Van's Air Force
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MP at idle
- Thread starter Plummit
- Start date
Kahuna
Moderatoring
Marc you will never be able to determine a leak this way.
Simple way:
Run engine at idle
get a can of spray ether. Starting fluid works.
run engine at idle chocked, tied down etc..
Safely!!!! Spray fluid around all intake tube ends, carb/fi bodies, vac lines etc. If you have an intake leak, there will be an audible difference in the engine. You will say Boom, there it is.
Good luck.
Simple way:
Run engine at idle
get a can of spray ether. Starting fluid works.
run engine at idle chocked, tied down etc..
Safely!!!! Spray fluid around all intake tube ends, carb/fi bodies, vac lines etc. If you have an intake leak, there will be an audible difference in the engine. You will say Boom, there it is.
Good luck.
AX-O
Well Known Member
I had this conversation with Don at Airflow performance.
At 800 rpm you should see MP between 9-10 inches leaned out. Thats how i found mine. I noticed at one point i was reading over 11. Then someone pulled my MP line on the FWF and it fell off on his hand.
Now i can hold it at 9.3-9.4 inches. Yours may vary a small amountt based on your set up.
At 800 rpm you should see MP between 9-10 inches leaned out. Thats how i found mine. I noticed at one point i was reading over 11. Then someone pulled my MP line on the FWF and it fell off on his hand.
Now i can hold it at 9.3-9.4 inches. Yours may vary a small amountt based on your set up.
Plummit
Well Known Member
Thanks Axel, glad you finally got yours worked out! I've checked everything and I still indicate 14" at idle. I'm ready to look at the valves now.
regards
~Marc
vic syracuse
Well Known Member
Be careful.
As much as Mike's advice could be right, working around a spinning prop is way dangerous. It is too easy to get focused on the task and forget that prop is spinning.
First, make sure your MAP gauge is correct. For the digital gauges turn your altimeter until it shows Zero feet. Hopefully you are within a couple of thousand feet of sea level. Your MAP guage should match the number in the BARO window.
There are a couple of safer ways to skin this cat. First, as someone mentioned, high EGT's will definitely be caused by a leak. It's easier to see this airborne when you pull back the throttle on base or final to land. Your EGT's will spike like mad on the cylinders that have a leak.
Another way is to pressurize the intake system with a shop vac and spray soap bubbles around the intake tubes. Slowly move the prop around (make sure the igntions are off) so you get to a compression stroke on each cylinder. That will keep the induction system somewhat pressurized for that cylinder. If it is an intake valve leak you may be able to hear it if you remove the top spark plug and try to listen over the noise of the shop vac.
Or use a borescope to look at the valve.
Vic
As much as Mike's advice could be right, working around a spinning prop is way dangerous. It is too easy to get focused on the task and forget that prop is spinning.
First, make sure your MAP gauge is correct. For the digital gauges turn your altimeter until it shows Zero feet. Hopefully you are within a couple of thousand feet of sea level. Your MAP guage should match the number in the BARO window.
There are a couple of safer ways to skin this cat. First, as someone mentioned, high EGT's will definitely be caused by a leak. It's easier to see this airborne when you pull back the throttle on base or final to land. Your EGT's will spike like mad on the cylinders that have a leak.
Another way is to pressurize the intake system with a shop vac and spray soap bubbles around the intake tubes. Slowly move the prop around (make sure the igntions are off) so you get to a compression stroke on each cylinder. That will keep the induction system somewhat pressurized for that cylinder. If it is an intake valve leak you may be able to hear it if you remove the top spark plug and try to listen over the noise of the shop vac.
Or use a borescope to look at the valve.Vic
All good advice
can't add much to this discussion but here is some good advice that will save you time and uncertainty when you are facing a problem such as the one you describe.
At the very beginning when my engine was new I established in writing a number of engine parameters including MP at idle and in flight.
At every annual or anytime there is a question regarding engine performance,
I look at these numbers and enter the current numbers to establish a trend
if any.
A leak in any of the intakes would show up as increased EGT's as Vic pointed out and simply point you in the right direction to start trouble shooting.
