Can anyone give me some information on how boost control works on a 1.4 tdi AFM engine? The car seems to go into limp mode at max boost. No fault codes present. I have no boost in limp mode and doesn't clear until I restart the engine. It seems to pull about 23psi of boost which seems alot to me.
Boost control AFM engine
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depronman
A2OC Donor
2.3bar is 0.2 bar to much for the std map, the SVBL (set at 2.1bar is coming into play and shutting down the turbo to protect it)
There are maps that control the boost curve for the turbo, and there is also a map called SVBL (Single Value Boost Limit) it is a map, but only as one value
The SVBL is there to protect the turbo, such that if the turbo map or any other engine condition tells or causes the turbo to go over the SVBL value it will not do so, and from what I read this will force the ECU into limp mode, by shutting down the turbo.
In the std Audi Maps the TURBO maps max out at 2100mb (which assuming normal atmospheric pressure at sea level is 1000mb) i.e. 1100mb (or 1.1bar) of boost pressure
All of the remap files that I looked at for both the A2 and other VAG Diesels increase the SVBL to 2.6bar and the turbo maps are reshaped and increased - the primary thing to change in order to get more power and torque is to burn more fuel, but in order to do so you need more oxygen as there is no point increasing the fuel unless you can get more oxygen into the cylinder to burn with the extra fuel, if you don't increase the oxygen, but increase the fuel you will get black smoke which is simply un burned fuel. The only practical way to increase the oxygen is to increase the turbo boost pressure, as the other options have already been incorporated i.e the inter cooler to cool the air charge. Increasing the efficiency of the inter cooler is another option, but rather costly
I guess other things (other than a dodgy remap) that would push the ECU into Limp mode would be the vacuum/solenoid setup that control the turbo, it is all well and good the ECU commanding via the turbo map, that the boost pressure is reduced to keep it under 2.1bar, but if the vacuum/solenoid setup or the turbo linkage is sticking then the turbo will continue to provide boost, if this exceeds 2.1bar for any length of time once the ECU realises this, it will shut down the turbo to protect it (limp mode). What I'm not sure about is how the ECU knows what pressure is being produced by the turbo, there may well be a sensor in play possibly the MAP (manifold absolute pressure) sensor.
Cheers,
There are maps that control the boost curve for the turbo, and there is also a map called SVBL (Single Value Boost Limit) it is a map, but only as one value
The SVBL is there to protect the turbo, such that if the turbo map or any other engine condition tells or causes the turbo to go over the SVBL value it will not do so, and from what I read this will force the ECU into limp mode, by shutting down the turbo.
In the std Audi Maps the TURBO maps max out at 2100mb (which assuming normal atmospheric pressure at sea level is 1000mb) i.e. 1100mb (or 1.1bar) of boost pressure
All of the remap files that I looked at for both the A2 and other VAG Diesels increase the SVBL to 2.6bar and the turbo maps are reshaped and increased - the primary thing to change in order to get more power and torque is to burn more fuel, but in order to do so you need more oxygen as there is no point increasing the fuel unless you can get more oxygen into the cylinder to burn with the extra fuel, if you don't increase the oxygen, but increase the fuel you will get black smoke which is simply un burned fuel. The only practical way to increase the oxygen is to increase the turbo boost pressure, as the other options have already been incorporated i.e the inter cooler to cool the air charge. Increasing the efficiency of the inter cooler is another option, but rather costly
I guess other things (other than a dodgy remap) that would push the ECU into Limp mode would be the vacuum/solenoid setup that control the turbo, it is all well and good the ECU commanding via the turbo map, that the boost pressure is reduced to keep it under 2.1bar, but if the vacuum/solenoid setup or the turbo linkage is sticking then the turbo will continue to provide boost, if this exceeds 2.1bar for any length of time once the ECU realises this, it will shut down the turbo to protect it (limp mode). What I'm not sure about is how the ECU knows what pressure is being produced by the turbo, there may well be a sensor in play possibly the MAP (manifold absolute pressure) sensor.
Cheers,
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So is the waste gate operated by vacuum and a control valve? My feeling is that something has shat itself stopping the waste gate opening. The day after the remap I noticed an increase in performance which coincided with the limp home mode. In fairness I had given it a sound kicking for over 100 miles. Fuel economy during the 2 days after remap was 53 mpg. Virtually all of those miles were driven harshly.
There is a schematic of the turbo boost pressure control system on page 62 (ish) in this SSP - http://www.volkspage.net/technik/ssp/ssp/SSP_223.pdf
Cheers Spike
Cheers Spike
Id say the same , its either the N75 sticking which is meant to be a common issue or one of the tiny boost pipes is leaking , most of the pipes are conected together at the solinoid valves up under the pasengers scuttle and any one leaking slightly will cause limp mode more so with a remap
kp 115
A2OC Donor
These type of vacuum hoses perish internally in my experience on Audi engines, I've had success in the past by purchasing a 1m length of new vacuum hose from vw/Audi dealers & systematically replacing each piece in turn, just measure tube length & cut with a sharp Stanley knife on a piece of wood.
If you think this is likely cut a removed section of tube longitudinal to give 2 equal pieces& then bend it back on itself you will almost see a host of small cracks these become porous when under vacuum, all this is neatly hidden under the braided outer.
Kp115
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If you think this is likely cut a removed section of tube longitudinal to give 2 equal pieces& then bend it back on itself you will almost see a host of small cracks these become porous when under vacuum, all this is neatly hidden under the braided outer.
Kp115
Sent from my iPhone using Tapatalk