Here is my posting [1987 Truck "choke" sticks on], that may help you. When I found that the water temp sending unit was not fully connected, and then reconnected it, it made a HUGE difference. My truck is an automatic, and would puff tons of black smoke (running rich) out the tailpipe. I would also pop it out of gear, rev the engine, it ran even richer for a second, (lots of black smoke), then smoothed out, seemed like it would fix the problem for about two or three seconds, then run super rich again. Anyway, my temperature sending unit connection was the problem.
My original posting:
My truck is a 1987 Nissan, 2.4 liter with Throttle Body Injection. At completely random times: rolling or not rolling, high or low engine rpm, engine hot or cold, ambient air temperature hot or cold, etc, the engine goes into "choke" mode, runs very rich, black smoke coming out of tailpipe. Of course, I know there is no choke plate, but rather the injector pulse-width is being told to go rich via the computer. The engine often cycles in & out of "choke" mode instantly, that is, electrically, like someone is opening & closing an electrical switch. I have not checked the fuel pump pressure, but did replace the fuel filter (was pretty clogged).
Update: January 26, 2010
I was about to put a stick of dynamite under the truck because I was so frustrated by its super rich mixture, when I decided to re-check all of the electrical connectors. I found the connector going to what I believe is the water temperature sending unit, (hiding below the intake mainfold area, pretty hard to see) had pulled out just a smidge. I must have jostled it when I was changing the oil. I clicked it back into place, and the truck runs 3000% better. It still will run very, very rich on its intial start-up in the morning, for about the first mile or so, but here in East Texas, winters are really mild, so once it has a little engine temperature, and the water temperature circuit shows some heat, it comes out of "choke" mode, and runs great. I plan to also get that warm-up circuit working, where intake air is pulled across the exhaust manifold, and up the the metal tube that goes to the air cleaner snorkle tube. (The metal tube, the sensor, and the vacuum lines that operate that warm-up mode diaphram are all missing).
Tuesday, January 26th, 2010 AT 9:23 AM