Mega overboost then finally limp mode

Feb 1, 2007
1,602
1
Nottingham
Personally Brad I dont think the oil temp will have anything to do with overboosting. What makes boost is the speed of the turbo and cant possibly be influenced by the temp of the oil. It must be a sensor issue or map realted problem. You can only get overboost if the vanes are in the wrong position due to either being stuck and the vac cannot control them or for some reason thats the boost its delivering due to a sensor/info to ecu fault.
Have you bought a 3 bar sensor yet? I renewed mine last week and it was about £38.
Glynn
 

brad1

Guest
but what I want to know is if your so sure it's issue due to not having a 3 bar map sensor, how will a 3 bar map sensor stops this mega overboosting??? Will it cure this?
 

jonjay

50 Years of 911
Jun 27, 2005
5,843
1
Essex
Well its worth a try.

What 3bar map sensor does brad need? 300kpa? What make model. Guessing all hybrid users need a 3bar map sensor as ours read only 2600?
 

Viking

Insurance co's are crap.
May 19, 2007
2,317
4
Near Richmond, North Yorks
If your ECU map (not MAP sensor) is set to produce higher boost pressures than your MAP sensor can read then it'll go into limp mode. Do you accept this? If so then you need to either increase the effective range of the MAP sensor to suit the required boost, or reduce the boost to within the range of your current MAP sensor.

How are you reading your boost pressure, btw.
 

brad1

Guest
If your ECU map (not MAP sensor) is set to produce higher boost pressures than your MAP sensor can read then it'll go into limp mode. Do you accept this? If so then you need to either increase the effective range of the MAP sensor to suit the required boost, or reduce the boost to within the range of your current MAP sensor.

How are you reading your boost pressure, btw.

My boost pressure is read using my boost gauge which is in psi
 

brad1

Guest
I will try a 3 bar map sensor this week then, but what i want to know is how this will cure the mega overboost problem cause i can see me getting a 3 bar one and it still doing it
 

Viking

Insurance co's are crap.
May 19, 2007
2,317
4
Near Richmond, North Yorks
The MAP sensor tells the ECU when the required boost is reached. If the MAP sensor can't read the boost then how can it report to the ECU correctly?

Let's take an example:

On a standard map, with a standard Map sensor (for arguments sake, let's say peak boost is 20psi and the MAP sensor reads up to 25psi) then the MAP sensor reads the boost all the way up to 20psi and reports this figure to the ECU. That's all it does. It doesn't control the boost in any way, just reports the actual boost to the ECU. Once the ECU gets the 20psi signal from the MAP sensor it controls the turbo vanes to stop overboosting.

On a remapped ECU with the same standard MAP sensor (let's say peak boost is now 26psi and the MAP sensor reads up to 25psi) then the MAP sensor reads boost all the way up to 25psi and then stops. After that, all it can do is report to the ECU that 25psi has been reached, but the ECU is requesting 26psi, so keeps the boost on, waiting for the required figure from the MAP sensor. A figure that it's never going to get because the MAP sensor has already topped out at 25psi and can't say anything else.

Remember, the ECU relies on the MAP sensor to tell it how much boost there actually is, and then controls the turbo to limit boost to the map settings. Eventually it'll overboost so much that the ECU will decide that the MAP sensor is failed due to no change in the reading, despite calling for maximum boost, and it'll decide there's a problem and shut down.

Basically, once the MAP reaches it's ceiling then the two stop talking to each other.
 

brad1

Guest
So what 3 bar map sensor do I need? What is the part number? Also do I only need to fit it and job done or do I need to get it mapped in by the mapping company AmD for instance??
 

Robb1990

Active Member
May 14, 2008
299
0
I may also limp from the high oil temperature, depending on how long you can overboost for. The MAP sensor not reading over a set amount may not put the engine into limp itself. 150 celcius is hot!
 

jonjay

50 Years of 911
Jun 27, 2005
5,843
1
Essex
The MAP sensor tells the ECU when the required boost is reached. If the MAP sensor can't read the boost then how can it report to the ECU correctly?

Let's take an example:

On a standard map, with a standard Map sensor (for arguments sake, let's say peak boost is 20psi and the MAP sensor reads up to 25psi) then the MAP sensor reads the boost all the way up to 20psi and reports this figure to the ECU. That's all it does. It doesn't control the boost in any way, just reports the actual boost to the ECU. Once the ECU gets the 20psi signal from the MAP sensor it controls the turbo vanes to stop overboosting.

