and at 5000rpm (actually it should be about 4800 but who's going to argue 1/4 of the idle rpm) the governor will stop the engine revving further by limiting fuel flow.

I am wondering if the NPS is getting involved, but I suspect a connectivity issue is causing the problem. Pop a boost gauge on it and see what the turbo's doing at those revs - it will well and truly be up in peak area 18psi+. If your turbo is dropping off at higher RPM it won't be through a lack of turbine energy. It could be through vane control - although you have rebuilt the turbo and replaced the vac hoses, control is provided by the boost control solenoid which is a small black widget that is mounted on the back of the intercooler's hard pipe on the hot side (so it can 'see' the turbo). This device pulses at 100Hz and allows more or less vacuum in to the turbo actuator - it might not be functioning properly at all times.

Are you hearing any abnormal noises like squealing as the turbo spools up? You might have a boost leak. Not dangerous at all, but it will restrict performance. Check for black oily emissions from any of the air path between the turbo and the intake manifold.

 

[Pro32]

Hey guys, I am new at this forum, wanted to know if this original issue been solved, I am having the same problem, I own an automatic gearbox 2.5 yd25 Navara and from time to time when accelerating it runs to 5000 rpm without performing a gear change, the car has a new solonoid, turbo and injectors and runs great, also tried to replace maf sensor and front boost sensor with no change, I am thinking maybe to look into the timing chain or throttle valve ? any ideas ?

 

[Old.Tony]

Hey guys, I am new at this forum, wanted to know if this original issue been solved, I am having the same problem, I own an automatic gearbox 2.5 yd25 Navara and from time to time when accelerating it runs to 5000 rpm without performing a gear change, the car has a new solonoid, turbo and injectors and runs great, also tried to replace maf sensor and front boost sensor with no change, I am thinking maybe to look into the timing chain or throttle valve ? any ideas ?

The OP hasn't been seen since 2018 so we probably won't get a response.

I doubt it's your timing chain. The gearbox is aware of the input (engine) speed, engine load, vehicle load etc. The decision - barring any sensor that's not consistently providing data to the ECU - is done by the TCM in the gearbox.

I went to an auto gearbox guy and he hooked up a widget to my OBD port which queried the gearbox. All sorts of wonderful info was presented, including slippage rate of the torque converter, gears, speeds etc. I would suggest letting a gearbox guy take a look at it - but if it's a small company with just a couple of guys, pay them to provide the diagnostic info but that's it. Take the car elsewhere (like a large company) to make any changes.

 

[[email protected]]

dont thing this is your problem but i had an auto car which did that all the time between 3rd and 4th, untill engine reached normal operating temp , it was caused by thermostat being stuck open

 

[OldManBeard]

Hey guys, I am new at this forum, wanted to know if this original issue been solved, I am having the same problem, I own an automatic gearbox 2.5 yd25 Navara and from time to time when accelerating it runs to 5000 rpm without performing a gear change, the car has a new solonoid, turbo and injectors and runs great, also tried to replace maf sensor and front boost sensor with no change, I am thinking maybe to look into the timing chain or throttle valve ? any ideas ?

None of the things you listed will affect gear changing. There are at least three things you need to do.

1. Check the transmission fluid. I'm going to bet you've never done that, especially as there's not even obvious where the dipstick is and it's definitely not designed to be checked easily.
2. If the fluid level is okay then check for vacuum leaks.
3. Perhaps most importantly, either drive the car like a diesel should be driven or start looking for a more appropriate car to replace it with. If you keep hitting 5,000 RPM it's only a matter of time before this one dies on you. You've got a diesel ute with a rather small engine, which is already highly stressed during normal use, let alone as 5.000 RPM. It's a good machine when used as intended but a high revving powerhouse it's not.

 

[Pro32]

Thanks all for the help, Transmision fluid is new, also thermostat new and original, maybe one of the gearbox solonoids has a lag and prematures the gearchange causing the lag after the engine peak, a bit frustrating issue, I normally dont go above 2.5 RPM, but this problem causes uncontroled revs by not shifting upwards on time