Cherokee Six, 32-300 1969. Lycoming engine is fuel injected with 450 SMOH. Cold starts are easy: 1/2" throttle, full rich, fuel pump on and hit starter after fuel flow starts. Runs great once running. Hot starts are hit or miss. If it sits over an hour it may start but if I miss it it has to sit for at least another hour till I try again or forget it. I've tried 1/2" throttle, full lean with and without fuel pump; full throttle, full lean with and without fuel pump and all combinations I can think of. Most of the time it spins without any cough or catch. Due for 50 hour oil change and will ask that plugs and magnetos are checked. I'm afraid to go anywhere for fear of being stranded for hours.
The issue is undoubtedly vapor lock. In the fuel injected Lyc 540, the fuel injection plumbing is on the top of the engine which is the cold side of the engine when you are flying but when parked, heat rises! The following procedure runs cooler fuel through the plumbing while flooding the engine, then the flooded start procedure is necessary.
First, check your POH for the hot start procedure for your plane. If not there, try this as it is for a very similar airplane:
Hot Starts on the Saratoga PA-32-300:
Intentionally flood the engine. This runs cool fuel through the plumbing and "breaks" the vapor lock.
- a) Full rich
- b) Wide open throttle
- c) Fuel pump on, watch fuel flow gauge
- d) When gauge registers flow, wait 3-5 seconds then red knob to ICO and pump off.
Crank engine with red knob still at ICO and with throttle wide open at first. Gradually close throttle (at a rate that will take you about 10 seconds to close the throttle) and it should start up at some point.
When engine catches, do several things more or less simultaneously:
- a) release ignition key
- b) throttle to idle to avoid over-revving
- c) mixture full rich.
No need to run the fuel pump as @Skip Miller says. (though it may say that in the Saratoga manual)
I have done the following with success for hot starts on a IO-320, IO-360, and IO-540.
- Throttle Full Open. (Push in or forward)
- Mixture Full Close. (Pull out or back)
- Crank engine.
- Once it starts firing, put the mixture back in and pull the throttle back to idle.
Happy engine starts!
Also have the injectors checked. The symptoms you describe can occur when one of the injectors is not closing completely, causing flooding or an overly rich mixture.