16183977 PCM Information $EC Turbo Diesel [Archive]

RobertISaar

10-21-2013, 04:08 AM

so..... information explosion here:

http://www.10000cows.com/stanadyne-ds4.htm

Stanadyne DS4 and GM PCM.... yea, quite a piece
of work.

The Stanadyne DS4 injection pump has a few issues...
obviously. So does the software in the PCM. Let's start with my first rant... a
fair number of people bitch at the EPA and blame them for all of the automaker's
woes and all of this emission control and 'other crap we don't need'. Well, that
would be acceptable, perhaps, if you had a life expectancy of, oh, twenty five
years or maybe thirty, thanks to automobile pollution. Automotive emission
controls is one of the more important inventions in automobiles. Well, maybe
not. Perhaps we would be all driving electrically-operated vehicles instead.
Emission controls really do not add that much cost to a vehicle. Safety
equipment such as air bags, crush zones, and crash testing all add lots of cost
and time and complexity. We complain about those, too, unless we're on the
receiving end of that safety equipment - if it saves your life. The radios and
DVD players, now they add cost and complexity. All of the gadgets like
windshield wipers that run automagically in the rain, or windows that open so
you can close the door, then close once you're done, that's added (and probably
unnecessary) complexity. Electronic engine management is not that expensive, and
even many of the developing countries (India, China) have been running
electronic diesel controls for a few years now - it can't cost that much. Delphi
is building common-rail diesel injection systems for LAWNMOWER ENGINES! That
can't be terribly expensive!

Why does the 6.5L have so many problems? People tend to
blame electronics (or the EPA) but there has not been a highway truck built
since the late 1980's without electronic engine management. The well-loved
Detroit series 40, 50, and 60 are all electronically controlled - the engines
were designed that way. Even the last V92 family received electronic fuel
injection. The Cat 3406, Cummins ISX, (and ISL, ISC, and
ISB), Powerstroke, and DT466E - these are engines that last a million miles
between rebuilds, and all electronically controlled. You can breathe the air
thanks to all of this technology. You want to see what happens when you don't do
this? Go visit India and China and Russia. Visit a bus barn in Hungary or Brazil
full of Rabas or 'Old Smoky' Mercedes OM352. So what went wrong? Let's look at
what we are working with....

The 1994-1995 6.5L TD ECM consists of a fairly low-tech set
of chips. The main processor is a 68HC11F1 running with a 12.59 MHz crystal.
There's about 48k of code and calibration space available. A Delphi IOR chip
supplies 240 bytes of RAM and also some I/O ports and four PWM channels. A
configurable timer chip is used to process pulses from the diesel pump's optical
encoder and also the CKP signal. Not a big problem except that the people
writing the software screwed up a bit. There are a few bugs in the software. The
ones I have found include:

The software filter used to prevent ECTS-based tables from
chattering with sensor noise is not functional. There is supposed to be a
deadband of 2 degrees C, however, that deadband comparison is screwed up because
of a missing # sign in a CMPB instruction in the source code. Something of note
is that the OBD-II version of the software does not correct this.
A flag fetch from calibration does not get the correct
mask. The problem here is a missing # sign in a BIT instruction in the source
code. There are a couple of cases of this. One of them may actually cause a fuel
dropout in the case of certain unrelated DTC's setting. It looks like that part
of the code was rewritten for the OBD-II version.
The SCI interrupt is not equipped to be interrupted by the
CKP, CMP, VSS, or OSS interrupts. That would be fine if the interrupt just
stored the appropriate data and called the main program loop to actually form an
SCI message. But it doesn't. So what happens is you miss interrupts if you have
a scan tool connected. The correct solution would have been to disable the 160
Hz interrupt, disable the SCI interrupt, re-enable global interrupts, format the
outgoing data stream, disable global interrupts, re-enable the SCI interrupt,
re-enable the 160 Hz interrupt, then return from SCI interrupt. The OBD-II
version checks during long interrupt-disabled conditions now so this is not a
problem any more.
The subroutine used to calculate the desired EGR pressure
is called twice in a row. This was corrected in the OBD-II version of the
code.
In several spots, a double-precision arithmetic operation
(subd, addd) only loads half of the input, leaving the other register containing
some random stuff.
In several spots, engine speed (and sometimes other things
- but engine speed happens multiple times) is calculated, then is just thrown
away.

