Diagnosing Digital EGR Valves

Counter Point
Volume 3 Issue 4, October 1999
T H E
E L E C T R O N I C,
D I A G N O S T I C
A N D
D R I V E A B I L I T Y
Diagnosing Digital
EGR Valves
E
xhaust gas recirculation
(EGR) is used on most
engines to reduce the
formation of oxides of nitrogen (NOX) in
the exhaust. NOX is a pollutant that is now monitored
by a growing number of “enhanced” emissions testing programs.
These programs use dynamometers to check
vehicle emissions under simulated driving
conditions. So knowing how to diagnose the
EGR system when a NOX failure occurs should
reduce the unnecessary replacement of
EGR valves.
First, a little background: the basic concept
of EGR hasn’t changed since it was introduced
back in 1973 to meet federal emission
regulations. An EGR valve is used to open a
small passageway that connects the intake and
exhaust manifolds. Intake vacuum then siphons
some exhaust back into the engine to dilute the
air/fuel mixture. This lowers combustion
temperatures to reduce the formation of NOX.
EGR also helps the engine resist detonation
under load. (A typical earlier-style vacuum
EGR valve is shown in Figure A.)
When the EGR valve opens, it has much the
same effect on engine performance as a
vacuum leak (idle roughness, lean
misfire and hesitation). For this reason,
the EGR valve should not open until the
engine is warm and above idle speed. On earlier
R E S O U R C E.
of EGR as well as when it occurs. Some EGR
valves (Ford mostly) from this generation have a
valve position sensor that provides additional
feedback to the computer about how much EGR
the engine is receiving.
In the 1990’s, electronic (digital) EGR valves
began to replace vacuum-actuated EGR valves
because they can respond much faster to changes
in operating conditions and work independent
of intake vacuum. Several different types
are used:
• Single-stage (A single solenoid is used to open
the exhaust passageway valve). The computer
monitors various sensor inputs to determine
when EGR is needed, then cycles the EGR valve
solenoid on and off to control the amount of
exhaust gas recirculation.
• Multi-stage (Used on various late-model
General Motors applications, this type has two
or three solenoids that open separate exhaust
passageway valves. See Figure B.) With this
setup, the computer uses a step strategy to
increase EGR in stages. If only a little EGR is
needed, one solenoid is energized. As more EGR
is needed, the second and third solenoids are
energized. On the three-solenoid applications,
up to seven different combinations may be used
to control EGR flow.
SCREW
ASSEMBLY
SOLENOID &
MOUNTING
PLATE ASSEMBLY
ARMATURE
ASSEMBLY
EGR BASE PLATE
EGR BASE
EGR BASE
GASKET
FIGURE A
vehicles with vacuum-operated EGR valves,
a ported vacuum switch prevents vacuum
from reaching the EGR valve until the engine
is warm.
In the 1980’s, computer-controlled solenoids
began to replace vacuum switches in EGR
systems. By monitoring engine speed,
temperature, load, throttle position and vehicle
speed, the computer varies the duty cycle (on
time) of the EGR solenoid to vary the amount
INSULATOR
GASKET
FIGURE B
• Linear (Uses a small stepper motor instead of
solenoids or a vacuum diaphragm to open the
exhaust passageway valve). A linear EGR valve
works much like an idle-speed control motor in
that it moves in small increments. This allows
the recirculation of exhaust gas to be increased
or decreased with a higher degree of precision.
continued on page 3
WHAT’S INSIDE:
Diagnosing Digital EGR Valves…Page 1 & 3 / FINE TUNING…Page 2 / QUALITY POINTS: These CAPS Are Lightweight & Tough …Page 2 & 3 /
HOT OFF THE WIRE: WELLS Catalog Judged The Best…Page 4 / Publisher’s Information…Page 4
insulation and not be easily detected. This can cause
reduced primary current flow, resulting in engine
misfire under load. Eventually, all of the strands can
break resulting in a no-start condition.
