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FI hot start fixes?

BruceMe

BruceMe

Well Known Member
I recall seeing in an IO-360 RV-8 a long time ago with a system that recirculated the fuel and kept it from boiling off and causing hot start issues. I'm not sure how well it worked or if it worked. I know port injection will fix it for good. But wondering if there are good alternatives.
 
Yes, the purge valve that AFP sells. I'm installing one now on my 9A IO360, at 140 hours flight time because I'm tired of dealing with the hot starts. I run 91E10 fuel which makes the situation worse than 100LL.
 
1

Using Lycoming's start procedure for over 6 years has never failed. Boost pump time for cold start is about 8 seconds, hot start three seconds. Starter run time for hot may be a few seconds longer than for cold. My wife is usually doing the flying and has the starts down. Rarely does she ever require a second start attempt.
 
Single point of failure?

airguy said:
Yes, the purge valve that AFP sells. I'm installing one now on my 9A IO360, at 140 hours flight time because I'm tired of dealing with the hot starts. I run 91E10 fuel which makes the situation worse than 100LL.
Click to expand...

We had contemplated installing a purge valve on our RV-7, but had concerns that this would introduce yet another failure point.

I assume you made a choice based on hot start difficulty vs the likelihood of the purge valve sticking open.

Am I missing something else obvious?
 
KatanaPilot said:
We had contemplated installing a purge valve on our RV-7, but had concerns that this would introduce yet another failure point.

I assume you made a choice based on hot start difficulty vs the likelihood of the purge valve sticking open.

Am I missing something else obvious?
Click to expand...

I discount fairly heavily the possibility of the purge valve failing open while in flight, if its going to happen its most likely to happen during the attempted start when you try to close the valve and the cable breaks - in which case the engine doesn't start and it's not a probelm. A good stiff spring on the valve arm to hold in the closed (run/rich) position solves that issue.

Of higher concern to me was having another fuel line running back to the tanks for the return. I installed a check valve in that line where it ties into my return lines near the fuel selector, to ensure that in an abnormal position following emergency landing I will not flow fuel forward through that purge line. Steel fittings and firesleeved FWF, of course.

As for the hot start difficulty - because I'm running 91E10 I don't just boil the fuel FWF like 100LL does - I will actually boil some of the cool fuel that comes forward when it hits the hot servo body and flow divider as well, the vapor pressure of the 91E10 is just too high, especially with the winter mix. The purge valve lets me cool those components to below the boiling point before the start attempt. With 100LL it's not as much of an issue.
 
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airguy said:
I discount fairly heavily the possibility of the purge valve failing open while in flight, if its going to happen its most likely to happen during the attempted start when you try to close the valve and the cable breaks.
Click to expand...

Your assumption is wrong. I had a cable break in flight. A $2 spring save my airplane.
 
What worked for me...

Most of my problems with FI hot starts went away with two items....

Procedures.

P-Mag.

Getting a good procedure nailed down that gave a high likelihood of start while minimizing the possibility of flooding/fire helped-a lot.

I posted a picture of the factory-recommended procedure by Lycoming I snapped at AirVenture last year here (post #4):

http://www.vansairforce.com/community/showthread.php?t=140524

I have used it religiously ever since, and it works superbly. Lycoming's big concerns with running the boost pump before a hot start is a fire due to flooding, and this procedure minimizes that risk.

Additionally, since late last fall, I've had the added benefit of flying behind 1 P-mag, and it's built-in "start mode" of enhanced, multiple-times-per-second ignition strikes (as well as a fatter, hotter spark between a wider gap) seems to get things running much quicker than with the old Slick mag I'd had before. I'm getting lightoff after 4-6 blades on a hot start now vs the extended crank cycle it took before.

No more "fuel injection hot start" anxiety issues anymore....
 
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I hadn't seen the Lycoming method but it is very close to what I have been doing for the past couple months since I started flying my newly finished 7A.

The key, I think, is keeping the mixture closed during hot start with the throttle open. I've gotten good at moving both levers in opposite directions with one hand :D
 
KatanaPilot said:
We had contemplated installing a purge valve on our RV-7, but had concerns that this would introduce yet another failure point.

I assume you made a choice based on hot start difficulty vs the likelihood of the purge valve sticking open.

Am I missing something else obvious?
Click to expand...

I think using a high quality cable such as used on the throttle with a rod end bearing attaching it to the purge valve has little chance of failure. That's how I've done it for years. You can add the spring as mentioned in another post, but that is just kind of belt and suspenders if using High quality control cables, not the solid wire "choke" cables.

Vic
 
There were some really great responses so far.

The solution I'm considering is the EFI/EI produced by SDS. Once installed and setup correctly the hot start issue is but a memory as I understand it.
 
http://airflowperformance.com/index.php/product/purge-valve

$300

https://www.aircraftspruce.com/catalog/appages/hbshutoff.php

$29.70

Stupid question... why doesn't a regular fuel valve work for this?

... as far as hot start procedure. I know it very well, I've done it a lot, but it's voodoo and give all the times I've dumped fuel on the ground... let's keep the fuel in the lines and out of the ports. It's also particularly bad in my RV. By far the worst I've ever seen and that probably has to do with how the lines run.
 
