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Mack Chassis - Emcon (Spark Assist) Engine
Aftertreatment System Troubleshooting Check
Sheet - US10 Emissions
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Internal Content

It has been found that on these older chassis it is best to eliminate all
the basics prior to opening an eService case. Pressure test the
complete intake and exhaust systems. There is zero tolerance for
leaks in these systems. Next, go over all the wiring harnesses to see if
there are crispy spots No rub spots, loose areas are tolerated. Next
check the chassis air supply system to be sure the customer has been
draining the air tanks nightly and servicing the air dryer every 6
months with a fresh COALESCING type air dryer cartridge. This DPF
system cannot tolerate ANY water or oil moisture at all for it to
function correctly and reliably. Repair any leaks, electrical and air
system issues before starting to dig into the Aftertreatment system.

Related links and
attachments
US10 SYMPTOM BASED
CHECK SHEET W2034.2

Use the US10 Spark Assist Check Sheet to compare sensor and
component values during fault tracing for spark assisted regeneration
troubleshooting.
Please refer to the reference documentation below.
• US10 Regen Design and Function
• Combustor Inspection

a

Tags

SPARK ASSIST

CHECK LIST

CHECK SHEET

K15552222

CHECKLIST

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US10 TRU DPF Regeneration Companion Sheet
(v1917.3)

Spark Assist (Mack only US10+6)

Before starting to diagnose Regeneration issues with this system, a thorough investigation of the
condition of the complete chassis needs to be done.
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•
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Has the Chassis Air System been serviced correctly base on published service information? If
not, correct the issues. The air dryer needs to be properly connected and the filter serviced
with the recommended Coalescent cartridge. The air pressure in the system needs to be
regulated within the correct tolerances. If the dryer system comes in by-passed or inoperative,
the air tanks and lines supplying the Aftertreatment air system may need to be cleaned out.
Otherwise, the Air Atomization Module (even a new replacement) will not last at all.
An additional coalescent filter may be installed for extra protection if desired. Refer to
FSB254-006 for information if the customer wants this option.
Has the fuel system been serviced correctly based on published service information? If not,
inform the operator that the fuel system needs to be serviced.
Is the engine air filter flowing correctly and not plugged? If not, inform the operator that the
filter needs to be serviced.

Combustion Air Flow. 400+ LPM is required during Regeneration at 1,200 RPM for US10 to attain the
required 1850* to 2100* flame temperature for a good Regeneration.
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•

US10 – The CAV (DRV style) is controlled by a solenoid mounted on the EATS rack. There is NO
orifice in the intake manifold where the valve mounts. There is a 9/32” orifice in the Combustor
Housing. Any leak, kinks or blockage in the small steel braided hose from the solenoid valve
to the CAV will cause Regeneration failures. Any leak, kinks or blockage in the large steel
braided hose from the CAV to the Combustor Housing inlet will cause Regeneration failures.
A stuck open EGR valve will cause this issue.
Some US10 combustors have been reported to have failed or had bad welds at internal
components. One test is to insert an appropriately sized screw driver straight up through the
9/32” orifice hole in the combustion air inlet port and verifying there is a plate ¾” to 1 ½” up
blocking the screwdriver and the plate does not move. It should be solid. This plate is actually
a type of vane that directs the air in a swirling pattern within the mantle for better combustion.

Vane plate

9/32” orifice
•
•
•

¾” air inlet elbow
Typically, the Spark Assist system will complete a Stationary Service Regeneration even when
there is NO combustion air flow from the CAV. However, it will only display Flame Temp
readings of only around 1700*F rather than the proper 1850 – 2100*F during a
Regeneration. There is typically enough oxygen remaining in the exhaust stream to support
combustion under stationary Service Regeneration conditions but the flame will be cool and
burn rich. This has fooled many in the past giving the impression of successful Regenerations
but when under load or on the road, the oxygen from the engine is all used up by the engine
combustion process and moving Regenerations will fail. So, it needs Combustion Air (boost air)
under these conditions to support successful combustion.

Note that any leaks in the intake or exhaust systems will cause issues. The best way to diagnose
these leaks is by using the smoke test machine.

Air Atomization Module (AAM) flow chart
Fuel System
100 PSI fuel pressure is Nominal. Allowable pressure range is 95 to 105. 95 psi is at the very low
limit. 94 or less psi will cause Regeneration reliability issues. The pressure is controlled by the
Atomization Module (AAM) and not the pump.
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If fuel pressure is low, remove the fuel return line from the AAM at the fuel tank tee
fitting to look for the amount of return with the engine running and pump active. Cap
the tee to prevent spills. It may be necessary to add a short piece of hose to the line to
prevent spills.
LOW fuel pressure – LOW return flow indicates a bad pump or restriction from the
engine supply to the pump inlet.
LOW fuel pressure – HIGH return flow indicates the pressure control valve in the AAM is
stuck open.
Another indication of the Atomization Module dumping fuel, is in the engine pressure
sensor values during a Regeneration, the fuel pressure lower than 40 psi, engine load
higher than 15% and slightly lower boost pressure. These are indications of fuel
starvation. This is more important on the US07 engine platform because the
Atomization Modules in this platform do not have pressure sensors and the Regens are
done at idle.

