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Harder and harder to cold start

Draker

Draker

Well Known Member
Looking for some things to try, technique or otherwise. IO-360-M1B. This has been my cold start process since day one:

  1. Throttle - OPEN to ¼" of travel
  2. Prop - HIGH RPM
  3. Mixture - RICH
  4. Fuel Pump Switch - ON for 5 SECONDS or until fuel pressure levels off
  5. Fuel Pump Switch - OFF
  6. Mixture - IDLE CUT-OFF
  7. START
  8. Mixture - MOVE slowly to RICH as engine starts
  9. Throttle - OPEN to max 1,000 RPM

For this new engine's first 60 hours, it has always fired right up on the 2-4th spin. Lately (last ~4-5 flights, 5 hours) this process has failed me. Starter spins strong, but engine does not catch. I've started having better luck with setting the throttle and mixture half way in while starting. I've also experimented with throttle full-in while priming with the pump. It still can take maybe 10-20 spins to catch though.

After the engine starts, there's a period of 30-45 seconds or so where the engine is running really rough, and requires half throttle just to keep turning. Hard to describe, kind of a on and off "braaaap... braaaap... braaaap..." instead of smooth running. As it warms up, it gets smoother and I need to slowly back off the throttle to keep RPM around 1000. Finally, after 1.5-2 minutes of warmup, it's running smooth, idles correctly, runs up well, and otherwise works like a champ. This post-start behavior also coincides with the start-up difficulty. The engine has not behaved like this for its first 60 hours.

I've had a look at all the easy things: Ignition wires, plug gaps, connections on all sensors and mags, air flow path through the filter and snorkel. The fact that it runs normal and strong after a brief warmup is puzzling too. I guess I'd expect problems starting = problems flying. Also, maybe it's just the cold weather???

I know I'm asking for an opinion war bringing up startup technique. I've read the 5,000+ threads on fuel injected cold startup technique, and most of them boil down to "this is what I've always done". If there's something obviously and explainably wrong in my procedure, I'm totally fine with changing. Last time I tried changing my startup procedure, I deformed my air filter, so I'm cautious about change.
 
Step One

If I were working on it, the first thing I would do is clean the injectors, along with checking fuel flow downstream from the divider. Sounds like the system isn't delivering enough fuel.
And, most people cold start mixture rich.
 
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I had very similar issues that you describe regarding a cold start, except my hard starts began way before 60 hours.

I found that if I prime with WOT and full rich, and run the boost pump for only about 1 second, then leave the mixture at full rich for the engine start, with the throttle only about 1/16" open, the engine consistently fires within one rev of the prop and idles pretty close to 1,000 rpm. Very satisfying!
Once running, I adjust to keep it at 1,000 rpm and lean quite a bit prior to taxi.

"Someone" extremely knowledgeable about ALL things RV who I did transition training with suggested WOT and full rich to prime, then to leave the mixture at full rich for a cold start. But later I found the engine was getting harder and harder to start when cold. So I eventually found that I was just priming too long with the boost pump, leaving all other parameters the same.

As stated earlier, for a hot start, I don't prime, and start with the mixture at ICO and 1/16" throttle position until the engine catches, then push the mixture in relatively slowly (about 1 second of travel time). Once the engine is running, I proceed as I do when it's cold.

For me, priming for only 1 second instead of 3-ish seconds while waiting for fuel pressure to show, was the ah-ha moment for cold engine starts. I was flooding the engine that way (with WOT during prime).

I should probably mention this procedure works really well for my IO-320 with one mag and one EI, not a carb.
 
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Draker said:
Looking for some things to try, technique or otherwise. IO-360-M1B. This has been my cold start process since day one:

  1. Throttle - OPEN to ¼" of travel
  2. Prop - HIGH RPM
  3. Mixture - RICH
  4. Fuel Pump Switch - ON for 5 SECONDS or until fuel pressure levels off
  5. Fuel Pump Switch - OFF
  6. Mixture - IDLE CUT-OFF
  7. START
  8. Mixture - MOVE slowly to RICH as engine starts
  9. Throttle - OPEN to max 1,000 RPM
Click to expand...

Yep - this is what I do except I start with mixture at cutout, turn on the boost pump moving the mixture to full rich for 5-7 seconds, then mixture back to cutout and turn off the boost pump.

The discussion here is what has changed from when all was well?

