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Old 05-19-2013, 03:53 PM   #1
 
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Default Exhaust gas recirculation (egr) system 1989 tbi
EXHAUST GAS RECIRCULATION (EGR) SYSTEM


GENERAL DESCRIPTION


PURPOSE

The EGR system is used to lower NOx (oxides of nitrogen) emission levels caused by high combustion temperatures. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber to decrease combustion temperature.

The main element of the system is an EGR valve
operated by vacuum, and mounted on the intake manifold.

OPERATION

The EGR valve is opened by vacuum to let exhaust gas flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion will not occur. For this reason, very little exhaust gas is allowed to pass through the valve, especially at idle. The EGR valve is usually open under the following conditions:

• Warm engine operation
• Above idle speed


EGR CONTROL


Solenoid 2.5L, 4.3L (except ST), 5.0L & 5.7L (Under
8500 GVW)


To regulate EGR flow an ECM controlled solenoid is used in the vacuum line. This is a normally closed solenoid vacuum valve which is opened when the ECM completes the ground. The ECM will energize the EGR solenoid (EGR "ON”) when the engine is warm and above idle. There is little EGR flow at wide open throttle due to lack of vacuum.

2.5L Only

On cold engine start-up the ECM receives input from the MAT sensor (manifold air temperature), and if the MAT reading is less than 12C (57F) the EGR solenoid is "OFF” until the coolant warms to 80C (176F). If there is a malfunction of the MAT sensor then the ECM receives input from the coolant sensor.

EVRV 2.8L, 4.3L (ST), 7.4L & 5.7L (over 8500 GVW)

To regulate EGR flow, an ECM controlled electronic vacuum regulator valve (EVRV) solenoid is used in the vacuum line. The ECM uses information from the following sensors to regulate the solenoid:

• Coolant Temperature
• Throttle Position (TPS)
• P/N Switch
• Distributor (rpm Signal)

The EGR vacuum control has an EVRV solenoid that uses "pulse width modulation”. This means the ECM turns the solenoid "ON” and "OFF” many times a second and varies the amount of "ON” time ("pulse
width”) to vary the amount of EGR.





TYPES OF EGR VALVES

Two types of EGR valves are used on these
engines:

• Port (2.8L, 4.3L (ST), 7.4L & 5.7L over 8500
GVW)

• Negative backpressure (2.5L, 4.3L (except ST),
5.0L & 5.7L under 8500 GVW)

Port EGR Valve

This valve is controlled by a flexible diaphragm which is spring loaded to hold the valve closed. Vacuum applied to the top side of the diaphragm overcomes the spring pressure and opens the valve in the exhaust gas port. This allows exhaust gas to be pulled into the intake manifold and enter the engine cylinders.




NEGATIVE BACKPRESSURE EGR VALVE

The negative backpressure EGR valve has the bleed valve spring below the diaphragm, and the valve is normally closed. The negative backpressure valve
varies the amount of exhaust gas flow into the manifold depending on manifold vacuum and variations in exhaust back pressure. The diaphragm on this valve has an internal air bleed hole which is held closed by a small spring when there is no exhaust backpressure. Engine vacuum opens the EGR valve against the pressure of a large spring. When manifold vacuum combines with negative exhaust backpressure, the vacuum bleed hole opens and the EGR valve closes. This valve will open if vacuum is applied with the
engine not running.




EGR VALVE IDENTIFICATION

• Positive backpressure EGR valves will have a "P”
stamped on the top side of the valve after the part
number.

• Negative backpressure EGR valves will have a
"N” stamped on the top side of the valve after the
part number.

• Port EGR valves have no identification stamped
after the part number.




DIAGNOSIS

RESULTS OF INCORRECT OPERATION

With too much EGR flow at idle, cruise, or cold operation, any of the following conditions may occur:

• Engine stops after cold start.
• Engine stops at idle after deceleration.
• Vehicle surges during cruise.
• Rough idle.

If the EGR valve should stay open all of the time, the engine may not idle. Too little or no EGR flow allows combustion temperatures to get too high during acceleration and load conditions. This could cause:

• Spark knock (detonation).
• Engine overheating.


