Q: Dear Paul, could you help me solve a problem I have in the #4 cylinder of an IO-540-K1K5 engine, which is mounted on a Pillan T-35 aircraft of the Chilean Air Force?
We already checked the draft of the magnets and their fall. These are OK.
The other cylinders are working well. We checked the fuel injectors and the fuel distributor and they are also OK. The baffles and fairings are also OK, as well as the signals to the instruments.
Could you tell me something else about this single-cylinder isolated fault?
Mario Rodríguez Yáñez, Santiago-Chile
A: Mario, your question could have several answers, but I’ll begin with some simple troubleshooting that I would do if I were there with you.
Since I have been to the international airshow FIDAE several times in Santiago, I am familiar with the Pillian T-35 aircraft.
I’d like to begin by asking you a question: Does this engine have a 6 probe cylinder head temperature gauge system or just a single probe system? If it has a CHT probe in each cylinder, my suggestion would be to swap the #4 probe with either the #2 or #6 cylinder to determine if the high temperature remains with the probe or with the #4 cylinder.
I also would like you to check the manifold pressure at engine idle (650 to 700 RPM). It should be 10 or 11 inches of MAP. If the manifold pressure is higher, like 14 or 15 inches, this may indicate an intake leak on the #4 cylinder, causing that cylinder to run lean, resulting in a higher cylinder head temperature.
Also be certain to inspect the connection between the intake pipe and the oil sump for clamp tightness, etc.
That #4 cylinder may also have a partially blocked nozzle.
If you haven’t flow checked the fuel nozzles in each cylinder, that would be my next recommendation. This is a simple procedure that requires removing the fuel lines attached to the nozzles. Then remove each nozzle, being careful to keep both pieces together with each nozzle. Reconnect the fuel line to its respective nozzle and tighten as required.
Locate six small containers of equal size and put the nozzle just inside to collect the fuel.
At this point you will want to turn the aircraft master switch to the on position and turn on the fuel boost pump. Open both the throttle and mixture to full open for approximately 30 seconds. Closely observe the flow pattern from each nozzle, which should be a straight stream of fuel from each nozzle.
If you notice any nozzle having an erratic pattern other than a straight stream, I would close the throttle and mixture controls and turn off the boost pump. If all is well, there should be an equal amount of fuel in each container. If not, remove the nozzle in question and clean that nozzle in accordance with Lycoming Service Instruction 1275C.
You must remember that the nozzle has two pieces and these may be separated, but never mix them with any other nozzles because they are a precision matched pair.
You may also may want to clean the other five nozzles at this time.
Once the suspect nozzle has been cleaned, I’d suggest holding it between your thumb and index finger, then hold it up to a light. While rolling the nozzle between your thumb and index finger, closely look through the center hole in the nozzle for any foreign material that may fall across the fuel hole, possibly something that was caught between the fuel and air side of the nozzle.
If no obstructions are observed, I would then return the nozzles to the engine and reconnect them to each fuel line and rerun the flow check as previously done.
I hope what I have suggested here will allow you to troubleshoot the engine and locate the problem and replace the bad nozzle, if that is the cause of the problem.
I am confident you will discover what is causing the problem and once the situation is repaired I highly recommend you celebrate by consuming several Pisco Sours, as long as you enjoy one for me.