Assuming the checks you list are all good, this leave a couple of things left to check:
- Spark Plug center conductor resistance. If it goes high the mag will have a harder time firing the plug.
- Fuel system air leak. Riding the throttle to get the engine to not quit after start is a classic symptom. Try doing the same procedure except leave the boost pump on during start.

Carl
 
OKAV8r said:
If I were working on it, the first thing I would do is clean the injectors, along with checking fuel flow downstream from the divider. Sounds like the system isn't delivering enough fuel.
And, most people cold start mixture rich.
Click to expand...

Yes, cleaning the injectors is one of the "easy" things I have not done yet. Good call.
 
I always hate to comment on these things because while there are certain rules that work for all engines, every engine has its “sweet spots” that you have to learn. We’ve got four Lycomings in our hangar right now, and they all have slightly different priming requirements for instance.

Basically though, your steps 1-6 are “squirt some fuel into the cylinders”. My only thought is that if the throttle is only cracked when you squirt fuel, then you aren’t going to squirt much fuel. I always go full throttle, full mixture to prime, and then I know where I am when I “count seconds” for the fuel pump “on” step. I vary the number of seconds depending on the engine and the temperature. With the throttle only cracked, you’re telling the servo to deliver a very small amount of fuel.

Truth is, you need to experiment, and that is tedious because once it starts, you have to let it cool down to get another true “cold start”. Make a little score card to keep in the cockpit. Every time you start it, try a different number of seconds of prime, and record the results. Graph them after you have some data points. After ten flights, you’ll have a good picture of what works best.

Paul
 
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Draker said:
Looking for some things to try, technique or otherwise. IO-360-M1B. This has been my cold start process since day one:

  1. Throttle - OPEN to ¼" of travel
  2. Prop - HIGH RPM
  3. Mixture - RICH
  4. Fuel Pump Switch - ON for 5 SECONDS or until fuel pressure levels off
  5. Fuel Pump Switch - OFF
  6. Mixture - IDLE CUT-OFF
  7. START
  8. Mixture - MOVE slowly to RICH as engine starts
  9. Throttle - OPEN to max 1,000 RPM
Click to expand...

Yes. This is pretty much what I was taught to do on my IO-320. Two differences are that I hit the fuel pump with throttle wide open then close it to 1/4" open before cranking, and I don't crank with any of the avionics on and therefore I don't see the fuel pressure. Just a 5-count and crank.
 
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Paul Dye has hit the nail on the head.

DO NOT _ DO NOT remove your injectors for cleaning. They will be more likely to go back dirty and with a tiny obstruction.


Your problem is this......it's been getting colder up there for you guys, needs more priming and you have not been giving it enough. I may sound blunt but stop following all the random ideas.

Throttle - WIDE OPEN
Prop - HIGH RPM
Mixture - RICH
Fuel Pump Switch - ON for 3 SECONDS - AFTER fuel pressure hits reasonable numbers (not level off, a bit before that)
Fuel Pump Switch - OFF
Mixture - IDLE CUT-OFF
Throttle - about where 1000 rpm would be
START
Mixture - MOVE briskly to RICH as soon as the engine coughs
Throttle - to max 1,000 RPM, then lean aggressively (refer John Deakin engine articles)

You should find this works every time. Hot starts are simple, begin the same procedure at the Mixture ICO point and all will be good.
 
RV10inOz said:
Paul Dye has hit the nail on the head.

DO NOT _ DO NOT remove your injectors for cleaning. They will be more likely to go back dirty and with a tiny obstruction.


Your problem is this......it's been getting colder up there for you guys, needs more priming and you have not been giving it enough. I may sound blunt but stop following all the random ideas.

Throttle - WIDE OPEN
Prop - HIGH RPM
Mixture - RICH
Fuel Pump Switch - ON for 3 SECONDS - AFTER fuel pressure hits reasonable numbers (not level off, a bit before that)
Fuel Pump Switch - OFF
Mixture - IDLE CUT-OFF
Throttle - about where 1000 rpm would be
START
Mixture - MOVE briskly to RICH as soon as the engine coughs
Throttle - to max 1,000 RPM, then lean aggressively (refer John Deakin engine articles)

You should find this works every time. Hot starts are simple, begin the same procedure at the Mixture ICO point and all will be good.
Click to expand...

This is how I started all my Lycoming engines. 3 - 4 seconds of prime using fuel pump depending on OAT temperature, with throttle full open and mixture full rich to prime.
 
