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Engine missing - out of ideas

N23WL

Member
Consultation: RV9a with a TMX-360 Air Flow fuel injection, dual e-Mags, @ about 300 hrs. TT engine and airframe. About four months ago it began to miss occasionally on decent and lower RPM at operating temperature at or > 155-170 degrees F. The condition has continued and increased to the point that on let-down to pattern altitude, I am afraid to let the RPM drop below 1,000. To save many of the diagnostics questions, here is additional information.
Key points:
Runs perfectly below oil temperature 155 degrees and above 100 degrees until it starts to miss
Use only 100 LL
The inline filter was never installed but I do have good pressure distally at the air filter
Condition is worsening as time goes on.
Mixture setting and boost pump do not play a part
Loaner set of new E-mags are properly installed/timed - doesn?t change the problem.
Old plugs never gave a hint if a problem. Replaced with iridium
I don?t know - but don?t really suspect a stuck exhaust valve
Compressions all in the mid/high seventies.
More: Mag check revealed normal loss during runup, continues to run with the master off if the RPM is above 900 RPM. Engine will stop if the mags are placed in the test position below 900 RPM. E-mags (Company) have check my set and found them to be serviceable and even loaned me a set for testing. The leads are new and the plus are new and iridium.
All grounds have been tested and secure. The master and solenoid have been changed because the cost was low based upon the theory that the solenoid (internally grounded) might be the culprit. Actually, by chance or design worked for three hours flight then the problem continued.
Voltage: Good battery 13.4-13.8 at the post. 12.6 at the firewall ground. 12.3 at the master. Full load, i.e., master, mags, radios, transponders, cooling fans, etc. showed a drop only to 12.1 volts.
The alternator checked out while cool and continues to leave the battery charged after running.
I have not checked the fuel injectors.
Thought about the diaphragm on the fuel pump but again, the pressure seems good and the boost pump doesn?t help. Mixture doesn?t change the problem.
I would appreciate discussion, questions and any ideas anyone has.

Thanks!
 
Just a thought, and I'm sure more knowledgeable folks will be along soon, but have you checked for intake leaks? What does your EGT do when the engine starts missing? Lastly, do you have log data to analyze?
 
Mark,

Thanks for responding. Your question is good but I can't answer specifically because my GRT CHT & EGT is unreliable. I ran the engine from startup to operating while conducting a series of IR temperature readings on all cylinders; This includes both at the exhaust manifold and on the cylinder walls.

The temperatures, though not true as they would be from the probes were entirely consistent and within the norms from the start of the test when the engine was cold until full operating temperature. I too was looking for an inconsistency in a cylinder or exhaust temperatures but didn't find one.

That was a good question and I am sorry I did not include that information in my initial post.

Thanks!
 
Thoughts

I have zero experience with Lycoming but a fair amount with auto engines - obviously, I am not an expert but - I'd first change the 'new' plugs out for another new set. Sometimes, you will get a bad plug right of the box. Next, I'd ohm out your spark plug wires and replace all of them if one of them is bad. These can deteriorate with time on any engine. Probably would check for sticking valve first. Please let us all know which action solved this problem - good luck.
 
I had a Lyc 0-360 in my Starduster Too that had a strange miss. It went away after I checked the valve lash and adjusted the push rod lengths to meet spec. Its an easy check.
 
Has the engine been run and then set idle ( put aside during the build) for an extended period of time? If so it's possible to be the dreaded Lycoming cam & tappet rust . I hope I'm wrong but if performance gets worse at an accelerating pace ( just 5-10 flight hours) this could be it . An oil filter inspection in a few more hours can confirm or exclude .
 
You are really handicapped not having the EIS working properly. The info you could download and analyze would greatly simplify your diagnostics.
I think the suggestion to check your valve lash is a good one based on what you?ve told us.
Good luck
Tim Andres
 
TMX 160 engine missing

I want to thank everyone for the suggestions. I have the suggestions in hand and will move forward in this order.

1. Check the valve lash and adjust the push rod lengths to meet specifications. I had not thought of that.
2. I have checked the plugs and plug wires and they pass resistance testing
3. I am considering cleaning the injectors.
4. The engine has never been idle for any length of time but I'll consult a pro on the rust issue.