Other than that, the ECM probably will do its job,
more-or-less all of the time. Automotive ECM's have been shown to be rather
reliable and there's no particular reason to think this one has a big
problem.

The pump driver module has a reputation of blowing up. Yea,
probably it deserves it. To start with, it appears to use a couple of huge
bipolar transistors configured as a high-side switch, and also as a linear
current regulator. I don't think I would do it that way. Using MOSFETs to switch
the solenoid valve along with a high-speed PWM current regulator would be a much
better solution IMHO. The Cummins ISC system, which uses a similar pump control
solenoid, uses PWM control. The current trace is a straightforward linear 12A
current limit. That would make a peak power dissipation (not including clamping)
of around 100 watts. This (http://www.gearhead-efi.com/Fuel-Injection/PumpDriverOriginal.pdf) might be
interesting for someone who is circuit-minded.

The optical sensor has issues. It is bathed in diesel fuel,
and is at the mercy of whatever is in there. Air bubbles? Funny thing is that
Bosch has a VP44 pump with an optical encoder, as well, and it does not have a
bad reputation. Does an 8-cylinder VP44 pump exist? Perhaps a good retrofit kit
would be a VP44 and a new ECM.

The diesel pump. It is a solenoid-controlled rotary pump.
There are several ways of modulating fuel and timing in an electronically
controlled diesel pump. They are...

Sliding rotor (EPIC). This limits plunger travel
mechanically, using hydraulic pressure. The ECM controls the pressure using a
pair of solenoid valves.
Mechanical start-of-injection, solenoid spill (Lucas,
Stanadyne DS4 in pump-spill mode). Start-of-injection is mechanical so the
stresses on the pump are only huge. End-of-injection has some pretty substantial
forces associated with it.
In-line sleeve pump with prestroke control. Injection
quantity is controlled via fuel rack, start-of-injection is controlled by timing
rack. Based on the old Bosch inline pump, used on John Deere tractors, and a
Zexel version is used on some older Isuzu trucks.
Control collar (Bosch VP37). This controls fuel quantity
usually via fuel throttling (cavitation of the pump) or stroke control. Timing
is controlled via servo-controlled timing piston, similar to mechanical pumps.
Injection timing must be measured with an electromagnetic injector.
Solenoid SOI, solenoid spill (Bosch VP30, VP44, Stanadyne
DS4 in spill-pump-spill mode). Most flexible until we get to common rail
(Duramax).
Brute Force Electronic Unit Injector,
spill-pump-spill.
Diesel timed injector. Uses liquid plunger made with diesel
fuel to vary plunger length and injection timing, Cummins ISX.
Common rail or distributor brute-force injection. Uses a
solenoid valve as in a straightforward metering system (very much like a
gasoline fuel injector). Duramax, Cummins ISC, Smart ForTwo CDI.

The design requirements for solenoid spill are substantial.
Stanadyne didn't get one or two of them right. Things that they might have got
not-quite-right:

Slope of cam too aggressive (desired pressure or pumping
rate too high) for materials.
Pump cavitation is causing an issue.
Resonances in the pump causing multiplication of forces
beyond expected values.
The pump appears to rely on centrifugal force to pull the
plungers out - the whole case seems to be pressurized about equally. I think
that is a function of the fill/spill solenoid arrangement. If the inlet of the
injection pump is at a significantly higher pressure than the rest of the pump,
more solid operation should be assured. I'm not 100% sure on this but the
pumping plunger assembly looks a bit suspect to me. I'd probably want to get a
dead pump and disassemble it to figure out if this would be an issue or not,
perhaps my understanding of the internal plumbing and case pressure control is
flawed.

