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Lycoming Injected - cold starts now different

blaplante

Well Known Member
I've got an IO-320 with the standard Bendix RSA-5 servo.

Lately I've noticed my cold starts are different. In the past the engine would nearly always fire right up. Lately, it fires up and then dies as I'm advancing the mixture. Try again, same result. By about the 3rd try I need to prime some more. Sometimes takes four tries to fire up and run. Sounds great every time it catches, but promptly 'goes out'.

Ignition is a Lightspeed and a conventional Bendix non-impulse mag.

Start procedure:
1/4" throttle
Boost pump on about 5 seconds with mixture full rich
Mixture to idle cutoff
Pump off

Crank
On catching, Advance the mixture.

These are cold starts and the temps have been moderate here (around 60 degrees). I suppose the engine might be colder than that with overnight lows in the upper 40's.

Once running all seems normal. Mag checks are as usual. Engine is at about 300 hours.

Anything I need to look at?

Thanks!
 
I hate to jump in here because you are going to get 400 opinions and different techniques, but here’s mine. I do exactly what you do except that I have full throttle during the priming.

Full throttle/Full mixture rich
Boost pump on 4-5 seconds, then off
Throttle 1/4
Mixture idle cutoff
Crank
When it catches I don’t go full rich, but I’m also in Colorado. But even at sea level you don’t need to go full rich.

Mine starts pretty much every time like that.
 
Full throttle
Full rich
Prime as required
Retard throttle and crack open
Crank


Only variable you need is prime time - seems every boost pump combo is different. The RV-8 is no more than 1 second; my Hiperbipe was almost 10.
 
Full throttle
Only variable you need is prime time - seems every boost pump combo is different. The RV-8 is no more than 1 second

Same on my 7. If I prime it the 3-5 sec. in the Lycoming operators manual it floods the holy pee pee out of it!

For me it's a quick in and out with the mixture knob to prime.
 
For cold, I crack throttle 1/4" mixture full rich. Boost pump to prime and time is variable based upon ambient temp (inverse logrithmic relationship between temp and prime required. Rarely an issue starting. I tend to under prime and if it doesn't kick, I prime another 2 seconds and try again. Never more than 2 attempts unless it flooded.

No real need to over prime and go to ICO when cold.

Larry
 
Please NOTE

Note my original concern - the technique, unchanged, no longer seems to work. But previously did. If my technique was 'wrong' I would have always had starting issues.
 
Note my original concern - the technique, unchanged, no longer seems to work. But previously did. If my technique was 'wrong' I would have always had starting issues.

Perhaps your idle mixture setting is too lean now that the temps have changed?
IIRC, from an idle of 6-700 rpm, lean the mixture slowly to ICO should detect a 25 rpm rise in the process. Check the book, as I said this from memory. When was the last time the plugs were clean, injectors, timing checked? I really would check the mixture first. It likely, and quite easy to verify.


larry
 
Throttle full forward, mixture rich,prime for 4-5 seconds....throttle cracked,mixture full rich and its starts everytime within a few blades. Engine IO-320
 
Is it possible the boost pump is a little weak? It the “non RV” plane I fly it’s prime three or four seconds AFTER the fuel flow gage needle moves. Sometimes that varies.
 
I've got an IO-320 with the standard Bendix RSA-5 servo.

Lately I've noticed my cold starts are different. In the past the engine would nearly always fire right up. Lately, it fires up and then dies as I'm advancing the mixture. Try again, same result. By about the 3rd try I need to prime some more. Sometimes takes four tries to fire up and run. Sounds great every time it catches, but promptly 'goes out'.

Ignition is a Lightspeed and a conventional Bendix non-impulse mag.

Start procedure:
1/4" throttle
Boost pump on about 5 seconds with mixture full rich
Mixture to idle cutoff
Pump off

Crank
On catching, Advance the mixture.

These are cold starts and the temps have been moderate here (around 60 degrees). I suppose the engine might be colder than that with overnight lows in the upper 40's.

Once running all seems normal. Mag checks are as usual. Engine is at about 300 hours.

Anything I need to look at?

Thanks!

I experienced a similar behavior change with starts on my IO-360 a little over a year ago except my issue started occurring during hot starts. I traced the problem to an intake tube seal leak and once fixed, the starting behavior returned to normal.

My starting procedure is similar to yours except I prime at full throttle for 2-3 seconds, then retard the throttle to 1/4”and mixture to ICO for start. I have found this method to be very reliable. I have also found that the engine likes to be primed a little longer in cool weather than in warm weather.

Skylor
 
Last edited:
Perhaps your idle mixture setting is too lean now that the temps have changed?
IIRC, from an idle of 6-700 rpm, lean the mixture slowly to ICO should detect a 25 rpm rise in the process. Check the book, as I said this from memory. When was the last time the plugs were clean, injectors, timing checked? I really would check the mixture first. It likely, and quite easy to verify.


larry

I’ll echo what Larry said... perhaps the plugs and or injectors could use a cleaning? How are the plug wires? When was the last time you checked the wire resistance?
 