Fine Tuning
Q: “We have a supercharged 1995 Pontiac
Bonneville 3.8 VIN 1 that has a surge at
idle with codes P0131 and P0171. We have
checked the O2 sensor, fuel pressure,
timing, and vacuum hoses and connections
for leaks. The ISC counts are low but seem
to be okay at around 13 or 14. This car
does this all the time and temperature
seems to have no effect.”
Stevens’ Shell, Elizabeth, NJ
With your scan tool connected, if the ISC counts stay
less than 15, and the long/short-term fuel trim remains
greater than 140, you should expect an air leak. One
place you didn’t mention checking was the supercharger
outlet gasket. Check for leaks, especially around the
pulley end, as this is a common area for leakage to occur.
CHECK THIS AREA
FOR LEAKS
Q: “I have a 1996 Buick Skylark with the
2.4L SFI that has a problem with a rough
idle, repetitive stalling and hard starting.
This problem is very intermittent and only
seems to happen after the car has been
sitting for a while, like overnight, and
seems worse in colder weather. Scan tool
data seems to check out OK, but sometimes
Fine Tuning questions are
answered by Jim Bates, WELLS’
Technical Services Director.
there are misfire codes (P0300 through
P0304). Any suggestions?”
Bill Renton, Billings, MT
If you haven’t checked the oil pressure, you should do so,
as there have been reports of the type of problem you are
having due to excessive oil pressure caused by a sticking
relief valve. This would cause the lifters to raise the valves
off of their seats, resulting in a loss of compression and
engine misfire and/or stalling on initial start-up. To
check this, install an oil-pressure gauge that can read at
least 150 psi in an oil pressure port and check the oil
pressure at 3000 rpm. The oil pressure should not exceed
100 psi even in very cold operating conditions and
should not exceed 85 psi with the engine warmed up to
operating temperature. If the oil pressure exceeds these
limits, you will have to replace the oil pump cover that
has an improved pressure relief valve.
Q: “I am working on a 1997 Chevy Astro
with the 4.3 VIN W engine. This van has an
intermittent stalling condition and lousy
performance and has a DTC P0300.
Distributor cap, rotor, coil, plugs, plug
wires, engine vacuum, compression, fuel
pressure are all good. Cam and crank
position sensor signals are consistent.
The primary wiring and connectors have
all been checked as well. The engine runs
good at idle and in gear most of the time,
but when driven, performance is poor.
Any ideas?”
George Mills, Atlanta, GA
The MAP sensor should read about 4.5 volts with the
key on, engine off (KOEO) at sea level and about 1.5
volts or so at about 20” of vacuum. Since the average
vacuum at idle is about 17” to 23”, a MAP output of
2.9 volts is too high. Besides a defective MAP sensor or
cracked sensor housing, be sure to check for damaged
gaskets, hoses, EGR, ignition or cam timing, engine
mechanical damage, etc.
MAP SENSOR
CHECK THIS AREA
FOR CRACKS IN
THE MAP SENSOR
HOUSING
INTAKE MANIFOLD
Brian Williams, St. Louis, MO
Check the ignition coil wires where they attach to the
primary terminals. These wires can get brittle near the
connector and the wire strands can break inside of the
Quality Points
These CAPS Are Lightweight & Tough
Distributor caps and rotors may seem like a
“generic” product to some. After all, most
replacement caps and rotors look pretty
much the same. But appearances can be
deceiving because the performance of the
materials from which these parts are made
can vary significantly.
Q: “We are working on a 1995 Chrysler
Concorde with a 3.3L MFI. The problem
we are trying to fix is an extremely rich
mixture. You can smell the gas in the
exhaust. No codes. Injection goes from 5.9
to 6.2 ms right at start-up and doesn’t
change with propane or induced vacuum
leak. I used both a scanner and a scope to
verify that injection was really what was
indicated. The scanner shows MAP output
to be 2.9 volts at idle, but I can’t find any
information for voltage specs for Chrysler
from idle to WOT that we can use for
reference. Thanks for any help.
As a leading supplier of original equipment
ignition components, WELLS’ engineers have
the inside track on what works and what doesn’t.
