Vintage iron
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I have been working on military trucks full time for a few years now. I have found some of the same issues with the fuel system on M923 and M923A1. Customers will bring me a truck that has hard starting or rough idle or weak throttle response.
First thing I do is change the fuel filter. while i have it out I clean the filter housing and the petcocks. ALWAYS use the new gaskets that come with your filter. Fill filter housing with fresh diesel. I put the filter back on but don't use the primer pump. I instead, take a vent line off. I have made a air line that I run through a pressure regulator at 5 PSI. I pressurize the system. then crack open a line at the pump till fuel comes out. It is amazing how many times this solves the problems. so many times the filter is not tight enough or the seals are not sealing properly. everything needs to be clean, clean, clean.
Second, I always put ATF in the tank and fuel system treatment. A lot of issues come from bad fuel and gummed up fuel system. The ATF lubricates the pump and injectors. The Fuel system treatment bring up the Cetane and cuts the crud. This second part is always a good idea.
third, I check all the hoses and lines for abrasion or ares that could produce holes. Recently I have found a new air leak spot. THE PRIMER PUMP! I disconnect them. put a plug in the fuel line. but I cap the pump and zip tie the hose up, just in case you need it in a pinch. the primer uses a plastic hose. The hose should have a insert to keep the ferrule from collapsing it. So the there will always be a leak.
these are just a few of the things I found. I hope these help.
First thing I do is change the fuel filter. while i have it out I clean the filter housing and the petcocks. ALWAYS use the new gaskets that come with your filter. Fill filter housing with fresh diesel. I put the filter back on but don't use the primer pump. I instead, take a vent line off. I have made a air line that I run through a pressure regulator at 5 PSI. I pressurize the system. then crack open a line at the pump till fuel comes out. It is amazing how many times this solves the problems. so many times the filter is not tight enough or the seals are not sealing properly. everything needs to be clean, clean, clean.
Second, I always put ATF in the tank and fuel system treatment. A lot of issues come from bad fuel and gummed up fuel system. The ATF lubricates the pump and injectors. The Fuel system treatment bring up the Cetane and cuts the crud. This second part is always a good idea.
third, I check all the hoses and lines for abrasion or ares that could produce holes. Recently I have found a new air leak spot. THE PRIMER PUMP! I disconnect them. put a plug in the fuel line. but I cap the pump and zip tie the hose up, just in case you need it in a pinch. the primer uses a plastic hose. The hose should have a insert to keep the ferrule from collapsing it. So the there will always be a leak.
these are just a few of the things I found. I hope these help.