Draker said:
Looking for some things to try, technique or otherwise. IO-360-M1B. This has been my cold start process since day one:

  1. Throttle - OPEN to ¼" of travel
  2. Prop - HIGH RPM
  3. Mixture - RICH
  4. Fuel Pump Switch - ON for 5 SECONDS or until fuel pressure levels off
  5. Fuel Pump Switch - OFF
  6. Mixture - IDLE CUT-OFF
  7. START
  8. Mixture - MOVE slowly to RICH as engine starts
  9. Throttle - OPEN to max 1,000 RPM
Click to expand...
Your technique looks fine to me.

For this new engine's first 60 hours, it has always fired right up on the 2-4th spin. Lately (last ~4-5 flights, 5 hours) this process has failed me. Starter spins strong, but engine does not catch. I've started having better luck with setting the throttle and mixture half way in while starting. I've also experimented with throttle full-in while priming with the pump. It still can take maybe 10-20 spins to catch though.

After the engine starts, there's a period of 30-45 seconds or so where the engine is running really rough, and requires half throttle just to keep turning. Hard to describe, kind of a on and off "braaaap... braaaap... braaaap..." instead of smooth running. As it warms up, it gets smoother and I need to slowly back off the throttle to keep RPM around 1000. Finally, after 1.5-2 minutes of warmup, it's running smooth, idles correctly, runs up well, and otherwise works like a champ. This post-start behavior also coincides with the start-up difficulty. The engine has not behaved like this for its first 60 hours.
Click to expand...

These symptoms and timing seem consistent with the colder temps we have been seeing in the last 60 days in central CA.

I've had a look at all the easy things: Ignition wires, plug gaps, connections on all sensors and mags, air flow path through the filter and snorkel. The fact that it runs normal and strong after a brief warmup is puzzling too. I guess I'd expect problems starting = problems flying. Also, maybe it's just the cold weather???
Click to expand...

If the only thing that’s changed is the weather, that’s a clue!

Trying priming a little more volume and being patient while she warms after kicking off.

Unless you go to EFI and ignition, you can’t expect it to operate like a modern car …
 
I’m with Paul on this one. For the last say, 50 plus years every injected Lycoming I’ve flown behind has had all the knobs pushed full forward to prime, then mixture ICO, throttle open a smidge, bit not more than a hair, and crank. After it fires slowly up withe the mixture and go fly.
 
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RV8iator said:
I’m with Paul on this one. For the last say, 50 plus years every injected Lycoming I’ve flown behind has had all the knobs pushed full forward to prime, the mixture ICO, throttle open a smidge, bit not more than a hair, and crank. After it fires slowly up withe the mixture and go fly.
Click to expand...

+1. At least for the IO540, that’s also what the Lycoming operator’s manual says.
 
Electrical

I would check the starter connections and engine ground. Maybe it just isnt cranking as fast as before.
 
Draker said:
Looking for some things to try, technique or otherwise. IO-360-M1B. This has been my cold start process since day one:

  1. Throttle - OPEN to ¼" of travel
  2. Prop - HIGH RPM
  3. Mixture - RICH
  4. Fuel Pump Switch - ON for 5 SECONDS or until fuel pressure levels off
  5. Fuel Pump Switch - OFF
  6. Mixture - IDLE CUT-OFF
  7. START
  8. Mixture - MOVE slowly to RICH as engine starts
  9. Throttle - OPEN to max 1,000 RPM
Click to expand...

The one "trick" that has helped my IO-540 start with great consistency is to use FUEL FLOW (GPH) instead of fuel pressure or time (# of seconds) for priming. I also prime with throttle 1/2 open.

Assuming you have a fuel flow readout (??), use GPH reading, not time or pressure, for priming. The sweet spot for my engine is prime till fuel flow hits 4.5 GPH. You have to anticipate it, because it comes up quickly and will go too rich if you wait to see 4.5 P GPH before turning pump off. (it'll keep climbing a bit after after turning off pump)

This method (verses counting seconds) works every time regardless of temp or how long the plane has sat idle since last flight or how open your throttle is (1/4, 1/2 etc...). Your planes GPH number may be different than mine, but play with that number to find your engines sweet spot.

One last possibility, that hopefully won't have you chasing too many rabbits.... years ago, my Mooney M20J had the same problem with starting. Found out the mag internal timing was off. Once that got fixed, started perfectly every time.
 