This only works if you have an established base line but you can start this chart anytime and it will be useful in the future.
can't add much to this discussion but here is some good advice that will save you time and uncertainty when you are facing a problem such as the one you describe.
At the very beginning when my engine was new I established in writing a number of engine parameters including MP at idle and in flight.
At every annual or anytime there is a question regarding engine performance,
I look at these numbers and enter the current numbers to establish a trend
if any.
A leak in any of the intakes would show up as increased EGT's as Vic pointed out and simply point you in the right direction to start trouble shooting.
This only works if you have an established base line but you can start this chart anytime and it will be useful in the future.
Jesse
Well Known Member
I understand how an intake leak would react if carb cleaner was sprayed, but if we are talking about a fuel injected engine where the fuel is injected into the cylinder, would an intake leak really affect the mixture? The cylinder doesn't really care where it gets air from, as long as it gets it. It will get it from the path of least resistance, most of which will come through the normal channel, and a little of which comes through the leaky intake. The manifold pressure shouldn't change and neither should the mixture, except the leaky input air would be warmer than the normal path air.
On a carbureted engine, any leaking air at the intake would have no fuel with it, so this would effect the mixture.
Am I wrong in this thought process?
On a carbureted engine, any leaking air at the intake would have no fuel with it, so this would effect the mixture.
Am I wrong in this thought process?
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Plummit
Well Known Member
Jesse, I'm obviously no expert but I think that the missing part of your scenario is in the route the air takes to get to the cyl.
In an injected engine all of the combustion air should go through the servo, which adjusts the amount of fuel going to the flow divider. If the air gets to the cylinders without going through the servo, then there will be no more fuel added which causes a lean mixture. The higher MP would come from getting more air to the deck. At least that seems to be the way things work, but what do I know? I never really thought about this until you posed this question.
What I don't understand is how the MP gets a reading for the manifold when it's taken off of one cylinder (#5 on my engine). It would seem like it would only measure the one cyl. Also, with an air leak why would the EGT go up if you throttle back? I would think the opposite would happen.
regards
-Marc
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vic syracuse
Well Known Member
It gets leaner
The EGT's go up with an induction leak because the mixture gets leaner. More air is allowed to get into the cylinder becuase it is taking a route other than the fuel-mixing route, whether it is at the carb or the injection servo. Both systems have metering devices based upon the airflow (simple description). Allow air to come in from another source and all bets are off. The mixture is now much leaner.
Vic
The EGT's go up with an induction leak because the mixture gets leaner. More air is allowed to get into the cylinder becuase it is taking a route other than the fuel-mixing route, whether it is at the carb or the injection servo. Both systems have metering devices based upon the airflow (simple description). Allow air to come in from another source and all bets are off. The mixture is now much leaner.
Vic
Jesse
Well Known Member
I agree with this. The overall mixture gets leaner, but not the mixture in the cylinder that has the leak versus the other cylinders. My point was that you can't necessarily find the leak by comparing EGT's on a fuel enjected engine versus a carbureted engine.
EGT's at ground idle
The safe , fast and accurate method, to ID what cylinders may have an induction leak, is to use your EGT at ground idle. Lean the engine to max RPM at about 700 - 750 RPM. Then see what if any cylinders EGT rise above the others.
If your probes are connected to the instrument to indicate the actual cylinder # , then have a close look at the intake flanges and the intake tubes for fuel stains.
Also, have you checked the accuracy of your MP instrument, in the range of interest? After you do the normal EGT /idle test, just for your own interest/satisfaction loosen the MP fitting at the cylinder and do the idle EGT test again for a few seconds and observe the difference.
The safe , fast and accurate method, to ID what cylinders may have an induction leak, is to use your EGT at ground idle. Lean the engine to max RPM at about 700 - 750 RPM. Then see what if any cylinders EGT rise above the others.
If your probes are connected to the instrument to indicate the actual cylinder # , then have a close look at the intake flanges and the intake tubes for fuel stains.
Also, have you checked the accuracy of your MP instrument, in the range of interest? After you do the normal EGT /idle test, just for your own interest/satisfaction loosen the MP fitting at the cylinder and do the idle EGT test again for a few seconds and observe the difference.
