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  #1  
Old 09-13-2017, 09:30 PM
Chris Engler Chris Engler is offline
 
Join Date: Aug 2012
Location: Greene, NY
Posts: 52
Default XP-400 Still Coughing

I posted last week after a first start regarding some issues with a CS WW prop not moving and the XP-400 coughing /stumbling at high RPM. Happy to say the prop issue is resolved but the engine stumble is still a mystery. The engine is new and the fuel system is the standard Silver Hawk EX-5VA1. The ignition system is standard mags with the G3i system.

The engine starts and runs perfectly until 2400 RPM then if the throttle is advanced further, the engine will cough/sputter. If the mixture is leaned (about half travel on the throttle quadrant) I can keep the engine from running rough and at full throttle maintain around 2600 RPM.

All EGT/CHT readings are in the green and fuel flow is 18-19 gph at full throttle.

At 2400 RPM (just before sputtering) and full rich, when I lean, EGTs increase by about 150 degrees to peak and EGT spread is around 50 degrees hottest to coldest.

The coughing is present with the G3i ignition system switched both on and off so we don't believe that's a factor. Since I can lean to eliminate the cough at full throttle, I assume the mixture is simply too rich but there's no adjustment for full throttle mixture.

I've spoken to the folks at Precision a couple of times and they're stumped as well. Yesterday I pulled the FI system off the engine and shipped it to them for bench testing.

Thought I'd post here to see it anyone knowledgeable with the Silver Hawk servo has any ideas....

Thanks!
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RV 8 Under Construction (N184CE Reserved), Showplanes Fastback, Superior IO 400; Dual 10.4 HXr

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  #2  
Old 09-14-2017, 10:59 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Any other data you can post? 150 ROP should not be rich enough to cause coughing/sputtering; It is pretty much what you are looking for. Symptoms you describe are classic for overly rich, but your testing seems to show you are not.

Did you confirm the EGT movement on all 4 cylinders? It is possible that you have a problem with one of your nozzles allowing too much fuel into one cylinder. You should confirm the EGT status for each cylinder if you haven't done so already, ensuring that you track the trend for each.

Also, what condition are you seeing 18-19 GPH? Is that at 2600 full rich or peak EGT. I don't know the chart for a 400, but it seems a bit high for 2600 RPM, especially if at peak.

Larry
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Last edited by lr172 : 09-14-2017 at 11:03 AM.
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  #3  
Old 09-14-2017, 11:25 AM
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Low Pass Low Pass is offline
 
Join Date: May 2006
Location: Houston
Posts: 1,858
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Quote:
Originally Posted by Chris Engler View Post
I posted last week after a first start regarding some issues with a CS WW prop not moving and the XP-400 coughing /stumbling at high RPM. Happy to say the prop issue is resolved but the engine stumble is still a mystery. The engine is new and the fuel system is the standard Silver Hawk EX-5VA1. The ignition system is standard mags with the G3i system.

The engine starts and runs perfectly until 2400 RPM then if the throttle is advanced further, the engine will cough/sputter. If the mixture is leaned (about half travel on the throttle quadrant) I can keep the engine from running rough and at full throttle maintain around 2600 RPM.

All EGT/CHT readings are in the green and fuel flow is 18-19 gph at full throttle.

At 2400 RPM (just before sputtering) and full rich, when I lean, EGTs increase by about 150 degrees to peak and EGT spread is around 50 degrees hottest to coldest.

The coughing is present with the G3i ignition system switched both on and off so we don't believe that's a factor. Since I can lean to eliminate the cough at full throttle, I assume the mixture is simply too rich but there's no adjustment for full throttle mixture.

I've spoken to the folks at Precision a couple of times and they're stumped as well. Yesterday I pulled the FI system off the engine and shipped it to them for bench testing.

Thought I'd post here to see it anyone knowledgeable with the Silver Hawk servo has any ideas....

