Diagnostic Procedures
DIAGNOSTIC PROCEDURES1. Attach MUT or Scanner to vehicle. After starting vehicle, use normal selection process and go to EGR Temperature Sensor display. Run until engine reaches full operating temperature. At idle, EGR temperature should read 60° C +/- 10°. If EGR temperature is reading -12° C, either the EGR Temperature Sensor is unplugged or defective.
Figure 1:
2. Block off the vacuum bleed (SEE FIG. 1) to the EGR Solenoid by removing and plugging the vacuum hose (yellow stripe) at the throttle body port marked "A". Raise engine RPM to 2500. Observe EGR temperature, if temperature exceeds 120° C, then the mechanical components of the system are functioning properly; proceed to step 4. If the temperature did not exceed 120° C disconnect the vacuum supply line at the EGR Valve and attach a manual vacuum pump. Raise the engine RPM to 2500 (the engine will stall if the EGR is opened at idle) and apply vacuum. Observe EGR temperature, if it exceeds 120° C proceed to step 3. Otherwise, remove the EGR and check for blockage in the passageway. A complete inspection of the passageway could require removal of the intake manifold.
Figure 2:
3. If the EGR Temperature Sensor and Valve have tested okay up to this point, then the vacuum supply could be restricted. The restriction can be in the throttle body or in the vacuum hose leading to the EGR Valve. There are two styles of throttle bodies; the old style (before Production Date: 12/13/94) has the vacuum orifice in the throttle body, the new style (beginning at Production Date: 12/13/94) has the orifice in the vacuum hose (green stripe) going to the EGR Valve (SEE FIG. 2).
WEAR SAFETY GOGGLES WHEN PERFORMING THE FOLLOWING PROCEDURE:
Old style (<12/12/94)
I. Remove vacuum hose (green stripe) from the throttle body vacuum port marked "E".
II. Spray carburetor cleaner into the vacuum port on the throttle body.
III. Using shop air pressure, blow into the vacuum port.
New style (>12/13/94)
I. Remove green stripe vacuum hose from the "E" port on throttle body to the three way tee, (SEE FIG. 1).
II. Remove & replace Orifice. SEE FIG. 2 for Orifice location. (see table below for part number).
III. Reinstall "Hose & Orifice Assembly", making sure that the orifice is closer to the three way tee than the throttle body.
4. Using HDS to check EGR Solenoid and related wiring (if HDS is not available, see below).
I. Connect HDS to vehicle.
II. From HDS HOME VIEW Screen select SIMU-TECH.
III. Go thru normal vehicle selection process.
IV. Go to SIGNAL WAVEFORMS, then select EGR Solenoid and display as ANALOG RECORD, hit RUN. Raise engine RPM to 2500.
You should observe a Duty Cycle, (12 to 16 volt square wave, SEE FIG. 3). If no Duty Cycle is observed, the EGR Solenoid is not being grounded by the the ECM. Before replacing the ECM, run a current draw test on the EGR Solenoid using HDS SWEEP TEST. If current draw exceeds 42O Diagnostic (M)Amp, replace EGR Solenoid and retest.
IF HDS IS NOT AVAILABLE:
You can check for Duty Cycle by backprobing the Brn/Wht wire at the EGR Solenoid with a voltmeter; with the engine running you should observe a decrease in voltage as you raise the engine RPM to 2500.
You can run a current draw test by connecting an ammeter in series between the Brn/Wht wire at the connector and the EGR Solenoid. If current draw exceeds 420 (M)Amp replace the EGR Solenoid and retest for Duty Cycle.