3.0 Liter Isuzu DMax 2008. TPS is stuck on 100% regardless of vehicle speed, poor acceleration, butterfly valve moves

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Customer: 3.0 Liter Isuzu DMax 2008. TPS is stuck on 100% regardless of vehicle speed, poor acceleration, butterfly valve moves immediately key is turned to on position but reverts to fully open. No engine check light, cruise control won’t engage as well
JA: Is the cruise control light blinking or flashing, or is it solid? When did you first notice it?
Customer: The cruise control light lights up when the vehicle is just switched on, and that’s it. Vehicle was in motion with cruise control engaged, then it turned off independently, power from engine reduced, cruise control hasn’t engaged ever since. There has been a build up of carbon in the intake manifold thereafter but that was cleaned out
JA: What's the approximate mileage on your 2008 D-Max?
Customer: It’s 56,000 km. The vehicle was parked for 9yrs from 2010 to 2019
JA: Anything else you want the Mechanic to know before I connect you?
Customer: Nothing more, everything else seems to be working
Answered by Gary in 3 mins 2 years ago
Auto Mechanic

7,542 satisfied customers

Specialities include: Automotive Mechanic, Small Engine Repairs, Auto Body Repairs, Diesel Engine Repairs

Hello! My name is Gary.
Welcome to JustAnswer.
I'm reviewing your question now, and will post back with a reply shortly.

Alright, I will wait

The throttle butterfly is wide open at all times, it only closes to help the engine shut down.

It is not used to control engine speed, it is a diesel.

No check engine light, you need to be looking at fuel pressure from the tank pump.

No cruise control, have you checked the brake lights, and clutch switch adjustment?


The break lights work and the clutch switch is in a good position including the cable. A new pump was installed in the tank after the original one was found to have ceased. Power from the engine has reduced and vehicle struggles to accelerate and fails to reach 160km/hr. It’s been fully serviced, turbocharger, actuator and solenoid valve are also fully functional. There’s no vacuum leak as well

Ok, this a 4JJ1 engine, correct?

Are you quite sure no codes are set?

Live data from the ECU at engine idle, doesn’t show any deviation from the data in the manual
it’s a 4JJ1 engine. The only code appearing is the SRS airbag. This was there when the vehicle was performing well

So you can enable cruise, but cannot set a speed, correct?

How long ago was the ute performing normally?

It’s been 3 months. I cannot set the cruise control, the major problem is that the vehicle is low on power and the loss of power was sudden and not gradual. At the same moment cruise control disengaged as well and does not engage anymore. That happened while the vehicle was in motion
I had suspected a vacuum leak to the solenoids but after a thorough inspection of the pipes there was no leakage.

With a sudden loss of power, I would say unusual to not set a code and put the check engine light on.

Something has to be wrong in engine data, which you should see on data display on your scan tool.

Example would be commanded versus actual fuel pressure.

If there is a large discrepancy, then the fuel pressure reg or sensor could be faulty.

Can you should show a screen shot of your data on your scan tool please?


I can get that data later in the morning. I’m not having the scan tool right now

That's fine.

If you can post a photo of your screen data, while the low power is occuring, that will help us both.

Just come back when you are ready.


That’s fuel pressure from idle to 2000rpm while the vehicle is stationary

Seems fairly normal.

Of course the fault is not occuring at that point.

What you really needs is Tech2 with the Isuzu card to take a snapshot while driving. Then a review of the recording frame by frame might show your issue.

Do you have an Isuzu or GM dealer nearby?


I’m working in a remote area for now, it could take a month a so before I can get the car to the nearest dealership. The scan too I’m using is a bit limited and more suited to American Vehicles. I can still capture data while driving but it only shows the entire recording during playback in a scrolling manner and not an entire session graph. I could try to capture enough information within a short time so than the graphs can fit on one screen. A few other parameters remain constant from vehicle switched on, idling or in motion.

Ok, I understand. It can be difficult to diagnose faults remotely, especially when a special tool might be required.

This is your vehicle, or a customers vehicle?


It’s a personal vehicle. I bought it on auction in 2018. It’s had a cylinder head change and more work which was done in 2010 after it was driven without water in the radiator. MAF sensor and speed sensor were replaced because they were missing after it stayed in the workshop. the smallest ground cable to the ECU was inactive but was activated through a temporal bypass. After it was restored it operated just fine. A few items which were stolen have been replaced with genuine components. I also replaced the clutch (vehicle vibrated when engaging clutch, but the clutch was still new, the vibration was loss of power). I also have a 2008 DMax 2.5L (85kW) 300,000km on the odometer, it currently feels more responsive than the 3.0L

What was the last job you did on this vehicle, and how long ago?

