2004 Discovery 2 TD5 overboosting at high RPM

**Young1** · 11th March 2020, 11:15 PM

Hi all,

I would really appreciate the help on this one.
I owned my discovery (ODO 275,000 kms) for almost 4 years now, and don't quite a bit of work on it (does maintenance count as work

).
For the last 2 years it has been over-boosting at higher rpm and heavy throttle usage on and off.
Seriously i will buy a carton for whoever can help my solve this.

Brief History (last 1 year):

Prior to my ownership always serviced at LR specialists, new fuel pump fitted.
Head Gasket repaired (at 250,000 kms but LR specialist) 1 year ago after a coolant over pressurization / overheating saga. This included new injector O-rings and washers. New coolant top hose because it exploded once.
New expansion tank and expansion tank cap after expansion cap failed and caused some coolant issues.
New MAF fitted after car became increasing sluggish (disconnected MAF showed vast improvement).
New wastegate modulator fitted (after overboosting continued). Replaced the wastegate modulator small hoses.
New injector wiring harness (was very oily).
New Glow plugs after strange starting struggles (more on this later).

More Recent History (last few months)

Full service including all oil filters
Cleaned ECU red plug (no visible oil present)
Cleaned MAF
Cleaned MAP (was clean)
Cleaned IAT (was clean)
Checked waste gate, confirmed not sticking.
Checked fuel pump providing required pressure, no fuel leaks.
Bypassed wastegate modulator (even though this is a new unit) and there was a slight improvement.
Checked all intake hoses to De-lamination (they are not original hoses and are in good condition).
Adjusted up and down the waste-gate actuator rod (gets worst if increased or decreased threads on the rod).

The car continues to hit and overboost condition (too much boost or not enough fuel?) when i use heavy throttle.
Under "slow and steady" acceleration it can usually get to 3500 RPM but feels like its struggling.

The car is certainly Drive-able, and feels "okay" in the mid range. However, fast acceleration and high rpm it feel gutless.
i am getting a mileage of 14L/100kms on average (when i first got the car it was a 9-10L / 100kms on highway driving )

My three leading theories are:

Faulty MAP sensor?
intake air boost leak, but where?
Fuel filter non-return valve?

Can anyone help, i cant really afford to keep replacing parts hoping it will fix the problem.
its a very clean car and it is leaving a sour taste not being able to diagnose the problem.

Thank you in advance.

P.S. I have read just about every thread on this site (and the internet) on overboosting TD5's
P.P.S. I have the RAVE manual and reasonably familiar with it.

**SPROVER** · 12th March 2020, 10:28 AM

Have you got a boost gauge or nanocom to know what exact boost you are running?

**onebob** · 12th March 2020, 10:58 AM

Originally Posted by SPROVER

Have you got a boost gauge or nanocom to know what exact boost you are running?

X2 on the boost reading .... and factory setting for the wastegate actuator rod is fourteen threads exposed +/- one - what is yours set to?

**sierrafery** · 12th March 2020, 12:15 PM

As log as the overboost is not confirmed with tester IMO it's rather the so called "MAF cut-out" when the sucction exceeds 680 kg/hr which seems like overboost and it's very common on late modells especially on autos so first of all the symptom must be clearely diagnosed.

**Young1** · 12th March 2020, 01:07 PM

Originally Posted by onebob

X2 on the boost reading .... and factory setting for the wastegate actuator rod is fourteen threads exposed +/- one - what is yours set to?

Hi, I don't have a nanocom unfortunately, I might have to start beg, borrowing and stealing one.

I think my actuator rod has been at 12 exposed threads (since I have had the car). Hmm possibly I'll try dialling it back to 14 threads.

Is there a way to test the MAP sensor with a multimeter?

Cheers for the help

**Young1** · 12th March 2020, 01:11 PM

Originally Posted by sierrafery

As log as the overboost is not confirmed with tester IMO it's rather the so called "MAF cut-out" when the sucction exceeds 680 kg/hr which seems like overboost and it's very common on late modells especially on autos so first of all the symptom must be clearely diagnosed.

Yeah right, so it's likely getting too much boost, sucking too much air and the MAF is reaching its limit (and ecu cuts fuel)?

If I disconnect the MAF, this would stop the MAF reading controlling the fuel cutout?

I will try again withe the MAF disconnected to see if it is still causing issues.

Cheers
Hayden

**discorevy** · 12th March 2020, 02:49 PM

above is most likely scenario, also worth looking closely at the small hoses from turbo outlet pipe to modulator and modulator to actuator , also put air into the actuator ( no more than 20 psi ) to make sure that is working

**Young1** · 12th March 2020, 11:05 PM

Originally Posted by discorevy

above is most likely scenario, also worth looking closely at the small hoses from turbo outlet pipe to modulator and modulator to actuator , also put air into the actuator ( no more than 20 psi ) to make sure that is working

So today i drove to/from work, i adjusted the thread of the waste-gate actuator to 14 threads (i previously thought it was 12 threads stock?)
I tried both the waste-gate modulator bypassed (waste-gate actuator hose straight to turbo intake), and the waste-gate modulator installed correctly.

both scenarios had no noticeable differences, still over-boosted on heavy throttle.

I will try with/without MAF sensor plugged in tomorrow (i have my doubts it is the MAF sensor being faulty, as it is only 4 months old).

I'll report back tomorrow.

**sierrafery** · 12th March 2020, 11:16 PM

Originally Posted by Young1

I will try with/without MAF sensor plugged in tomorrow (i have my doubts it is the MAF sensor being faulty, as it is only 4 months old).

I'll report back tomorrow.

It's not about faulty MAF but about a real reading of 680 when it cuts out and if that's the case the symptom will go away with unplugged MAF cos it goes to default. That means that the turbo is spinning fast and the succrion is high while the boost which should be high as well at that sucction is not getting to the inlet for some reason or the MAP sensor is reading low. You really need a tester to properly diagnose this issue

**onebob** · 13th March 2020, 10:54 AM

Originally Posted by sierrafery

It's not about faulty MAF but about a real reading of 680 when it cuts out and if that's the case the symptom will go away with unplugged MAF cos it goes to default.

####That means that the turbo is spinning fast and the succrion is high while the boost which should be high as well at that sucction is not getting to the inlet for some reason or the MAP sensor is reading low ####.
You really need a tester to properly diagnose this issue

Yes, need a tester ..... #### but continue to eliminate mechanical causes, consider waste-gate creep or related actuator problems. As suggested in an earlier post put air into the actuator to test if it is functioning - you can use a sports ball or bicycle hand pump.

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