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Junior Member
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Discussion Starter #1
Hello everyone,

Need a bit of advice on troubleshooting a fuel system problem on a 3116 Cat Engine in a 1996 Chevy 8500 (270 hp). I've been chasing a fuel system problem for a while and would like validation on my next hypothesis.

I apologize for the length of this post in advance!

Full story.

Chapter 1.

The engine was running a bit rough and was smoking badly so i took it to a local repair shop to have it looked at. They diagnosed two failed injectors (5&6). They replaced the injectors and attempted to set the valve lash. When setting the valves they said that the intake on Number 6 "kept coming up". They wanted to pull the head and do a valve job. Knowing this engine only had a 100000 miles on it I cried foul and had them put it together enough to get it home.

Chapter 2.
Being mechanically inclined and not a stranger to the world of diesels I ordered the repair manuals and verified their work. After pinning the engine correctly I determined that they were trying to set the valve lash 360 degrees out. I was able to correctly set the valves to spec. Because I wanted to ensure accuracy I also purchased the correct tooling and set the injector timing and synchronization.

Chapter 3.

The engine is running much better. But it is still puffing white smoke after its warmed up and I rev it up. No smoke at idle when it's warmed up. This smoke smells like unburnt fuel.). To continue troubleshooting this I pulled the fuel lines and inspected them. I also installed clear tubing on the fuel supply and return lines. I ran the lines into a bucket of clean fuel. I noticed two curious things. A). The return line has some small bubbles in it. B). The remaining fuel in the bucket darkened when it was run for a while.

My current hypothesis is improper seating of the injectors on the cups. My plan is to remove the valve cover and test each injector individually while running by pushing in on the fuel rod on each injector. Im going to look for the injector that causes extra bubbles. Am I going down the right path? Or should I be looking elsewhere? If I find the problem can I simply order the tools and reseat the injector?






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Junior Member
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40 Posts
I have not been around in a while and you are probably done. However if not those engines are bad to crack injector sleeves. Bubbles in the return line from the head is normally an indication of that if there are no bubbles in the fuel supply to the head. A local company had so much trouble with their fleet they bought the tools. Pulled the heads and did them all at the same time. It is possible to do just one with the head installed if you have the tooling and knowledge.
 
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