Vehicle was purchased in September 2008 and had an incident in February 2010. Actual details were not disclosed because a high-ranking officer was driving. But the suspected cause was lack of water in the radiator. The vehicle was being used as a road works supervision vehicle so it never ventured far from the office.
The following has been done of the vehicle
By the Dealer: Engine overhaul kit including timing components and cylinder head (old components removed from the vehicle were found in the cabin). The dealer did not run the engine because the ECU Relay was buzzing when they tried to start the vehicle.
Vehicle was removed from the dealer’s workshop in 2010 after some items went missing or were swapped out with old ones (steering rack, gearbox, 4x4 actuator, speed sensor, mass air flow sensor and turbocharger) the condition of the vehicle was not recorded therefore it became hear-say. The cost to restore the vehicle was increasing every day due to items being stolen by the dealer’s workers so the vehicle was parked at the company workshop.
The company auctioned all old vehicles and non-runners.
Work done with the dealer’s mechanic late 2018 (who also maintained the other DMax): Full Service including clutch kit, restoration of stolen sensors and other components (4x4 actuator, in-tank fuel pump, Steering Rack) except Gearbox and Turbocharger. Communication with ECU was restored and engine started. Started driving the vehicle in 2019 December, the vehicle was driving normally but was low on power. MIL light came on with Turbocharger Actuator Solenoid Stuck Error. The mechanic had glued back a broken pipe. (the excess resin glue was removed and the solenoid was fully functional and there was no error.
The vehicle was driving normally and did not struggle even with acceleration uphill or overtaking truck on a hilly road, but it used to have momentary loss of power on certain days (fuel usage indicator would also indicate increased fuel usage). The suspect was the turbo solenoid because it was probably passing air. The solenoid pipe to the Air filter was broken (this was rectified) the large vacuum horse to the brake booster was also broken (this was also rectified) (a replacement Turbo solenoid was purchased and installed at a later time in 2020).
When I drove to check the performance of the Turbo Actuator solenoid, I had engaged cruise control and let the vehicle drive at 110km/hr, then I simulated an overtake by accelerating to 140km/hr, that was when the cruise control disengaged and vehicle was low on power.
Diagnostics showed all systems normal. So, I inspected the entire vacuum line and also tried to blow from brake booster and no air leak as was the case before the line was restored.
Engine vibrated when engaging clutch and there was a ping in the morning. Someone else had driven the vehicle before this started, (a new clutch was bought since clutches wear out over time therefore there was no loss if it was not the problem, it turned out the clutch in the vehicle was as good as new).
An inspection of the throttle valve showed a build up of carbon (I was operating in a remote area and suspected contaminated fuel) turbo whine was also not consistent as before and was feint) so I suspected the intake manifold or the throttle valve. (at this point best fuel consumption in city driving was while driving at 1500to 1600rpm or gear 4) The throttle valve was tested and was ok, the signal was also checked with a volt meter and was also ok. The intake manifold and EGR Valve were cleaned (another much older vehicle had a very clean intake manifold) the turbo was passing a bit of oil so that was identified as the possible problem except its state had not changed from the time the vehicle was driving normally. So a new turbocharger was purchased from Taiwan and fitted. The gearbox was not changed and from my experience its been smooth and gear changes were effortless when the engine was providing normal torque and power, but its now jerky from gear 2 to 3 considering the engine revs drop very fast or maybe torque is lost when changing gears due to lower than normal power or torque. Injectors are relatively quiet and the mechanic has ruled them out as possible causes.
The engine did loose a bit of power and became loud when ordinary diesel was used but 500ppm Low Sulphur Diesel has been used consistently whenever available.
After restoring all suspected components, the vehicle still lacks power I’m probably getting 50% to 60%, considering the 2.5L powered DMax doesn’t struggle that much under similar conditions despite halving 45kW less in terms of power.

Thanks for your information.

Do you feel it has low power at any throttle input, or only low power when you put your down?

I would connect a boost gauge for in-cabin diagnosis.


That was acceleration to 80km/hr. I will need to look for a boost gauge but that’s from the MAP sensor. Command EGR is constantly 0%, the manual states that it should be less than 30%, Command TAC is constantly 87%, I don’t have a direct reference for this one. When I depress the accelerator I don’t get the same response as before even when the engine is within the high torque rev range, so when I’m following a truck moving at 60 to 80km/hr, it now takes long to accelerate and pass it. with the old 2.5L I would get immediate acceleration if the engine rev was above 1500rpm

I would say you have low boost pressure, which could be a restricted exhaust.


150 kpa on your data is only about 1/2 atmosphere of boost, 7psi.

Thank you... I will have the exhaust checked again. The mechanic had checked the exhaust manifold which I had also suspected though I forgot to ask him to check the rest of the exhaust.

The catalytic convertor is the first part to check for restriction/meltdown.

I have kicked cats off the back of the turbo, and driven the vehicle, a bit noisier, but if the power is a big difference, we know the fault is in the exhaust.

Different vehicle, but I recently had a VE Maloo with undriveable power/misfire etc. One cat had melted and the entire centre went down and blocked the y-pipe between both banks. A bit of effort to get the cork out. Cleaned everything up, 2 new cats, etc. New car again.


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