Gp40-2's with F-O-S have no comparison with GE's and the same problem. EMD's use a unitized injector where pressurization, metering, and injection are all performed within the same housing. GE's use a two piece per cylinder method. Fuel is pumped around 70 psi through headers that run along each bank of the engine. The headers bolt to a "pump" on each cylinder. The pump is actuated by a push rod off of each cylinder. From the top of the pump is a high pressure fuel line that carries I would like to say around 10,000 psi (depends on the locomotive and whether or not it has EFI). The high pressure fuel line is connected to a "nozzle" atop each cylinder. The nozzle converts the pressure and velocity of the fuel and atomizes it through atip with multiple fine holes drilled on the bottom of it. I know GE messed around with increasing the high pressure on the output of the pump with some of the Dash 8's, especially the early EFI models, and experienced a problem with the tips of the nozzles breaking off - which ultimately lead to a fire out the stack situation. Thus would result in loading up the exhaust and enventually coming out as a fire ball. Generally speaking from my experience with them, fire out the stack on a GE could be caused by an array of issues. Most notable is if there's a problem with a fuel pump. They can wear out. Sometimes it could be a camshaft or camroller problem, I have seen them jammed up before. Sometimes it's the turbo. If the turbo has problems spinning, especially on a GE, an imbalance between air sucked in, air forced in and an excessive back pressure on the exhaust trying to spin it can often result in FOS. Plugged air filters on rare occasion can also be tied in with the same problem. Mostly FOS becomes evident particularly when the throttle is advanced quickly and heavily. As noted above any added resistance forces the engine to suck harder and compensates with fuel. GE turbos get very hot sometimes and creates the perfect environment for FOS. EMD's on the other hand rarely experience fire out the stack. The few cases I have dealt with usually relate to a bad turbo or a severe problem with fuel. I have witnessed some EMD's with FOS, but again the turbo or a really bad injector was the culprit. EMD turbos can and will get plugged with carbon, and the imbalance can cause a phen. known as woofing but rarely have I ever seen it lead to any flames, just alot of smoke and really unusual noise.