SYSTEM CHECK

Diagnosis of the EGR system is covered in the following charts. These charts begin on page 9-4.

• EGR System Check on a 2.5L, 4.3L (except ST),
5.0L & 5.7L (under 8500 GVW) engine.

• EGR System Check on a 2.8L, 4.3L (ST), 7.4L &
5.7L (over 8500 GVW) engine.



ON-VEHICLE SERVICE

EGR VALVE

Remove or Disconnect:

1. Air cleaner.
2. EGR valve vacuum tube at valve. (Figure 9-5
to 9-10).
3. Bolts or nuts.
4. EGR valve and g a sk e t from manifold
(Figures 9-11 to 9-15). Discard gasket.

[B]! Important !/B]

Do Not wash EGR valve in solvents or degreaser - permanent damage to valve diaphragm may result. Also, sand blasting of the valve is not recommended since this can affect the operation of the valve.


EGR Manifold Passage

Inspect

If EGR passage indicates excessive build-up of deposits, the passage should be cleaned. Care should be taken to ensure that all loose particles are completely removed to prevent them from clogging the EGR valve or from being ingested into the engine.
















EGR SYSTEM CHECK

2.5L, 4.3L (EXCEPT ST), 5.0L & 5.7L (UNDER 8500 GVW)

Circuit Description:

The ECM operates a solenoid to control the exhaust gas recirculation (EGR) valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass to the EGR valve. The ECM control of the EGR is based on the following inputs:

• Engine coolant temperature - above 25C.
• TPS - "OFF” idle
• MAP

If Code 24 is stored, use that chart first. Code 32 will detect a faulty solenoid, vacuum supply, EGR valve or plugged passage. This chart checks for
plugged EGR passages, a sticking EGR valve, or a stuck open or inoperative solenoid.

Test Description:

Numbers below refer to circled numbers on the diagnostic chart.

1. Checks for solenoid stuck open.
2. Checks for solenoid always being energized.
3. Grounding test terminal should energize solenoid
and vacuum should drop.
4. Negative backpressure valve should hold vacuum
with engine "OFF”.
5. When engine is started, exhaust backpressure
should cause vacuum to bleed off and valve to fully
close.

Diagnostic Aids:

• Before replacing ECM, use an ohmmeter and check the resistance of each ECM controlled relay and solenoid coil. Refer to "ECM QDR Check” procedure in Section "3”. See ECM wiring diagram for coil terminal I.D. of solenoid(s) and relay(s) to be checked. Replace any solenoid where resistance measures less than 20 ohms.
















EGR SYSTEM CHECK


2.8L, 7.4L, 4.3L (ST), & 5.7L (OVER 8500 GVW)


Circuit Description:

The EGR valve is controlled by a normally closed solenoid (allows a vacuum to pass when energized). The ECM pulses the solenoid to turn "ON” and regulate the EGR. The ECM diagnoses the system using an internal EGR test procedure. The ECM control of the EGR is based on the following inputs:

• Engine coolant temperature - above 25C.
• TPS "OFF” idle
• MAP

If Code 24 is stored, use that chart first. Code 32 will detect a faulty solenoid, vacuum supply, EGR valve or plugged passage. This chart checks for
plugged EGR passages, a sticking EGR valve, or a stuck open or inoperative solenoid.

Test Description:

Numbers below refer to circled numbers on the diagnostic chart.

1. With the ignition "ON”, engine stopped, the solenoid should not be energized and vacuum should not pass to the EGR valve.

2. Grounding the diagnostic terminal will energize the solenoid and allow vacuum to pass to valve.

3. Checks for plugged EGR passages. If passages are plugged, the engine may have severe detonation on acceleration.

4. The vehicle must be driven during this test in order to produce sufficient engine load to operate the EGR. Lightly accelerating (approximately 1/4 throttle) will produce a large and stable enough reading to determine if the ECM is commanding the system "ON.”

