Charlie...[Quest#1]Do you know FOR SURE that the waste gate is set at 18 psi?
[Quest#2]Or is it closed and just getting to only 18 psi because the exhaust flow isn't that hot?... Charlie
I really appreciate your contributions. The best answer I can give is to spell out what I am sure I do know: the WG CAN be set to limit at 18 psig. To even address Quest#2, I would need an EGT sensor, and I would need to find a way to add more fuel/heat. I do not have either [yet.] But more fundamentally – given the way the system works – I cannot answer your second question as an "or" question.
a. Regarding boost pressure, measured as psig, there appear to be (2) distinct ‘set’ or limit points defined by independent parts of the overall system.
b. One limit is defined by the ECU. It sets fault codes when the boost pressure sensor signals ≥ ±23.5 psig, and it puts the overall system into ‘limp’ mode.
c. The ECU may use additional data than only from the boost pressure sensor; the system also includes sensors for boost air temperature, atmospheric pressure, coolant temperature, common rail pressure, etc. I have no access to the ECU code, so I cannot determine with certainty what it uses.
d. The second limit is defined by the mechanical construction of the waste gate actuator [WGA], by the combination of the diaphragm stiffness on the inlet side and the spring resistance on the output side of the sealed WGA body.
e. I am quite certain that there is no ECU control over the WGA; and the WGA has as input only air pressure from the output (compressor) side of the turbocharger.
f. While the ECU defines a constant limit, the WGA has a range of possible limits. In its ‘unadjusted’ [factory] state, the WGA opens the WGValve so as to limit boost at 18psig. In ‘disabled’ state [all turbo boost blocked as input], the WGA does not operate at all, the boost pressure will rise to ± 23 psig and the ECU sets a fault code. The WGA can also be ‘adjusted’ [by creating a pressure differential relative to the intake manifold pressure]; it will then open at any pressure between 18 and 22 psig. For example, when the WGA is ‘adjusted’ to open he WGValve and limit at a max of 22psig, the engine operates continuously up to 22 psig and the ECU does not set fault codes. Hill climbing performance was no better at 22 than at 18 psig.
So, I can't really answer your second question as an “or”. And, I can't tell whether the exhaust gas is or is not getting as hot as it could. If I understand the system, even if I added more heat, I'd have to adjust the WGA to get more boost at the intake manifold: Without adjusting the WGA, the additional heat/pressure from more fuel would simply be dumped when pressure exceeded 18psig.
It seems to me that for me to move beyond my present state, I will have to do two things: add an EGT sensor AND find a way to add some variable amount of fuel.
[I am exploringwhether I could: i) ‘adjust’ the operation of the Suction Control Valve, ii) add a chip, and/or iii) limit EGR to increase combustion temp.]
With both EGT and more fuel, I could see if boost and/or temperature went up as a function of fuel. Furthermore, I could investigate changes in performance on the local 5.5% grade. However, if I cannot find a way to vary the amount of fuel injected, then no further steps are really worth a darn. I might find monitoring EGT interesting or even valuable on a hot summer day while climbing hills, but if I can’t manipulate fuel then I have no means to affect either heat-to-boost or performance.
Do you read things the same way? Others?