On a remapped ECU with the same standard MAP sensor (let's say peak boost is now 26psi and the MAP sensor reads up to 25psi) then the MAP sensor reads boost all the way up to 25psi and then stops. After that, all it can do is report to the ECU that 25psi has been reached, but the ECU is requesting 26psi, so keeps the boost on, waiting for the required figure from the MAP sensor. A figure that it's never going to get because the MAP sensor has already topped out at 25psi and can't say anything else.

Remember, the ECU relies on the MAP sensor to tell it how much boost there actually is, and then controls the turbo to limit boost to the map settings. Eventually it'll overboost so much that the ECU will decide that the MAP sensor is failed due to no change in the reading, despite calling for maximum boost, and it'll decide there's a problem and shut down.

Basically, once the MAP reaches it's ceiling then the two stop talking to each other.
I understand what you mean now.

I am guessing then Brad needs a new map sensor as well as other hybrid leon's on here to? If so which one? I am suffering from overboost if I work the car very hard and currently waiting to get a lower boosting map put on. Better get a new map sensor.....?
 

Viking

Insurance co's are crap.
May 19, 2007
2,317
4
Near Richmond, North Yorks
I may also limp from the high oil temperature, depending on how long you can overboost for. The MAP sensor not reading over a set amount may not put the engine into limp itself. 150 celcius is hot!

That's an interesting theory. I wonder if the ECU reads high oil temp as an error and goes to limp mode. There's the issue of the error code though which the ECU is recording as overboost. An oil temperature issue would report as something else. Unless the ECU is reading a flat signal from the MAP, an increase in airflow from the MAF, an increase in engine temps, and deciding that the only possibility is overboosting. :think:
 

volvic

It's just water
Jun 28, 2008
791
0
House of Batiatus
I understand what you mean now.

I am guessing then Brad needs a new map sensor as well as other hybrid leon's on here to? If so which one? I am suffering from overboost if I work the car very hard and currently waiting to get a lower boosting map put on. Better get a new map sensor.....?

+1

i'd like to know what map sensor would be best... could we nab one from a big vag diesel?
 

volvic

It's just water
Jun 28, 2008
791
0
House of Batiatus
random thought....

this problem happens after some active driving... since we have learning ecu's would it be requesting more boost than normal during the eventful driving?

(this ignores the oil temp problem, so probably not an issue)
 

Viking

Insurance co's are crap.
May 19, 2007
2,317
4
Near Richmond, North Yorks
No, the ECU learns driving style and adjusts fuelling and boost slightly to suit, but within the parameters of the mapping. It won't ask for more than the maximum set by the map.
 
Feb 1, 2007
1,602
1
Nottingham
Brad this problem has nothing to do with oil temperature or overheating.
The map sensor does control boost! See how much boost you get when its disconnected!
A broken water pump will not really make the oil too hot unless you overheat gthe engine. The hotter it gets the less power you would have.
Glynn
 
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Viking

Insurance co's are crap.
May 19, 2007
2,317
4
Near Richmond, North Yorks
Brad this problem has nothing to do with oil temperature or overheating.
The map sensor does control boost! See how much boost you get when its disconnected!
A broken water pump will not really make the oil too hot unless you overheat gthe engine. The hotter it gets the less power you would have.
Glynn

Glynn, the MAP sensor just reads boost, it doesn't control it. The ECU takes the MAP sensor reading and controls boost according to what it reads from the MAP. Disconnecting the MAP sensor just means that the ECU has no data to read, so defaults to limp mode.
 
Feb 1, 2007
1,602
1
Nottingham
Yes viking you are right it only reads but in Brads case what i mean is faulty map sensor crazy boost levels or no boost levels. Listen to the change in the exhaust note if you disconnect it when the engine is running. Only does this if you can clear the check light!
Glynn
 

s1 evoloution

Active Member
May 16, 2016
96
0
the oil cooler on diesels is built in to the engine oil filter its a metal box as i had one break on a audi 80 tdi the engine coolant had black and brown crud in the engine the only way to find out if its mucking up the water is to bridge both water pipes together flush the cooling system then if the car runs with clear coolant all the time the oil cooler has failed internally .i e where the engine oil and water mix.
 
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