TECHNICAL SERVICE BULLETIN
Bulletin Number: TSB 21-0001
Date: 07-23-2021
Subject: Parker Veriflo Regulator Outlet Pressure Adjustment
Models: All Fuel Systems
Background
Cummins Clean Fuel Technologies utilizes a Parker Veriflo regulator to supply the
correct fuel pressure to the engine. With the introduction of the Cummins X12N
engine in 2018, the HD family of on highway engines no longer all have the same
allowable ranges for fuel pressure to the engine. The table below shows the
allowable fuel pressures for Cummins CNG engines.
Parker Veriflo Regulator (typical)

Engine Pressures
Engine Model
ISLG
ISX12G
6.7N
L9N
X12N

Min
Pressure
70 psi
70 psi
70 psi
70 psi
60 psi

Max
Pressure
150 psi
150 psi
150 psi
150 psi
100 psi

Development and testing were done with Parker to develop a regulator and a
single pressure setting that will work for all engines so different regulators or
different pressure settings are not required for the different engines.

Condition
In some cases, vehicles equipped with a Cummins fuel system may see a
message on the vehicle dash that says something similar to “Fuel Pressure Too
Low-Safely Pull Over and Stop Eng. Immediately.”

Cummins Clean Fuel Technologies, LLC.
1051 Republic Drive Ste 200
Roanoke, TX 76262
1-844-CNG-TANK

Cause
The fuel pressure delivered to the engine is out of range too low to the engine.
Cummins does not log a low-pressure fault code on the current natural gas
engine, 6.7N, L9N, 12N, and instead only have the message on the dash. If the
engine fault codes are pulled up using Cummins Insite no fault codes for this issue
will be present.

Correction
The outlet pressure on the high-pressure regulator on the Cummins fuel system
can be easily adjusted. The adjustment will need to be made while the engine is
running at idle and had a chance for the engine to warm up. The regulator needs
to be at least warm to the touch.
The outlet pressure of the high-pressure regulator should be 80 psi while idling
with a fuel system pressure of 3600 psi. The outlet pressure varies inversely to
the inlet pressure. The lower the inlet pressure to the regulator, the higher the
outlet pressure will be. For every 1000 psi below 3600 psi inlet pressure, add 4
psi to the outlet pressure setting. For example, 2600 psi should be 84 psi,
2400 should be 85 psi.
See the table below for the low pressure setting vs. system pressure:
Cummins Clean Fuel Technologies, LLC.
1051 Republic Drive Ste 200
Roanoke, TX 76262
1-844-CNG-TANK

Pressure Setting Table
Veriflo Regulator Settings
Fuel System Pressure
Inlet Pressure (PSI)
4000
3900
3800
3700
3600
3500
3400
3300
3200
3100
3000
2900
2800
2700
2600
2500
2400
2300
2200
2100
2000
1900
1800
1700
1600
1500
1400
1300
1200
1100
1000
900
800
700
600
500

Cummins Analog Gauge
Outlet Pressure Setting(PSI)
78.4
78.8
79.2
79.6
80
80.4
80.8
81.2
81.6
82
82.4
82.8
83.2
83.6
84
84.4
84.8
85.2
85.6
86
86.4
86.8
87.2
87.6
88
88.4
88.8
89.2
89.6
90
90.4
90.8
91.2
91.6
92
92.4

Cummins Clean Fuel Technologies, LLC.
1051 Republic Drive Ste 200
Roanoke, TX 76262
1-844-CNG-TANK

Cummins Insite
Fuel Regulator Intake Pressure (InHg)
156.8
157.6
158.4
159.2
160
160.8
161.6
162.4
163.2
164
164.8
165.6
166.4
167.2
168
168.8
169.6
170.4
171.2
172
172.8
173.6
174.4
175.2
176
176.8
177.6
178.4
179.2
180
180.8
181.6
182.4
183.2
184
184.8

There is an access plug located on the top of the FMM:

After removing the plug, remove the acorn nut from the top of the regulator:

With the engine at idle speed, adjust the set screw on top of the regulator using a
1/8” Allen wrench. It is recommended to set the final outlet pressure by initially
going approximately 5 psi above final desired pressure, and then reducing the
pressure to the final set pressure.

Reinstall the acorn nut and torque to 100 +/- 10 in-lbs (8.3 +/- .8 ft-lbs) with the
engine still at idle and verify outlet pressure did not change.

Cummins Clean Fuel Technologies, LLC.
1051 Republic Drive Ste 200
Roanoke, TX 76262
1-844-CNG-TANK