Fuel Dilevery Mystery

I have 10 hours or so on a new Barrett IO 360 with a Silver Hawk fuel injection servo in an RV8. All was well until today when I stopped by a local airport to top the tanks. As soon as I took off the engine started coughing and running rough. I pulled the power back and things smoothed out a bit but couldn't run much above 1/2 throttle (as I recall my fuel flow rate was around 6.5 gph at this point) without the missing/roughness. EGT's were high 1300s/low 1400s at 1/2 throttle and full rich on the mixture....much higher than normal. Clearly seemed to be fuel starved.

Once I landed, I pull each of the 4 injectors and minimal fuel would flow into a cup with mixture set to full rich and electric fuel pump on.

Pulled the fuel input to the injector and could flow 60 gph so plenty of fuel is getting to the servo.

Fuel pressure is 28 psi.

Fuel flow on the discharge side of the servo is rather low (not sure if this is normal). Had a spare servo so swapped the servos and still no joy.

In the past, I've pulled an injector and have seen excellent flow into a cup but for whatever reason, now it's little more than a trickle. Any thoughts/comments would be greatly appreciated!

Is there a filter in the servo??

Could your mixture cable or arm have come loose so you are no longer getting full rich when you push the red knob in?

Mike...I believe there is a filter in the servo but haven't checked...I assume swapping the original servo with the spare servo would eliminate the servo (unless both have a low fuel flow issue but that seems unlikely). I did confirm mixture linkages on both the original and the spare servo were providing full travel.

Contaminated fuel?

The first thought that comes to mind, based on the circumstances, is whether the fuel that was most recently added is contaminated? It would be interesting to have a close look at what comes out of the tank drains and whether that might have blocked something downstream.

Completely agree Paul... I called the airport this morning and gave them a heads-up in case others reported similar issues. I'm planning to check the tank sumps when I get home tonight and will pull the filter on the fuel injection servo to see if there's any debris there. Very coincidental that the problem right after a fill up.

Chris Engler said:

EGT's were high 1300s/low 1400s at 1/2 throttle and full rich on the mixture....much higher than normal. Clearly seemed to be fuel starved.

Click to expand...

While circumstances may agressively point to fuel starvation, don't rule out an igntion issue. It can also show high EGTs (much higher than peak EGT), as well as only supporting part throttle power (as MAP increases, the charge becomes harder to light and often shows weakness in an ignition system-This is why lycoming recommends 2000 RPM for runup). Remember, any EGT that is higher than observed peak EGT at that RPM under normal operations, is not being caused by a mixture issue. A very lean or very rich mixture will report LOW EGTs. Or at least lower than normal.

You have proven fuel flow to the servo and a second servo proves the servo is not the issue. Not sure how likely it is that a spider or misc lines downstream of the servo can cause rough running across all cylinders. I am assuming you have confirmed that the mixture linkage is creating full rich at the servo.

Every thing is suspect on a new engine. Many parts are most likely to fail within a few hours of first use. Most engine bolts lose torque after the first few heat cycles, especially those used on gasketed interfaces, and that includes the mag hold down bolts, that when loose allow timing drift. I have rebuilt two engines and both required re-tightening of most engine fastners after the first couple of hours. On my 320, I had to retorque the mag hold down bolts several times over the first 50 hours. Not sure why, but necessary none the less.

Larry

You don?t say how much fuel you took on but is there any chance you got jet fuel instead of 100LL? You might want to pull a sample and look as well as smell it.

Thanks for the thoughts and advice. Stopped by the airport yesterday and did some additional trouble shooting:

1. Fuel is blue so definitely 100 LL (took on 30 gallons before the trouble started).

2. Checked fuel via tank sumps and no trace of contamination.

3. Pulled the fine screen from the fuel injection servo and no trace of contamination.

4. Pulled the top off the spider and no trace of contamination.


Tonight I'll try running the engine with the "spare" servo and see what happens...this one is a head scratcher!

I had a nearly identical problem in a mooney and it turned out to be a plugged fuel injector. Once of the cylinders wasnt getting fuel.

Definitive information needed.

Chris, run a fuel flow test with back pressure to 30 psi. Remove the hose at the servo and connect a bypass with a small ball valve. Route to a clean container or back to the tank.

