REFLECTOR:Rough Rider - Lycoming Fuel Injection

[Ronnie Brown]

I think the numbers you are giving for fuel pressure with and without the
boost pump on are correct for a Lycoming fuel injected engine.  That is
similar to my IO360.  I'm guessing that the slight increase in pressure is
increasing the flow just enough to prevent vaporizing the fuel and the rough
idle.  Mine idles a bit rough - but not as badly as yours after landing.  My
cold idle is set around 750 rpms - hot idle is just a bit less and it
stumbles and misses.  Increasing the rpm to 900 or so improves the
roughness.

(the 6 psi fuel pressure is more normal for a carbureted engine that has a
engine driven fuel pump)

I think this is pretty normal for a Lycoming fuel injected engine.  I hear
fuel injected planes on the taxiway at our airport doing the same thing.

For a while Velocity suggested relocating the fuel spider to below the
engine to alleviate this problem, but no longer.  Make sure all of your
lines are fire sleeved if they haven't been.  Some suggest fire sleeving the
small 1/8" lines going to the injectors, but I didn't. That might help to
keep the fuel lines cool.

Ronnie


----- Original Message -----
From: "Chuck Jensen" <cjensen@dts9000.com>
To: <reflector@tvbf.org>
Sent: Saturday, July 19, 2003 10:24 AM
Subject: REFLECTOR:Rough Rider


| I have an engine issue that two mechanics have looked at...and that's all
| they've done.  I wondered if anyone has ideas on avenues of
| investigation/solution.  I'm running a 540 with mag/EI combo.  The engine,
| particularly after a long flight (less so after starting cold), runs rough
| at ramp speed (1,000 rpm).  Here are the symptoms with a hot engine after
| flight:
|
| As long as the booster pump is on, runs smooth as glass.  VM-100 indicates
| 30 psi (from another post, is that way too high??) and approx. 4.0 gph
@1000
| rpm.  If the booster pump is secured, fuel pressure drops to 28 psi, fuel
| flow shows 1.7 and engine bounces between 650-700 and just barely stays
| running.  Turn the boost back on, and it immediately goes back to smooth
| operations with the first set of values.  Turn the boost off, and it's
right
| back in the dumps.
|
| At cruise or high power operations, the boost pump on/off makes no
| difference in fuel pressure, fuel flow or smoothness of operations.
|
| One mechanic suggested that the idle speed needed to be increased.  ??
| Seems he was missing the point.  I'm intentionally setting it at 1,000 rpm
| with the booster, then engine goes in the toilet when the booster is cut.
|
| The second mechanic increased the richness setting which may have been too
| lean since I did not get a temporary rpm increase when cutting off the
| mixture, but the reliance on the booster pump did not change for smooth
ramp
| operations (especially when hot).
|
| Induction plenum has been checked thoroughly but that would seem to be
| unrelated to the observed symptoms.
|
| Questions:  1) are my fuel pressure values way out of line (earlier post
| talked about 5-6 psi)?  2) if my numbers are bogus, do I
| have a bad fuel pressure sensor or ground?
| 3) what do others run for fuel pressure/flow at 1,000 rpm on
| a 540?
| 4) is the main fuel pump going in the crapper? (its been
| this way for a long time with no further
| degradation/change)
| 5) is this type of poor low power performance characteristic
| of deterioration of the positive displacement type
| fuel pump?
| 6) is there a way to check the main fuel pump performance?
|
| I was in the camp that the main fuel pump is going downhill but I don't
| understand why, if it is putting out that much pressure, why the fuel flow
| should fall so much when the booster pump is secured.
|
| By all rights, these questions should be investigated and fixed by a good
| mechanic (which exempts me), but since that avenue has been unproductive,
I
| thought I'd check out the collective wisdom/experience of the
Reflectorites.
| Best idea wins an official Atta Boy award; redeemable wherever good ideas
| are sold.
|
| chuck
| N27GV
|
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