Starting a hot Fuel Inj. engine

[Chadzat]

After doing a fair bit of searching on here and being told a number of different methods to try, I haven't come across a "works every time" method of starting hot fuel injected engines. I will be flying a Continental IO-470 Debonair and have been told by the owner to "tickle the fuel pump when it sounds like dying". Sounds very hit and miss to me!

Any helpful tips that people have discovered that work more often than not when starting a hot continental?

Cheers

[Erebus]

It's been a long time since I flew Bonanzas and Barons, but I remember their Continental IO-520s being much easier to start when hot than the comparable Lycomings on the Aztec.
Open the throttle just a little, select the mixture to Rich, turn the boost pump on and leave it on until the fuel flow stabilises on the fuel flowmeter, turn the boost pump off, select the mixture to Idle-cutoff. Now you can start the engine, and when it fires, smoothly advance the mixture to Rich. Works every time, whether the engine is hot or cold.
I think your IO-470 will start in a similar fashion.

[puff]

Lots of different techniques out there but this one has never failed me with IO-520s anyway. Mixture Idle Cut off, Throttles Fully open. HP fuel pump on for 30 seconds. Then straight away carry out the cold start procedure. Will get lots of cold fuel through the lines and i've never had a mis-start using said procedure.

I'm sure there will be other techniques, but this one seems less hit and miss.

[Desert Duck]

If all else fails - get a hold of the engine handbook and see what the manufacturer says.

[Richo]

Well said DD, as you would know about starting hot engines especially the IO540 (Lyc).

I am NO expert, but do have significant time flying both the Lycoming 540 and the Continental 520 engines, I don't mean to preach (especially to those who already know) but to have an understanding of the engine manufacturer will help you with your choice of starting techniques.

The two engines of choice for the 6-8 seat single have traditionally been the
Lycoming IO-540 (and its many variants TSIO etc) and the
Continental IO-520 also with a few mods and derivatives.

Lyc engines have the fuel injection nozzles in such a place that the fuel (vapour) is sprayed directly onto the back of the intake valve. When you prime you get lots of effective fuel (vapour) in the immediate area of the valve and at least one cylinder gets a good shot of fuel.
Therefore over priming floods the engine. When starting you need to take away a lot of the fuel (vapour and liquid) before the best mixture is obtained in the cylinders for the spark to be able to ignite it. In other words the engine seems to crank for a few seconds before it fires. Then reintroduce the fuel with the mixture control.
This is why you start in ICO (idle Cutoff) so no new fuel is introduced which will guarantee a flooded start.

This is also the preferred manufactures start method. ie With the Mixture rich for only a short (3 sec) prime, them Mixture ICO until the engine fires on start.

For a HOT start the engine should NOT be primed. Ie the fuel pump should only be run for a very short time (to pressurise the fuel lines) with the mixture in ICO (no fuel flows to the injectors) as the fuel vapour already present after the shutdown will be sufficient to get a start.

Continental 520 series engines have the injector further away from the intake valve. In this case fuel (vapour) tends to sit back from the valve. When cranking (low suction) only floating vapour in the intake can get into the cylinder and ignite. This is almost opposite to the Lyc engines and means you need lots of fuel to get the engine to fire. The continental engine need mixture rich and really decent prime to get a good start.

HOT starting the conti. engine is done the same as for a cold start but you do have a higher chance of a "Vapour Lock" occurring.
(Vapour locks occur in all of these type of engines, but the Cont. 520/470 seems to be the most common to see it)
Simply a vapour lock is caused when the warm (hot) engine creates a low density of air in the manifold, the suction in the cylinder has trouble moving this low density air containing fuel vapour into the cylinder, and the air that dose make it has a very low effective mixture.
The answer is to prime the engine a bit more, and as the manufacturer recommends you can use the primer during start to boost the fuel/air ratio to achieve a start.
Most Conti. engines exhibiting a vapour lock will start, then die (use up the available prime fuel) so you need to give it a good prime, and then when it starts to die (tickle it) until it is self sustaining.

CAUTION as over priming during start can and WILL cause induction fires (a fire in the induction manifold) or in the engine bay (as the over primed fuel leaks into the engine bay from the manifold drains).
This is why you should NEVER delay a start after fuel pump priming (Always Prime, Clear Prop and Start within a few seconds).

Having said ALL of the above, all engines are slightly individual and while many different methods DO work it is best to use the method given to you by the aircraft/engine manufacturer.

CHADZAT while this question gave me and others a good chance to dribble on for a few pages, the only real question to ask is "Where is the POH, mate"

Have fun the Debo is a very nice thing to fly.

Richo

[Chadzat]

Thanks Richo (and others) that information is invaluable and in-depth engine characteristics should be taught up to CPL.

POH- On closer inspection :O there is a note that says:

"If the engine is hot, place mixture control in IDLE CUT-OFF, switch auxiliary fuel pump to ON for 30 to 60 seconds, then OFF. Return mixture to full rich and continue with cold start procedure."