16183977 ECM (1994-1995)

Here is a photo of the guts of the 1994 to 1995 ECM. I have
never seen a photo of this ECM's guts, so I took the liberty of making this one.
I think a lot of people get lost from here down, but what follows is something
that any ECM hacker probably could figure out with a meter and the ECM in front
of them.

http://www.gearhead-efi.com/Fuel-Injection/DSCN0689_small.JPG (http://www.gearhead-efi.com/Fuel-Injection/DSCN0689.JPG)

Parts on the board of note:

16055199 = voltage regulator
16166240 = quad driver module with diagnostics
16034993 = stepper motor driver
16064606 = serial output driver
16084523 = SO-20 VR sensor amplifier for transmission input
shaft speed
16158016 = 74HC4067 analogue mux
45555 = LM339 comparator
48025 = SO-14 quad NAND gate, 74HC00
27375 = SO-14 dual AND/NOR gate, 74HC51
50610 = LM2904 dual op-amp
49226 = LM393 dual comparator
27377 = LM2902 quad op-amp
66285 = PLCC-68, Delphi IOR, mapped at $1400
16156598 = PLCC-68, MC68HC11F1, 3MHz rating
16180988 = PLCC-68, timer I/O module
EPROM carrier, T+B 'BLUE' carrier

I/O Assignments:

AN0 = APP
AN1 = APP
AN2 = Transmission force current monitor
AN3 = APP
AN4 = battery voltage
AN5 = boost pressure, via Sallen-Key filter
AN6 = analogue mux
AN7 = EGR/baro pressure, via Sallen-Key filter
PAI = 4004 pulse per mile VSS input
TIC1 = Pin C15, VSS
TIC2 = Pin C12, transmission input shaft speed, through
84523 buffer
TIC3 = 8X CMP signal (low-res pump encoder signal). Also
fed into 16180988 IC.
TIC4 = 4X CKP signal (from engine CKP). Also fed into
16180988 IC.
TOC4 = backup injector pulse width generation
TOC3 = I/O pin disables injector from TIO chip, timer
channel used for 160 Hz task scheduler
TOC2 = TCC PWM generation
PD5 = powerdown to power supply IC
PG0 = ODM2-7
PG1 = ITS-9 (ITS phase)
PG2 = ITS-6 (ITS phase)
PG3 = SCI transceiver control

AN Mux:

MUX0 = pin B8, glow plug voltage monitor
MUX1 = pin B11, fuel temperature signal
MUX2 = pin A12, diagnostic switch input
MUX3 = Pin C8, ECTS voltage
MUX4 = pin B9, spare, 220k pulldown
MUX5 = pump calibration
MUX6 = QDM1-14 fault input
MUX7 = pin C13, glow plug relay supply voltage
MUX8 = QDM2-14 fault input
MUX9 = pin B4, A/C request
MUX10 = pin B12, intake air temperature
MUX11 = pin D10, optical sensor 5V power supply
MUX12 = Pin B5, unused, 20V range, 3k pullup to key
power
MUX13 = pin C9, Transmission temperature sensor
MUX14 = APP 2 sensor 5V power supply
MUX15 = unused, grounded on input mux

IOR:

1400.7 = PCS Low Drive
1400.6 = TCC on/off output (4L60E)
1400.5 = shift solenoid
1400.4 = shift solenoid
1400.3 = EGR vent valve
1400.2 = Service Throttle Lamp
1400.1 = ITS Enable
1400.0 = Glow plug relay enable
1402.7 = AMUX3
1402.6 = AMUX2
1402.5 = AMUX1
1402.4 = AMUX0
1402.3 = Pin E2 - 4WD axle switch
1402.2 = Pin E3 - Performance shift mode switch
1402.1 = Pin E4 - Manual shift mode switch
1402.0 = Pin F3 - cruise on/off
1404.7 = Pin F11 - cruise resume/accel
1404.6 = Pin F15 - cruise set/coast
1404.5 = Pin E10 - PRNDL B
1404.4 = Pin E9 - PRNDL C
1404.3 = Pin E8 - PRNDL A
1404.2 = Pin F5 - TCC Brake Switch
1404.1 = Pin A6 - Brake Switch
1404.0 = Pin A6 - PTO request
1407.3 = MIL
1407.2 = Read pump trim resistor enable
1407.1 = Pin C9 Transmission Temp Pullup Select
1407.0 = Pin C8 IATS Pullup Select
1408 (PWM) = PCS current control
140A (PWM) = Boost modulator control
140C (PWM) = spare, not sure what it is used for yet.
Probably the 3-2 shift solenoid, 4L60E.
140E (PWM) = EGR frequency