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Plummit
Well Known Member
Here's what I know so far:
* Barrett IO540 with 9:1 pistons and AFP 200 FI system built in 2009. Aero composite 3-bladed CS prop. Rod Bower ram air. 2 Bendix 1200 series mags that were newly overhauled at engine build. 185 hours tach time since new.
* At 150 hours hobbs time the number 1 cylinder was pulled and sent back to Barrett for "excess carbon build up". Barrett honed the cylinder and either lapped or ground the valves.
* The engine had a variation at idle of 150-200 RPM when I first flew it 6 month ago, but otherwise seemed to run fine and always made good power. Lately it's developed a miss at idle and during runup, with an occasional miss in cruise flight. The miss is not mag specific. The MP at 700-800 RPM idle is 14 inches.
* So far I have replaced all the plugs with Tempest fine wire plugs. I have cleaned the injectors and checked for equal fuel flow using the baby jar method. I have replaced all of the intake gaskets, top and bottom. 2 gaskets looked suspicious, like they may have been leaking.
The flares on some of the fuel lines in the tunnel looked imperfect, and these were either corrected or remade. The mechanical fuel pump was bypassed and the engine run with just the electric pump in case the mechanical bump was leaking air into the fuel system. I cleaned the sniffle valve and made sure the ball inside could move freely.
* After the fuel lines were corrected the engine was started cold and ran really bad, even after warming up some.
* So far I've had two A&P I/A mechanics help with the work and one person who used to work at AFP help check then FI system, but he didn't check the servo or flow divider as that has to be done on a flow bench at AFP.
Today I will either remove the sniffle valve and plug the opening or block it so no air can get in that way. I doubt that anything I do today will resolve the issues but I'll at least rule out one more thing. I will also verify the MP reading before engine start.
I will also video the engine page of the 900X and post it. I realize that there may be multiple issues such as an air leak, sticky valves, and a bad servo or flow divider. I don't have the experience to deal with the valve guides or FI system, but I'm open to suggestions.
This is a poor video that was done with he sniffle valve removed and blocked off.
https://youtu.be/zi-ZM-qn_Ao
regards
-Marc
* Barrett IO540 with 9:1 pistons and AFP 200 FI system built in 2009. Aero composite 3-bladed CS prop. Rod Bower ram air. 2 Bendix 1200 series mags that were newly overhauled at engine build. 185 hours tach time since new.
* At 150 hours hobbs time the number 1 cylinder was pulled and sent back to Barrett for "excess carbon build up". Barrett honed the cylinder and either lapped or ground the valves.
* The engine had a variation at idle of 150-200 RPM when I first flew it 6 month ago, but otherwise seemed to run fine and always made good power. Lately it's developed a miss at idle and during runup, with an occasional miss in cruise flight. The miss is not mag specific. The MP at 700-800 RPM idle is 14 inches.
* So far I have replaced all the plugs with Tempest fine wire plugs. I have cleaned the injectors and checked for equal fuel flow using the baby jar method. I have replaced all of the intake gaskets, top and bottom. 2 gaskets looked suspicious, like they may have been leaking.
The flares on some of the fuel lines in the tunnel looked imperfect, and these were either corrected or remade. The mechanical fuel pump was bypassed and the engine run with just the electric pump in case the mechanical bump was leaking air into the fuel system. I cleaned the sniffle valve and made sure the ball inside could move freely.
* After the fuel lines were corrected the engine was started cold and ran really bad, even after warming up some.
* So far I've had two A&P I/A mechanics help with the work and one person who used to work at AFP help check then FI system, but he didn't check the servo or flow divider as that has to be done on a flow bench at AFP.
Today I will either remove the sniffle valve and plug the opening or block it so no air can get in that way. I doubt that anything I do today will resolve the issues but I'll at least rule out one more thing. I will also verify the MP reading before engine start.
I will also video the engine page of the 900X and post it. I realize that there may be multiple issues such as an air leak, sticky valves, and a bad servo or flow divider. I don't have the experience to deal with the valve guides or FI system, but I'm open to suggestions.