Diagnostic Aids:

• Before replacing ECM, use ohmmeter and checkresistance of each ECM controlled relay and solenoid coil. Refer to "ECM QDR Check” in Section "3”.
See ECM wiring diagram for coil terminal identification of solenoid(s) and relay(s) to be checked. Replace any relay or solenoid if the coil resistance measures less than 20 ohms.






Clean

1. With a wire wheel, buff the exhaust deposits fromthe mounting surface and around the valve.
2. Look for exhaust deposits in the valve outlet. Remove deposit build-up with a screwdriver.
3. Clean mounting surfaces of intake manifold and valve assembly.

Install or Connect

1. New EGR gasket.
2. EGR valve to manifold.
3. Bolts or nuts.
4. Vacuum tube to valve.
5. Air cleaner.

SYSTEM HOSES

Refer to Vehicle Emission Control Information label for routing of system hoses. When replacing hoses, use hose identified with the word "Fluoroelastomer”.






















EGR SOLENOID 2.8L, 4.3L (ST), 7.4L & 5.7L (over 8500 GVW) (Figure 9-16)

Remove or Disconnect

1. Negative battery cable.
2. Air cleaner, if necessary.
3. Electrical connector at solenoid.
4. Vacuum hoses.
5. Bolt(s) and solenoid.
6. Filter, if required.

Install or Connect

1. Filter, if required.
2. Solenoid. Tighten bolts to 24 N-m (17 ft. lbs).
3. Vacuum hoses.
4. Electrical connector.
5. Air cleaner, if removed.

EGR FILTER CLEANING / REPLACEMENT

1. Grasp and pull filter off with a rocking motion.
2. Push new filter on making sure cut-out for wires is properly aligned.
3. Negative battery cable.

EGR VACUUM SOLENOID 2.5L, 4.3L, 5.0L & 5.7L (under 8500 GVW) (Figure 9-17)

Remove or Disconnect

1. Negative battery cable.
2. Electrical connector at solenoid.
3. Vacuum hoses.
4. Bolt(s) and solenoid.

Install or Connect

1. Solenoid. See Figures 9-5 thru 9-10 for torque specification.
2. Vacuum hoses.
3. Electrical connector.
4. Negative battery cable.





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Old 05-19-2013, 05:29 PM   #2
 
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Default EGR 87-95 Part II
This guide is for troubleshooting EGR problems on TBI engines (1987-1995) using a negative pressure (vacuum-operated) valve, which are the majority of the TBI 5.0 and 5.7 truck engines. If in doubt, check the part number on the valve, it should end with an "N" for negative.

This is written for use by your average DIY'er there are no instructions that require a GM Tech 1 scanner or any special tools other than a simple vacuum tester (Mityvac) and a multimeter. It is not an exhaustive guide on the entire system and every potential possibility, but an attempt at a brief explanation of operation, and identifying the common failures.

What the EGR system does and when:


The EGR system allows exhaust gas to be introduced into the intake stream in order to cool combustion chamber temperatures under load. This reduces NOx emissions and helps prevent pinging (detonation.) The EGR valve is closed at idle. On throttle application, the EGR valve will be commanded open by the PCM as needed.

How the PCM tests the EGR system:

The PCM waits for many conditions to be met before running the EGR test. From 1994 factory manual: PCM must be in closed loop, above 32 MPH, throttle position 10% to 25%, steady throttle with no more than 2% change, MAP reading above 47.5 kPa or below 15 kPa, maximum short term fuel trim less than 6 counts for 3.2 seconds, desired EGR command greater than 93%.

In simple terms? This tends to happen when you're cruising on flat ground on the highway.

At this point the PCM will momentarily de-energize the EGR solenoid to close the valve. The PCM watches the fuel integrator counts to see if they increase compared to normal EGR operation. If it fails twice in a row, code 32 is set and check engine light is illuminated.

