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« Last post by Garyman on April 17, 2024, 01:20:38 »
My SL sits for years, starts no problem with 87 regular. It is a gas quantity issue on warm up. My 1st guess would be in the injection pump cold idle controls. This is not going to be easy for a newby because the throttle linkage and injection pump warmup process are subtle and don't look at all familiar or similar to any other motor. You can easily determine if it is too little or too much gas by disconnecting the pump link and giving it more or less gas.
Its good that is starts and runs with your foot on the gas. That tells me several things are good: spark, compression, Gas on start, fuel pump, and the initial start function on the injection pump. I suspect the fuel is not rich enough once the cold start solenoid turns off, and the cold start solenoid is working to start the motor. It stays on for a few seconds. Its on the far side on the intake manifold with a wire and a metal tube going to it.
So, the next step is why does it start but then need more gas? There is heated coolant piped to the warmup valve on top of the IP (injection pump) It is the metal cylinder with two hose connections and two pipes going in parallel to it. My guess is the thermo expansion bulb inside that cylinder is stuck in the hot motor position: extended. As it heats up, a copper ampule pushes a metal pin out of a rubber chamber, which pushes a lever in the ip that reduces the extra gas needed for the cold motor. When cold that ampule retracts the pin to enrich the fuel mixture. You may be familiar with a carburetor choke enriching the fuel mixture by reducing the air. Fuel injection enriches the mixture by increasing the gas. On cold start the manifold gets a spray of gas from the electric start valve and the thermo valve should be retracted causing the ip to give extra gas while the motor warms up. As the motor warms the ampule pushes the pin out, gradually decreasing the extra gas needed by the cold motor. Pretty slick?
It doesn't take too long for the motor to warm up to where it doesn't need the extra gas. Just a few minutes and the coolant starts warming up. First thing I would try is keeping it running until the motor temp is up. You can do that on the motor with the linkage and feel the heat warming that cylinder on the ip with your hand. It warms up pretty fast. It warms up to due to the coolant flowing through the two connections on it. One supplies coolant, the other feeds the coolant back to the motor.
If after warmed up the motor is ball park idling, you found the problem. You need to carefully remove the two flat head screws connecting the cylinder to the ip. Don't let it get too hot, the coolant will get pressurized and you'll have to wait for the cool down. Some warm coolant will be lost, not much. The copper ampule is inside the cylinder and available on line or the dealer. When replacing it make sure the cylinder is aligned up and down with equal tightening of the two screws. And get a good seal. the seal requires the screws to be pretty snug and they probabably have been xposed to the eliments for a long time. I think I had to use vice grips on a big screw driver to get mine out at about 100K miles on mine. It doesn't take that much tightening to to reseal.
There is much help in the W113 forums on calibrating, correctly adjusting, the throttle linkage. Hopefully it is just the ampule, they don't last for ever and they usually fail in the extended position (not retracted to give extra fuel).
Good luck,
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