Thanks!
Interesting. I'm having similar symptoms. New Silverhawk system on IO-360. Please reply back with the findings on your FI system from the evaluation.
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Last edited by Low Pass : 09-14-2017 at 01:07 PM.
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  #4  
Old 09-14-2017, 05:20 PM
Chris Engler Chris Engler is offline
 
Join Date: Aug 2012
Location: Greene, NY
Posts: 52
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Larry - the 18-19 gph figure is at 2400 RPM full rich. I've confirmed that the EGT's are consistent across all cylinders and as you say, the 150 degree increase to peak at 2400 is just about right. Funny thing is the engine runs flawlessly everywhere except above 2400 RPM full rich...really has us stumped!

Bryan - interesting that you're having similar issues.....yours runs fine everywhere except top end and can lean to overcome the coughing?

I'll keep you posted on what Precision says....hope to hear back from them by end of next week.

If the throttle servo gets a clean bill of health, next step is to replace the mags but really seems like a fuel mixture issue.
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RV 8 Under Construction (N184CE Reserved), Showplanes Fastback, Superior IO 400; Dual 10.4 HXr

Kitfox 7; Rotax 914, Built and Sold

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  #5  
Old 09-14-2017, 05:22 PM
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Low Pass Low Pass is offline
 
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Quote:
Originally Posted by Chris Engler View Post
Larry - the 18-19 gph figure is at 2400 RPM full rich. I've confirmed that the EGT's are consistent across all cylinders and as you say, the 150 degree increase to peak at 2400 is just about right. Funny thing is the engine runs flawlessly everywhere except above 2400 RPM full rich...really has us stumped!

Bryan - interesting that you're having similar issues.....yours runs fine everywhere except top end and can lean to overcome the coughing?

I'll keep you posted on what Precision says....hope to hear back from them by end of next week.

If the throttle servo gets a clean bill of health, next step is to replace the mags but really seems like a fuel mixture issue.
No, I've not tried leaning at full power. But I will.
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  #6  
Old 09-14-2017, 06:54 PM
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Dbro172 Dbro172 is offline
 
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Location: Moorhead, MN
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Any chance you have a fuel leak somewhere, perhaps at some fitting, causing cavitation?
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  #7  
Old 09-14-2017, 07:51 PM
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Low Pass Low Pass is offline
 
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Quote:
Originally Posted by Dbro172 View Post
Any chance you have a fuel leak somewhere, perhaps at some fitting, causing cavitation?
With mine, no. Pressure and flows, steady. No fuel smell inside the plane. Same conditions, right or left tank. Something in the servo? Possibly.
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  #8  
Old 09-14-2017, 09:05 PM
Chris Engler Chris Engler is offline
 
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Location: Greene, NY
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No sign of a fuel leak with mine either and with it not coughing when I lean, indications are that it's stumbling rich. The A&P I'm working with noted puffs of black smoke from the exhaust during the stumble....another indication it's rich.
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RV 8 Under Construction (N184CE Reserved), Showplanes Fastback, Superior IO 400; Dual 10.4 HXr

Kitfox 7; Rotax 914, Built and Sold

VAF donation gladly paid through July 2018
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  #9  
Old 09-15-2017, 09:43 AM
mahlon_r mahlon_r is offline
 
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Try checking the low pitch blade angle on the prop...maybe too steep.
Good Luck,
Mahlon
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  #10  
Old 09-15-2017, 09:54 AM
Chris Engler Chris Engler is offline
 
Join Date: Aug 2012
Location: Greene, NY
Posts: 52
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Thanks Mahlon....we had thought about that possibility as well but figured it would be similar to a full throttle static run-up of a fixed pitch prop (i.e., solid running at a static RPM of 2300-2400) rather than inducing a cough. If I keep my throttle at full without leaning, my engine will actually quit. I tried putting cowls on and doing a couple of high speed taxi runs and had the same result...once throttle fully advanced, heavy coughing.
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RV 8 Under Construction (N184CE Reserved), Showplanes Fastback, Superior IO 400; Dual 10.4 HXr

Kitfox 7; Rotax 914, Built and Sold

VAF donation gladly paid through July 2018
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