OEM caps and rotors must meet rigorous test
standards for performance and durability.
That’s why WELLS uses a special lightweight
thermoplastic polyester resin in its OEM and
2
Please send your questions to: Jim Bates c⁄ o WELLS
Manufacturing Corp., P.O. Box 70, Fond du Lac, WI
54936-0070 or e-mail him at technical@wellsmfgcorp.com.
We’ll send you a WELLS shirt if your question is published.
So please include your shirt size with your question.
aftermarket distributor caps and rotors that
outperforms the heavy, mica-filled components
of yesterday.
The thermoplastic polyester resin that WELLS
uses has outstanding chemical resistance to oil,
gasoline, underhood chemicals and other
automotive fluids. It also has excellent
dimensional stability. The dimensions remain
stable regardless of temperature, humidity
or chemical attack, so the parts fit correctly
when they’re installed, and continue to fit
perfectly for years to come.
WELLS caps and rotors have very low moistureabsorption characteristics resulting in superior
dielectric strength. This allows them to better
continued from page 1
Diagnosing Digital EGR Valves
EGR PROBLEMS
With earlier-style vacuum-operated EGR
valves, failure of the vacuum diaphragm
or carbon buildup on the pintle valve are the
main causes of trouble. A leaky diaphragm will
prevent the EGR valve from opening, causing
not only an increase in NOX emissions but
often detonation (spark knock) when the engine
is under load. Carbon can also build up inside
the manifold passageway and block the flow of
exhaust. Carbon deposits that prevent the valve
pintle from closing will produce driveability
symptoms like a vacuum leak (hard starting,
rough idle, lean misfire, hesitation and possibly
stalling after cold starting).
With digital EGR valves, the driveability
symptoms are the same: elevated NOX
emissions and detonation with loss of EGR,
or idle problems if the valve fails to close.
HOW TO DIAGNOSE
On earlier vehicles, visually inspecting the EGR
valve to see that it moves when the engine is
revved is one way to check its operation.
Another is to apply vacuum directly to the EGR
valve and listen for a drop in idle speed when
the valve opens (but this only works if the valve
is not a back-pressure-sensing type).
Back-pressure-sensing EGR valves only open
when back-pressure exceeds a certain
level, so be sure to raise the engine
speed to about 2000 rpm before
applying vacuum.
On vehicles that have a vacuum-type EGR valve
with a solenoid in the vacuum supply line,
vacuum should pass to the EGR valve when the
engine is warm and above idle. No vacuum?
Check for voltage at the solenoid. No voltage
would indicate a wiring problem. The computer
should energize (ground) the solenoid when
EGR conditions exist (engine warm, running
above idle). If EGR is not occurring, the
problem may be a bad solenoid, wiring,
computer or sensor problem. The solenoid itself
can be checked by jumping it to battery voltage.
No click will tell you the solenoid needs to be
replaced. The next most likely causes would be a
loose wiring connector, faulty coolant sensor, or
resist arcing and burning, which are the leading
causes of many cap and rotor failures.
The material also provides high heat resistance.
Components will not distort at high underhood
failed driver circuit in the computer. With
digital EGR valves, a “Check Engine” light
accompanied by any of the following
fault codes may indicate a problem in the
EGR system:
• Ford: 31, 32, 33, 34, 83, 84
• Chrysler: 31
• General Motors: 75, 76 and 77
• All OBD II vehicles (1996 & up): Diagnostic
Trouble Code (DTC) P0401 insufficient flow,
P1406 EGR sensor
On some vehicle applications, a scan tool can
also be used to access and display EGR valve
position and status.
FIGURE C
BENCH TESTS FOR A DIGITAL
EGR VALVE
To check a three-solenoid GM digital EGR
valve, (Refer to Figure C) and measure the
resistance of each solenoid:
• Terminal A to B: 20 ohms
• Terminal A to C: 10 to 17 ohms
• Terminal A to D: 20 to 30 ohms
If any resistance reading is outside the range of
specifications, the unit is defective and needs to
be replaced.
