Subaru FI 2.5/2.2 vapor lock?

dunc

RAF/Sparrowhawk/SC 2.5 FI
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During taxi on a 90 degree day, my newly returned to service (and new to me) engine suddenly shut down, and was difficult to restart. it would run for a few seconds, then shut down. "Typical vapor lock" symptoms says I as raised in Phoenix and am accustomed to this when flying other FI fixed wing aircraft. However the after market fuel pressure gauge, connected just before the final fine fuel filter, was steady at 40 PSI, running the other pump made no difference, and bypass fuel was easily heard going into the fuel tank all the time. No ECU engine monitor light flashing. Further taxi tests later that day, and morning flights made on the following day had no further problem.

I have a 2.5 short block running under 2.2 FI manifold, sensors, and stock ECU.

Suggestions?
 
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eddie

RAF, turbo subaru 230hp
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Fixwing really don't vapor lock the injector lines on top of the engine gets hot when setting and the fuel evaporates in the lines

running the boost pump cools the line with fresh fuel and makes it easier to start.

fuel injected engines don't really vapor lock and the RAF has everything out in the open,so it

could never happen. Its just got to be something else.

Rob when you solve the problem please let us know what it was.

Sorry we cant be of more help !
 

AirCommandPilot

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Maybe the computer is killing the ignition for some reason. Is there a way to put a data logger on it to see what the sensors are doing when it shuts down?
 

eddie

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Bobby this engine has the stock Subaru computer on it with all of the unnecessary sensors on it,could be anything.
 

Kolibri

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dunc, have you yet isolated the matter between spark vs. fuel?
(A lack of compression doesn't seem to be involved here.)

This may be a grounding issue, perhaps to the injectors.

Also, does it throw any engine codes?

You may need a Subaru mechanic to help you chase the problem.
Being an A&P, you can sign off on his work if he balks about working on an E-AB aircraft.

You're very fortunate that the stoppage occurred on the ground.

Regards,
Kolibri
 

dunc

RAF/Sparrowhawk/SC 2.5 FI
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By the time we returned to the hangar, it ran fine, so unable to determine sprk vs. fuel other than fuel pressure was fine throughout the incident. No error codes were thrown. No grounds or engine cabling has been touched, and it flew four hours with no issue during the preceding two days. Yes, I thank my guardian angel, although we never flew outside the airport pattern.
 

AirCommandPilot

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I know this will sound basic, but try running it while you "wiggle" and "twist" each wire connector. There may be corrosion or a misaligned pin that inconsistently looses contact.
 

Kolibri

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I know this will sound basic, but try running it while you "wiggle" and "twist" each wire connector. There may be corrosion or a misaligned pin that inconsistently looses contact.
Such basic things often tease out the trouble; good advice.
 

dunc

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I am unsure how a loose connection would allow the engine to start again, run for a few seconds, then die. That said, the engine connections were indeed disassembled, cleaned with contact cleaner, and reassembled after returning to the hangar. Since the engine was already running again with no issues right after we returned to the hangar, it is unclear if these efforts had any effect. It flew twice again for another two hours without problems on the following morning.

Hence "vapor lock" was my best conclusion.
 

eutrophicated1

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Don't recall any occurances of vapor lock in everyday engines running fuel pressures higher than 6-12 psi. I do remember plenty of times dirty or corroded fuel tanks, or lines plugging things up, after sitting unattended for weeks or months.
Still, because the problem presented itself as a go-nogo situation, my first diagnostics would be to check everything electrical, and maybe change out the Subaru VCU for an 'engine-only' unit. Digital units can be royal bitches to trouble shoot.
 

eutrophicated1

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Automotive 'Vehicle Control Units' can have computer code that checks up to 64,000 calibrations, most of which are 1, 2, even 3 dimensional tables. There can be 2 to 3 dozen sensors that feed information to the VCU's on a real-time basis.
 

Uncle Willie

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dunc;n1138854 said:
... Hence "vapor lock" was my best conclusion.
OK, Dunc, I am going to go out on a limb here and assume that you are an intelligent fellow with reasonable powers of observation.

When the engine "Just Quit", did it lose power as if a switch was turned OFF?
Or, did it give a slight gasp, miss, or hesitation a half second before it stopped.

An electrical issue where the plugs just stopped firing will give no warning. Instant silence.
If the fuel pressure was lost, Vapor Lock, there will be a short time that as the pressure dropped, the engine would lean out as it quit.
There will always be a little fuel remaining for a few weak strokes in the lines as the hoses contract as the pressure drops.
Fuel loss is not instantaneous.

So, what do you remember it sounded like when it quit.
Instant Silence?
Or Pop, Pop, Fhwit, Silence?
- - - - - - - - - -

P.P.A. (Post Posting Addendum)

dunc;n1138636 said:
... However, the aftermarket fuel pressure gauge, connected just before the final fine fuel filter, was steady at 40 PSI ...
Could there be an issue with the Final Fuel filter giving an intermittent blockage?
It is not highly probable but may be something you should not overlook either.
 
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dunc

RAF/Sparrowhawk/SC 2.5 FI
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I think the pop, fhwit most closely described the sound. Recall that measured fuel pressure was always good. All filter are brand new, < 20 hour use.

I built my first ham radios at the age of 14. I received my initial BS Electrical Engineering from Arizona State back when computers took up rooms, and we programmed using punch cards, submitted to the Data Processing staff, went to lunch, received results in another set of punch cards that we could run through a printer. From that austere start, and years of analog and digital hardware systems design, working with DARPA, I was among the first dozen employees appointed to the Motorola Microsystems business unit (damn Intel :Cry:), and designed their computer systems including disk drives, intelligent CRT terminals, and other peripheral products. This also honed my programming skills, made my brain turn "soft", and I left Moto to enjoy many years as a traveling programmer consultant, and recently sold my own website development and hosting startup. All aviation customers BTW. I have been a pilot for 50 years, CFI, A&P for 30. I don't think I am dumb, have always built upon my previous experiences, and know when I don't know enough, and need to ask fo help. I am very thankful this help group exists for a gyro newbie like me.

Turbo RAF Eddie has also suggested that I simplify my ECU for future troubleshooting. Meanwhile, one of my thoughts will be to heat soak each sensor in turn with a heated air gun to see if I can induce another failure. I have some other issues to resolve first, with the major aspect of sudden engine outage not being lost upon me.
 

eddie

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Well Rob it sounds like you really don't need our help,your probably the go to guy we will need when we have

a computer/electrical problem. Let us know what the fix is.
 

Uncle Willie

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Rob,
It sounds a lot like my start in the late 1960's, IBM360 Batch processing, punch cards, output on a chain drive line printer. Those printers sure were fast!
As you have learned over the years, just because a part is fresh out of the box, does not mean that it is good until proven good.

Pop, Fhwit sounds like a fuel problem.
As part of the process of elimination, and for our peace of mind, pull that final filter and cut it open just to prove it was good all along. Cheap Insurance.
 

dunc

RAF/Sparrowhawk/SC 2.5 FI
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Eddie - as I said: "I know when I don't know enough, and need to ask for help." All my experience is simply in other electrical/electronic things, and other aviation disciplines. I have no gyro experience, and no gyro owners nearby to lean on.

All the filters I utilized have removable elements and new ones are on order. Although I flushed out the fuel tank and replaced entire fuel system, utilizing the fuel pump you suggested, I am also aware that this gyro did not receive proper previous care and debris happens. I considered removal and cleaning of the injectors as I do on my own Cessna with each annual. But one injector would not cause the engine to stop and I avoid MIFs.
 
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