Might pay to read the notes in future :O

Being an (almost) newbie CPL these sorts of "informative posts" are invaluable to me as I am sure there are heaps of Ppruners out there that have a heap of this knowledge stored up. In particular the characteristics and facts that go beyond the POH wording.

Keep the discussion going!

Cheers

[bushy]

Somewhere in my office there is a very bent conrod, out of a C310 engine. This engine was primed before the starter was engaged, and the prop only turned about 15 degrees and stopped.
The engine was wrecked. Conrod, piston, crankshaft, crankcase-all unuseable.
One cylinder had been full of fuel.
This engine had a problem with the fuel control unit, but there was also a note in the POH saying not to prime unless the propeller was turning. This applies to Cessna 340's and some C310's.
Read the book!!!

[youngmic]

Your bosses tip of tickling the boost pump does have a basis in sound science.
As you probably know or do now from the previous threads. When a hot fuel injected engine sits it is often possible for the fuel contained within the 1/8 stainless steel fuel lines from the flow divider to the fuel injector nozzles to vapourise or boil off. You then have nothing but basically air in those lines.

Lycoming and TCM have somewhat different fuel metering systems and if you have the time, Aircraft Fuel Metering Systems by Aviation Maintenance Foundation Inc. is worth a read and explains the various systems well. You often find this range of publications in the various pilot shops and they are quite cheap. i digress.

The idea of selecting ICO (idle cut off) and full throttle and boost pump on, allows cooler fuel to be pumped into the body of the flow divider but it doesn't go to the injector lines due ICO being selected. From here it returns to the fuel tanks via the vapour vent line attached to the flow divider. The 60 seconds allows enough time for the cooler fuel to replace the small amount of fuel in the divider and remove some of the heat in the body of the divider.

So when you do finally introduce fuel to the injector lines (by coming out of ICO) it is hopefully cool enough to last sufficient time in the lines to get you started before it to vapourises.

Or maybe not. Here is where your bosses tip comes in. The engine fires but then starts to die, you've just struck some air in the line and a quick flick of the boost pump sends a rush all be it small rush of fuel up the injector line and hopefully you catch it before it dies.

Hope this gives you some insight, but please don't take my scribblings as a definitive description of this small part of the system. Grab a tech manual sometime. You might also find the principals of the air bleed injector different to what many would tell you.

Best of Luck
M

[Bevan666]

"If the engine is hot, place mixture control in IDLE CUT-OFF, switch auxiliary fuel pump to ON for 30 to 60 seconds, then OFF. Return mixture to full rich and continue with cold start procedure."


When performing this procedure, check the fuel flow guage. The FF should not register when you have the mixture at ICO and the boost pump on. If you see any indication of fuel flow, some fuel is flowing past the spider (the round silver distibutor at the top of the engine) into the intake manifold. 30 seconds of this could be a lot of fuel, so I tend to skip the next prime (that found in the cold start procedure) and start cranking.

There is a little rubber gasket in the fuel control unit, and unless its just been overhauled, it'll always leak a bit at ICO. I havent yet seen a IO-520 that didnt register some fuel flow at ICO.

Bevan..

[wigga]

CHADZAT, I was taught the 'tickling' procedure aswell. Works everytime. :D

[Chadzat]

thanks for the replies guys. :)

[Big Kev]

I'm reading a really good book by Chris Markham about Fuel Injected engines and there is just something that I need to clarify about my knowledge with Fuel Injected engines.

When a Fuel Injected engine is hot, it forms air bubbles in the fuel lines particulary near the fuel distrubution unit and the injector lines. The method that he and a lot of others prescribe in this situation is to close the throttle, close the mixture control (mixture ICO) and put the fuel pump on so as to squirt fuel into the lines and get rid of the air bubbles BUT this will only work up to the Fuel Control Unit.

Because the mixture is left in ICO, then no fuel will be pumped past this point, but past this point is where air bubbles also exist and I would of thought that the general rule of thumb would be to leave the mixture control rich so that it can get past the fuel control unit and purge those parts of the fuel system from air bubbles as well.

Don't want to leave it in too long as flooding the intake port with fuel will occur which will cause a chemically incorrect mixture so there is a limit but can someone please explain why he and others say to leave the mixture ICO....surely this is not circulating fuel around the entire system right?

Thanks in advance


BK

[185skywagon]

I'll give it a go. Once past the FCO, fuel is away from any pumps and metering units. This means that there should not be any chance of cavitation in these lines. If there are vapour lock/gas bubbles in the lines up to the divider, they are not of concern once past the fuel pump etc. When you do a circulation with mixture in ICO, you are getting rid of hot fuel/vapour (in the fuel pump and FCU) in exchange for cooler fuel that the fuel pump and FCU can pump as well as meter. The same with Diesel injection pumps and air. Once you bleed the injection pump, Air will be expelled from the lines and injectors in due course.
Any clearer??