Possible symptoms of EGR trouble:


- Rough idle and rough part throttle operation (valve opening too easily or stuck open)
- May stall during transition from idle to part throttle (valve opening too easily or stuck open)
- Noticeable pinging (detonation) especially when engine is under load (valve inoperative)
- Trouble code 32 (valve inoperative)
- Hard or no start although fuel and spark are present (valve stuck wide open)

Possible Failure Modes:

- The vacuum supply from the TBI unit to the EGR solenoid can be disconnected, broken, clogged, or incorrectly connected
- The EGR solenoid can be faulty or the electrical connection to it can be missing or damaged
- The vacuum supply from the EGR solenoid can be disconnected, broken, clogged, or incorrectly connected
- The EGR valve can be faulty, clogged, or the incorrect part for the application
- The EGR passages in the intake can be clogged with carbon

Check connections (see pics):

- Vacuum line from the lower passenger side of TBI to front side (single port) of the EGR solenoid
- Vacuum line from the barbed port on the rear side (two ports) of the EGR solenoid to the EGR valve
- Smooth port on rear side of EGR solenoid should be OPEN, or sometimes a small foam filter may still be present from factory; either is fine
- Check plastic lines for breakage and be sure hose boots are still pliable and grip well; if they have hardened or cracked they will not seal
- Wiring harness connection to the EGR solenoid (gray and pink/black wire)









Troubleshooting:

The most common EGR system failure on our trucks is the valve itself; the diaphragm fails so the EGR valve will not open. You can eliminate this possibility right off the bat by testing the valve with a vacuum tester (Mityvac.) Shut the engine off and connect the tester directly to the EGR valve. Pull vacuum (around 15 inches is plenty) and be sure it holds for a minimum of 20 seconds. If it does not build or hold vacuum, the valve could be held open by a chunk of carbon, which you could attempt to clean out but most likely, the valve is bad and needs to be replaced.

If the valve passes the hold test - with vacuum still showing as holding on the tester, have a helper start the engine while you watch the gauge. The vacuum should bleed off immediately.

Determine whether the EGR passages in the intake are clogged by carefully depressing the EGR diaphragm with your fingers. Take care to not burn your fingers or get them caught in the openings under the EGR. When you press the diaphragm, the engine should stumble noticeably, and possibly stall. If there is little or no response, the passages in the intake are likely clogged with carbon. Effective cleaning of these passages requires removal of the intake manifold.

Check the vacuum source to the EGR solenoid. Connect a vacuum tester (Mityvac) to the line leading from the TBI unit to the front (single port) side of the solenoid. There should be full vacuum at idle, around 20 inches/Hg on a stock engine. If not, remove the line from the TBI and connect the tester directly to the TBI to verify vacuum. If none, the port itself may be clogged.

Reconnect the line from the TBI to the solenoid and move the tester to the line exiting the rear of the solenoid. At idle there should be NO vacuum reading (be sure you purged your gauge if necessary so that it reads zero before connecting.) Snapping the throttle should show some activity on the gauge as the solenoid briefly commands the EGR open.

With the meter set on ohms, you can test the EGR solenoid coil across the two pins in the socket; any reading less than 20 ohms indicates a bad solenoid winding.

With the meter set on DC voltage, or using a test light, check the EGR solenoid harness terminal A (pink/black) to ground. Key on, meter should read 12V or the test light should light up. Do not pierce the wire to test, simply unplug it and touch the test lead to the connector pin.

Another possible failure that is difficult to test for is a weak spring inside the valve allowing it to open too easily. If you have exhausted all other efforts you may consider replacing the valve.

Replacing the EGR valve:


The best bet for getting the correct valve is to go to the dealer. If you are unable to, at the very minimum, get a Delphi brand from the parts house. Avoid other brands, especially universal types where you change the size of the orifice by installing washers. These are the worst. TBI engines are very picky about the EGR valves.

IF THE DEALER TRIES TO SELL YOU AN AFTERMARKET TYPE VALVE you should hit the parts house and check out a Delphi direct replacement instead. I have recently gotten info that some GM dealers are offering aftermarket "one size fits many" valves. I would avoid these at all costs. They may work, may not; I'd rather have a direct replacement.