Draker said:
Looking for some things to try, technique or otherwise. IO-360-M1B. This has been my cold start process since day one:

  1. Throttle - OPEN to ¼" of travel
  2. Prop - HIGH RPM
  3. Mixture - RICH
  4. Fuel Pump Switch - ON for 5 SECONDS or until fuel pressure levels off
  5. Fuel Pump Switch - OFF
  6. Mixture - IDLE CUT-OFF
  7. START
  8. Mixture - MOVE slowly to RICH as engine starts
  9. Throttle - OPEN to max 1,000 RPM

For this new engine's first 60 hours, it has always fired right up on the 2-4th spin. Lately (last ~4-5 flights, 5 hours) this process has failed me. Starter spins strong, but engine does not catch. I've started having better luck with setting the throttle and mixture half way in while starting. I've also experimented with throttle full-in while priming with the pump. It still can take maybe 10-20 spins to catch though.

After the engine starts, there's a period of 30-45 seconds or so where the engine is running really rough, and requires half throttle just to keep turning. Hard to describe, kind of a on and off "braaaap... braaaap... braaaap..." instead of smooth running. As it warms up, it gets smoother and I need to slowly back off the throttle to keep RPM around 1000. Finally, after 1.5-2 minutes of warmup, it's running smooth, idles correctly, runs up well, and otherwise works like a champ. This post-start behavior also coincides with the start-up difficulty. The engine has not behaved like this for its first 60 hours.

I've had a look at all the easy things: Ignition wires, plug gaps, connections on all sensors and mags, air flow path through the filter and snorkel. The fact that it runs normal and strong after a brief warmup is puzzling too. I guess I'd expect problems starting = problems flying. Also, maybe it's just the cold weather???

I know I'm asking for an opinion war bringing up startup technique. I've read the 5,000+ threads on fuel injected cold startup technique, and most of them boil down to "this is what I've always done". If there's something obviously and explainably wrong in my procedure, I'm totally fine with changing. Last time I tried changing my startup procedure, I deformed my air filter, so I'm cautious about change.
Click to expand...

This has nothing to do with the start routine. The fact that it runs very poorly for a minute after startup, says this has nothing to do with how you are starting it, though your start routine does need to change with colder temps.

cold engines need more fuel than warm ones and this is most notable in the first 30-60 seconds after starting. IMHO your issue is in the fuel system not providing enough fuel to handle the needs of a cold engine and cold air (Don't forget also that colder air is denser and generally needs a richer mixture accordingly). The fact that this coincides with colder weather just confirms the diagnosis. Hard to say exactly what is causing it without hearing it struggle. This is an area where intake leaks could cause issues, so worth checking. The spiders are known to have debris caught in them when new, so worth checking them. The highest item on the list is the idle mixture setting. At 1000 RPM, you are still mostly metered through the idle circuit. While you could have gotten away with a too lean mixture in the summer, the colder temps will show the fault. THe setting here is a compromise. It will be a bit rich in the summer and a bit lean in the winter. If you bias towards a summer mixture, you struggle in the winter. I tend to set my idle mixture when it is around 50*, which is a mid point in my climate. By raising the throttle to 1500, you get mostly on the main circuit and things get better, though there is still some influence here from the idle circuit. You can come back down to the idle circuit after 2 minutes, as now the engine is warm enough to accept the leaner mixture.

In regards to the actually starting, as the temps drop, you must increase the amount of prime in order to get a good start and the need is not linear, but logrithmic. 70->40* = need more prime; 40->10* = need A LOT more prime. When I program EFII systems, I am using 4-5 times the amount of fuel at 30* as I am at 70* while cranking. THe after start encrichment (~2 min) is also greatly increased at these temps, however, this tapers down across that time period. Due to the high fuel demands, the hot start routine that you use is sub-optimal in cold wx. It is enough to get it to fire off, but the leanness seen after it does creates issues. I discourage that technique for cold starts in cold climates like mine for the reasons stated. Instead, it is reserved for hot starts. Guys in NV might get away with it, but creates real problems when starting at 20*

Larry
 
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Thanks, Larry. This is more where I was hoping the discussion would go. The many different cold start techniques are interesting, but I've read them all before. Something changed to cause this problem, and one thing that I have not changed was startup process. Understood about the denser cold air and need for more fuel, though.

