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Re: Will an EMD 2 stroke run away like a Detroit?
Author: Dr Zarkoff
Date: 02-03-2012 - 23:05
>Which brings up the question - does a newer GE or EMD have runaway problems if the EFI fails? I talking about a metering valve jamming open and constantly dumping fuel into a cylinder.
EMD engines with EFI still use a unit injector which is very similar to the ones used with non-EFI. With both, the plunger is driven by a camshaft to produce injection pressures. With EFI, the layshaft with rack and pinion which rotates the intector plunger to vary the amount of fuel injected is done away with, the function instead being controled by a solenoid valve connected to the injection computer. GE (Cooper-Bessemer) uses camshaft-driven, individual Bosch jerk-pumps on each cylinder assembly (the jerk-pump itself looks almost identical to those used on Alco 251 engines, only there is no governor and layshaft control). With EFI GE engines, the opening and closing of these is controlled the same way the EMD unit injector is. The computer measures RPMs with a sensor which which watches for a magnet attached to the "flywheel". It counts the number of revolutions per unit of time and arranges all engine events in correlation to this signal. It's been a while, but I think there may be a second magnet and senor which measures crankshaft angularity.
Most of the time when there are problems with an EFI system, the engine plain old doesn't run, and the addition of computer control adds a lot of other complications. Lube oil seeping into the electrical connectors on the sensors and various control cables is a big one, and a GE will shut down and refuse to start with no error message appearing anywhere if one paritcular connector gets full of oil. There aren't governors and layshafts with EFI, nor are there mechanical OS tips. Still, lube oil leaking into an EMD airbox will cause a runaway, for the simple reason that the lube oil will act as a completely unregulated supply of fuel. The same is true with any of the other sources of "lube oil fuel" mentioned in this thread.
Neither EMD nor GE use a distributing valve scheme like that found in diesel pick-up trucks. With EMD (and those 71 series Detroits), injection pressures are contained within the injector. With GE (and Alcos) there is a separate high pressure pump on each cylinder assembly. Both are cam driven. "Stuck injectors", actually nozzle valves with weak or broken springs, cause a lot of exhaust smoke, even raw diesel fuel coming out the stack, at least with locomotive scale engines, not sure about automotive ones.
EMD engines with EFI still use a unit injector which is very similar to the ones used with non-EFI. With both, the plunger is driven by a camshaft to produce injection pressures. With EFI, the layshaft with rack and pinion which rotates the intector plunger to vary the amount of fuel injected is done away with, the function instead being controled by a solenoid valve connected to the injection computer. GE (Cooper-Bessemer) uses camshaft-driven, individual Bosch jerk-pumps on each cylinder assembly (the jerk-pump itself looks almost identical to those used on Alco 251 engines, only there is no governor and layshaft control). With EFI GE engines, the opening and closing of these is controlled the same way the EMD unit injector is. The computer measures RPMs with a sensor which which watches for a magnet attached to the "flywheel". It counts the number of revolutions per unit of time and arranges all engine events in correlation to this signal. It's been a while, but I think there may be a second magnet and senor which measures crankshaft angularity.
Most of the time when there are problems with an EFI system, the engine plain old doesn't run, and the addition of computer control adds a lot of other complications. Lube oil seeping into the electrical connectors on the sensors and various control cables is a big one, and a GE will shut down and refuse to start with no error message appearing anywhere if one paritcular connector gets full of oil. There aren't governors and layshafts with EFI, nor are there mechanical OS tips. Still, lube oil leaking into an EMD airbox will cause a runaway, for the simple reason that the lube oil will act as a completely unregulated supply of fuel. The same is true with any of the other sources of "lube oil fuel" mentioned in this thread.
Neither EMD nor GE use a distributing valve scheme like that found in diesel pick-up trucks. With EMD (and those 71 series Detroits), injection pressures are contained within the injector. With GE (and Alcos) there is a separate high pressure pump on each cylinder assembly. Both are cam driven. "Stuck injectors", actually nozzle valves with weak or broken springs, cause a lot of exhaust smoke, even raw diesel fuel coming out the stack, at least with locomotive scale engines, not sure about automotive ones.
