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gkrangers

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Seriously, why are these god damn fuel injected 172s such a bitch to start sometimes?

Today, started right up. A few hours later, starting it again, took me over 30 minutes and 10+ tries.

Whhhhhyyyyyyyyy?

*goes to corner to cry*
 

GravityHater

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Post your normal and hot-start procedure, maybe we can discuss alternative methods
 

viper548

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sounds like you're doing something wrong if it's taking you 10 tries to get rid of vapor lock
 

MTpilot

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Hot start; try mixture idle cutoff, throttle full, crank til it kicks, then, mixture rich and throttle a thousand or so. I think thats right.
 

GravityHater

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No prime?

MTpilot said:
Hot start; try mixture idle cutoff, throttle full, crank til it kicks, then, mixture rich and throttle a thousand or so. I think thats right.
 

EagleRJ

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MTpilot said:
Hot start; try mixture idle cutoff, throttle full, crank til it kicks, then, mixture rich and throttle a thousand or so. I think thats right.
That's actually the flooded start procedure, but a lot of times that will work if you get too enthusiastic trying to start a vapor-locked engine.
I've never flown a FI Skyhawk, but I usually had luck starting the bigger FI engines by using as much prime as I could get away with to get some cool fuel in the lines. If I went too far and flooded it, the vapor lock was cleared, so I just did a flooded start and it usually fired right up.
Don't flood it on purpose- that's bad operating procedure and will cause accelerated wear- but if that's where you wind up, you can still get the engine started if you know what's happened.
 

jackotron

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If it is really hot, sometimes I leave the fuel pump on low, mixture full lean and throttle to full. Crank the engine, when it catches, bring the throttle back, mixture in and fuel pump off.

Sorry that it took you ten tries. It took me almost that long to get it right one day, I sure felt like a jacka$$.

Jack

(kind of ironic huh?)
 

viper548

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jackotron said:
If it is really hot, sometimes I leave the fuel pump on low, mixture full lean and throttle to full. Crank the engine, when it catches, bring the throttle back, mixture in and fuel pump off.

Sorry that it took you ten tries. It took me almost that long to get it right one day, I sure felt like a jacka$$.

Jack

(kind of ironic huh?)
That always worked for me
 

gkrangers

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viper548 said:
sounds like you're doing something wrong if it's taking you 10 tries to get rid of vapor lock
its a damn cessna...i tried everything several times.

finally got it to start going with no fuel pump, mixture rich, throttle open a touch, I think...can't even remember which configuration got it too work.

Normal: throttle open 1/4", mixture rich, pump on for a few seconds, pump off, mixture idle cutoff, ignition...advance mixture when it starts.

hot: throttle full, mixture idle cutoff, start.

They have been giving me issues lately at times....last spring I had no problems whatsoever with the SPs.

And the term vapor lock is thrown around a lot, but what is it exactly and how do we get rid of it ?

I know I'm showing my inexperience here...but damn, I've never had to try more than 3 or 4 starts till tonight.
 
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minitour

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gkrangers said:
And the term vapor lock is thrown around a lot, but what is it exactly and how do we get rid of it ?
The fuel injector is on top of the engine. When the engine is run and is sitting there after shutdown, the heat goes up. The fuel in the injector "lines" vaporizes because of the heat. You need to send some "cool" fuel into the lines so you have liquid in there.

Your hot start listed above sounds like a flooded start.

For a normal hot start (engine was running recently), try doing the normal start only without the priming steps. That's the procedure for the 172R (IIRC) and it seemed to work well.

If it doesn't start, just let it cool for 30 minutes (I know the delay sucks but...) and it should start fine for ya.

How'd the DUATS thing go?

-mini
 

FN FAL

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minitour said:
The fuel injector is on top of the engine. When the engine is run and is sitting there after shutdown, the heat goes up. The fuel in the injector "lines" vaporizes because of the heat. You need to send some "cool" fuel into the lines so you have liquid in there.

Your hot start listed above sounds like a flooded start.

For a normal hot start (engine was running recently), try doing the normal start only without the priming steps. That's the procedure for the 172R (IIRC) and it seemed to work well.

If it doesn't start, just let it cool for 30 minutes (I know the delay sucks but...) and it should start fine for ya.

How'd the DUATS thing go?

-mini
On our Cessna 320, vapor lock was such a problem that I would pop the side panels to the cowling open when I would stop for a while. There were long side panels on both sides of the cowling that could be opened, so no matter what direction the wind was blowing with relation to the plane, you were going to have some cross ventilation regardless. That helped a lot, especially since that was turbocharged.

It seems like there's a knack to getting the different ones started, once you get it down you'll quit wearing out the starter and your ego. I'd probably have to re learn it all over again myself now that I haven't flown injected for quite a few years.
 

minitour

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FN FAL said:
That helped a lot, especially since that was turbocharged.
That would have to make it twice as sucky...I mean...take a normal IO-360. They can be a pain, but managable. Take a TSIO-360 and...man...wouldn't that just double or tripple the heat?

Hot starts in a turbo have to be a sh!tty deal.

Was that pretty much SOP to open up the cowling or just something you picked up on?