Using a 9-volt battery or sensor tester, run
battery positive (+) current to the “A” terminal,
then ground each of the other terminals (B, C &
D) one at a time (see Figure C). Each solenoid
should click and open its respective pintle valve.
No click or movement would indicate a faulty
solenoid.
With the battery and jumpers disconnected,
spray a small amount of carburetor cleaner into
each orifice (Figure D), being careful not to get
the cleaner in the center hole. If the cleaner seeps
out of any orifice hole into the center, the pintle
is not seating properly and the EGR valve needs
to be replaced.
If a digital EGR valve passes the above tests but
there are fault codes present, the problem may
exist in one or more of the following: the
powertrain control module (PCM), manifold air
pressure (MAP) sensor, the oxygen (O2) sensor,
throttle position sensor (TPS), a plugged intake
manifold passageway, a clogged catalytic
converter, a blown fuse or a wiring problem.
temperatures (which isn’t true of some lesser
quality aftermarket caps and rotors). WELLS
caps and rotors can withstand operating
temperatures above 400 degrees F!
Finally, WELLS caps and rotors have an
extremely high strength-to-weight ratio and
will not crack even under severe operating
conditions. This eliminates the risk of thermal
cracking around inserts and vanes that may
occur in lesser quality caps and rotors.
3
SPRAY INTO THESE
THREE HOLES
FIGURE D
TESTING A DIGITAL EGR VALVE
ON THE VEHICLE
The same resistance checks can be made between
the terminals (A to B, A to C and A to D).
If resistance is within specs, check the operation
of the EGR valve by back-probing and
grounding each solenoid terminal (B, C & D).
This must be done with the engine at normal
operating temperature, idling in closed loop.
When each solenoid is grounded (energized),
there should be a momentary drop in idle speed
if the EGR valve is opening and the intake
passageways are unobstructed. The computer
will immediately compensate for the drop in
idle speed by opening up the idle air-control
valve to increase rpm, so you may have to use
a tachometer to detect the rpm drop. No change
in idle speed would indicate a faulty EGR valve
or blocked passageways.
Note: This test can also be done with a
bi-directional scan tool by selecting EGR
output test and then energizing each solenoid
to check for the rpm drop.
If the EGR valve passes these tests but is not
functioning, the problem is in the wiring,
PCM or one of its sensor circuits (coolant,
MAP, TPS or O2). These items should all be
checked to isolate the fault.
WELLS MANUFACTURING CORP.
P.O. Box 70
Fond du Lac, WI 54936-0070
INSIDE:
DIGITAL
DIAGNOSING
ES
LV
VA
R
EG
Hot off the Wire
WELLS‘ Catalog Judged The Best
WELLS’ winning streak in the annual National
Catalog Managers Association (NCMA)
competition continues with the “President’s
Award” for 1999.
In the past 14 years, WELLS has received awards
eight times against some very stiff competition.
Catalogs from various aftermarket parts suppliers
are judged by a panel of six industry experts
according to various criteria. These
include the overall organization of
the catalog, layout, appearance,
print quality, paper quality,
indexing and timeliness of listings.
This latest NCMA award proves
that WELLS is committed to
producing high-quality, easy-to-use
catalogs. If you don’t have the latest
one, contact:
WELLS Manufacturing Corp.,
P.O. Box 70, Fond du Lac,
WI 54936-0070
Publisher’s Information
WELLS President .............William Allen
Vice President Sales ........Gavin Spence
Technical Services Director .....Jim Bates
Newsletter Editor ...............Ron Raposa
Counter Point is a quarterly publication of WELLS
Manufacturing Corp., P.O. Box 70, Fond du Lac, WI
54936-0070. Letters and comments should be
directed to: Counter Point Editor, c/o WELLS
Manufacturing Corp, P.O. Box 70, Fond du Lac, WI
54936-0070.
© COPYRIGHT 1999 WELLS MANUFACTURING CORP.
All rights reserved. No reproduction in whole or part is permitted
without the written consent of WELLS Manufacturing Corp.