I own a 1995 GMC Vandura six cylinder, automatic, and rear wheel drive. I think that's all you need to know about it to help me out. I bought it used, and about five months later the CPI unit went "out" according to the repair shop. It cost me about $700 to replace it. Within three months it happened again. The engine had a rough idle, was hard to start, and this time they replaced the CPI unit for free under the repair shop warranty. Now the CPI unit went out for the third time and cost me $800.
I contacted GMC and they said there was no program or recall having to do with the CPI. Do these parts go bad that often? What can cause this kind of problem? I think three times in thirteen months is a bit excessive!
Let's start by explaining exactly what a CPI unit is. CPI stands for "Central Port Injection", as opposed to TBI (Throttle Body Injection), or PFI (Port Fuel Injection). The CPI unit is an injector assembly consisting of a fuel meter body, a fuel pressure regulator, fuel injector, and six poppet nozzles at the end of six fuel tubes.
The theory behind this system is to keep the injector on top of the engine away from the higher temperatures closer to the cylinder heads. The fuel travels from the injector through the fuel tubes to the poppet nozzles, located directly at the intake ports. The poppet nozzles are similar to Diesel applications, and can handle high temperatures and adverse conditions more effectively than an electronic fuel injector.
Let's get back to your problem. The CPI unit is a complete non-serviceable assembly, which means you have to buy the whole thing no matter what part fails. When this system first came out there were a number of cases of poppet nozzle failures causing performance and hard start conditions, but there were much fewer instances coming into the 1995 model year. The fact that you have gone through three units in thirteen months has me suspecting fuel contamination.
After the failure of the second unit the fuel should have been examined. If contamination is found, the proper way to deal with it is dropping the fuel tank and having it professionally cleaned, thoroughly flush all fuel lines and hoses, and replace all non-salvageable components such as injectors, fuel pump etc.
If gas is clean, there is also a conversion kit to bring the system back to standard port injection.