Be sure to buy a new gasket for the EGR valve, and apply a very thin coat of anti-seize lubricant on both sides of it. This will tend to make the gasket re-usable in the event you need to remove the EGR valve in the future.

If you have EGR system problems, by all means please troubleshoot and repair them instead of removing the valve. Removing the valve guarantees increased NOx emissions, higher potential for harmful pinging, constant code 32 with check engine light illuminated, and instant failure of any smog test that may apply in your area.
Attached Images
File Type: jpg EGRTBI1.jpg (78.8 KB, 76 views)
File Type: jpg EGRTBI2.jpg (84.3 KB, 76 views)


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84 Chevy Silverado C20 454/Turbo 400 14FF 3.73 Peg Legger -- http://www.gmsquarebody.com/forum/showthread.php?t=286
85 GMC Sierra Classic K1500 350/Th350/NP208 10Bolts 3.73's --http://www.gmsquarebody.com/forum/showthread.php?t=368
85 Chevy Silverado K10 350/A883/NP208 14FF/10B 4.10 w Lockers --http://www.gmsquarebody.com/forum/showthread.php?t=279
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Old 05-19-2013, 05:35 PM   #3
 
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Default
OK, so between the 2 posts, we should have some great info here for you TBI 87-91 guys and all of you have done TBI conversions to your earlier trucks like Jims86 concering your EGR system.

Don't forget to Rep up 89Suburban for a great thread !!!
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84 Chevy Silverado C20 454/Turbo 400 14FF 3.73 Peg Legger -- http://www.gmsquarebody.com/forum/showthread.php?t=286
85 GMC Sierra Classic K1500 350/Th350/NP208 10Bolts 3.73's --http://www.gmsquarebody.com/forum/showthread.php?t=368
85 Chevy Silverado K10 350/A883/NP208 14FF/10B 4.10 w Lockers --http://www.gmsquarebody.com/forum/showthread.php?t=279
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Old 05-19-2013, 05:50 PM   #4
 
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Year: 1990 Chevy Suburban
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Rep Power: 113

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I'm still trying to figure out what is wrong with mine.


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Old 06-01-2013, 11:42 AM   #5
 
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Default Exhaust gas recirculation (egr) system 1989 tbi
Here is a great write up on the BP EGR valve.

http://www.tomco-inc.com/Tech_Tips/ttt26.pdf


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Old 09-22-2013, 01:39 PM   #6
 
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Rep Power: 113

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CHART C-7E - PULSE WIDTH MODULATED (PWM) EGR SYSTEM CHECK

Circuit Description :

PWM EGR is an ECM control that pulses the vacuum signal to the EGR. This is accomplished through a normally open EGR solenoid which when energized by the ECM shuts off the vacuum to the EGR valve diaphragm. This system can pulse the solenoid many times per second (PWM). The EGR solenoid is always energized (EGR off) when any one of the following conditions are met:

- Throttle Position greater than specified.
- Coolant temperature less than specified.

Test Description :

- Checks to see if the EGR passages are restricted or if the valve is stuck open.

-A cold engine is simulated by disconnecting the coolant temperature sensor which will also energize the EGR solenoid.

- With the 4 wire EST connector disconnected, the ECM thinks the engine is not running. Grounding the test terminal, under this condition, causes the ECM to pulse the EGR solenoid "ON" and "OFF" for testing which will result in a controlled vacuum supply to the EGR valve diaphragm at 2000 RPM.

- By disconnecting EGR solenoid electrical connector, control by the ECM is overridden and the normally opened EGR solenoid will pass available vacuum. At 2000 RPM EGR valve should move if EGR control system is functioning properly.

- If vacuum is below 23.6 kPa (7" Hg) at 2000 RPM with EGR solenoid electrical connector disconnected, a leak or restriction between test point (EGR diaphragm) and source is evident.

- Checks EGR solenoid electrical control circuit. The test light should "flicker faintly" if the ECM, harness and connections are OK. "Flicker faintly" refers to a slightly pulsing glow as opposed to a "bright steady" glow from a continuous ground path.

Steps 1, 2, and 3 represent an EGR system operation check.






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