ECU drops boost on very warm days
21 June 2010, 09:40 AM
#1
ECU drops boost on very warm days
i have a MY99 UK Turbo. totally standard except newage WRX intercooler & prodrive metal Y-pipe
i've noticed lately the boost has dropped to a max 11.7psi (0.8bar), from 14.8psi (1 bar). im assuming this is due to warm weather and heat soak etc where ECU will reduce boost & advance to prevent det - but is that much of a drop normal?
checked for cracks in pipes etc but everything is grand, and cleaned out the boost solenoid on friday night also
i've noticed lately the boost has dropped to a max 11.7psi (0.8bar), from 14.8psi (1 bar). im assuming this is due to warm weather and heat soak etc where ECU will reduce boost & advance to prevent det - but is that much of a drop normal?
checked for cracks in pipes etc but everything is grand, and cleaned out the boost solenoid on friday night also
21 June 2010, 10:21 AM
#2
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It shouldn't be boosting quite at 1 bar in the first place - just over 0.9 is the correct target - so you might be getting a little bit of overboost, or, if it holds consistently at that level, it may simply be a slightly generous gauge.
As for why it's dropping, the only way to find out for sure what's happening is to log it and see. However I would suspect that the main reason isn't down to the ECU consciously "reducing" anything at all.
It is incapable of directly responding to changes in ambient/intake/charge temperatures because it doesn't have a temperature sensor. It can't proactively "reduce boost" either - the only option it has to vary the boost target is to switch it off completely (or, in practice, limit it to actuator pressure) if the ignition advance multiplier drops very low.
It will reduce advance (and add fuel) if it detects det, yes, but this shouldn't significantly affect held boost unless you are experiencing very significant amounts of correction.
If you're seeing a reduction of the magnitude you're reporting, either all of it (or at least a significant percentage) will be down to the fact that the turbo (and engine as a whole) will naturally be more responsive to colder, thicker intake air than the warmer stuff. If your ECU had temperature compensation it would be able to increase boost solenoid duty on warmer days (and decrease it on cold ones) to maintain consistent turbo response. As it doesn't have that feature, you would naturally see more pressure when it's cold, and less when it's hot.
As above though, the only way to find out for certain what's going on with your car would be to look at it in detail.
As for why it's dropping, the only way to find out for sure what's happening is to log it and see. However I would suspect that the main reason isn't down to the ECU consciously "reducing" anything at all.
It is incapable of directly responding to changes in ambient/intake/charge temperatures because it doesn't have a temperature sensor. It can't proactively "reduce boost" either - the only option it has to vary the boost target is to switch it off completely (or, in practice, limit it to actuator pressure) if the ignition advance multiplier drops very low.
It will reduce advance (and add fuel) if it detects det, yes, but this shouldn't significantly affect held boost unless you are experiencing very significant amounts of correction.
If you're seeing a reduction of the magnitude you're reporting, either all of it (or at least a significant percentage) will be down to the fact that the turbo (and engine as a whole) will naturally be more responsive to colder, thicker intake air than the warmer stuff. If your ECU had temperature compensation it would be able to increase boost solenoid duty on warmer days (and decrease it on cold ones) to maintain consistent turbo response. As it doesn't have that feature, you would naturally see more pressure when it's cold, and less when it's hot.
As above though, the only way to find out for certain what's going on with your car would be to look at it in detail.
Last edited by Splitpin; 21 June 2010 at 10:22 AM.
21 June 2010, 11:10 AM
#4
@Splitpin - yep i was thinking the 14.8 may have just been a spike. the boost figures are coming via the PSI3 data monitor.
id reset the ECU after cleaning the boost solenoid, so i just reset the peak values in the PSI3 also, then had it a decent run out yesterday, which was an el scorchio day over here. Cheers for info.
@his-n-her-scoobs - everydays a school day!
id reset the ECU after cleaning the boost solenoid, so i just reset the peak values in the PSI3 also, then had it a decent run out yesterday, which was an el scorchio day over here. Cheers for info.
@his-n-her-scoobs - everydays a school day!
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