Full throttle
Full rich
Prime as required
Retard throttle and crack open
Crank


Only variable you need is prime time - seems every boost pump combo is different. The RV-8 is no more than 1 second; my Hiperbipe was almost 10.

This is basically a zero-throttle start technique and it works every time!

After learning to start large radials on the primer - understanding the nuances of fuel to air ratio - how it's not fuel that makes the bang, but fuel vapor - then throw in a handful of backfires because of things are too lean, and you'll understand why this technique is the best.

The key is creating the proper fuel vapor to air ratio to light off. If the engine and fuel is cold it takes more liquid fuel to create the proper vapor quantity. The colder the fuel and engine the more liquid fuel required. This is why most "flooding" and fire potential happens in cold climates. Hot starting requires zero priming because the engine and fuel is warm and fully vaporizes to meet the vapor/air mixture quicker. There only one way to fix this issue and thats preheating.

However, you can control the other factor...air! That's what your throttle is for! If you have a cold engine or a cold day you use the throttle as a choke. As long as your engine idles fine under normal conditions...this is the easiest way to start. The 1/4" throttle technique is bogus, and I wish I would have learned the zero throttle technique long ago.

Here's a great podcast on the best practice in starting:
http://airplaneownermaintenance.com/019-ladies-and-gentlemen-start-your-airplane-engines-but-please-take-it-easy-on-them/

An while you're at it subscribe to Dean's posts! Very informative and he's like the Bob Ross of aviation maintenance...very relaxing and positive personality.
 
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Note my original concern - the technique, unchanged, no longer seems to work. But previously did. If my technique was 'wrong' I would have always had starting issues.

I had a similar problem with my hot start technique, worked for many years then started being a pain. I pulled my plugs and thoroughly cleaned and carefully re-gapped and checked resistance. Almost every plug had to come in a bit on the gapping. They weren't horrendously dirty, ohm'd in spec, and didn't have to be squeezed much so I wasn't thinking it was going to help as I was doing it, but it helped tremendously.

It's still a little more difficult to start hot than it used to be, but I'm no longer having 2 or 3 extended cranks and worrying about my battery.

easy thing to check anyway.
 
We are addressing the change in starting behavior. I will echo some points already mentioned:
Clean injectors- Remove them and soak them in Hoppes overnight. You will be surprised how dirty the solution is the next day.
Check fuel delivery - pump, injector lines, fuel filters. Make sure there are no restrictions
Check air delivery - No leaks in intake tubes, gaskets, etc. Clean air filter.
Plugs- Clean, gap, and test. There should be no more than 5K ohms resistance through the plug.
Check timing on your ignition
Check compression

Something has changed. If the engine is running normally, it is probably just a minor adjustment or cleaning. Good luck. IO starts are a bit of magic, as you can see from all the techniques.
 
It appears everyone has forgotten the importance of tongue position during hot starts. Not one mention of this critical factor. During a waning moon my tongue has to be on the right side, waxing moon on the left and for a full moon dead neutral!
 
Note my original concern - the technique, unchanged, no longer seems to work. But previously did. If my technique was 'wrong' I would have always had starting issues.

Your technique is not wrong but it leaves little room for operational and environmental variation...lets us break down your technique before you start tearing your engine apart looking for a problem that may not be there:

Start procedure:

1/4" throttle

This increases the air volume, which increases the amount of fuel vapor required to light off, which subsequently requires more liquid fuel. How much more? Depends primarily on fuel temperature. The fact is if your engine idles well under normal operations, there is zero need to start a cold engine with 1/4" throttle. Especially if you have the mixture to idle cutoff (don't recommend), because you're just introducing more air, and no fuel.

What is 1/4" anyway? We really have no idea exactly what this equates to in fuel/air. It's really a technique we probably brought over from another aircraft type. However, the funny thing is, you can have the same engine hung on different aircraft types but the starting procedure in the POH is completely different. Why? There is no reason. However, you do know exactly what idle is on every engine because there's a physical stop and if things are adjusted correctly, the engine runs just great there.

Boost pump on about 5 seconds with mixture full rich
Obviously you're priming here, but you only have the throttle cracked at 1/4". You may need more...especially a cold start. 60 degrees may not seem warm but it's not, when you're trying to vaporize fuel. Remember, no fuel can't burn unless vaporized. Not even wood (a fuel) can burn. It must heat to the point a vapor is created to ignite. Don't believe me...google "How's does wood burn?" Jet-A...not technically flammable because it takes temperature >100F to create the required vapor. Fuel is the same way...you need to get fuel vapor, and cooler days and cold engines it takes more gas. How much more? That's the variable we can focus on because if you use the zero throttle technique every time, then you removed the air variable.

