Throttle body issues?

[Jeff R]

I have been flying my RV-9A about 10 hours now, but the engine is making me nervous.

Here is the background information:

The engine is a YIO-320-D1A obtained new in mid-2008. It has been mounted to my airframe since late 2008. I used desiccant plugs for rust prevention. I have the Precision Airmotive Silver Hawk experimental fuel injection system, and I run a PMAG with BR8EIS auto plugs on the top and a standard Slick mag with standard aviation plugs on the bottom.

Ever since the first engine start the engine has run rough on the ground. We have adjusted the idle for about 750 RPM, but the RPM will vary and drop down below 500 (which is why we have a somewhat high idle speed). I have most always leaned aggressively on the ground to peak RPM to minimize plug fouling.

However, when doing a mag check at 1700, I often see drops exceeding 250 RPM, even 300, which occurs on both the PMAG and Slick. Sometimes, if I lean it out at runup, the mag drop will be around 150 - 200 on each. Sometimes when going to idle the engine will sputter to under 500 RPM and has even died on several occasions.

I can find no induction leaks. We have ried to set the mixture adjustment to give about a 50 RPM drop, though the adjustment is tricky as the RPM is often so variable, so the RPM increase might be closer to 100.

In flight, the engine has been perfect. I have been nervous about pulling it to idle, but it hasn't skipped a beat and has run flawlessly. I went up this morning and was going to go up again this afternoon but aborted due to the high mag drops and failure to clear it out with leaning during runup. (Drops were around 200 this morning - which is high, but 300 is well beyond by comfort range).

Pulling a top plug this afternoon showed lots of black (no fouling), which seems to indicate a too-rich mixture.

I have tried BR8EX and BR9EIX plugs with no noticeable difference. Taking plugs out and cleaning them makes no difference.

With equally bad performance on both mag and Pmag it appears problems in the electrical system can be ruled out. We have checked fuel low to the injectors and all looks fine, so the pump system can be ruled out. I have tried running with the boost pump on and off, where the pressure is 29 psi on and 27 psi with boost pump off. Not much difference. I also checked the filter at the throttle body and it was clean.

Fuel burn seems a bit high perhaps. Today I was burning 9.9 gph at 2070 RPM at 22.6 MP. The Skyview said the power was 63%. This was at pretty much full rich at 1,600 feet with a DA of about 3,000 ft. Isn't this a bit high?

I am wondering if the throttle body is putting out too much fuel. Even so, I can lean the mixture on the ground and the RPM will still vary by 100 RPM and more.

Any ideas?

[mahlon_r]

For starters, try checking that all the vents in the fuel injection nozzles are clear and that all he stainless orifices are in each nozzle. To check the vents remove the nozzle and place you finger over the outlet and blow into the inlet. The will force your breath out the vents. They should allow flow and the back pressure should feel about equal on all 4 nozzles when you do it.
When you have the big mag drops is the engine really, really rough or just grumbly?
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."

[thinkn9a]

remove and clean nozzles,..
use 20 min soak in Hoppes #9 gun cleaner, rinse with stoddard solvent (?mineral spirits?)

would also give them a call,..

my YIO-320 called for 175 rpm drop,.. but had note from factory that it was a little higher on test cell

[Jeff R]

Originally Posted by mahlon_r

For starters, try checking that all the vents in the fuel injection nozzles are clear and that all he stainless orifices are in each nozzle. To check the vents remove the nozzle and place you finger over the outlet and blow into the inlet. The will force your breath out the vents. They should allow flow and the back pressure should feel about equal on all 4 nozzles when you do it.
When you have the big mag drops is the engine really, really rough or just grumbly?
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."

We cleaned the injectors previously (and did the flow test into baby food jars) and noted no improvement. When I get the 300 RPM drops, the engine RPM is highly variable and the engine certainly doesn't sound right. Grumbly might be a better word than rough. When it is in the 200 range, it sounds decent enough but the RPM will still vary several tens of RPMs each way. In flight, the RPM is dead solid, even at idle. After landing, it will start to vary again and the engine will be grumbling.

We triple checked the timing. CHTs seem reasonable. MP seems reasonable. Plugs are dry - sometimes dark and sometimes a darkish gray. I thought the RPM was low for takeoff but I called Van's and they said with my 79" pitch prop the 2,150 to 2,200 I am getting is normal.

I have an IA and A&P stumped. I am thinking of calling an engine expert in to run tests.

[rocketbob]

Sure sounds like a miscalibrated fuel injection servo to me. But before you send it off...

Induction leaks typically manifest themselves in rough or high idle so I would for grins remove the induction tubes and replace all of the gaskets. Easy to do and the most likely source of an induction leak. Make sure you lubricate the gaskets when putting them on. I use TiteSeal.

[ColoCardinal]

Are you certain of the engine construction? You may want to do a compression test with an eye towards checking the valve rods. If they are slightly long, it could cause the same problems.
I wouldnt let it leave the ground until the problem was located and cured.

[mahlon_r]

Originally Posted by Jeff R

We cleaned the injectors previously (and did the flow test into baby food jars) and noted no improvement. When I get the 300 RPM drops, the engine RPM is highly variable and the engine certainly doesn't sound right. Grumbly might be a better word than rough. When it is in the 200 range, it sounds decent enough but the RPM will still vary several tens of RPMs each way. In flight, the RPM is dead solid, even at idle. After landing, it will start to vary again and the engine will be grumbling.

