Twice I have had this on startup. One cylinder (was #4 and then #2) showed zero EGT for maybe 5-10 seconds. The engine accordingly vibrated quite a bit.
It looks like a blocked injector, but what would cause that and then get unblocked? There is a very fine fuel filter, then there is another one at the fuel servo inlet.
My plan is to get a new fuel distributor, which is quick and easy and not expensive. I believe this has spring-loaded valves which feed a constant pressure to each injector. If these are getting stuck, that would do it.
Peter wrote:
The engine accordingly vibrated quite a bit.
Maybe not very related, but at ULPower in Belgium they had an engine we could “play” with. Removing one injector was hardly noticeable regarding vibrations or sound at idle, and this was a 4 cylinder engine. You still have the full compression stroke and partly the combustion stroke. Increasing the power will of course create much more vibrations. I would think a stuck valve would cause much more vibrations than loss of an injector.
Presumably a valve can’t be stuck shut as that would bend something. If a valve was stuck open, would you get any combustion at all?
All PA31 TIO540s start “one cylinder at a time.” I have flown tens of them and they are all like that.
Peter wrote:
Presumably a valve can’t be stuck shut as that would bend something. If a valve was stuck open, would you get any combustion at all?
An exhaust valve stuck open will result in that cylinder not running, and a smaller loss of power than some other non-combustion event as there will be 0 compression.
An intake valve stuck open (on many engines) will cause the engine to stop completely.
The funny thing is that I have not noticed this previously, in 17 years of owning this plane.
Incidentally, why does a stuck-only intake valve stop the engine?
The open intake valve will allow the piston in that cylinder to ruin the mixture distribution going to the other cylinders as it is allowed to freely suck and blow into the intake manifold past the stuck open valve (certainly on a typical carburetted engine, where the carb is attached to an inlet manifold that goes to all the cylinders). It happened to me in my Cessna 140 many years ago – it was like the fuel had been turned off – no rough running, just an engine that suddenly stopped.
Does anyone else get this on startup?
