Manifold Pressure high logged 3030

I have a constant fault on the Hawkeye...clear it, start it and even just run on drive the code reappears.

3030 manifold pressure.

Any ideas, I have put a new sensor in and just the same.

If it has any bearing....EGR removed long ago

1 2 3 4 5 sport?

lynall said:

1 2 3 4 5 sport?

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sorry..forgot. Disco 2 TD5, pre facelift.

I presume you replaced the MAP sensor did you? so if the sensor is new read live data with hawkeye and report what you get on the MAP sensor then we'll speak again

sierrafery said:

I presume you replaced the MAP sensor did you? so if the sensor is new read live data with hawkeye and report what you get on the MAP sensor then we'll speak again

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Thanks, truck is baing a pain at the moment! had it 16 years so know it well.
I replaced the sensor in the top of the inlet manifold held in with two bolts.
I did look at Haykeye live data before I posted......it confused me (does not take much on modern c
ecu type cars !!) as it seemed to be circa 230kpa at idle but rev engine stationary and dropped exactly to 100kpa.
I can do it again if we need correct readings.
I thought today whilst checking out the other issue of dodgy indicators that the boost pressure was down....my gauge fittewd on it usually maxed out at about 18-19 psi (it reads a bit high I think) but today floored it maxes at about 15psi

Russell Marlow said:

it seemed to be circa 230kpa at idle but rev engine stationary and dropped exactly to 100kpa.

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It should be the other way around, about 100kpa at idle and go up to 230 under load, at this point i can presume a wiring issue or ECU fault

try to read live data with sensor unplugged as well then read the code again

It could also be a charge air leak opening up under boost.

Graculus said:

It could also be a charge air leak opening up under boost.

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how would that explain 230kpa reading at idle ?

Venturi effect.

Graculus said:

Venturi effect.

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... you should explain that cos AFAIK for that some pressure is needed while at idle it's not. A 230kpa reading at idle for me can be a momentary short circuit between the sensor's supply and output wires so without any pressure the return signal(input) to ECU is above 4V and that can be around 230(close to it's max which is 250Kpa at 4.9V) or an ECU fault that's what iwas curious if the fault code with sensor unplugged changes to open circuit or not

sierrafery said:

how would that explain 230kpa reading at idle ?

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it has boost...15psi. Dont think it has a leak.

If you have a charge air leak (i.e. post turbo) then air can be drawn in through the leak thereby increasing the uncommanded manifold pressure, once the turbo comes sufficiently 'on boost', the point of the leak can/will become an outlet and the measured MAP will drop. I've seen this on many vehicles (and some manufacturers include a 'guided diagnostics' test for it in their software) but as we're operating remotely, so to speak, it was a suggestion not a diagnosis. Personally, I'd be carrying out a smoke test of the inlet & charge air containment, but that's because I have the facilities, the checks can be done by other means but it will be more laborious.

I understand that explanation thanks........but driving it does hold steady boost

Then what is the reading with ignition on/engine off? it should be at, or close to barometric pressure.

Russell Marlow said:

I understand that explanation thanks........but driving it does hold steady boost

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If that's on the gauge it's irrelevant for the management, and as you said:

Russell Marlow said:

....my gauge fittewd on it usually maxed out at about 18-19 psi (it reads a bit high I think) but today floored it maxes at about 15psi

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"about 15psi" means about 1 bar(14.5psi) and that's a default mode for AAP sensor failure but i've seen this with MAP signal failure too even though it's not particulary mentioned it's still around 1bar(100kpa)... that 18-19psi(1.3bar) under loadf is the normal with a good MAP for an untuned engine with factory wastegate setup






this issue needs further investigations so concentrate on live manifold and ambient pressure readings while driving

Graculus said:

Then what is the reading with ignition on/engine off? it should be at, or close to barometric pressure.

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It should be quite the same as at idle, as you say close to barometric pressure and that's around 100kpa as the standard pressure at sea level 101.3(1013hpa) ... for the venturi effect extra pressure is needed not ambiental afaik that's the gist of it

On a well working Td5 the MAP(manifold absolute pressure) reading at idle(or engine off) should be very close to the AAP(ambient air pressure/the sensor on the airbox)... then as the rpm/load grows te MAP should grow up to max 242kpa(overboost limit) which is arund 1.4 bar boost and the AAP might drop a bit due to the sucction... the ECU calculates the boost by extracting the AAP reading from MAP reading(MAP - AAP = boost) that's how the `Td5 works boost wise

I'm aware of that, the reason (as I'm sure you're aware) for asking is that an offset at key on / engine off will quite often be an indicator of a failed / unreliable sensor and also give a baseline measurement, yes, it'd be quicker to diagnose with live indicated values and comparable measured values - but this is the internet, so best guess with a bit of confirmation bias is probably as good as it gets.

Russell Marlow said:

it seemed to be circa 230kpa at idle but rev engine stationary and dropped exactly to 100kpa.

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IMO the essence is there ^^^

Thinking deeper it becomes more suspect to me that there is a short circuit to supply on the MAP circuit hence the "manifold pressure high" fault code which is logged after ignition when the ECU is going through the system test protocol cos then it gets around 4V input from the MAP sensor(corresponding to 230kpa reading) which is obviously hight at idle when the return voltage(sensor output) should be close to 0 then after the code was stored and the test finished the ECU goes to that 100kpa predetermined value and to the restricted performance mode with around 15psi boost confirmed by the gauge.

to clarify, the description in the WSM for MAP is as follows but it's not 100% accurate cos in reality the MAP's output is between 0.1 - 4.9V (at around 4.7 it's overboost), i made live measurements not once... and btw, the sensor is not "producing" anything, it gets a 5V input from the ECU and works with that.

Thanks to you both, the 18-19 psi I had set previously when working on the truck. Strangely the lower 15 psi boost has only manifested SINCE changing the sensor on the manifold. I may put back the old one I took out to see what happens.
I only removed it because I had the over pressure code all the time.

Russell Marlow said:

...Strangely the lower 15 psi boost has only manifested SINCE changing the sensor on the manifold.I may put back the old one I took out to see what happens. I only removed it because I had the over pressure code all the time.

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You insist too much on the gauge reading IMO, all i explained untill now is about the engine management, as long as you keep getting that fault code and those MAP readings that engine will not run well, it will be in the restricted performance mode regardless of what boost you see on the gauge