This is a poor video that was done with he sniffle valve removed and blocked off.
https://youtu.be/zi-ZM-qn_Ao
regards
-Marc
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A few similar symptoms
For what it is worth.. I had a frustrating couple of years with a 9.5:1 540 CBB5 not terribly different from what you have described.
I did have 2 significant induction leaks show up at idle EGT indications. Gaskets cured that.
I did the flow test at the injectors with finely graduated cylinders. Not perfect, but not wildly bad either. Then new spark plugs. No joy so I replaced the injectors with a new set of silverhawk injectors. Considerable improvement with matched EGT's in flight, but no joy with a power issue. Then the gascolator quick drain started a slow weep that turned into a blue streak. It was an Andair gascolator with AN -6 ports. The screen was always clean. Never any water. So I replaced the quick drain and it was like I had afterburner thrust instantly restored on take off. Then in less than one year my bird almost killed me on take off with the mother of all stumbles just airborn on a short strip. Reducing throttle saved my bacon and restored enough power to fly. The weep/drip and blue streak had instantly returned with the new quick drain. 2 strikes and your out, If you are a problem child gascolator in my ship. I replaced it with a high pressure / high flow auto racing machined housing fuel filter. After burner thrust restored. No missing and no stumbles. Just smooth massive power.
I will not trust my life to an Andair gascolator ever again. Fuel flow and engine power were within the gascolator specifications, however, the engine was making enough fuel suction or negative pressure to open the quick drain. Life is too short. Even a more robust quick drain still would have left high negative presssure in the fuel system within the gascolator, so it had to go. The filter area in the new unit is 3 - 4 times what the Andair unit had.
This might not be your issue at all, but it could be part of it. Best of luck in resolving your problems. FWIW you might find inspiration in Tom Martins recent post about the 270Kt club. A lot to be said for lower compression factory Lycoming cylinders and pistons.
For what it is worth.. I had a frustrating couple of years with a 9.5:1 540 CBB5 not terribly different from what you have described.
I did have 2 significant induction leaks show up at idle EGT indications. Gaskets cured that.
I did the flow test at the injectors with finely graduated cylinders. Not perfect, but not wildly bad either. Then new spark plugs. No joy so I replaced the injectors with a new set of silverhawk injectors. Considerable improvement with matched EGT's in flight, but no joy with a power issue. Then the gascolator quick drain started a slow weep that turned into a blue streak. It was an Andair gascolator with AN -6 ports. The screen was always clean. Never any water. So I replaced the quick drain and it was like I had afterburner thrust instantly restored on take off. Then in less than one year my bird almost killed me on take off with the mother of all stumbles just airborn on a short strip. Reducing throttle saved my bacon and restored enough power to fly. The weep/drip and blue streak had instantly returned with the new quick drain. 2 strikes and your out, If you are a problem child gascolator in my ship. I replaced it with a high pressure / high flow auto racing machined housing fuel filter. After burner thrust restored. No missing and no stumbles. Just smooth massive power.
I will not trust my life to an Andair gascolator ever again. Fuel flow and engine power were within the gascolator specifications, however, the engine was making enough fuel suction or negative pressure to open the quick drain. Life is too short. Even a more robust quick drain still would have left high negative presssure in the fuel system within the gascolator, so it had to go. The filter area in the new unit is 3 - 4 times what the Andair unit had.
This might not be your issue at all, but it could be part of it. Best of luck in resolving your problems. FWIW you might find inspiration in Tom Martins recent post about the 270Kt club. A lot to be said for lower compression factory Lycoming cylinders and pistons.
Plummit
Well Known Member
Update
Tonight we checked the valve clearance on the number 1 cylinder then pulled the pushrods on a couple of others and decided that the clearances were ok. Put it back together and decided to run it again. Out of desperation my mechanic happened to check the nuts that secure the servo to the mounting plate and the plate itself. One nut required 3/4 of a turn to tighten! We then ran the engine again and found that it suddenly would die if the throttle was pulled to idle position. Also, the flow divider was spitting fuel out of the vent hole in the bottom. A closer look showed that the flow divider had been leaking for a while, just not very much at a time.
We pulled the servo, purge valve and flow divider to send to AFP for repair.
