I have recently acquired a 92 Astro with a 4.3 v6 and rear wheel drive. I have owned several of these great vans and all have been throttle body up until this point. Much to my surprise I discovered this is a multi-port application and is not throttle body. Lots of life left in this old vehicle I have registered the vehicle and am driving it daily. Most recently I notice the van idles worse and worse each day and I do know it sat for a couple of months unused. When idling the fuel mixture is very strong and the exhaust it dark and sometimes black like there's lots of fuel getting where it doesn't belong.The former owner couldn't describe to me what it was doing only that there was an issue. It acts like a bad map sensor but the test I had done today by a mechanic tells me he suspects the fuel regulator in the plenum. How do I access this unit and what am I looking for? Often have to hold the gas pedal down partway to restart it after running and complete warm up. Started great and went up on fast idle this morning in 30 degree weather. Idles rough and poorly and is drinking tons of fuel. How do I save the old girl and how much will it cost me? Have been pulling wrenches most of my life have never come across this application before. Thanks very kindly in advance. Is it the fuel regulator in the plenum?
The 4.3-liter in a 1992 Astro van is equipped with a Central Multiport Fuel Injector (CMFI) system. And it's had a lot of problems. It's non-serviceable (fuel regulator built in), and uses tubes from the injectors leading to poppet valves at each cylinder. Often times the poppet valves stick open or shut and cause symptoms such as hard start, no start, and rough idle. There is a cleaning procedure which requires special tools that can repair the stuck poppet valves, but not always. That's why GM recommends replacing the entire unit if cleaning doesn't work, or if the problem comes back. They also recommend replacing the Central Multiport Fuel Injector (CMFI) system with a conversion kit which uses a more conventional multiport fuel injection system (no poppet valves). With that said, the CMFI is a common failure, but you really need to attach a fuel pressure gauge (test pressure, pressure drop and fuel quality) and a scan tool (trouble codes and data) to accurately determine the cause of your problem. It could be something related to the fuel pump, ignition misfire and so on.