You didn't state how many hours are on the engine and sometimes that might make a difference. So let's cover the basics.
First the G3600 A3 must be tuned correctly. Here are the basics; the complete text is in Service Manual (Form RENR5908-11) Sys Ops, Testing and Adjusting, beginning on page 79, using an exhaust analyzer. The target tuning for a .7 g NOx engine is 70 ppm; for a .5 g NOx engine, the tuning target it 50 ppm. Only version 11 of this SM has the correct procedure; all earlier versions are incorrect. If the engine is not tuned correctly, it will be difficult to keep the performance consistent. If the load is high and the engine speed becomes unstable, it is common for the engine to go down because of detonation.
Considering the engine is properly tuned, the next item to consider is the governor gains (gain, stability and compensation). These parameter blocks are found in the configuration screen using ET and a communication adapter connected to the service connection on one of the junction boxes.
The governor is usually tuned somewhat sluggish when used in a gas compression application. I usually start with these governor settings: gain-45, stability-40 and compensation 45. This is a good place to start; these settings might have to be tweaked to find just the right setiings for best engine performance (stability and response to load changes). The default settings of 100 for all three settings for both the wastegate and the choke usually work. If the engine is loaded and has a slight rpm swing and tuning the governor gains does not take the slow speed swing out, you might have to take the wastegate settings a bit lower (maybe down in the 80s).
If the engine has a lot of hours on it, you might consider that the air side of the aftercooler is plugged. This can occur on a high hour engines. Your symptoms are the kind of action you might see with a plugged aftercooler. Along with this, you also might see the wastegate position a bit lower; it might even be down close to 25 or 20 when the normal wastegate position is near 40-45 under high load.
You might also have some misfire and this could cause the engine speed upset if the load is at 100% or higher. If you have a high load and a cylinder misfires, the other cylinders have to pick up the load of the cylinder that misfired. I would also expect to see the code E242-Overload if the misfire takes the engine over 110% horsepower. You might or might not see a code for the misfire; this would depend on the type,cause, and duration of misfire. This probably would not affect the cylinder port temperatures.
More rare is that the engine might be getting a slug of liquid hydrocarbon fuel (high btu). This could upset the engine performance but this is way down on the list of possible causes.
These are the areas that I would check. It sounds like the engine needs correct tuning first then check the other items.
If you don't have this latest SM, I can email the tuning section to you. Just give me an email address; here is mine hunt_al@cat.com
Good hunting!
Al Hunt
United States / Canada
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