Maybe we are finally getting closer to resolving the problems,
-Marc
Tonight we checked the valve clearance on the number 1 cylinder then pulled the pushrods on a couple of others and decided that the clearances were ok. Put it back together and decided to run it again. Out of desperation my mechanic happened to check the nuts that secure the servo to the mounting plate and the plate itself. One nut required 3/4 of a turn to tighten! We then ran the engine again and found that it suddenly would die if the throttle was pulled to idle position. Also, the flow divider was spitting fuel out of the vent hole in the bottom. A closer look showed that the flow divider had been leaking for a while, just not very much at a time.
We pulled the servo, purge valve and flow divider to send to AFP for repair.
Maybe we are finally getting closer to resolving the problems,
-Marc
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Plummit
Well Known Member
Update X 2
Talked to Airflow performance this morning and they had to rebuild the flow divider and repair the fuel controller. The system was set up too lean, and the leak in the flow divider was making things worse. Also, there was wear in the the fuel controller from a loose nut - I think it was the throttle - and they had to replace a part (not sure which).
Bottom line is it should run like it's supposed to once we get the fuel controller readjusted to run without the air leak. Interestingly, everyone pretty much felt that the FI system was OK, and the problem was elsewhere. Turns out there were 3 separate problems.
I'll post a followup when we get it running again.
regards
~Marc
Talked to Airflow performance this morning and they had to rebuild the flow divider and repair the fuel controller. The system was set up too lean, and the leak in the flow divider was making things worse. Also, there was wear in the the fuel controller from a loose nut - I think it was the throttle - and they had to replace a part (not sure which).
Bottom line is it should run like it's supposed to once we get the fuel controller readjusted to run without the air leak. Interestingly, everyone pretty much felt that the FI system was OK, and the problem was elsewhere. Turns out there were 3 separate problems.
I'll post a followup when we get it running again.
regards
~Marc
Hopefully a divider rebuild will fix Marc's problem.
You're right...so is Vic
At any large throttle opening, it would be hard to detect a leak via an EGT reading, as the leak itself will be very small...there's no significant pressure delta across the leak path.
At a throttled setting, there is a pressure delta, and the leak becomes a significant portion of the air supplied to the individual cylinder. That's why Vic said the EGT will spike when the throttle is pulled entering the pattern.
You're right...so is Vic
At any large throttle opening, it would be hard to detect a leak via an EGT reading, as the leak itself will be very small...there's no significant pressure delta across the leak path.
At a throttled setting, there is a pressure delta, and the leak becomes a significant portion of the air supplied to the individual cylinder. That's why Vic said the EGT will spike when the throttle is pulled entering the pattern.
Bubblehead
Well Known Member
I struggled with intake leaks for quite a while. Bad gaskets, bad o-rings and flange cracks until I switched to the Superior cold air sump.
The test I prefered is found in a Diagnostic Manual from Electronics International http://buy-ei.com/wp-content/uploads/2013/06/Pilots-Manual.pdf
That booklet has a lot of great information in it including an Intake Leak Test that is done in flight. It's pretty easy and you're not working close to a swinging prop. The test is done in two parts, first, at full power, full rich, level flight. Record EGTs and then reduce power to about 55%, full rich, level flight, and record the EGTs again. Calculate the difference between the EGTs for the cylinders at the different power levels and they should all be about the same. A leak will make a cylinder go leaner since MAP<BP and EGT probably went up.
I also learned to watch EGTs when I do a power reduction into the pattern. A leak would show up as a big spike in EGT.
The test I prefered is found in a Diagnostic Manual from Electronics International http://buy-ei.com/wp-content/uploads/2013/06/Pilots-Manual.pdf
That booklet has a lot of great information in it including an Intake Leak Test that is done in flight. It's pretty easy and you're not working close to a swinging prop. The test is done in two parts, first, at full power, full rich, level flight. Record EGTs and then reduce power to about 55%, full rich, level flight, and record the EGTs again. Calculate the difference between the EGTs for the cylinders at the different power levels and they should all be about the same. A leak will make a cylinder go leaner since MAP<BP and EGT probably went up.
I also learned to watch EGTs when I do a power reduction into the pattern. A leak would show up as a big spike in EGT.
