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Discussion Starter #1 (Edited)
I'm trying to get a sense for how a "fully stock" V8 should be running, in terms of intake manifold pressures, under the full spectrum of operating conditions. So, I am wondering what is the typical range ---- from the low end at idle demands up to the high end under full boost ---- of pressure values seen only at the MAP sensor ???

I have no auxiliary boost / manifold pressure gauge on my car, so I am referencing the data purely by monitoring MAP values as recorded with OBD monitors (scanner software, etc.).

My current data is as follows ----


@ idle [for closed loop mode only]

7-10 inHg (3.4-4.9 psi) (0.24-0.34 bar)

@ peak boost [max for all loads / speeds / gears]

38-40 inHg (18.7-19.6 psi) (1.29-1.35 bar)

I'm trying to make sure that all is as it should be on my car (suspecting a possible wastegate malfunction). Are these values comparable to what you guys are seeing with your cars ???

I am making the assumption that the MAP sensor measures "gauge pressure" rather than "absolute pressure", btw, so correct me if I am wrong there. In particular, it seems that my values at idle may be running a bit high (I would expect to see lower pressures / possibly even a small amount of negative pressure [i.e., vacuum] here), and that my maximum boost may be a bit low ? But, I don't have much experience with how the turbo management is set up on these engines ---- especially for idle characteristics.

Thanks.
 

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The manifold pressure at idle is below the atmospheric pressure (partial vacuum), so with the scanner you're using it must be representing the values as absolute pressure since your idle readings are positive values.

With the way your figures are being represented, you should be getting 1.75 bar at boost. Looks like the boost you're seeing is the boost you'd get with no boost control from the ECU.

Knut



...

My current data is as follows ----

@ idle [for closed loop mode only]

7-10 inHg (3.4-4.9 psi) (0.24-0.34 bar)

@ peak boost [max for all loads / speeds / gears]

38-40 inHg (18.7-19.6 psi) (1.29-1.35 bar)

I'm trying to make sure that all is as it should be on my car (suspecting a possible wastegate malfunction). Are these values comparable to what you guys are seeing with your cars ???

Thanks.
 

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Isn't 19 psi of boost blow-up-your-engine-like-Gonzo levels of boost?
 

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The MAP sensor (Manifold ABSOLUTE Pressure) is measuring absolute pressure. Subtract barometric pressure to get boost above barometric. If you are at sea level that would be about 14.6 PSI so, 19.6-14.6 = 5.0 PSI of boost. Which is the mechanical set boost level in the Lotus
 

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Discussion Starter #5 (Edited)
...With the way your figures are being represented, you should be getting 1.75 bar at boost. Looks like the boost you're seeing is the boost you'd get with no boost control from the ECU.

knut
The MAP sensor (Manifold ABSOLUTE Pressure) is measuring absolute pressure. Subtract barometric pressure to get boost above barometric. If you are at sea level that would be about 14.6 PSI so, 19.6-14.6 = 5.0 PSI of boost. Which is the mechanical set boost level in the Lotus
Thanks guys, I realized the MAP sensor was likely indicating absolute pressure, but I wasn't sure whether or not the OBD data was taking into account (subtracting) the pressure value from the BARO sensor --- thus, outputting the values as gauge pressures.

So, it sounds like my values at idle are expected --- in terms of gauge pressure at about -11.3 to -9.8 psi (partial vacuum).

But, unfortunately, it appears I am not getting any boost control / increase from the ECM (over the mechanical base settings) :( So, I've got an electronic problem somewhere, which sucks because I was hoping it was a mechanical problem (as they are usually easier to diagnose).

Any suggestions as to what I should be looking for as the problem ? I am currently getting NO DTCs detected / stored in the ECM, so is there another way to troubleshoot why the ECM does not seem to be supplying any boost control signals ?

Are there any "usual suspects" here in this scenario ---- any sensors (other than MAP) that could be malfunctioning ?
 

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If you have one of the two scanners which will read the Lotus enhanced PIDs Hex value PID $0201 is WDCP (wastegate duty cycle percent). Under full boost this runs around 65% at average barometric pressure values. It's the value the ECU is commanding the wastegate control solenoid to. If you are seeing this level commanded, it could still be the driver transistor in the ECU or the solenoid itself. You need an oscilloscope to tell which. The ECU will not allow additional boost until water temp is above 82* C and TPS is greater than 85%. Again look at the PID values with your scanner.
 

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Discussion Starter #7
Thanks so much, Wayne !

That is very instructive. I do have Peter M.'s Esprit V8 s/w, so I can look at the individual PIDs. In addition to the parameters you have indicated to verify, I think I will also have a close look at the solenoid for any electrical / mechanical problems.

Thanks again, Sir :)
 
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