Economy (Vacuum) Gauge Test: 300SD
- Locate vacuum gauge hose source at 4-way or 5-way connector behind brake booster. Disconnect 4-way or 5-way connector's vacuum hose coming from engine. With engine idling, check for vacuum at this hose.
- If vacuum exists, connect engine vacuum hose to vacuum gauge hose using hose union and check for economy gauge operation. If gauge operates correctly, check for vacuum leak in other related vacuum hoses, such as air conditioning system or automatic transmission diaphragm line.
- If gauge does not work, check/repair complete vacuum line to gauge or replace defective gauge. If automatic transmission diaphragm is defective, fluid will be drawn into vacuum hoses, plugging hoses. If A/C system has defective diaphragm or servo, an incorrect vacuum reading on economy gauge will result. Repair as required.
- If vacuum does not exist in step 1), clean vacuum port at engine, check for leak in hose from engine to connector and repair/replace as required. Recheck for vacuum.