-mini
 

FN FAL

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minitour said:
That would have to make it twice as sucky...I mean...take a normal IO-360. They can be a pain, but managable. Take a TSIO-360 and...man...wouldn't that just double or tripple the heat?

Hot starts in a turbo have to be a sh!tty deal.

Was that pretty much SOP to open up the cowling or just something you picked up on?

-mini
It was just an idea I had after vapor lock was explained to me and I looked at the cowling and saw the panels.

Also, we incorporated this other technique that seemed to work. Keep the mixtures off and run the boost pumps on high for about 10 seconds. Supposedly, that allowed the fuel to purge the system up to the bendix valve, with the vaporized fuel being returned to the mains. You might want to check with a mechanic first, because it's been a while and your fuel system may be different.
 

aucfi

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It doesn’t matter what starting procedure you use if the mags are out of time and the impulse couplings have gone bad.

What kind of mag drop do you get? To the limit? How much difference when switching between L & R?

I know this is bad to do but carefully pull the prop through very slowly and listen for the click from within the cowling. There should be 1 click for each rotation of the prop. If you hear 2 clicks, then the mags are out of time and should be checked by a mechanic.


The click is your impulse coupling (located inside the mags) which retards the ignition so the plugs fire at Top Dead Center (TDC) instead of 20-25 degrees prior to TDC. They also increase the voltage to help aid starting the engine.

One of our older carbureted 172's had this problem and was a beeotch to start. Some engines dont have impulse couplings at all (C65 on the J3 for example) and rely strictly on properly timed mags for easy starting (which is nice being YOU are the starter lol).

Vapor lock, a flooded engine, and/or bad timing on the mags will ruin your day. Hope this helps.

au
 

U of I Tweak

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Impulse coupling

aucfi said:
It doesn’t matter what starting procedure you use if the mags are out of time and the impulse couplings have gone bad.

What kind of mag drop do you get? To the limit? How much difference when switching between L & R?

I know this is bad to do but carefully pull the prop through very slowly and listen for the click from within the cowling. There should be 1 click for each rotation of the prop. If you hear 2 clicks, then the mags are out of time and should be checked by a mechanic.


The click is your impulse coupling (located inside the mags) which retards the ignition so the plugs fire at Top Dead Center (TDC) instead of 20-25 degrees prior to TDC. They also increase the voltage to help aid starting the engine.
Correct me if I am in error, but don't most engines only have one impulse coupling and only utilize one mag for start? When the key is in the start position it grounds out one of the mags (the one that does not have the impulse coupling). Also, I assume that the impulse coupling would click four times for every rotation of the propeller, one for each igntion event/power stroke.
 

erj-145mech

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As far as the mag timing goes, the mags are not timed to the impluse couplings, they are timed to the point opening. You'll get an impulse click per prop blade rotation on a four banger. Some aircraft engines have two impulse couplings per engine, mine for example does (TCM IO-360) but most Lycomings don't.

When I was working on the Rockwell Commanders, there was a service bulletin out to remove a bus bar from the back of the mag switch that grounds the right mag when you go to the start postion. What this bar did was to ground the right mag during the start (key to the start postition), so with the bar removed, you were getting two start sparks, one just after top dead center and the other at the normal crank position.

The impulse coupling not only retards the spark, but it also speeds up the rotating magnet in the mag to build a higher voltage. The magneto makes its own electricity, but it needs about 300 rpm to do so. The engine may not make that while starting, so the impluse makes up for the low speed.
 

cforst513

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tried starting it 10 times? what'd your battery juice look like after that? next time, give the starter a rest and just let it cool down for, as mentioned before, 30 minutes or so. i've found if you just let them sit a bit longer there are no problems.
 

gkrangers

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cforst513 said:
tried starting it 10 times? what'd your battery juice look like after that? next time, give the starter a rest and just let it cool down for, as mentioned before, 30 minutes or so. i've found if you just let them sit a bit longer there are no problems.
I let the starter rest in between...at one point I had enough, and just chilled watching the planes (and a nice Falcon jet) for 20-30 minutes....took another 2-3 attempts after that break, but it started.

Battery was ok.

So I guess the idea is to just sit and wait if you are vapor locked ?

91W never gives me any problems! I'm gonna start flying that again. :D
 
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gkrangers

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minitour said:
The fuel injector is on top of the engine. When the engine is run and is sitting there after shutdown, the heat goes up. The fuel in the injector "lines" vaporizes because of the heat. You need to send some "cool" fuel into the lines so you have liquid in there.

Your hot start listed above sounds like a flooded start.

For a normal hot start (engine was running recently), try doing the normal start only without the priming steps. That's the procedure for the 172R (IIRC) and it seemed to work well.

If it doesn't start, just let it cool for 30 minutes (I know the delay sucks but...) and it should start fine for ya.

How'd the DUATS thing go?

-mini
I don't think I have filed since, but I'm sure I'll have no problem.
 

gkrangers

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aucfi said:
It doesn’t matter what starting procedure you use if the mags are out of time and the impulse couplings have gone bad.

What kind of mag drop do you get? To the limit? How much difference when switching between L & R?
Mags were dropping ~100 RPM, both of them.

I attribute it to vapor lock and me bein a dumbass.
 
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