TIO:

1AFA.1 = ODM chip select to retrieve diagnostic
status
1AFA.2 = ODM chip select to retrieve diagnostic
status
1872 = closure time response
187C = timing delay counter
187E = fuel quantity counter
1880 = split pulse delay counter
1882 = pilot quantity counter (first pulse)

16193570 ECM (1996+)

Parts on the OBD-2 version of the board
(16216588):

16055199 = voltage regulator
16166240 = quad driver module with diagnostics
16034993 = stepper motor driver
20686 = SAE J1850 transceiver and controller
66285 = PLCC-68, Delphi IOR, mapped at $1400
16202476 = PLCC-68, MC68HC11F1
39985 = PLCC-68, timer I/O module
16183784 = AN28F010 128k by 8 flash memory module
16206550 = ?

I/O Assignments:

AN0 = APP
AN1 = APP
AN2 = Transmission force current monitor
AN3 = APP
AN4 = battery voltage
AN5 = boost pressure, via Sallen-Key filter
AN6 = analogue mux
AN7 = EGR/baro pressure, via Sallen-Key filter
PAI = 4004 pulse per mile VSS input
TIC1 = Pin C15, VSS
TIC2 = Pin C12, transmission input shaft speed, through
84523 buffer
TIC3 = 8X CMP signal (low-res pump encoder signal). Also
fed into 16180988 IC.
TIC4 = 4X CKP signal (from engine CKP). Also fed into
16180988 IC.
TOC4 = backup injector pulse width generation
TOC3 = I/O pin disables injector from TIO chip, timer
channel used for 160 Hz task scheduler
TOC2 = TCC PWM generation
PD5 = powerdown to power supply IC
PG0 = ODM2-7
PG1 = ITS-9 (ITS phase)
PG2 = ITS-6 (ITS phase)
PG3 = Firmware bank selection

AN Mux:

MUX0 = pin B8, glow plug voltage monitor
MUX1 = pin B11, fuel temperature signal
MUX2 = pin A12, diagnostic switch input
MUX3 = Pin C8, ECTS voltage
MUX4 = pin B9, spare, 220k pulldown
MUX5 = pump calibration
MUX6 = QDM1-14 fault input
MUX7 = pin C13, glow plug relay supply voltage
MUX8 = QDM2-14 fault input
MUX9 = pin B4, A/C request
MUX10 = pin B12, intake air temperature
MUX11 = pin D10, optical sensor 5V power supply
MUX12 = Pin B5, unused, 20V range, 3k pullup to key
power
MUX13 = pin C9, Transmission temperature sensor
MUX14 = APP 2 sensor 5V power supply
MUX15 = Flash memory Vpp monitor

IOR:

1800.7 = PCS Low Drive
1800.6 = TCC on/off output (4L60E)
1800.5 = shift solenoid
1800.4 = shift solenoid
1800.3 = EGR vent valve
1800.2 = Service Throttle Lamp
1800.1 = ITS Enable
1800.0 = Glow plug relay enable
1802.7 = AMUX3
1802.6 = AMUX2
1802.5 = AMUX1
1802.4 = AMUX0
1802.3 = Pin E2 - 4WD axle switch
1802.2 = Pin E3 - Performance shift mode switch
1802.1 = Pin E4 - Manual shift mode switch
1802.0 = Pin F3 - cruise on/off
1804.7 = Pin F11 - cruise resume/accel
1804.6 = Pin F15 - cruise set/coast
1804.5 = Pin E10 - PRNDL B
1804.4 = Pin E9 - PRNDL C
1804.3 = Pin E8 - PRNDL A
1804.2 = Pin F5 - TCC Brake Switch
1804.1 = Pin A6 - Brake Switch
1804.0 = Pin A6 - PTO request
1807.3 = MIL
1807.2 = Read pump trim resistor enable
1807.1 = Pin C9 Transmission Temp Pullup Select
1807.0 = Pin C8 IATS Pullup Select
1808 (PWM) = PCS current control
180A (PWM) = Boost modulator control
180C (PWM) = spare, not sure what it is used for yet.
Probably the 3-2 shift solenoid, 4L60E.
180E (PWM) = EGR frequency

