Ask Paul: One and done

Question for Paul McBride, the General Aviation News engines expert: I’ve recently been experiencing a starting problem with my Mooney 201. The first start of the day is typical. However, after the first flight, it most likely will not fire.

I’ve noticed during the attempts to start it the fuel pressure gauge fluctuates erratically.

I’ve learned if I wait an hour or so, it may start. I crack the throttle, I push in the mixture control, have the electric fuel pump run for a few seconds, then push in the starter, but it won’t fire. My suspicion is the mechanical fuel pump is failing.

If I do get it to fire, it may run for few seconds, but then stop, which I believe is because the fuel pump isn’t supplying fuel flow. I have been able to turn on the electrical fuel during short runs and it has kept running.

Your comments and suggestions will be greatly appreciated.

Thank you.

Jim Waymire

Paul’s Answer: Jim, from the information you provided I think I can offer you some ideas to consider in order to solve your starting problem.

There are many possible causes for what you’re experiencing, but I have a couple of questions for you.

First, if you are operating in a hot environment, it may be that the outside air temperature and the heat under the cowl is causing the fuel to boil, which may be the reason behind the second start causing the problem.

Have you noticed the engine oil turning black in a short number of operating hours?

In some instances, if the fuel pump diaphragm somehow gets a tiny pinhole in it, it causes the fuel to dilute the engine oil, causing it to turn black in a short period of time. It may also cause the fluctuation in fuel pressure you’re seeing.

Just as an aside, I hope the spark plugs are in good condition and the magneto to engine timing is correct.

Once you’ve determined the answer to these questions we’ll move on to more troubleshooting.

As you might imagine, if the OAT is high after the first flight, the temperature under the engine cowl can be quite hot. It’s not unusual for the fuel to boil under these types of conditions, and the result is an inconsistent flow of fuel to the engine.

My suggestion is that you refer to your Airframe Operator’s Manual for the recommendations of conducting a “hot start” procedure.

Failing that, I’d suggest you try to start the engine by turning on the boost pump and putting the mixture control briefly in the full rich position and cracking the throttle. Once the engine fires, slowly bring the mixture control up to the full rich position.

With the boost pump on we are making sure we’re getting a solid flow of fuel, which should purge the engine fuel system of any vapor that may have been caused by the high temperatures in the engine compartment.

All of this sounds simple, but I’m betting that what we’re fighting here is an old-fashion case of not having a good solid supply of fuel under hot conditions.