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Kevin,
<... you guys have any ideas
...>
No, but your problem sounds EXACTLY like mine. I have a Lyc
IO-360 that did that between SPI and IJX last fall. I had CHT/EGT on
all four cylinders, but no fuel pressure. I recovered at IJX and found
a head separating from #3 barrel and replaced the jug. Next 6 takeoffs
resulted in power sag to around 2200 rpm somewhere between 1000' and
5000'. No CHT or EGT indications to point to a particular cylinder,
Mag and E-Mag both working (numerous in-flight Mag checks). I finally
got on a test hop to about 4000' before it went south and cruised
around the pattern for better part of an hour trying stuff and calling
the instrument readings to a friend on the ground with a hand-held
taking notes.
Sounded and felt like the engine was running about 300 rpm LOP. It ran
for an hour, so after the next shot at a solution I headed home to
CSV. Got to 5000' before it SAG'd and limped home nearly 350 mi (had a
suitable airport about every 20-40 mi along the way but didn't need
them). At CSV, letting down in the pattern, suddenly it worked fine -
26" MAP (at between 3000' and 4000'), 2500+ rpm, good climb, etc. For
NO REASON WHATEVER!! I landed and decided that a) the engine driven
fuel pump was failing partially in flight and giving me waaaay low fuel
flow; b) Electric boost pump had been failed for years but I had no
way of knowing since it made enough pressure to start the
airplane. Modified the fuel lines so I could plumb in a fuel pressure
transducer to confirm my theory. Damned if fuel pressure wasn't just
right at 25-30 psi. Now I'm totally out of answers. MAP was
consistent with rpm (2100-2200 rpm, maybe 21" MAP at 2000'). I never
tried to reduce throttle to a position commensurate with RPM to see if
it smoothed out, but at the moment I'm confident it would, just like
yours.
Again, CHTs were pretty normal (and all were within 350-400F range -
normal WOT cruise at altitude is 400-425F) F from one another); EGTs
were a bit erratic, but no dead holes. Looked consistent with trying
to run the engine 300 rpm LOP. Couldn't be a vacuum leak because it
idles perfect, and idle is when vacuum leaks are most obvious. Takes
one hell of a vacuum leak to make it run rough at WOT and my engine is
injected anyway.
NOT ignition
NOT fuel pressure
NOT a bad cylinder (CHTs & EGTs would indicate that glaringly)
NOT oil pressure - over 60 psi the whole time
INTERMITTENT - ground tests perfect. Can over temp on ground if I run
it hard enough
NOT clogged air filter (I don't have one) or intake ducting (inspected,
much of it replaced)
NOT contaminated fuel - tested for water many MANY times
NOT exhaust - 2-into-1 system very much intact
NOT fuel filters - were new and changed anyway
Vapor lock? Why can't that be replicated on the ground? Why now when
nothing's changed on the airplane for a looong time (except for
installation of E-Mag). Happened in Nov of last year. Plane flew fine
throughout the summer.
Air in fuel delivery system? Don't think so. All that was checked and
tightened up with no effect.
I'm at my wit's end. If you figure this one out, I WANT TO KNOW ...
Jim S.
kevin lane wrote:
I realize that this isn't
exactly the right forum, but you guys seem to have excellent debugging
skills. my local RV group is totally worthless ("I find the carnauba
wax doesn't show fingerprints as much as the....")(except Mike!) the
on-field mechanics are sick of me coming by.
my O-320 RV-6A is having
RAG (rpm attention getter) problems. it runs fine until about 300' on
take-off, then the rpm's drop to like 1700 (from 2200). switching mags
to electronic ignition(Rose) makes no difference. mixture no diff.
pulling the throttle it will seem to run fine at 1700rpm. I have 4 new
cyls that I am attempting to break in. ground run ups can only go like
2 minutes before CHT's exceed 400 degrees. I discovered I can get the
rpm drop on the ground if I run it a minute or so full power. cht's
will typically approach 415 degrees when the drop takes place. I don't
know if the temp is significant or not, it does seem that way. I have
a brand new slick left mag. rose checked the electronic ignition and
could find nothing wrong, even put it in an oven to test. I installed
a new carb since the old one showed signs of leakage (and I'm at whits
end). no change. my fuel pressure has been showing 8psi this last
year, up from 6 psi when originally installed.(no idea why) I
installed a pressure regulator in-line which works like a charm. I can
dial whatever pressure I like. 2 psi makes no difference. I bypassed
the mechanical fuel pump and ran it just on the facet electric. 2 psi,
no difference. I discovered that you can run the carb for maybe 30 secs
with no fuel pressure while it burns off the bowl gas. premier engines
suggested induction leak making the engine run lean. no leaks detected
cold or hot engine. (pressurized intake with vacuum, sprayed soapy
water)
if the engine didn't run
right to start with then many explanations would hold. but it runs
fine for several minutes. it runs the same under mag or electronic
ignition both before and after the problem kicks in. everyone really
wants to blame the rose ignition, but I'm not seeing any connection.
with such a quick run-up my oil temp barely registers, so I doubt parts
are seizing. I have new mineral oil in it for breakin right now.
there is a bit of MMO in the fuel too I believe, left over from a
mechanics "what the hell" attempt from way back. my cyls are all new,
rebuilts, so no valve problems. I checked the push rod lengths when I
reinstalled them. the engine isn't missing when the problems occurs,
it simply won't run faster and it seems to prefer the throttle pulled
back to match the rpm it is putting out. I can't figure out any more
lean mixture scenarios to try. the new carb runs just like the old one
did. I recently replaced the mag harness with a much newer, used one.
I tested it and it was fine. the plugs are all new, but again, no diff
between mag and elec ignition. if I flip the ignition to R and shut
off the elect ig then the engine quits as would be expected, no wiring
problems.
fuel, spark, air,
timing, that's all there is. this damn lycoming lawn mower has me
stumped. my engine has been running fine up until this (hey, we all
have "cracked" cylinders, get out your microscope and look!). you guys
have any ideas?
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