Good morning my dudes. Hope you are all having a great weekend. I’ve been having an issue with my 2007 5.9 where when I start the truck in the morning it fires right up and sounds normal. No smoke. The last couple months I’ve had an issue where after driving for just a few minutes MAYBE not even really warmed up yet when I turn off the truck and then turn it back on it cranks for 5 seconds before it pop fires. I have been giving it throttle during this time and thought I was assisting in it starting but I talked to a local diesel tech the other day and he informed me that NO the throttle doesn’t do anything until the truck has started. ( Is that true ? ) I’m guessing it is true because I stopped giving it throttle during hard starts and it fires up the same as it did when I was giving it throttle. Usually when the truck fires up I’ll get a puff of black smoke but other than that it never smokes EVEN under heavy throttle.



I’m sure there are a 1000 threads regarding this issue but I can’t find the exact issue. The tech said the engine sounded fine when started and there are no obvious codes but we didn’t hook it up to a scanner while I was there…. the guy is super busy and he took some time out to take a look.



Thank you for your expertise fellas

 

A friend of mine had that issue, and it was due to worn fuel injectors. The injectors flow a certain amount of fuel into return flow normally, but as they wear that volume can increase. There are some special fittings to separate the injector return flow from the CP3 and pressure relief, and a spec to measure volume with 1 minute of running.

If they flow too much, the CP3 has difficulty achieving the rail pressure needed to fire the injectors when at cranking RPM. I presume return flow must be higher when hot, because his problem was more pronounced when attempting hot start.

There is a block off cap to cap off one port on the common rail, remeasure the return flow, and do the math to see if the eliminated injector is flowing too much, and if the remaining injectors are flowing too much. If you then know that more than one injector is out of spec, I'd guess best to stop there and plan on doing the set.