I will report back

Thank you for taking the time to help me through this.
 
My 9A does something that I assume is similar and its heat based. When coming in to the pattern on a hot day the engine will stumble a bit due to fuel flashing in the fuel lines. I was able to minimize this by shielding the fuel lines from exhaust heat but I have yet to completely eliminate it.

Do you have issues with the engine stumbling at idle on hot taxi's? I do.
 
EIS

As Tim suggested, I'd call GRT and get the EIS working right. That will really help diagnosis.
 
Mark,

Thanks for responding. Your question is good but I can't answer specifically because my GRT CHT & EGT is unreliable. I ran the engine from startup to operating while conducting a series of IR temperature readings on all cylinders; This includes both at the exhaust manifold and on the cylinder walls.

The temperatures, though not true as they would be from the probes were entirely consistent and within the norms from the start of the test when the engine was cold until full operating temperature. I too was looking for an inconsistency in a cylinder or exhaust temperatures but didn't find one.

That was a good question and I am sorry I did not include that information in my initial post.

Thanks!

You are really handicapped not having the EIS working properly. The info you could download and analyze would greatly simplify your diagnostics.
I think the suggestion to check your valve lash is a good one based on what you?ve told us.
Good luck
Tim Andres

As Tim suggested, I'd call GRT and get the EIS working right. That will really help diagnosis.
I know this does not solve your problem but can you detail exactly why you see your GRT as 'unreliable'? As others have posted, these readings can tell you a lot. I have had many conversations over the years with GRT personnel over the past decade. They are the best when it comes to customer support.

On another note, you might think about looking at fuel injectors. I have not had the stumble you mention but I have had problems with one cylinder that we resolved when we cleaned the injector screens.
 
Darin,

Your message is of particular interest because I suspect I may have been cooking fuel for some time now. I have shielding material available to construct a shield and test it this afternoon. This makes particular sense given the proximity of the fuel lines to the exhaust/and relative easy for me to test. Thanks!

I ordered a new GRT and was not able to get it because of a delay on their part. I have located a distributor and am making progress in getting something going so I have reliable engine readings on all perimeters.
 
As you come back to idle, the flow divider comes into play. You might want to disassemble it (it's in the AFP manual) and check for junk - especially since you say you did not install the inline filter.

If you are not comfortable disassembling the flow divider, send it off to Don and he'll check it on the bench for you.

Similarly, the fuel servo has an idle circuit that could be coming into play. It would need to go to Don for that check, IMO.
 
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As for cooking the fuel - it's entirely possible. I double-firesleeved my FWF fuel lines to give them more insulation and put heat shields on the exhaust where it was needed, and that would be more than sufficient for running 100LL. Running Mogas or 91E10 can still be challenging with a good heatsoak.
 
I have similar issues (AFP FI, dual P-mags) with the fuel injection lines boiling in any warm weather (and its always warm in San Diego). Engine just will not idle happily below 1000 rpm when we are taxiing. As long as I have some airspeed on descents the spider lines stay cool enough, but as soon as I land and start taxiing, then I have to keep the rpm's above 1000.

I have the red cube on the firewall, so that adds a bit of unneeded length to the fuel lines firewall forward, and I have the dual mufflers on the Vetterman exhaust, which transfers a lot of heat behind the baffling. Both of these probably contribute. Also I'm swinging a lightweight composite prop. I did try insulating and shielding the spider lines, but it really had no effect. The engine runs fine as soon as the RPM's come up. I just don't let the RPM's go below 1000 when flying. I've heard of some other potential solutions, which is to put in a heavier spring in the fuel flow divider, and/or smaller injector nozzles to keep a bit more pressure on the fuel. Search here and you'll find other threads with the same story.
 
TMX 360 Missing

Update for everyone that has been good enough to provide suggestions and experience to help resolve this problem. We have looked at each of your posts and are 1) monitoring or have 2) ruled out...R/O for now, at least.

I found the new solenoid I put in earlier (three hours operating time) may have failed. This is an oddity in itself since they rarely go bad. This morning, I'll install a new one and orbit the field and see what happens.

If I have lost a second solenoid, it is time to look closely at what would have caused it, a bad part or something in the charging system.

I'll report.