We triple checked the timing. CHTs seem reasonable. MP seems reasonable. Plugs are dry - sometimes dark and sometimes a darkish gray. I thought the RPM was low for takeoff but I called Van's and they said with my 79" pitch prop the 2,150 to 2,200 I am getting is normal.

I have an IA and A&P stumped. I am thinking of calling an engine expert in to run tests.

You didn't mention if you checked the nozzle vents as described. If you did and they were ok, then I would get the servo off and to a warranty station.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."

[RetiredRacer]

Originally Posted by Jeff R

I have been flying my RV-9A about 10 hours now, but the engine is making me nervous.

Here is the background information:

The engine is a YIO-320-D1A obtained new in mid-2008. It has been mounted to my airframe since late 2008. I used desiccant plugs for rust prevention. I have the Precision Airmotive Silver Hawk experimental fuel injection system, and I run a PMAG with BR8EIS auto plugs on the top and a standard Slick mag with standard aviation plugs on the bottom.

Ever since the first engine start the engine has run rough on the ground. We have adjusted the idle for about 750 RPM, but the RPM will vary and drop down below 500 (which is why we have a somewhat high idle speed). I have most always leaned aggressively on the ground to peak RPM to minimize plug fouling.

However, when doing a mag check at 1700, I often see drops exceeding 250 RPM, even 300, which occurs on both the PMAG and Slick. Sometimes, if I lean it out at runup, the mag drop will be around 150 - 200 on each. Sometimes when going to idle the engine will sputter to under 500 RPM and has even died on several occasions.

I can find no induction leaks. We have ried to set the mixture adjustment to give about a 50 RPM drop, though the adjustment is tricky as the RPM is often so variable, so the RPM increase might be closer to 100.

In flight, the engine has been perfect. I have been nervous about pulling it to idle, but it hasn't skipped a beat and has run flawlessly. I went up this morning and was going to go up again this afternoon but aborted due to the high mag drops and failure to clear it out with leaning during runup. (Drops were around 200 this morning - which is high, but 300 is well beyond by comfort range).

Pulling a top plug this afternoon showed lots of black (no fouling), which seems to indicate a too-rich mixture.

I have tried BR8EX and BR9EIX plugs with no noticeable difference. Taking plugs out and cleaning them makes no difference.

With equally bad performance on both mag and Pmag it appears problems in the electrical system can be ruled out. We have checked fuel low to the injectors and all looks fine, so the pump system can be ruled out. I have tried running with the boost pump on and off, where the pressure is 29 psi on and 27 psi with boost pump off. Not much difference. I also checked the filter at the throttle body and it was clean.

Fuel burn seems a bit high perhaps. Today I was burning 9.9 gph at 2070 RPM at 22.6 MP. The Skyview said the power was 63%. This was at pretty much full rich at 1,600 feet with a DA of about 3,000 ft. Isn't this a bit high?

I am wondering if the throttle body is putting out too much fuel. Even so, I can lean the mixture on the ground and the RPM will still vary by 100 RPM and more.

Any ideas?

WE have a Rotec TBI on 0-235 9a, and we were getting the same idle problems as you are (and sometimes a falter or rough running on T/O, but would clear itself).
Our 0-235 2C2 has a 6.7-1 comp ratio with two PMags with auto plugs. Because of the low compression I reduced the plug heat range down until we had "6" heat range plugs fitted. this helped some but didn't solve the problem.
Because it always seemed worse in hot weather I fitted a blast tube down onto the fuel inlet side of the TBI and went berserk with insulating the TBI and it's regulator, plus all the fuel lines (especially the steel fittings). 95% improvement (The idle is still not 100% smooth but heaps better) and even seems to have more power.

[RV10inOz]

Most likely the idle mixture is too rich. You should do your mag check leaned for best RPM at 1700, not full rich unless you are comparing something for diagnostics purposes.

http://www.precisionairmotive.com/Pu...s/25-020_a.pdf

Page 14 and 15 might be what you need to set your idle mixture properly.

Double check your timing!

[Jeff R]

Thanks for all the suggestions.

One thing I didn't do when I removed the injector tubes was close up one end and blow through. I only did a visual on that, though I did blow through some oil end to end. It won't be much trouble to remove the tubes again and do the blow-with-one-end-closed test to be sure.

The engine was new from Lycoming so I would not expect any leaks, but who knows? I have done a visual and found nothing to indicate there is a leak. If all I have to do is replace some seals, I will remove the tubes to check them. I read somewhere about needing a sweging tool however.....

I never thought about a blast tube. I had doubled up on the fire sleeve covering the TB input fuel line to try to prevent fuel vaporization. The outlet line from the TB doesn't pass close to any exhaust pipes. But, I suppose it gets pretty hot down there with all of the exhaust pipes. However, will blast tubes be effective on the ground?

It is difficult to set the mixture properly. The RPM is varying all over the place and one has to attempt a mental averaging of the readings on the Skyview. I think I am seeing around a 50 RPM increase as I lean out at idle, but seeing a 20 to 40 RPM change, when the RPM itself is bouncing by 50 RPM is difficult. Again I note that, in the air, the RPM is rock solid. When I do a mag check, I typically go to 1700 RPM and do it, I don't wait 30 seconds as recommended by Precision Airmotive. But, when I get large drops (300 rpm) I will run at 1700 and lean aggressively and that often gets the drop down to around 200. I will try the recommendation and see what happens, but I don't think it is going to solve the problem.

Thanks to everyone for their suggestions. I will report back.