TeleflexGFI was well known in North America for the systems it provided domestic OEM car manufacturers (Ford and General Motors) for their OEM GFI (Gaseous Fuel Injection) dual fuel systems. These systems were not a success (some might say a dismal failure) and were the reason that the domestic OEMs completely dropped their propane vehicles. It has been reported that this is likely the reason that Ford dropped the LPG program, as it was the single highest warranty and customer dissatisfaction program Ford ever undertook!
The TeleflexGFI systems were used on such vehicles as the Ford F150 pickup truck and probably worked extremely well when it was new. Ford integrated the TeleflexGFI system with their OBD II computer system and the Ford computer was flashed to communicate with the GFI Compuvalve (integrated computer and metering valve). Much of the problems with these TeleflexGFI systems had to do with the failure of the key system components. Notably, the Compuvalve and the GFI vaporizer were problematic and expensive to repair. There were generally two leakage areas with the GFI vaporizers. These vaporizers would either leak at the gasket between the vaporizer's two halves or at the first pressure reduction piston seat. To make matters worse, LPG system failures often resulted in a complete engine shut-down and an expensive tow back to a Ford dealership for repair.
Normally, the system starts either on gasoline or on propane. However, there is no way to switch to propane operation on-the-fly once the engine is running on gasoline. This interlock was intended to prevent backfires during switching such as in the case when drivers want to compare propane and gasoline power during uphill, full throttle acceleration. Such switching in the large plenum Ford intake manifold can easily result in an explosive failure.
The system was designed to minimize backfire failures by switching to back to gasoline operation under high loads. Under high loads with a cold engine, propane pressure in the vaporizer can drop and the TeleflexGFI computer is programmed to switch back to gas a predetermined vaporizer pressure set-point. Once back on gasoline operation, the only way to get back to propane operation is to shut down the engine and restart in propane mode.
In addition, to protect catalytic converter from a lean fuel mixture, the TeleflexGFI system is also designed to switch back to gasoline operation when the LPG tank reaches approximately 3 gallons. The Compuvalve estimated the fuel volume by reading the LPG tank sender voltage. If the engine was running in propane mode prior to refuelling, the Compuvalve required the engine to be restarted in propane mode. The obvious problem with this strategy is that a tank sender failure prevented the engine from being restarted in gasoline mode. Sometimes the Compuvalve would fail which would then prevent fuel mode switching or cause a premature switch-over.
The Compuvalve is a proprietary item and is priced accordingly. It is pretty much impossible to replace this part with one from another manufacturer because the Compuvalve is so integrated with PCM. The alternative to repairing the Teleflex GFI System is to completely replace it with another manufacturer's system (while keeping the LPG fuel tank and the fuel lines) but this means reflashing the PCM to gasoline-only operation. See CNG Forum: Bi-fuel Contours