2004 Discovery 2 TD5 overboosting at high RPM

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Originally Posted by Young1

I am officially confused.

Tested a few configurations today:

1. MAF plugged in,10 threads on wastegate actuator, wastegate modulator plumbed as per factory. max 16 PSI while driving.
2. MAF plugged in,10 threads on wastegate actuator, wastegate modulator plumbed as per factory but blanked at wastegate actuator (no hose to actuator). max 16 PSI while driving.
3. MAF plugged in,10 threads on wastegate actuator, wastegate modulator bypassed, wastegate actuator plumbed straight to inter cooler pipe. max 16 PSI while driving.
4. MAF plugged in,12 threads on wastegate actuator, wastegate modulator bypassed, wastegate actuator plumbed straight to inter cooler pipe. max 16 PSI while driving.
5. MAF plugged in, 9 threads on wastegate actuator, wastegate modulator bypassed, wastegate actuator plumbed straight to inter cooler pipe. max 16 PSI while driving.
6. MAF UN-plugged in,10 threads on wastegate actuator, wastegate modulator bypassed, wastegate actuator plumbed straight to inter cooler pipe. max 18 PSI while driving. (did not overboost)

Does this show that these is a boost leak in the system?

This boost leak must have appeared while i was at the shop fitting the MAF sensor (previously the car would not be limiting boost with the MAF unplugged)
The MAP sensor seems to be reading correct values on the last nanocom run.

Guess i will be taking out and checking the intercooler hoses tomorrow (for the third time now)

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You seem to have had the use of a nanocom at times with this problem?

If so is there any recorded logs?
I couldn't see any in the thread.

Cheers
James

[QUOTE]

How would that happen?

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Well the idea of shortening the rod is to delay the opening of the wastegate so the diaphragm is preloaded more .

The stroke of the diaphragm is therefore reduced.

The modulator pulses at below 15PSI but after 15PSI provides a pressure to open the wastegate.

So the wastegate will partially open after 15PSI even with the reduced stroke . The turbo will overcome the reduced wastegate opening but there will still be an amount of bleed off of boost.

The difference with a set boost cut with a Turbo Technics boost controller and shortened wastegate rod is really quite marked. The TT controller is just really a spring controlled adjustable valve which stays completely closed until it opens at whatever it is set at by trial and error. The boost controller diaphragm arm has to be set back to factory specs.
It works for me. I see 20 PSI just in normal driving .

Regards PhilipA
BTW there was a discussion about this a couple of years ago where Offtrack agreed that the manual Wastegate was the best solution at that time. AFAIR others have since said that the map controlling the boost modulator can now be altered to provide more boost before wastegate open signal . I do not wish to go any further with mine and do not have the skills to DYI. There is a blog somewhere that describes the change to the wastegate modulator map, but AFAIK it is not info that is generally available or DYI able without specialized computer stuff..

I have manual boost controller on mine with forge actuator which has longer travel, it's been there for years i know how it works: Discovery 2 Manual Boost Controller i just disagree wih the theory that with shortened rod the flap is partially opened or that it bleeds at the same pressure like with relaxed rod... i sustain that if you shorten it too much it won't bleed at all cos it goes to overboost before that, i'm a fan of MBC myself, i recommended to the OP to shorten the rod for test not that i like the ideea

I left my turbo rod at standard 12threads and run turbo smart boost T and it runs great boost 10 psi at 1500rpm and keeps going till 28psi at 3000

Hi All,

Many thanks for the help and guidance.
I have had some luck over the last few days.

After re fitting the inter-cooler hoses and inspected the inter-cooler i couldn't find any noticeable leaks / cracks.
After going for a drive the Boost leak that was limiting the boost to 16 PSI seemed to have disappeared.

I don't have a Nanocom but i do have a boost gauge tapped into the inter-cooler nipple hose that goes to the modulator. (at least for the time being until i install it properly in the manifold).

In summary, with a new VDO MAF and refitting the inter-cooler hoses the problem seemed to have gone away (surging under heavy acceleration).

Currently i am getting 18 PSI (pre-intercooler) under full acceleration, i will try adjusting the wastegate actuator to push to 20 PSI.
I will keep you updated if i have any further surprises, it is not getting driven much due to the COVID lockdown and working from home :( .

Many Thanks,

Hayden