TIO:

16FA.1 = ODM chip select to retrieve diagnostic
status
16FA.2 = ODM chip select to retrieve diagnostic
status
1472 = closure time response
147C = timing delay counter
147E = fuel quantity counter
1480 = split pulse delay counter
1482 = pilot quantity counter (first pulse)
140C = MAF time-since-last-pulse (pin C3 of the 32 pin
BROWN connector, NOT pin E1 (or sometimes called pin C1 of connector C3). THIS
IS WRONG in some service schematics!
140A = MAF pulse counter

This is a 68HC11 processor which should be very similar to
that used in the OBD-I version. It is a bit unusual (to my mind) to use a 68HC11
on the OBD-II ECM when pretty much all of the OBD-II petrol ECM's went to
68332's. I guess Ford pushed the EEC-V (8065, a 8096 variant) just into the
2000's before going over to the PowerPC's so why not, I guess. Just to be a pain
in the arse, the flash memory has some of its address lines swapped around.
There's space for two 32k memory pages (bank swapped using pin PG3) and one 24k
non-banked page shared between calibration and common (non-banked) code.
Communication is via SAE J1850 instead of SCI.

The Pump (and its control algorithms) - both OBD-I and OBD-II

How does the pump actually work, and how is it controlled?
It's not really that hard. I could write this sort of code in my
sleep.

The optical sensor has a 64 pulse per cylinder and a 1 pulse
per cylinder track. The 1 pulse per cylinder track fires at the pump reference
location which is 22.2 engine crank degrees before the start of injection. This
pulse is nominally timed at 25.66 crank degrees before TDC of the engine - this
is performed by doing the TDC reference offset procedure. This procedure assumes
that the timing of the engine CKP is spot-on, and the pump is out. This also
means that the most retarded SOI that the pump is normally capable of is 3.5
degrees of advance. Since the most retarded idle timing I have seen is about 6
crank degrees, that gives sufficient margin to accept the +/- 2 degrees allowed
in the TDC offset procedure. Note that these timing values only count at idle.
Due to variations in how a pump works, the actual timing of injection will vary.
Note that in theory, the TDC offset procedure should not even be necessary. The
TDC information is constantly there and could be used to learn the offset during
normal operation.

When looking at a scan tool, there are several values
displayed. The value 'Actual Injection Pump Timing' which shows about 28 crank
degrees at idle, is the engine clock count (in engine degrees) between the
injection pump reference pulse and the TDC reference pulse, corrected for TDC
offset. The measured injection timing (around 6 degrees at idle) is then taken
from the actual pump timing value, then subtract out the 22.2 crank degree
reference-to-SOI offset. The desired injection pump timing simply comes from a
summation of three lookup tables - base injection timing, ECTS adder, barometric
adder, and IATS adder. That's it - it's actually pretty simple.

With these two numbers, the ITS stepper motor is moved
back-and-forth, trying to maintain the measured injection timing at the actual
injection timing. If these values vary more than a couple of degrees from each
other, a DTC will set.