As for intake leaks or fuel flow blockage, wouldn't this be something I would notice during run-up and in-flight, too?

From what you say, idle mixture definitely sounds like something to re-check. I set mine only once when finishing everything up for airworthiness on a very hot August day, and haven't touched it since.
 
Draker said:
SNIP
As for intake leaks or fuel flow blockage, wouldn't this be something I would notice during run-up and in-flight, too?
Click to expand...

Not necessarily. The issue is fuel system leaks (sucking in air), not air intake leaks. Does the problem go away when you turn on the boost pump after start?

The other easy check is “shot glass test” on the output of the spider. Post #8 on this thread is example of a spider with a chunk of stuff floating around causing the problem during startup and idle. The problem went away during run up and such as the spider diaphragm opened with the higher fuel flow.

https://vansairforce.net/community/showthread.php?t=196906&highlight=Shot+glass+test

Carl
 
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Throttle - 1/4
Prop - HIGH RPM
Mixture - ICO
Fuel Pump Switch - ON
Mixture - Full rich to prime. I use about 7 seconds when outside temp is warm, more when it is cold.
Fuel Pump Switch - OFF
Mixture - IDLE CUT-OFF
START
Mixture - MOVE briskly to RICH as soon as the engine catches
Throttle - to max 1,200 RPM, then lean aggressively (refer John Deakin engine articles)
 
Morning sickness?

Fairly new engine, suddenly having trouble starting, runs bad for a minute tell it begins to warm up. First thing I'd check is to pull the engine through 4 blades while it's cold to be sure you don't have a valve or two hanging open. that would cause your problem.
 
rvanstory said:
The one "trick" that has helped my IO-540 start with great consistency is to use FUEL FLOW (GPH) instead of fuel pressure or time (# of seconds) for priming. I also prime with throttle 1/2 open.
Click to expand...

^^ This ^^

This is actually included in the instructions for the IO-360 Owners Handbook.
 
Russ McCutcheon said:
you get this figured out Ryan?
Click to expand...

I'm still experimenting and collecting results. I have not done enough flying to say I've fully solved the problem. I tried:

  1. Throttle wide open
  2. Mixture full rich
  3. Fuel pump until I see full fuel pressure and some fuel flow
  4. Throttle back to cracked 1/4"
  5. Mixture remains full rich
  6. Start

This resulted in a no-start. Likely too rich. Paused for 30 seconds, pulled the mixture out to ICO, and it cranked and eventually started.

I also tried:

  1. Throttle wide open
  2. Mixture full rich
  3. Fuel pump until I see full fuel pressure and some fuel flow
  4. Throttle to halfway
  5. Mixture halfway
  6. Start

This one started on like half a blade and surged (probably because of the throttle setting). So much more successful. Next time I'm going to try the same procedure but Throttle cracked and Mixture halfway.
 
Draker said:
I'm still experimenting and collecting results. I have not done enough flying to say I've fully solved the problem. I tried:

  1. Throttle wide open
  2. Mixture full rich
  3. Fuel pump until I see full fuel pressure and some fuel flow
  4. Throttle back to cracked 1/4"
  5. Mixture remains full rich
  6. Start

This resulted in a no-start. Likely too rich. Paused for 30 seconds, pulled the mixture out to ICO, and it cranked and eventually started.

I also tried:

  1. Throttle wide open
  2. Mixture full rich
  3. Fuel pump until I see full fuel pressure and some fuel flow
  4. Throttle to halfway
  5. Mixture halfway
  6. Start

This one started on like half a blade and surged (probably because of the throttle setting). So much more successful. Next time I'm going to try the same procedure but Throttle cracked and Mixture halfway.
Click to expand...

Did you pull the engine through 4 blades to verify you don't have any sticking valves? Pull through backwards by hand to be sure you have 4 cylinders making compression.
 
I have seen a few comments that I am not sure if they are quoting wrong or if they truly use this for a start sequence.
If you go ICO rich and then turn on the pump to prime but leave the ICO rich when you turn the pump off, you are still putting fuel to the engine until the pressure is back to zero.
I assume people mean that they turn the pump on and watch for pressure, then full rich for a few seconds to prime. Then with ICO pulled lean attempt engine start. Push ICO rich when you get first fire.
If I don't get fire in a few blades, I do the prime again.

You are flooding the engine if you leave pressure in the system and the ICO rich.
 
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