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DocThrock

Active Member
My buddy has a 7A with 180, cs, AFP pump, filter and injection. He took off relatively cold and the engine went to rough idle shortly on climb out and he made a safe landing. On touch down, then engine caught up and ran perfectly.

Test flight. No problems up to 8K altitude (from 580 Ft). This time, on pitch over, the engine did the same thing. Mags, fuel selector, boost pump, no effect. Negative Gs, positive Gs, hard banking, no effect. No frank indications on any gauges. Had to land again at rough idle. Got on the ground, tapped the brakes, engine caught back on and ran fine.

His A&P is baffled, and so am I. Any ideas?

Thanks!

CONCLUSION: Turned out to be contamination beyond the filter screen inside the Airflow Performance fuel controller. Some fibers had evidently slipped through the pores in the filter and clogged the inlet. When you pulled the filter out, nothing was in it. Up inside where it seated, a glob of clog blocked the fuel flow. The controller had to be completely disassembled (by Don @ AP) and returned to service. Very weird. No signs of any debris ANYWHERE in the entire fuel system. Hopefully pictures are forthcoming.
 
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How about checking the engine air intake to make sure there is plenty of air for proper fuel burned
 
Hours?

How many hours on the engine?
Sounds a lot like the classic Lycoming sticky valve guide to me.
 
Does he have the purge valve. Make sure all the fittings from the purge valve back are tight and there are no cracks in any of the flare fittings that would allow air in the system. I had the same thing happen on mine after I had the baffle off and I had only finger tightened the purge valve fitting. Don
 
DocThrock said:
On touch down, then engine caught up and ran perfectly.


Got on the ground, tapped the brakes, engine caught back on and ran fine.

His A&P is baffled, and so am I. Any ideas?

Thanks!
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There is a story here, ----- what is the common feature that landing will effect.

I would look closely at the fuel system.

Is there anything in the fuel tank floating around that could block the pickup???

Is there a flop tube than could be in the wrong position??

I have seen the same symptoms in a R/V aircraft that had the fuel pickup in the wrong location.
 
AFP pump, filter and injection.
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Just as the fuel line enters the AFP fuel controller there is a very small very fine filter. If it is starting to get clogged it will cause those exact symptoms.

It should be pulled and cleaned at every oil change.
 
N395V said:
Just as the fuel line enters the AFP fuel controller there is a very small very fine filter. If it is starting to get clogged it will cause those exact symptoms.

It should be pulled and cleaned at every oil change.
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This why I don't like to do blind "internet troubleshooting".

Doc said in his first post that he and his A&P are baffled, this would lead me to "assume" that they have done some preliminary troubleshooting which "to me", would normally include checking pressures, making sure there are no obstructions, cleaning/checking filters, checking fitting security etc etc..
 
Don't forget the issue with the flop tube coming off inside the tank. I didn't see that he switched tanks.
 
have done some preliminary troubleshooting which "to me", would normally include checking pressures, making sure there are no obstructions,
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I agree that blind internet troubleshooting is not optimal but when stumped posing the question to a broad audience may generate some not heretofore thought of options.

I was surprised when my filter clogged how many "builders" ,including
myself, and A&P/IAs where unaware of the filter.

Unfortunately early in the process of clogging fuel flow and fuel pressures were within normal limits.
 
Switched tanks. Checked flow. Changed mechanical pump. Checked vents. No flop tube. Airframe is an early 7a.

Based on everything we know so far it just about has to be firewall forward and fuel related. But I was not aware of a pre controller filter, nor morning sickness. Thank you all for the assistance. And we're still open to suggestions.
 
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Just heard from our friendly A&P. He was aware of the fuel controller filter and cleaned and checked it, along with the the others. Evidently that's where he disconnected the fuel line and measured that the pump ( and the mechanical pump plugs out and using starter) would put out about 50 gallons an hour.

The pilot described the problem as an abrupt power loss, with the engine going to a low rough idle. Morning sickness or ??? can do that? And the pilot said the gauges all seemed to read normal???

The A&P is considering taking the spider off and sending it to Don for overhaul.
 
Doc, Get the Airflow Performance manual out and look in the troubleshooting section. I still bet you have an air leak in the system. Don
 
Sticking valve/morning sickness (which involves one cylinder 99.9% of he time) isn't going to take you idle, as described in the initial report.

As for Internet troubleshooting, if it's so questionable, then why does anyone read or post here in the first place? Obviously, you have to take things read here with a grain of salt and do your own cross checking. I had a nagging, chronic (minor) engine problem that went on for years solved with Internet troubleshooting. Sure am glad I asked!
 
I misread the original post, I thought he pulled it it idle. I agree, a sticking valve would not cause the engine to go to idle.
 
Low Pass said:
As for Internet troubleshooting, if it's so questionable, then why does anyone read or post here in the first place? Obviously, you have to take things read here with a grain of salt and do your own cross checking. I had a nagging, chronic (minor) engine problem that went on for years solved with Internet troubleshooting. Sure am glad I asked!
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Why do people post, because folks like to speculate on things and it's "fun" to try to guess whats wrong (anybody can do it, no experience required :D).

However, troubleshooting is about solving a problem by going through a detailed step by step, logical, process of elimination.

About all the info given in the first post was my engine is cutting out and now I'm baffled, can you help. So I would suggest that if you are looking for good focused ideas then you need to provide very detailed information:

1) Specifics about the equipment involved (mags, FI or carb etc)
2) Recent work/repairs (when is the last time the plugs were cleaned for example)
2) How many hours on equipment (new low hour engine/ovh'd 3 times etc)
4) Exactly what things that have been done to try to solve the problem
5) Symptoms - did it start all of a sudden, getting worse, temp related etc.
6) Instrument readings such as EGT/CHT/fuel/oil/pressures/volts/amps etc.
 
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Bill.Peyton said:
I misread the original post, I thought he pulled it it idle. I agree, a sticking valve would not cause the engine to go to idle.
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To the unintiated though it may "feel" like it went to idle due to such a sudden loss of power.
 
I understand the "feel" of going to idle from full power, too. When my Rocket "lost power", it was actually still running at about 900 rpm. Don't know the exact figure for the RV7A, but it wasn't enough residual power to sustain flight.

Our A&P, IA, RV builder buddy finally was able to duplicate the issue on the ground. He's narrowed the problem to the fuel controller. It will be interesting to find out what the exact problem was with the controller.

Thanks for everyone's input. I know it's tough to troubleshoot on the internet, but I think it's critical to share safety and operational information like this. Even those folks who misread, or misdiagnose issues usually add something positive to the conversation. That's why I keep coming back here, there's just SO much to glean from sharing with others. Particularly others more experienced, those who have been there and done that.

I'll let you know what they find out.
 
Engine problem solved!

CONCLUSION: Turned out to be contamination beyond the filter screen inside the Airflow Performance fuel controller. Some fibers and gummy crud had evidently slipped through the pores in the screen and clogged the inlet. When you pulled the filter out, nothing was in it. Up inside where it seated, a glob of clog blocked the fuel flow. The controller had to be completely disassembled (by Don @ AP) and returned to service. There was even debris under the diaphragm. Very weird. No signs of any debris ANYWHERE in the entire fuel system. Hopefully pictures are forthcoming.

Tom, my Rocket is running great. I just replaced a defective electronic ignition controller. Insulating the firewall and adding blast air behind the avionics will not only keep the ignition controllers happier, it really reduced the cabin heat and cut down the noise a little.
 
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