Thanks
 
Just a couple thoughts: 1-I've had two bad master solenoids in a row, one was new as replacement for the original that failed before I even moved the plane to the airport. The second was bad out of the box, It happens. 2-be careful when you torque the connectors on the new solenoid as it's easy to over torque them and damage the solenoid. As I recall, no more than 35 in-lbs or something like that.
 
Compression tests often will not show a "sticky valve". I wouldn't rule that out. I can't count how many times members here have reported odd misses and after lengthy troubleshooting, have ultimately found it was a valve that wasn't behaving.
Your EMS is invaluable here.
 
Maybe

When you say on ?decent? the cylinders cool.
And the valve guides get a little smaller
And maybe that?s when the sticking exhaust
Valves make them selfs known.Try running some
Unleaded gas for a few hours to clean the valves
And then see what happens?
 
TMX-360 Missing

The second solenoid was replaced today, bring the total to three since the aircraft was built. The solenoid was the problem and now, the low RPM missing has been resolved and confirmed with a lengthy ground and flight test.

This is the third solenoid on this aircraft and the second in a week to be replaced. One has to ask the question - how often do two solenoids fail? It is unusual, to say the least and brings about a question of whether there might be a culprit lurking in the electrical system, e.g., the alternator. Time will tell.

I hope that this experience might help others by encouraging ruling in/out a problem systematically (and with help) and NOT just replacing parts in an attempt to fix a symptom. Frustrating as it might be, investigate.

Thank all of you for all the help.
 
What solenoid? You mean coil maybe?
I?m very curious to know how a solenoid could cause the engine to run rough....
Tim Andres
 
He did say he has E-mags; IIRC the original version was dependent on ship's electrical power. So I'm guessing he's talking about the master solenoid.
 
The second solenoid was replaced today, bring the total to three since the aircraft was built. The solenoid was the problem and now, the low RPM missing has been resolved and confirmed with a lengthy ground and flight test.

This is the third solenoid on this aircraft and the second in a week to be replaced. One has to ask the question - how often do two solenoids fail? It is unusual, to say the least and brings about a question of whether there might be a culprit lurking in the electrical system, e.g., the alternator. Time will tell.

I hope that this experience might help others by encouraging ruling in/out a problem systematically (and with help) and NOT just replacing parts in an attempt to fix a symptom. Frustrating as it might be, investigate.

Thank all of you for all the help.

Do you have the surge protection diodes on the solenoid? Van?s has them.

Surge protection diode for Master Switch
Part Number = ES DIODE MASTER
Price = $11.00

Bob
 
FWIW, you can make either of those protection diodes with a couple of ring terminals and a 1N400x (substitute any number between 2 & 9 for the x). Available everywhere, from Radio Shack to the best electronic supplier. Total cost, under a buck, after you buy the shrink tubing to go over it.

To the OP:

I'm late to this party, but your answer was hiding in your 1st post. You should see minimal voltage drop through your various connections and switches and/or relays/contactors. Over 1 1/2 volts of drop from battery terminal to buss says something is wrong, unless you have isolation diodes in the mix somewhere. And always use the negative battery post (not the terminal; the actual post) as reference when you're doing voltage measurements.

Charlie
 
TMX-36 Missing

Hello,

I will try to respond to some comments but only with my limited experience and learned knowledge on the subject.

I used he Van's Master solenoid and yes, it is protected and torqued to spec. I could NOT put the solenoid in with the recommended downward position because of space limitations. There is no space without a major rewire and new conduit through the firewall. That may affect the life of the solenoid.

Since I am using Van's parts and have encountered a failure on the second of three solenoids, I am watching to see if I encountered a fluke (solenoid failure) or do I need to look at other sources of possible spikes or down graded current.

Marvel mystery oil. Absolutely. I used t it now as both a fuel & oil additive.

E-mags? yes

Further testing? Scheduled for a high orbit f/ 1-2 hour flight today and if there is any mention of a miss, I'll report.

Thanks so much.
 
These solenoids should last a long time unless.......you have a start relay in place of a hold relay-solenoid. one is for intermittent operation and one is designed to remain on continues duty......:rolleyes:
 
I used he Van's Master solenoid and yes, it is protected and torqued to spec. I could NOT put the solenoid in with the recommended downward position because of space limitations. There is no space without a major rewire and new conduit through the firewall. That may affect the life of the solenoid.