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BruceMe said:
http://airflowperformance.com/index.php/product/purge-valve

$300

https://www.aircraftspruce.com/catalog/appages/hbshutoff.php

$29.70

Stupid question... why doesn't a regular fuel valve work for this?
Click to expand...

To be effective the valve needs to positioned so cool fuel gets right up to the flow divider. You'd need a valve capable of remote operation and then engineer your own mounting and actuating system. That tractor valve isn't going to cut it but Andair has one that might work but it's somewhat more expensive. If you're using the whole AFP system it doesn't make sense (to me) to reinvent the wheel.
 
Chkaharyer99 said:
...............The solution I'm considering is the EFI/EI produced by SDS. Once installed and setup correctly the hot start issue is but a memory as I understand it.
Click to expand...

I put SDS on one side and use it to start. Procedure did not change for hot starts though - Leave mixture at ICO, full throttle, cranks for a few seconds (5?) before firing up.

The SDS does provide for a beautifully soft start, plenty of time to adjust mixture and throttle before engine gets to idle RPM.
 
SMO said:
I put SDS on one side and use it to start. Procedure did not change for hot starts though - Leave mixture at ICO, full throttle, cranks for a few seconds (5?) before firing up.

The SDS does provide for a beautifully soft start, plenty of time to adjust mixture and throttle before engine gets to idle RPM.
Click to expand...

SMO,

No more cough, sputter, studder, complain, putt, putt? That would be nice! What ignition are you using opposite the SDS?

With my mechanical FI and Slick mags my procedure is ICO, activate starter and advance the throttle slowly until it starts. Once it coughs, sputters and starts the putt, putt, putt..., I open the mixture and slowly pull the throttle back to idle and turn on my electric fuel pump. It eventually smooths out. Once it does I lean aggressively for ground ops.

I would like to talk with you offline about your SDS EI experience.
 
Chkaharyer99 said:
SMO,

No more cough, sputter, studder, complain, putt, putt?
Click to expand...

Just putt,...... putt.....putt...putt putt PUTT RRRRRRR.

Never did have much coughing or sputtering on a hot start, but when it caught it was quite a bit quicker to roar to life and I had to be quicker pulling the throttle and advancing the mixture. Was never much of a problem if ready for it. Helps to have the starter button on the stick, easy to hold up elevator while starting.

I have a Slick on the other side.

You can call/text my cell at 250 two five three seventeen fifty. Or email through my profile on this site.
 
BruceMe said:
... as far as hot start procedure. I know it very well, I've done it a lot, but it's voodoo and give all the times I've dumped fuel on the ground... let's keep the fuel in the lines and out of the ports. It's also particularly bad in my RV. By far the worst I've ever seen and that probably has to do with how the lines run.
Click to expand...

Bruce, previous posts say you have an IO-320, so you probably have a Bendix RSA-5 fuel control. Is that correct?
 
AX-O said:
Your assumption is wrong. I had a cable break in flight. A $2 spring save my airplane.
Click to expand...

Do you think that had the spring not been there the valve would have moved to the ICO position on it's own? Not debating the merits of the spring, I'm just trying to understand how a broken cable with the valve in the run position would have resulted in anything other than having to shut the engine down the traditional way (mixture/ignition). I suppose its possible the valve with a broken cable could vibrate to ICO, just not sure how likely that would be.
 
I fly 3 different airframes with FI Lyc's and another without. All I can offer you is that a slick start is on all 3 of the FI Lyc's w/ NO purge valves, and red hot to cold and anywhere in between they all start like a Toyota. Easy with less than 2 revs most of the time. Just leave the mixture at cut off until after the iron is rolling , then open about 1/2 way and virtually instant power results.

FWIW I have watched guys with purge valves crank their battery dead. Some guys like them, but I like less parts and less items to fail.

Either way , understanding the fuel condition and technique as appropriate is what makes the job easy.

Best of Luck
 
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Raymo said:
I hadn't seen the Lycoming method but it is very close to what I have been doing for the past couple months since I started flying my newly finished 7A.

The key, I think, is keeping the mixture closed during hot start with the throttle open. I've gotten good at moving both levers in opposite directions with one hand :D
Click to expand...

Exatly, mix all the way out, throttle wide open. adjust both as neccessary. works for me every time.
 
BruceMe said:
I converted it from carbureted, Yup why?
Click to expand...

You mentioned fuel on the ground in post #12.

A Lycoming diaphragm fuel pump stores mechanical energy in a spring. When the pump cam rotates further, spring force provides the fuel pressure, with the spring sized for the pressure desired.

That fuel pressure is still present after the mixture knob is pulled to idle cutoff, starving the engine to stoppage. The disc mixture valve in an RSA-5 is assumed to have a very low leak rate....but if it does leak, there is 25 or so psi there to push fuel from the pump chamber, the lines, the RSA-5 itself, and the flow divider, all of which dumps in the intake ports. This leak will continue until pressure bleeds down to around 2 psi, at which point the flow divider cuts it off.

I assume your 320 sump is updraft, so most of that fuel would fill the airbox and saturate the filter. You got much blue stain in there?
 
Sorry I was being too terse. I was trying to say you are right on all counts, except I don't have an air fitler. It's a straight elbow to the throttle body, no filter.

Should I have the TB rebuilt to prevent the leaking?
 
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