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4 hours ago, tjs98jetta said:

 I don't believe the accuracy of the sensor in the engine is good enough to warrant the precision quoted in the manual

I would tend to think the sensor it's good enough, I don't know its real accuracy but its resolution is very thin, at least from the freescan point of view %) (I don't know the multiplier to get the real value from the byte received, though, it may be an illusion)

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57 minutes ago, Giniw said:

The Forge one is shiny!! :D
Seriously, I was considering the fact the forge one wouldn't rust, but that's all, they are about the same price anyway (the Forge one is often more expensive but I found a French website which is selling it at only 129,70€ including tax and shipping, so it's actually a bit cheaper than OEM)

https://www.gt2i.com/fr/wastegate/78367-wastegate-forge-lotus-esprit-4-cylindres-3661768598801.html

I’m sure I have a brand new unfitted one in the shed

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Only here once

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So, assuming its range is 1 bar (I heard the sensor doesn't go any upper than that) 1/256 so <0.004 bar, which is not bad at all! :)

I don't know what tool is supposed to be used but when I intended to adjust the rod length I checked the pressure with the MAP sensor connected to the wastegate while monitoring with Espritmon ^^ (but my wastegate wouldn't hold a steady pressure so I stopped there so far, hence why I know I need a new one!)

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I used a lab pressure gauge I had access to. Then you need to measure the offset at the spec pressure and this needs a micrometer really, so it's not so easy to do well. My comment was suggesting the absolute reading accuracy of the sensor may not be great, resolution is probably fine.  I found that I did not get the required activation of the by-pass relay until I set the actuator to at slightly higher actual value, as measured by my independent gauge, than the spec 0.65 bar.   In practice, 1/2 or 1 thread of the screw on the actuator rod.

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use the Forge.  i have for 12 years.  The spring rate only needs to be close.  the force to achieve the desired pressure setting is achieved by compressing the spring via the threads on the rod end.  different spring rates just mean more or less turns of the rod end.  If the selected spring rate is too far off, there won't be enough turns available on the rod end or it will be too sensitive to achieve desired pressure.  I think i use a 7-12 psi spring.  the spring rate was not given but those values are the achievable range using the rod end threads.

even if you set the OEM or the Forge incorrectly, the ECU logic has to deal with more error but still compensates well.  too far out of adjustment will allow boost spikes

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chris

90SE

just because I don't CARE doesn't mean I don't UNDERDSTAND

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Are you sure? (this is a real question!)

To me a spring rate is a force relative to the displacement, so a higher rate spring would mean that the wastegate rod won't move as much with the same air pressure applied to the diaphragm, regardless of the preload.

So I suspect the preload just affects the moment the wastegate will open without the ECU intervention (so it would be OK for the mechanical pressure limit), but on the other hand the preload probably doesn't affect the way the ECU tells how much the wastegate should open, so my understanding is that any higher rate spring in the capsule will make it move a bit less than the ECU is requesting at any moment? Of course it may have a back loop to monitor it but I am not sure about that and @sailorbob tells it's not that simple, apparently?

(I understand it may not be off very much, it's just that I like to learn new things ^^)

 

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22 hours ago, Giniw said:

assuming its range is 1 bar

It is a 2 bar MAP sensor.

14 hours ago, Giniw said:

Of course it may have a back loop to monitor it@sailorbob

The code uses some coarse RPM based adjustments ensure the values in the 'Boost MAP Maximum vs RPM' function are achieved, it is limited to a maximum of +48.8% and a minimum of -50.2% adjustment to the wastegate dutycycle.

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1 hour ago, sailorbob said:

It is a 2 bar MAP sensor.

Err it makes senses indeed, 1 bar of boost hence 2 bar absolute ^^

I don't really figure if 50% is a lot compared to the spring rate difference but, at the end of the day, I suspect you would pick the OEM capsule, wouldn't you?

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On 13/06/2019 at 14:40, Giniw said:

It would be tempting but I think I am going to order an OEM one for peace of mind 😃

And an oem one 👍 - I’ll grab a picture if it’s of any interest. 

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you are not wrong but the wastegate doesn't have to open much at all to kill the pressure. 

throttle position and coolant temp set the target boost.  this is changed if knock is encountered.  boost is determined by MAP.  The PWM will change to achieve the target boost pressure.  read EMH2 for the factory explanation of function.

anyway even if you use the OEM capsule, the setup indicated in the service notes is just to get it close.  you should then do a freescan log or 2 to see if it is responding properly.  graph wastegate duty cycle with MAP and TPS

something to consider when using OEM parts is how old they are.  Rubber bushings have a shelf life for example.  if the OEM capsule was assembled 20 yrs ago, the spring has been in some compression for that time whereas the Forge spring is shipped uninstalled.  I doubt very much there would be any significant difference, just something to think about when pondering OEM vs aftermarket.

one thing i don't like about the Forge is the mounting studs only engage a couple of threads of the capsule.  you have to be careful not to install the nuts too tight or the studs pull out and the capsule is scrap

hope that helps

cheers

chris

90SE

just because I don't CARE doesn't mean I don't UNDERDSTAND

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The ECU does not strictly aim for any specific boost value; when it controls the wastegate, the dutycycle is determined using a table of RPM vs throttle position. This dutycycle is then adjusted for barometric pressure, knock (if present) and any adjustment  when trying to ensure the values in the 'Boost MAP Maximum vs RPM' function are achieved.

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you are thinking of this, but above 5000 rpm and TPS above 75% the target value is .84 bar, TPS above 95% is 1 bar.  The wastegate solenoid will do what it has to do to achieve the target boost, starting with the values in this table and modifying them until it has.  I have some old logs with dc at 100%.  This graph shows the base settings that have the least error to achieve those targets.  Below 5000 rpm and TPS <75% there is no boost target.  This is slightly different for my Infinity ECU which I specify a boost target for the entire range, but still have to include the same duty cycle table for the ECU to use as base settings to get there.  Without the table the only safe way to do it would be to start at zero everytime and specify a ramp.  Make sense?

 

boost control.jpg

chris

90SE

just because I don't CARE doesn't mean I don't UNDERDSTAND

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boost control.jpg

The above table is actually the base DutyCycle table (without corrections) for the PWM operated boost solenoid.

There is another table in de ECU which defines the maximum allowable boost/MAP which is only dependant on the engine RPM. For my SE this is 186 kPa (absolute) until 5600 RPM, above 5600 RPM it is 182.9 kPa absolute. This table in conjunction with the actual MAP is used to "calculate" DutyCycle correction values which are applied to the base Boost DC table (these values are also stored in the ECU memory).

Some more corrections are added/subtracted on the Boost DC. (baro, Knock, Overboost).

 

Esprit Freak

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