Sure this is correct? On the -7, the MASTER goes on "rightside-up", and the STARTER goes on "upside-down" (ostensibly to prevent the starter contactor from engaging during high-G maneuvers). Drawings might show something different for your bird, dunno...

Do you have a pic of your setup?

ETA: seems obvious, but you never know...when installing the solenoids, you have to put a wrench on the studs to prevent them from turning while tightening down the nut holding your ring terminal. Well-known installation error that can lead to failures.
 
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TMX-360 missing

2018/02/02

1. I'll post photographs of the installation of the solenoid in a few days. Work interrupting...

2. There is no question, I am dealing with the Master solenoid, not the starter solenoid. and it is continuous duty.

3. To respond to the question is the engine missing or backfiring. It is a solid miss; not backfiring.

1/31/2018 I flew for 3.5 hours at a variety of altitudes, speeds, and conditions and never a miss. Once I landed and turned off the runway, the missing began. The characteristics are puzzling. It might miss one and stop or miss in succession and almost stall the engine. It has only stopped once in the months of dealing with the problem and only at taxi idle. Consensus remains electrical v fuel v. valve lash.

Back to my flight: I fueled, visited with airport residences and received numerous suggestions but that gave the engine time to cool (1 hr). Started up, again, no more missing until it reached an oil temperature of 175 D F.

4. I'll work for a few days and fly on my company's ticket and think.

Meanwhile, thank all who have shared their experience and knowledge.

Thanks again
 
This thread is confusing to me, as I thought the problem was reported to have been resolved through replacement of the solenoid. Now that doesn?t seem to be the case?

The description to me sounds like nothing more than a hot engine vaporizing fuel when there is minimal fuel flow and air flow. Very commmon and not really a problem. I have all the same symptoms. Just keep the idle speed up a bit after landing to increase the fuel flow slightly.

Erich
 
Engine missing

The 0-320-E2D in my airplane started acting up last Spring and it took me until last week to finally find the problem.
Despite the intake ducting not creating any foaming bubbles when pressurized with vacuum-cleaner exhaust and sprayed with soapy-water solution, I decided to change the rubber sleeves on the intake pipes and the gaskets between the cylinder heads and intake pipes, more out of desperation than any moment of inspiration.
I was most surprised to find-not one but two-of the pipes loose where they are swaged to the oil sump. I'm guessing that this part of the sump is the last part of the engine to stabilize at operating temperature and that could well explain why the engine would run fine until twenty-five minutes into flight and then start stumbling and shaking with an associated rpm loss. Two of the four cylinders were running too lean.
 
The 0-320-E2D in my airplane started acting up last Spring and it took me until last week to finally find the problem.
Despite the intake ducting not creating any foaming bubbles when pressurized with vacuum-cleaner exhaust and sprayed with soapy-water solution, I decided to change the rubber sleeves on the intake pipes and the gaskets between the cylinder heads and intake pipes, more out of desperation than any moment of inspiration.
I was most surprised to find-not one but two-of the pipes loose where they are swaged to the oil sump. I'm guessing that this part of the sump is the last part of the engine to stabilize at operating temperature and that could well explain why the engine would run fine until twenty-five minutes into flight and then start stumbling and shaking with an associated rpm loss. Two of the four cylinders were running too lean.

When rough running appears only at low MP/high vacuum, intake leaks rise to the top section of the troubleshooting list.
 
Is this a carb'd engine? If so, this may sound obvious, but have you checked each cylinder's injector/primer ports? I had a plug come out during a trip to OSH one year, in a recently purchased plane. Was running fine at one fuel stop, then when I reduced power to descend to a lower altitude, the engine shook like crazy. Raised the power back to cruise setting, and it smoothed out. Next stop I discovered the empty injector port. A trip to a local hardware store for a pipe plug got me back to 'normal'.

Charlie
 
I'm sorry, but I just can not resist a light-hearted joke. I see this thread title show up periodically as a new post is made, and each time I see it, I have the same reaction:

"Engine missing - out of ideas"

My Mom would say, "have you looked under your bed?" :rolleyes:
 
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