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Discussion Starter #1 (Edited)
EFI Turbocharger Wastegate control is part of a true Digital Vacuum Regulator, managed by PCM.

The turbocharger is an exhaust-gas driven turbine motor that powers a centrifugal fan which compresses intake air, making Boost pressure - a Wastegate in the turbine housing is used to bypass exhaust gas in order to regulate that pressure for safe engine operation

The Turbine Wastegate is controlled by a DIGITALLY REGULATED vacuum system consisting of the Manifold Air Pressure sensor (Boost sensor), the Vacuum Pump, the pulse-width modulated Wastegate Solenoid Valve, and the Vacuum-operated Wastegate servo-actuator, that round cannister on the side of the turbocharger.

PCM controls vacuum to Wastegate via pulses to the Wastegate Solenoid coil, by varying the width of the pulses, termed Duty Cycle - wide pulses open valve against spring pressure, narrow pulses allows spring to close valve.

Wastegate Solenoid consists of a three-port spring-loaded armature-driven valve, with a port to Wastegate Vacuum Servo cannister, a port to the Vacuum Source and a vent-port to Atmosphere.

When valve is closed, solenoid off, vacuum source is blocked off, and Wastegate port is vented to atmosphere - permits some actuating vacuum in Wastegate Vacuum Servo cannister to bleed off, allowing Exhaust Pressure to pass thru Wastegate into the exhaust elbow, bypassing the Turbine Blades.

Valve open ports vacuum to Wastegate Servo, restricting vent, but not closing it - this allows REGULATION of vacuum applied to Servo.

Wide pulses keep Solenoid valve open to vacuum source, narrow pulses allow spring to close valve.

Vacuum applied to Wastegate Servo forces Wastegate closed against Exhaust Pressure on Wastegate flapper valve.

Exhaust Pressure increases with RPM and heat, created as result of Fuel Combustion - as Exhaust Pressure increases servo vacuum must be regulated to maintain factory determined Boost levels, usually 7-8psi max without cooling and exhaust modifications, and without reduction of Charge-air temperatures via some form of heat exchange.

With 67% Duty Cycle to WG Solenoid at idle, any rising exhaust pressure immediately 'spools up' - increases rpm - the turbine blades, shaft, and compressor fan, creating instant Boost, which rises further as exhaust energy - pressure, volume, and velocity - increases.

As PCM senses rising Boost pressure via MAP sensor in intake plenum, Wastegate Duty Cycle is reduced as required to vent vacuum and maintain correct Boost levels.

MAP sensor signal - on pin B - to PCM varies from 0 volts at 0 psiA to ~2.4 volts at 15psiA, to ~5 volts at full Boost.

Note the unusual pressure figures in that statement - they are in Pounds Per Square Inch ACTUAL, which is based from ZERO Atmospheric Pressure = 0hg on the Barometer Column scale.

Since Vacuum is terminology for measurement of pressure less than Atmospheric, where ZERO Vacuum would be 15psia or 30"hg, Zero Baro would be (-)30" on the Vacuum scale

PCM calculations are based on 0 psia - MAP sensor is calibrated to 0 psia, such that it's output is actual Atmospheric pressure at ~15psia.

Boost Pressure is based from 15psia Atmospheric - 30" Barometric - where 15psig Boost would be 30psiA.

As PCM sees increasing voltage from MAP pin B, indicating increasing pressure,Wastegate Duty Cycle is reduced accordingly, reducing Vacuum to Servo, venting Exhaust Pressure around Turbine Blades, regulating Boost.

As PCM sees decreasing voltage from MAP pin B, indicating decreasing pressure, Wastegate Duty Cycle is increased - a true DIGITAL VACUUM REGULATOR .

Because Vacuum on the Wastegate Servo is infinitely variable, Wastegate does not simply 'blow open' to dump Boost, but is 'metered' to allow just enough exhaust gas to bypass turbine such that Boost level is maintained without wild swings, or reduced when necessary.

This is easily observable when a Boost Gage is installed - PCM may allow stock Boost to spike on sudden accel, but recovery is even and smooth, down to 7-8psia factory limit.

Digital Vacuum Regulation is used in EGR system, where equipped, also.

Voltage readings for testing -

PCM bases all pressure readings on actual pressure of 0 pounds per square inch, or psia, tho some call this pounds per square inch atmospheric

Since the Manifold Air Pressure sensor is calibrated for 0volts, repesenting Zero Pressure, to 5volts, representing some higher pressure, it's output is approx 2.4volts at Atmospheric pressure, or ~15psia Barometric pressure.

2.4volts is approx half of 5volts, so we would assume the max MAP output, at 5volts, would be a little above 30psia: 15psia Baro + 15psi Boost = 30psia.

PCM uses these voltages at the pressure input to control vacuum on the wastegate, regulating Boost pressure

The "S" engine, with EGR, uses a MAP sensor for Boost, with a separate pressure sensor on the firewall to measure Barometeric pressure and vacuum for EGR operation - the "F" engine has only the MAP sensor, using it to measure Baro pressure during Wait to Start, then measuring Boost when the engine is running - identical in appearance, their calibrated outputs are different and specific to the separate purposes, so cannot be interchanged for testing
 

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Discussion Starter #2
Here in Houston, MAP reads - engine idling, no offset adjust, everything normal - ~2.36v, indicating ~14.7psia.


GM does not offer any testing procedure for any of the pressure sensors, other than 'compare it to a known good one', so yours may read a little less or more.


I would, however, think 1.5v to be a little low.


Check your Baro Sensor, on the firewall, for about 4.9 v.
 