Use panel pressure and communicate with test buddy to set pressure. Then read fuel flow from panel. This will prove that some pressure bypass is not stuck open and the system to the servo is operating properly.

Yes it is a pain, but beats guessing in circles without hard diagnostic data.

The clogged injector theory got me thinking....went back and reviewed a couple of screen shots I took while I was having the problem. My initial recollection that all EGTs were high but screen shot indicates otherwise:

Cylinder 1: 1201
Cylinder 2: 1435
Cylinder 3: 1187
Cylinder 4: 1215


Cylinder 1: 1183
Cylinder 2: 1414
Cylinder 3: 1212
Cylinder 4: 1289

Sure seems like a clogged injector on Cylinder 2 may be the culprit and cleaning them will be tonight's project.

Is the consensus that a 20 minute soak in Hoppes #9 is the best approach?

If that doesn't solve the problem, I'll try the pressure/flow relationship test Bill suggested.

Mag Check?

Chris Engler said:

The clogged injector theory got me thinking....went back and reviewed a couple of screen shots I took while I was having the problem. My initial recollection that all EGTs were high but screen shot indicates otherwise:

Cylinder 1: 1201
Cylinder 2: 1435
Cylinder 3: 1187
Cylinder 4: 1215


Cylinder 1: 1183
Cylinder 2: 1414
Cylinder 3: 1212
Cylinder 4: 1289

Sure seems like a clogged injector on Cylinder 2 may be the culprit and cleaning them will be tonight's project.

Is the consensus that a 20 minute soak in Hoppes #9 is the best approach?

If that doesn't solve the problem, I'll try the pressure/flow relationship test Bill suggested.

Click to expand...

Have you tried doing a mag check? The high EGT on that cylinder is symptomatic of a failed/fouled plug or bad plug lead...

To have an increased EGT would require only a slight or partial blockage of the injector...

Skylor

Skylor - yes I did a mag check and it seemed normal. The problem tended not to show up until I was above the 1700 RPM I ran the Mag check at.

I'll double the sparkplug lead connnection both at the PMAG and plug itself.

I?m pretty sure that when you do the nozzle flow test you must have the throttle wide open and mixture full rich. If you did it with the throttle anywhere except wide open you won?t get the correct flow from the nozzles.

Chris Engler said:

Is the consensus that a 20 minute soak in Hoppes #9 is the best approach?

If that doesn't solve the problem, I'll try the pressure/flow relationship test Bill suggested.

Click to expand...

I use a wood toothpick (may need to sharpen it, depending upon quality). As you force it in, it conforms to the ID of the restrictor and clears debris. Rotate it once seated. The wood is much softer than the brass and can't hurt it. Rinse with laquer thinner or acetone and blow out.

Larry

Mystery Solved!

Closing the loop on this in case others have similar issues in the future...

Root cause was a partially blocked injector on the cylinder with the high EGT (thanks for putting me on the right track Larry!). Diagnosis was as follows:

1. First swapped EGT probes to be sure I wasn't getting bad data from a probe and confirmed probes were good.

2. Next swapped injectors on cylinders 1 and 3 and the high egt followed the injectors so I knew I was on the right track.

A couple of additional thoughts:

1. The engine (IO-360) had 10 hours on a "new" Barrett build that included swapping "old" accessories from the XP-400 that was recalled by Superior. That process took nearly a year so some residual fuel sat in the fuel injection servo and spider for a while.

2. The initial problem presented with excessive egt on a cylinder along with miss firing if I tried to push more than 8 gph or so through the engine.

3. After removal and soaking all injectors and reassembling, I could perform a full throttle static run up without miss firing but still had high egt on the "problem" cylinder. I assume the initial soak cleared some but not all of the blockage.

4. Removing the injector on the cylinder with high egt and inspecting the small injector sleeve with a magnifying glass revealed it was still partially blocked. Carefully running a very fine wire through the injector sleeve pushed the blockage (small amount of dark sludge) out.

Reassembled and all egt's are now at the expected temp and within 50 degrees at full power.

Thanks again for all the help and suggestions....it's great to have the airplane operational again!