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o

Note: In some cases, drops in engine power have been reported when the system goes
into Auto Regens while driving. In most of these cases, the issue is engine fuel
starvation due to the Atomization Module pressure control valve stuck open and
dumping fuel pressure. The engine fuel pump cannot keep up with the engine and DPF
fuel demand with this condition, and the fuel pressure drops.
HIGH fuel pressure – LOW flow indicates a blockage in the Atomization Module or the
return line. Test the return flow again but this time at the return fitting at the
Atomization Module using a made up test line to the tank. If flow returns to normal, the
issue is a blocked return line. If the flow remains low with high fuel pressure, the issues
is a blockage within the AAM.
Air Supply System

120 PSI air system air pressure to the AAM Nominal. 100 to 130 PSI is acceptable.
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Less than 100 PSI will cause issues. Pressures over 135 will cause issues. If the pressure is OK
stationary (not Regenerating), and drops during a Regeneration, there is a restriction in one of
the lines, or a sticking protection valve at the supply air tank, or a valve installed incorrectly, or
the air supply was modified by the body builder (we have seen air supply taken from the wrong
tank). The air system actually does not take all that much air. Atomization air is restricted
through the orifices in the nozzle and the flow should decrease as fuel is injected (sharing the
same holes).
The US10 DPF system does not have a supplemental air valve.
When checking the spray pattern at the nozzle, with Atomization Valve active and Injector
control active, you should have a heavy white fog. Not a stream of fuel and not a light mist.
Spark Ignition System

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When checking for spark quality, it should be checked during an active Service Regeneration
command, not with the Tech Tool test. For some reason, when tested with the Tech Tool, the
pulse rate is lower (longer coil charge time) than it is during an active Regeneration with the
nozzle removed from the Combustor Housing using a mirror.
A good test tool to have handy is a straight in-line spark tester (the style with the light bulb and
not the open gap type). Auto parts supply stores typically sell these for about $7.00. This tool
will indicate if the coil is actually sending the high voltage signal to the igniters. If the bulb lights
up, but no spark is observed in the hole, the coil should be OK but there is a spark plug wire, or
igniter issue, or there is something in the combustor housing shorting out one of the igniters.

General Electrical System
On the US10 system, it is recommended to monitor the ACM Battery and Ignition voltage using the
breakout box during the system test period when all components are turned on and again during an
active Regeneration. There should be no voltage drop at all compared to the main system battery
voltage. Battery Power is supplied by a dedicated fuse at the battery box and supplies ACM ECU supply
pins 60, 61, 62. Maximum voltage drop allowed during spark ignition is 1 volt. Key switch input is
supplied by fuse F69 through FRC1:A1, circuit F69A-1.0, MCFC:71 to pin 3 on ACM.

US10 Typical Service Regeneration with good results

Check weld quality
from exh inlet port

1.60 – 1.75”

Insert screw driver or suitable rod
in Combustion Air Supply port

Good weld contact on outer housing and
igniter plate all around with no gaps

Example of a good Combustor housing. Note that this shows only the outer housing and not the inner
mantle.

FAURECIA -- US10 FAILED REGEN CHECK SHEET

CHASSIS MODEL AND SERIAL NUMBER

ESERVICE CASE NUMBER

YES
1

(W2034.2)

NO

SMART SWITCH INHIBITTED?
SPN

FAULT CODES LOGGED

FMI

OCCURENCES

2

USE WITH GUIDED DIAGNOSTICS SYMPTOM-BASED DIAGNOSIS FOR THE FOLLOWING STEPS
YES

NO

3

ALL AIR TANKS DRAINED?

NEW

4

ANY WATER IN THE AIR TANKS?

NEW

5

IS THE CORRECT COALESCING AIR DRYER
INSTALLED?

6

WHEN WAS THE AIR DRYER LAST SERVICED?
(mm/dd/yyyy)

7

DPF FILTER PART NUMBER

BRAND

PART #

NEW
NEW

YES

NO

8

DPF DP SENSOR HOSES OK?

9

TEMP SENSORS CORRECTLY INSTALLED

10

CAV FLOW with engine running and CAV activated checked during Regen at 1200 RPM - not idle speed

LPM

11

PER SYMPTOM-BASED DIAGNOSTIC NEXT STEP IF CAV
FLOW IS LOW - what is CAV flow with the outlet of the tool
vented to atmosphere?

LPM

TOOL PART NUMBER 85112577
The tool may need to be tilted horizontally
then slowly tilted back vertically to get a
steady reading
DWYER VFC-132-EC CAN BE