My Generator Starts When Cold, But Not When Hot!


We live in a crazy world! I thought warm diesel engines should start easier than cold ones?! “My Generator Starts When Cold, But Not When Hot!” That is a true statement and remains true. The problem might not lie in the engine itself or the injectors or the injection pump or anything related to the engine specifically. It could lie in a supporting system.

Fuel, air, compression…the holy trinity of old-school diesels. Never forget it! Air is easy to check, so do it first. Make sure you have a clean filter.

Compression is easy to. Next time you get the generator running, crack each of your injection lines, just BEFORE they attach to each injector. If you have good compression and a good injector, every time you do this, the engine should noticeably loose some oomph and you should hear an audible difference. Do this for every injector. If you do this and you hear no change, chances are the injector could be failing or the compression in that cylinder could be terrible (e.g. broken ring, broken rod, etc.). Hopefully it is just a bad injector. If you keep a spare injector on hand, you can swap out injectors to test and try the same procedure. If that doesn’t work, you’re looking at a rebuild of some sort for at least that cylinder…

Now that compression and air have been ruled out (hopefully)…we are left with the usual suspect…fuel…So why would it start cold, but not hot? Does not seem intuitive. The easiest thing to test is to ensure a clean fuel system leading up to the injection pump. Injection pumps rarely work intermittently…They either work or don’t.  If they don’t they could be seized.  But in our scenario, the engine does work, when cold! So we know the pump is most likely good and the injectors are good enough.

On the MEP002A and MEP003A and on many diesel generators, there are lift pumps. On these units, they are facet fuel pumps 24v.  On these units the government installed 3 of them! Pretty nice as one is for aux fuel only. The other two are in series and only one must work to operate. Ensure:

  • Fuel tank is clean
  • ALL fuel lines have been blown out with compressed air
  • ALL filters are clean

Now check each of the two in-series 24v fuel pumps (also check the aux one eventually)…You can twist the bottom off of each one and check for crud build-up. There is a gasket and screen in each of these acting as a crude filter. If these units burned crude oil with thinner, there could be varnish and crud build-up that blocks these screens. If you need new screens for the MEP002A or MEP003A fuel pumps go here. If you’re lucky, you’ll see crud and hopefully be on your way to a successful and easy repair.  Tell us what you think and how things went. Any helpful hints can help others.

3 thoughts on “My Generator Starts When Cold, But Not When Hot!

  1. Keith J says:

    Also inspect check valves on the pumps. There are two and both must work freely. Best solvent is Diesel Mechanic in a Bottle. It rapidly dissolves gum.

  2. Alfredo says:

    I am 100% new to this…bought my first 803a…and it wont start when its hot. Looks like I have some investigating to do.

    I would add that yesterday it was running with a steady up and down in rpm…voltage was low and Hz were up and down with the RPM. This morning everything was running perfectly…and this afternoon…back to the same erratic behavior

  3. gmg says:

    Some of you may want to check the “check valve” in the fuel line just after the 3 filters and before the pump as well. This could stick open or closed do to vacuum pressure. But check your facet screens first!

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