The injection metering pulse width (which is in crank
degrees, and NOT in milliseconds), comes basically from the pump mapping tables.
It is the summation of two pump mapping tables, which contains the number of
crank degrees from the pump reference to EOI (end-of-injection). One mapping
table is the base delivery vs. pump rotation. The other includes pumping
efficiencies and is dependant on pump speed. The base pump map table is crank
degrees from RPM and desired fuel quantity (in cubic millimetres). The pump
resistor calibration causes a small shift in the pump mapping tables - maybe by
one or two crank degrees. The pumping cycle at idle is set up so that the
metering valve closes at the pump reference location. It actually accomplishes
this by generating a time delay of 83.58 crank degrees from the previous pump
reference location. The 6.42 crank degrees to make it 90 is calculated as the
measured injection opening delay of about 1.7 milliseconds at idle. The
'injector pulse width' shown on the scan tool is actually the injector response
time. It is measured by monitoring the dip in metering valve solenoid current as
the armature moves. Many other diesel engines using 12V injection actuation
(Detroit Diesel, Cummins CAP system) do this measurement so it's not that
unusual.

If you like graphics, here (http://www.gearhead-efi.com/Fuel-Injection/DS4PumpTiming0001.pdf) is a timing diagram.

Optionally, the metering valve can be closed later in the
pumping cycle - about 12 or 15 crank degrees - without affecting fuel metering
significantly. This is because the normal spill valve closure time is designed
to be in a flat spot of the camring so that the normal variance in valve closing
time does not affect fuel timing. In a backup mode, valve closing may be used to
control fuel timing, but normally the engine is running in a highly derated
mode.

The ECM supports split injection. I have worked on the
Cummins ISC which also supported split injection. It really does help warmup.
But the calibration file doesn't seem to use split injection, and I'm wondering
if the cold warmup would be more pleasant with it. I do not know the
thermodynamic properties of split injections in a prechamber diesel. On a direct
injection engine, the pilot injection really does make the engine much more
pleasant. It's certainly a lot quieter and smoother, anyways. The firmware in
this ECM does not handle split injection very well - it 'supports' it but not
well. For one, the firmware does not compensate for spilled fuel. The other is
that the algorithm splits after the pump maps which does not account for the
dead zone in metering. I don't think anyone gave split injection even an attempt
given that the software is a bit goofy.

A few of the other functions are pretty obvious. EGR is simply a servo loop
that sets the MAP sensor to the desired pressure value. During highway operation
the EGR system is turned off. It is only used in city driving. Boost pressure
control is also pretty obvious. It works exactly the same way as the EGR system.
The transmission uses pretty much the same code and logic as the gasoline
versions. For some drivetrain applications, engine torque can be reduced based
on torque converter slip (torque multiplication).

Back to the ECM hardware (and a bit of software).... Counter
Logic:

Engine clock counts is in units of 8192 / 720 crank
degrees
Injection Timing Counter: Start at pump reference, stop at
TDC reference, count in engine clock counts
Injection Response Counter: Start at first injector
energize, stop at closure detect, count in E/64 (fixed speed clock)
Injection Delay Counter: Start at pump reference, stop and
energize injector when counter reaches zero, count in engine clock counts.
Normally around 75-90 crank degrees of delay.
Injection Pilot/Initial Quantity Counter: start at injector
energize, stop and turn off injector when counter reaches zero, count in engine
clock counts. Normally between 20 and 35 crank degrees of delay.
Injection Pilot to Main/Split Delay Counter: Start at main
quantity counter expire, stop and turn on injector when counter reaches zero,
count in engine clock counts. Not used in the 6.5L.
Injection Split/Main Quantity Counter: start at pilot delay
counter expire, stop and turn off injector when counter reaches zero, count in
engine clock counts. Not used in the 6.5L.

Note that in 'backup mode' - where the high-res pump signal
is lost, the 68HC11 can generate injection timing signals based on the
low-resolution inputs, however, that is not the preferred mode that the ECM
wants to run in. In this case, the desired injector delivery is divided by
engine speed to generate a pulse width. At this point, the pulse is then
generated using the free-running TCNT system on the 68HC11.

