Wagoneer L6-258 4.2L VIN C 2-bbl (1982)
EGR Backpressure Transducer: Testing and Inspection
1. Inspect all EGR vacuum lines for leaks and correct routing.
NOTE: On 1975-76 models, make certain vacuum line from EGR CTO is connected to nipple with 0.030 inch restriction.
2. Using a tee fitting, connect a vacuum gauge in line between EGR valve and exhaust back pressure sensor.
3. With engine idling there should be no vacuum indicated on gauge.
NOTE: If vacuum is indicated at idle speed, check for correct vacuum line connections. Make certain manifold vacuum is not being used as a
vacuum source. If carburetor is providing vacuum, check for partially open throttle plate which could be providing premature ported vacuum to
back pressure sensor.
4. Accelerate engine to 2,000 rpm and check vacuum gauge for the following:
a. There should be no vacuum reading if coolant temperature is below 115° F.
b. Ported vacuum should be indicated if coolant temperature is above 115° F (black CTO switch) or 160 °F (yellow CTO switch).
5. If no vacuum was indicated during test, make certain vacuum is being applied to inlet side of back pressure sensor. If vacuum connections are
correct, remove back pressure sensor and inspect spacer port and tube for restrictions. Deposits caused by carbon or lead deposits can be removed
using a spiral wire brush. If no vacuum is obtained, replace back pressure sensor.
