More test results are needed to make a diagnosis, but I can get you started with some things to consider. An elusive cause of intermittent stalling is a collapsing or plugged pick-up screen inside the gas tank. That typically causes most problems when the largest volume of fuel is being pumped, which is during coasting. To verify that, connect a fuel pressure gauge, then watch what happens to pressure when you start coasting. Fuel pressure should drop a little, as in five pounds, but if it drops real low, suspect that pick-up screen.
Check if your transmission uses a vacuum modulator valve. Those are typically screwed into the right rear of the transmission and have a vacuum hose attached. If the diaphragm in them starts to leak, it will not respond correctly to engine load, so the shift points will be wrong. The transmission fluid will leak into the vacuum hose, get sucked into the engine, and come out the exhaust as black smoke. An additional symptom is that fluid will deteriorate the rubber plugs that cap off unused vacuum ports on the "vacuum tree" on the firewall. You will have a high idle speed problem if one of those mushy caps falls off.
There are two ways to find the oil leak. The first is to connect a smoke machine and inject the smoke into the oil dip stick tube, then watch where it sneaks out. This works for leaks in places where the oil is not under pressure, like the valve cover and oil pan. The smoke will not make it to passages where the oil is under pressure when the engine is running.
You can also wash the area, then add a small bottle of dark purple dye to the oil. Check a day later with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. Auto parts stores will have the dye, and those that rent or borrow tools should have a black light.
Friday, June 23rd, 2017 AT 5:17 PM