* Low Transmission Fluid: This is the first and easiest thing to check. Low fluid level or fluid that's dirty, burned, or incorrect can cause the transmission to not engage properly, leading to stalling. Check the fluid level with the engine running and warm.
* Transmission Problems: A failing transmission is a serious possibility. Worn clutches, a faulty valve body, or internal problems can cause the transmission to struggle to engage. This might manifest as slipping, harsh shifting, or simply stalling when put into gear.
* Torque Converter Issues: The torque converter is the fluid coupling between the engine and transmission. A faulty torque converter can cause the engine to stall under load (when put into gear). This often involves slipping before stalling.
* Engine Problems: While less likely to directly cause stalling *only* when put in gear, a weak engine struggling to produce enough power could cause stalling. This could be due to:
* Spark Plugs/Wires: Worn or faulty spark plugs and wires can lead to a misfire, especially under load.
* Ignition System Problems: Issues with the distributor, ignition coil, or other ignition components can also reduce engine power.
* Fuel Delivery Problems: A clogged fuel filter, fuel pump issues, or problems with the fuel injectors can starve the engine of fuel, causing stalling under load.
* Vacuum Leaks: A significant vacuum leak can affect engine performance and cause stalling.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle position. A faulty TPS can provide incorrect information, causing the engine to stumble or stall, especially under load.
* Mass Air Flow Sensor (MAF): This sensor measures the amount of air entering the engine. A faulty MAF can cause a lean condition, potentially leading to stalling.
Troubleshooting Steps:
1. Check Transmission Fluid: This is the absolute first thing to do.
2. Listen for unusual noises: Are there any grinding, whining, or clunking noises coming from the transmission when you try to put it in gear?
3. Check engine codes: Use an OBD-II scanner (even though 1989 might not be fully OBD-II compliant, it might still have some diagnostic capability) to see if any trouble codes are stored. A mechanic can also do this.
4. Inspect belts and hoses: Make sure all belts are tight and hoses aren't cracked or leaking.
5. Test the battery and alternator: A weak battery or alternator can also cause stalling.
Important Note: Without physically inspecting the vehicle, it's impossible to give a definitive diagnosis. The best course of action is to have a qualified mechanic diagnose the problem. Attempting repairs without proper knowledge could lead to further damage.
