Disco 2 Black smoke

Unplug the MAF it should run better

I did today and it made a little noticeable difference, the manifold pressure did not get higher than 1.87. Then with the MAF reconnected the pressure got to 2.23 easily without over boost, because I then unplugged the AAP at the same time. I reckon that the MAF is just not working well and not completely shot. It is only when I reconnect the AAP that I find the over boost occurs.

ScholtzID said:

I did today and it made a little noticeable difference, the manifold pressure did not get higher than 1.87. Then with the MAF reconnected the pressure got to 2.23 easily without over boost, because I then unplugged the AAP at the same time. I reckon that the MAF is just not working well and not completely shot. It is only when I reconnect the AAP that I find the over boost occurs.

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so read the AAP input cos that could be relevant ... low reading MAF would not lead to oberboost whatsoever only high reading MAP or AAP...i told you in the other forum that above 200Kpa MAP reading with AAP unplugged is not normal cos the management should cut fuelling as to limit boost at 100Kpa with AAP open circuit default which is 100 but even if it doesnt a low MAF reading would reduce the boost too not send it to oversboost...eventually connect a boost gauge to see the real boost if you want to get to the end of it

The AAP reading looks correct to me on Hawkeye. It starts at readings of about 99.9-100.1 and drops under acceleration to 98 or thereabouts. When I talk about the MAP readings it is Hawkeye readings, in other words when I say 1.87kPa the actual boost pressure is 0.87(deduct 1kPa from reading to get boost pressure). I am frantic to get my vehicle to run as designed and will not rest until I can get it right. With the AAP in place the ECU limits the fuel at a Hawkeye reading of about 2.45kPa. It is difficult to get an exact reading while driving.

Sierrafery, I am battling to understand what you are saying. I do not doubt your advice, I just do not grasp the facts because of the way you put your sentences together.
Tell me if I read your statements correctly:
The low readings of the MAF sensor is not causing the over boost.(Only happens with the AAP in place)
Over boost can only be caused by high readings from the AAP or MAP sensor. (Are you suggesting that one or both the sensors may be faulty?)
I do not have access to boost gauges etc. I only have Hawkeye which rely on the vehicle sensors for readings.

So, overboost occurs when the MAP reading gets to 242Kpa, that's the factory set limit in the ECU, under normal load on a well working engine at 230 Kpa MAP the MAF should be around 520Kg/hr and there's a preset max accepted limit of 680 for extreme load where the engine cuts fuelling as well ... my theory is that with AAP connected the fuelling is not affected and if you get overboost at around 400 MAF reading it's very possible that the MAP sensor to give higher than normal readings cos presuming the MAF is good at a 400kg/hr suction the boost should not be so high to get to overboost ...with AAP unplugged the ECU is supposed to limit fuelling as to not exceed 1bar boost(200Kpa MAP) so if you get above 230 then and provided the AAP + MAF are good the only logical conclusion is that the MAP is at fault....see the IAT(inlet air temp) reading too cos it's part of the same sensor(MAP/IAT) ...at this point if i was you i'd replace the MAP sensor though as i said the most relevant would be to read the real boost with a gauge and compare with the MAP reading...this behaviour with plugged and unplugged AAP while it's readings are OK is very odd though and what's also suspect is that you should see the wastegate moving even stationary if you kick down the throttle and you said you dont

A few years ago I would have cried in the corner at reading that paragraph, now it almost makes sense!

Thinking about it I may be having a similar issue though mine was solved by turning the boost down from 24psi to 18psi and chucking the boost box. Awaiting an uprated MAP sensor and ECU calibration to suit

Thanks for the feed back. As I said before my MAF readings are way below the figures you mention. With the AAP unplugged, I pushed hard today and at 120km/h MAF reads 450, MAP 230kPa and power is ok but not brilliant, it was 37 degrees Celsius today, so I assumed that the power would be down a bit.
I plugged in the AAP and at about MAP 230, the engine lost power and the MAP reading fell to 199.
I have ordered a genuine MAF sensor because I just do not trust it.
I will try to make up a contraption to measure the MAP before buying any more sensors.

You should have bought a MAP IMO...

Time will tell!

IMO the engine will tell sooner

At last I have an engine that is running well, no over boost. It turned out to be the turbo modulator - I fitted a new one again(I replaced it about 70 000km ago). Problem solved!
I also fitted a new genuine MAF that was already ordered earlier, it does not seem to have made any major change to my readings, it goes op to 500 now, I seem to remember getting 490 with the old one.