[tinpis]

Hot start from 30 odd years ago.

Fuel injected

Mixture rich /Throttle closed
Hit the primer and open throttle until you see the fuel flow .STOP!
Mixure idle cut off
Throttle set
Kick it in the guts
Mixture to rich when it fires.
(Throttle jiggling as required for extra pax appeal)

Adjust sunglasses and smoothly taxi over the chocks .


(Hows me memory Chuckles?)
http://www.augk18.dsl.pipex.com/Smileys/old.gif

[gaunty]

Good enuff, works every time.:D :ok:

[tinpis]

Never had me stuck with an unwanted overnight with the Oomeegooli tribe in PNG Gaunty :ok:

[GeneralAlfredHoziman]

Tinpis, you forgot one thing - hang arm out of the window (if possible - it may be a little hard in a Cherokee).

The final step, advancing the mixture to rich once the engine fires, is extremely important - especially when a testing officer is sitting next to you. This can be quite embarassing when after four attempts you still haven't worked it out and the testing officer throws his headset into his lap.

Alfred

[Chadzat]

speaking from experience there Alfred? hehe.

BK- I started a thread like this that got some comprehensive replies only a month ago. A search with the words "starting a hot fuel inj engine" should turn it up.

[185skywagon]

Woomera, Perhaps you could merge this withBK- I started a thread like this that got some comprehensive replies only a month ago. A search with the words "starting a hot fuel inj engine" should turn it up.
Chadzat's earlier thread on this.

[185skywagon]

Hot start from 30 odd years ago.
Fuel injected
Mixture rich /Throttle closed
Hit the primer and open throttle until you see the fuel flow .STOP!
Mixure idle cut off
Throttle set
Kick it in the guts
Mixture to rich when it fires.
(Throttle jiggling as required for extra pax appeal)
Adjust sunglasses and smoothly taxi over the chocks .
(Hows me memory Chuckles?)

Tin, I use this for the 185 and IO-520 (plus a bit of fuel pump tickling when it starts to fire up). Don't know how I came across it? Just started doing it this way to stop animated onlookers from observing induction fires.:O

[the wizard of auz]

Air will be expelled from the lines and injectors in due course.
Any clearer??
Ok, that might work on some engines, but not all. Lets remember that aircraft injectors work on a negative pressure.... or a pressure diferential, and Diesel injectors use a positive pressure to lift the valve plate and release the pintle.
Hence the High pressure part of the injector pump that diesels have and aircraft don't have. If the air bubble in the injector line in most diesels is big enough, it will just sit in the line and compress and decompress all day without building enough pressure in the injector for it to crack off, and therfore must be bled out from just prior to the actual injector.

Oh, sorry guys.......thread drift. :uhoh:

[belowMDA]

John Deakin covered this at length in his articles on avweb.

http://www.avweb.com/news/columns/182146-1.html

you may have to sift through a lot but it is in there. BTW there is a lot of interesting reading in most of those articles!

the upshot was that this will work for a continental but not lycoming. This was verfied to me by an engineer who had worked on our chieftains and had the misfortune of creating a large and somewhat flamable puddle under the machine while doing an engine run. But for the grace of god no fire occured.:oh:

[Woomera]

Thread to current whilst I experiment with this "merge" thingy..........


2 minutes later: Hallelujah!!! The Merge thingy worked.

First thing to work for me all day!!!

:} :} :} :} :}

Woomera

[chimbu warrior]

I'm with Richo............Lycomings and Continentals are different beasts and require different techniques accordingly.

Other little gems.....on early C310's with augmentor tubes, I was always taught that starting with a tailwind was VERBOTTEN. To prove the point, apparently some dude managed to overprime one one day with a healthy tailwind and succeeded in blowing the cowls off (in my day C310's had IO-470's, the 520's came later).

With any overprimed engine, turn it into wind and let things cool down before trying again (about a one-cup-of-coffee interval). This saves draining the battery and melting the starter. For improved cooling, open the oil access door too (but don't forget to close it again).

If all else fails, get something powered by PT-6's!

[Capt W E Johns]

Tinpis is right on. I've found that just a little squirt of gas down the pipes before start, then full lean until after the engine catches, works really well for the Lycoming 540. It avoids the most common error of over-priming, and if it doesn't start you're sure that it needs gas, rather than a flooding problem.

[the wizard of auz]

Hey Chimbu, I have a IO470V powered old 310 and found the best and fastest way to start it is mixture rich, throttle to idle, press starter button and after one rev, add the prime pump. will start every time, hot or cold and no overfueling or fuel in the augmenters. ;)

[pungamoose]

Flooding it then doing a flooded start works a treat on a 40 degree day out bush...... I find it worst about 20 mins after shut down. Don't flood it too much though or there might be a wee fire.:uhoh: