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  #1  
Old 04-10-2010, 12:49 PM
Olivier's Avatar
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Location: Edinburgh
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Question boost yoyo reaction, up and down

Hello,
took the car for a long spin and looked at the boost gauge, its very odd to me.
When I floor it it goes over 20 PSI, then less then 15 and again goes up at 17/ 18.
It seems that the highter the rev the less boost on the long strech. Like its going down below 15 at over 4000 RPM. I would have thought it would keep going up?

Questions :

Is the above normal behaviour? Would it be when the car is changing gears, 1, 2 ,3 as everytime there is a gear change the boost is cut the up again.

I am really going over 20 PSI or this is the momentum of the gauge that flick the needle up to there?

Is it the MAF playing with this pressure like a yoyo or this is the boost sensor or both?

Cheers.
Olivier

__________________
E300TD year 2000. RUSTY SOLD
cost a fortune to maintain on the road
but run well on WVO
Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long?
Third lasted a month then went away...
Fourth now... Corroded too...
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  #2  
Old 04-10-2010, 02:52 PM
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Join Date: Oct 2004
Location: Germany
Posts: 348
Hi,

could be different things.
Your waste gate might be stucky.
Your boost line might have a leak.
.
.
You might try an orifice before the waste gate actuator to see if it dampens then yoyo...

Boost is related to load this might be the reason for changing during the shifts.

Tom
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  #3  
Old 04-10-2010, 03:03 PM
Olivier's Avatar
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Location: Edinburgh
Posts: 570
Thank you Tom,
I am a wee confused with
"You might try an orifice before the waste gate actuator to see if it dampens then yoyo..."
How can I do this as I have no idea?
Thanks.
Olivier
Just to be sure, my acuator is vaccum. This is why I am a wee puzzle with Tom?
__________________
E300TD year 2000. RUSTY SOLD
cost a fortune to maintain on the road
but run well on WVO
Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long?
Third lasted a month then went away...
Fourth now... Corroded too...

Last edited by Olivier; 04-10-2010 at 04:19 PM.
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  #4  
Old 04-11-2010, 01:53 AM
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Join Date: Oct 2004
Location: Germany
Posts: 348
I did not see your car profile, I thought the actuator is boost.

But anyway it could be that your system is getting in resonance.
If you did not work on or changed something I'd check the free movement of the waste gate first.

An orifice also in the vac line to the (vac) actuator might indicate whether it is the resonance or just a restrictive waste gate.

Next look closer to the electrical parts to control the vac (I am not familiar with your engine year).

Tom
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  #5  
Old 04-11-2010, 05:35 AM
Olivier's Avatar
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Join Date: Jan 2009
Location: Edinburgh
Posts: 570
Hi Tom,
Resonnance? What would that be?
The wastegate move freely, no problems there
What is a restrictive wastegate? You mean build like this or a faulty one?

I tweaked the electronics on the car:

the boost sensor got a resistor that fool it a bit to increase the stock boost
the MAF is from another car that is suppose to increase the boost as well
the AIT sesor is replaced by a resistor that suppose to tell the engine the air is cold, so increasing the fuel supply( this is what I understood anyway) which is good as I got more boost.
the boost sensor is blocked as much as I coould to increase the boost but not enough to trigger any code

I think its about it?

Below is what one fellow here test on his wastegate and that seems a wee similar to what I am encountering?
A pressure actuator might be the solution to this? Anyone did it on the stock turbo? I am worry it might damage the gearbox as it would be full boost while shifting and this might be a bit too hard?

Originally Posted by mcreynol
I spent some time and instrumented the boost control signal on my OM606 G. This is a 10V PWM signal produced by the ECU. It controls a vacuum modulator that then pulls the wastegate closed. The results are interesting. The ECU is constantly playing with the wastegate.

Acceleration: the wastegate is held closed until the max boost is reached
Pedal lift: immediately opens wastegate
Idle: back on full boost (not that any boost will be produced)
Steady & flat @45mph: wastegate partially applied
Steady & flat @65mph: wastegate partially applied
Shift points under hard acceleration: wastegate momentarily opened between shifts
Driving on rolling hills moves the wastegate back and forth constantly.

__________________
E300TD year 2000. RUSTY SOLD
cost a fortune to maintain on the road
but run well on WVO
Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long?
Third lasted a month then went away...
Fourth now... Corroded too...
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