Mixture to idle cutoff
There is no reason to start this way, unless you're starting using the primer only which is not a normal technique on an opposed engine as it's injected into the jug rather that the blower on a radial, and it's a learned skill that has a lot of variability. We're trying to eliminate those in our starts.

Pump off
To stop the priming

Crank
On catching, Advance the mixture.

Try starting with the mixture full rich as others have suggested. Again, eliminating another variable! The timing and rate at which you reintroduce normally metered fuel should not be a concern to the pilot during a critical stage. Regardless of what you've been taught in fuel injected opposed engine ...think of the logic...you're dumping a bunch of fuel into a cylinder intake only to cut it off to the induction system. It doesn't make the remote amount of sense. Your incoming air should have the normal fuel vapor in it to sustain combustion.

I'm not saying there isn't something wrong here. Induction leak? Ignition? Clogged injector? Maybe, but if your engine runs normal otherwise than the likelihood of a weak component showing up during only a start is small and probably ignition related, but probably not if things light off normally. The easiest thing you can do is eliminate the marginal technique. We were all taught this technique and I used it for years before the enlightenment, but the starting struggles were always there until then. That's why there's so many opinions on starting, because it has been such a PITA since we were all taught it wrong.

I have a carb, so my technique is different but most certainly is at idle throttle every time to eliminate one of the starting variables.
 
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I hate to jump in here because you are going to get 400 opinions and different techniques, but here’s mine. I do exactly what you do except that I have full throttle during the priming.

Full throttle/Full mixture rich
Boost pump on 4-5 seconds, then off
Throttle 1/4
Mixture idle cutoff
Crank
When it catches I don’t go full rich, but I’m also in Colorado. But even at sea level you don’t need to go full rich.

Mine starts pretty much every time like that.

Same here.
 
Full throttle
Full rich
Prime as required
Retard throttle and crack open
Crank


Only variable you need is prime time - seems every boost pump combo is different. The RV-8 is no more than 1 second; my Hiperbipe was almost 10.

Yep, above is the way I do all engines.
 
Update

Q / A from the original poster :)

Fuel: Avgas 100LL, always relatively recent. Maybe 2 months old at most.

I've basically been just running the pump longer, basing my time more on the fuel pressure gauge than elapsed time, and this seems to be working much better.

My recent annual found 1 cylinder is low compression 80/62, warm. It's a ring problem (hearing blowby in the crankcase). This may be aggravating the starting issue. I also re-gapped the massive plugs, and replaced the Lightspeed plugs and cleaned the air filter (which wasn't dirty) at the same time.
 
I had a similar problem with an IO-320/Bendix system. Replacing the engine driven fuel pump solved it. The old pump that came out looked fine but the problem disappeared with the new pump.

George
 
Full throttle
Full rich
Prime as required
Retard throttle and crack open
Crank


Just curious...what does having the throttle at full (wide open throttle) do with respect to the priming of the engine when the engine RPM is at 0 RPM and no air is flowing through the servo?

What fuel flow do you see with the throttle WOT verses idle...would there be any difference?

I'm kinda new to airplane engines so I just crack the throttle (about the place it likes to idle at 1000 RPM), turn on electric pump and note 26-ish PSI and 0 GPH, open mixture to full and note 26-ish GPH and about 2-3 GPH, count 2 seconds and if I am shivering I let it go to 3-ishivering seconds, mixture idle note 26-ish PSI and 0 GPH.

If the throttle is moved to WOT does the GPH show greater than 2-3 GPH?

I could see that if the engine was cranking and the servo was sensing air flowing through the venturi then it would command more fuel to flow up to the fuel divider but from what I read I cannot see where there would be a difference.

Impressionable minds want to know?!?!?
 
Full throttle
Full rich
Prime as required
Retard throttle and crack open
Crank


Just curious...what does having the throttle at full (wide open throttle) do with respect to the priming of the engine when the engine RPM is at 0 RPM and no air is flowing through the servo?

What fuel flow do you see with the throttle WOT verses idle...would there be any difference?

I'm kinda new to airplane engines so I just crack the throttle (about the place it likes to idle at 1000 RPM), turn on electric pump and note 26-ish PSI and 0 GPH, open mixture to full and note 26-ish GPH and about 2-3 GPH, count 2 seconds and if I am shivering I let it go to 3-ishivering seconds, mixture idle note 26-ish PSI and 0 GPH.

If the throttle is moved to WOT does the GPH show greater than 2-3 GPH?

I could see that if the engine was cranking and the servo was sensing air flowing through the venturi then it would command more fuel to flow up to the fuel divider but from what I read I cannot see where there would be a difference.

Impressionable minds want to know?!?!?

Excellent question and would like to know how there can be any difference with the engine not cranking or running.

-Marc
 
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