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Assuming a 3.5 exhuast, mandrel 3" down pipe, mandrel crossover and opened up muff, then MAP sensor modded to run 10lbs, and intake mods (not WI, just opening up the intake,) how much of a hp/tq gain are you looking at without reflashing the ECU? Also is there a chance of running lean when running that much boost when doing it over a short time - say on a 1/4 mile run?





Also, isn't the MAP sensor the only way the ECU can determine if the truck is being over boosted? Obviously IATs and EGTs would be limiting, but just ignoring that, how else does the ECU know what boost is being generated?Edited by: Bumpin' Yota
 

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Good reading. Thanks gmctd.

Have couple of questions/comments, also I come from the Mitsubishi Turbo/ECU world, so please bear with me.

1. Find it hard to believe that factory wastegate vents to atmosphere,
probably exhaust downpipe. Smog nazis would kill for that one.

2. What is the function of knock sensor in all that? Is there even one on GM turbo diesel systems?



If there is none, then adding charge cooler (or intercooler for us
simple folks, actually aftercooler to be 100% excact) would not seem to
solve the PCM problem. Since PCM goes by the the MAP signal vs
knock/timing combination. Sounds like it will let you get more power by
allowing more fuel in the mixture, but not run higher boost (which is
the Holy Grail of power).

I guess reprogramming ECU by altering the threshhold boost values seems to be the only option.
 

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With a 94 you need a chip which is less $$$ than a reflash, is this a daily driver or a tow rig, daily driver or minimal tow WMI is a less expensive way to lower IAT than IC, IC more $$$ but best for a dedicated tow rig IMO. Probably 15-20 Hp is estimated gain not sure how much torq with those mods alone. Need to get some gages next, and go from there. IP & injector health will play a part in actual gain.


1200W sound system adds what another 4-5 Hp
 

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Discussion Starter #6
The paper is about Wastegate control - actual 'gate valve is in the turbine housing, bypassing the turbine wheel.


MAP Sensor is PCM's only input for Boost levels, referenced to Baro, and compared to rpm, fuel rate, air and coolant temps for control.


No knock sensor, because that's what Diesels do - knock.



If it ain't knocking, you need to find out why.



Charge-air cooler is between compressor and target - in our case, the Diesel engine


Intercooler is between stages of multiple compressors.


Aftercooler is between final stage of multiple compression and target.


Intercooler is easier to say than Charge-air cooler, so the term stuck.


A Diesel Engine cannot run lean -


1 - no venturi or throttle to impede air source, so a full charge of air is pumped on each cycle.


2 - fuel is injected to make the air pump (engine) self-sustaining. Add more fuel, rpm increases. Throttle back on the fuel, rpm decreases.


Go to 'lean' - reduced fuel - condition, engine will slow down until stoichiometric balance is achieved.


Factory fuel rates allow 20psi Boost, easy - but without Charge-air cooling, revised exhaust, and some coolant system enhancements, PCM immediately sets the 'too much' DTC's, and will cut fuel rate to protect the engine from over-temp conditions.


Fairly primitive, but it can be tweaked - read Turbine Doc's and ronniejoe's posts for upgrades, improvements and results on pickup and Suburban chassis'.
 

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shakmobil,


For a fairly decent conversation about water injection, go here:


http://dieselplace.com/forum/forum_posts.asp?TID=15225&K W=spindrift&PN=0&TPN=1


Water is injected post turbo, not pre turbo.


On a Mustang dyno, my WMI gave me an additional 14 HP and an additional 10 lbs. of torque. What was really impressive to me was the change in the torque curve from no charge air cooling to the WMI. With no charge air cooling, max. torque was reached at 2,650 RPM. Power was maintained at a fairly constant rate until it dropped off at 3,400 RPM. With the WMI system engaged, I was able to maintain max. torque throughout a greater torque range. Power didn't drop off until 3,650 RPM. Maximum sustained boost on all runs was 12 PSI.


Keep in mind, these runs were on a Mustang. This dyno is a two roller setup which uses load cells to pull the engine down from max rpm in order to measure the actual torque output curve. There is one camp that believes this type of dyno more accurately reflects real world conditions. However, it does have a "reputation" for providing lower numbers than the dynos which have the vehicle accelerating a heavy, under floor flywheel mass.


WMI has its fair share of critics. Inconvenience (the degree to which is entirely dependent upon your application) aside, I think the cost/benefit ratio of WMI can't be ignored.


Considering factors such as the type dyno used to provide these numbers, the fact that I do not have hi-flow injectors and the comparison of my performance numbers to those numbers which have been reported by other members, I am very, very satisfied with my truck. The fun part is...it ain't over.
Edited by: spindrift
 

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Discussion Starter #8
Here is another rundown -


Diesel fuel is not injected into any air stream, hot or cool.


Nor can it be carbureted into an air stream.


It is injected, at 1700psi, into a cylinder, where 1/2 quart of air has been compressed 21.5 times, with air temperature of ~1700degrees.


Think what that little bit of water mist might be undergoing, at 1700deg.


Might I suggest some time spent in the Technical Data section over on the Banks Diesel site - should give a better understanding, including how a 360cuin six cylinder engine, in a street-driven-pickup, can hold the world land speed record - 222mph - and it is Diesel fueled.


That entire section is written by an old Nascar head wrench, so he knows gasoline engines, as well.


You may recognize the name - the Diesel data is entertaining and educational.


I would recommend it to anyone attempting to cross over from gasoline engine technology.
 

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Critical for any WG troubleshooting is a vac gage as seen in pic found at Harbor Freight & elsewhere

At idle the vac pump main line vac should supply 20",
 

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