I have a 1990 Gehl 6635 skidsteer. 2400 hours on the machine and I have owned it since 1200 hours. The engine has been very reliable, but it has recently developed a miss. Ironically, this is my second 6635 and the first one developed the same miss at the same hours. I never got that machine diagnosed as it burned. The miss first appears slightly above idle and will continue through the mid range. It will go away at full throttle or idle. It sounds like one cylinder is laying down and the machine will puff black smoke. The black smoke suggests to me the cylinder is getting fuel, but isn't burning it. I tend to think this is not an engine health issue.
Here is a video of the issue. Notice that it comes and goes based on rpm:
I started by cleaning the low pressure pump screen. The screen was totally blocked. I then changed the fuel filter. To help protect the screen, I added an automotive style in line filter before the low pressure pump. I found the pump was not drawing the air out of the filter so I elected to replace the pump. This work had no effect on the engine running condition.
I then bought a cheap ($100 for a set of 4) replacement injectors and installed them. Not much of an effect on the engine running. I currently have the OE deutz injectors off to a shop for rebuild, but I'm doubtful this will help.
Looking for thoughts on what to check next?
Here is a video of the issue. Notice that it comes and goes based on rpm:
I started by cleaning the low pressure pump screen. The screen was totally blocked. I then changed the fuel filter. To help protect the screen, I added an automotive style in line filter before the low pressure pump. I found the pump was not drawing the air out of the filter so I elected to replace the pump. This work had no effect on the engine running condition.
I then bought a cheap ($100 for a set of 4) replacement injectors and installed them. Not much of an effect on the engine running. I currently have the OE deutz injectors off to a shop for rebuild, but I'm doubtful this will help.
Looking for thoughts on what to check next?