How do you get more power? Carefully. If the rest of the
engine will take it, you need to calibrate the injection pump table to make full
use of the pump. The total pumping range of the DS4 is about 80 or so cubic
millimetres of fuel - even more than the mechanical DB pump. However, adding
boost, lowering intake air temperature (via an intercooler), and careful mapping
of injection timing is the 'right' way to do it. Injection timing should be
mapped and adjusted for a careful balance of exhaust temperatures and NOx
formation. High exhaust temperatures are obviously not good. But neither is high
NOx - not only for the emissions aspect (you may not care about that), but also
for engine life (and you probably do care about that). Excessive NOx indicates
excessive cylinder pressures - pressures above the design rating of the engine.
Diesel engines don't really knock at high power, they just blow up, leaving you
on the side of the road with a lot of hot, oily pieces hanging out. Well, maybe
not that often, but keep in mind that there are plenty of TSB's for detecting
engine damage due to 'chipping'. The engine manufacturer knows the tolerance of
their engine production and how far they can push *all* of that engine model.
Yours may take more, or maybe not.

Advancing the timing and cranking up the fuel is a great way
to make a lot of smoke (ie. waste a lot of fuel), make only a little bit more
power, and shorten the life of your engine. Add an air-to-air intercooler to
your 6.5L diesel engine and it will be a lot happier. You will get more power,
lower exhaust emissions (not that most people care about that - it's a side
benefit), and longer engine life. I'm not going to go plugging the EGR system,
at least not on my truck. The engine is timed and calibrated assuming the EGR
system is working, and I have a bit of a concern for the environment. In
particular, what the EGR system goes after - the nitrogen oxides that cause the
brown haze.

I'm aware of some quotes and criticisms of this writeup,
especially regarding EGR removal and that sort of thing. I can't claim that the
6.5L will blow up or melt or whatever if you pull off your EGR system - probably
it won't. EGR lowers the PEAK combustion pressure while broadening its shape -
slowing the burn. In order to optimize power and fuel efficiency while reducing
NOx, the engine calibrator normally will compromise between EGR and timing to
give an acceptable ratio of PM (particulates) and NOx. By increasing EGR rate
you slow down the burn and to not drop power or efficiency, you have to advance
the injection timing a bit. Gasoline engines do this, as well. But in a gasoline
engine knock is occasionally expected so the knock detection system will prevent
engine damage. Back to NOx/PM. In this art compromise, you can increase PM and
lower NOx to meet the emissions requirements, or you can raise NOx and lower PM.
Lowering NOx may raise exhaust temperatures and drop efficiency so you have
those two items to worry about, too. Whether or not 'a bit' is an issue depends
on your design margins. I have seen engines blow up with just small things wrong
with the controller - apparently they had little margin for error. I have seen
natural gas engines that would melt pistons without EGR - engine knocking. I'm
not making that up, it's well published. A certain well-known natural gas engine
needed to have its redline lowered from 2400 to 2200 - well below the mechanical
limits of the engine. That was because they could not control EGR tightly enough
at full power conditions to prevent knocking - that's right, EGR at full power.
That engine had little margin and needed EGR to control engine knock and exhaust
temperatures even at full-tilt operation. The 6.5L may have lots of margin and
may 'take it'. I would guess that the injection timing of the non-EGR 6.5L
engines is less advanced than the EGR-equipped versions.

The other thing I'm aware of are some posts saying that this
emissions stuff is government communist crap since cows emit more than engines.
But cows only emit substantial quantities of CO2 and CH4, both fairly harmless.
Perhaps greenhouse contributors but I'm not too worried about that. Diesel
engines without aftertreatment spew out a toxic concoction of nitric oxide (acid
rain, brown smog, respiratory problems, rapid tarnishing of copper pub tables
and silverware), carbon monoxide (competes for oxygen transport in animals - it
suffocates you), unburned hydrocarbons which include some nasty circular
benzene-ish compounds (known carcinogens), and particulate matter (also
carcinogenic and respiratory irritants). Perhaps the tailpipe should discharge
right into the cab of the vehicle so the operator of the vehicle can enjoy their
exhaust as much as the people behind them.

My background, by the way, is an engine management designer
and calibrator, and I've blown up a bit of stuff here and there. Including
$10,000 prototype catalytic converters, a few engines, and even a
dyno.[/quote]