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Possible injection system problem

Bubblehead

Well Known Member
I've been battling gremlins for 6 months on my engine. Every time I think I have things solved, the engine proves me wrong.

For about 6 months the engine would start fine, run fine, the plane would fly about the same speeds as always, but occasionally would start running rough and lose a little power. I'd try richening, leaning, mag checks, throttle back, throttle up, and sometimes it would get better and sometimes not.

For a while I thought it was dirt getting into injectors. I inspected the sleeves with a magnifying glass. Sometimes I'd find a little piece of dirt but usually not. Sometimes the problem got better only to later to reappear. I checked the fuel filter and fittings and never found anything in the filter and the fittings look good.

A month ago I pulled the magneto cap (dual mag system) and ignition wires and found a spot worn through the insulation to the conductor. I ordered a new harness and cap, but it has not arrived yet. I repaired the damaged area with silicone stretch-tape and carefully routed the wires. For a few flights things were smoother but Sunday I flew to Midland, TX from Ft Worth and back to visit family and it acted up a little going and a lot coming home. 1 hr 15 mins is a long time when an engine is running intermittently rough.

For most of the 6 months I did not have a way to record data from the EIS, but before leaving Sunday I plugged in my EIS Mate and recorded the 3 hours of flight time. I graphed EGT and fuel flow and noticed that EGTs are fluctuating about 50 to 100 degrees and fuel flow is fluctuating about 1 gph. I noticed that while in flight yesterday but did not realize how bad it was.

I went back over data from flights last spring and last fall, and in the fall it varied a little, and got a lot worse in the spring, but not as bad as it is now.

I noticed one other strange indication yesterday. Usually when I turn my boost pump on or off the fuel flow changes about 0.3 gph and then within a few seconds returns to the same fuel flow as before. Yesterday it jumped up about 1 gph and took a minute to return to the old flow rate.

Does it sounds like the fuel injection servo or spider might be bad? It has 600 hours on it on this airplane but I'm not sure how much total time it has on it. My next guess is mechanical fuel pump is going bad.

I need to call Don at Airflow and get his opinion but I thought I'd start here and learn more before taking some of his time.

One additional piece of data. I just did a little statistical look at the cruise portion of the flight from Midland, TX to Ft Worth, TX.

Cylinders 1 and 3 had the biggest variation of EGT temperatures with a standard deviation of 23.9 and 22.3 respectively compared to 9.3 and 11.9 for cylinders 2 and 4. Whatever is causing this seems to be affecting the right side cylinders more than the left side.

Fuel flow varied from 7.7 to 9.2 gph. Not sure why it drifted up to 9.2 but it did and I then leaned back to about 8.5.
 
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What airbox are you using, and do you have an alternate air door on it?

I have an Airflow Performance injector on my RV-7A, it's mounted vertically on an IO-360 and attached to the Filtered Air Box (FAB).

I have the alternate air door that is cable operated. One time I flew from Minneapolis to Oshkosh and had very weird symptoms. The engine wouldn't lean correctly, fuel flow was all over the map, and I had to run the engine a LOT richer than normal to keep it smooth. When I landed I discovered the alternate air door had come disconnected from the cable and had subsequently opened. The turbulent airflow resulting from taking air through the door caused the injection system to act strangely.

Perhaps you have something disrupting the airflow in your airbox?
 
Old snorkel

Great question. I have a horizontal induction system with what I am told is the original Vans snorkel type intake. It has a spring loaded alternate air door, so I have no way of knowing if it is open or not. I have to do an oil change this week so will take a look at that while the cowl is off. Perhaps the spring is weak. maybe I'll tape it up to see if it changes.

I just checked my log book. Since 8/29/10 I've flown the plane 30 hours. For about 27 or more of them the engine ran fine. It sure is getting old.

I think a call to Don Rivera is in order. I think that the variations in fuel flow are causing variations in power and variations in EGT especially in #1 an #3. Either injector problems or spider problems or servo problem or all three.
 
A couple observations -

Fuel flow does change if intake air is changed, probably because there is a change in air flow and pressure. The controller is very sensitive to these changes. The air filter may need cleaning and/or changing, or the spring at the door is inadequate.

It appears you have no idea how old the fuel controller and divider are. It may be time to send both to AFP for a rebuild and bench test.
 
I agree that it may be time for an overhaul of the injection system but hate to pull it all off the plane, have the plane down for a month, and spend a few hundred dollars just to find out that was not really the problem.
 
I was going to add that I originally had the magnetic door on the FAB in my -7A. I had no end of fuel flow anomalies until I replaced it with the cable operated version. In particular takeoff power would cause it to open and this caused fuel flow to go through the roof. However, it would also partially open at other times causing fuel flow to fluctuate in strange ways. At takeoff power my fuel flow showed 22+ GPH instead of the 16.5 I was expecting (and got, once the door stayed closed).

If your spring operated door is doing something similar this would match what I encountered when mine was malfunctioning.


Mark Olson N407V RV-7A N16XV F1-EVO Rocket
 
More of the same

This weekend I had this same problem again. I thought I had found the source of earlier problems - induction leaks. I found two intake tubes with cracks around the flange that sits up against the cylinder, and all four o-rings were bad. I guess I did not get the root of the problem solved because the rough engine came back in spades Saturday and I had to land in Enid, Oklahoma and hitch a ride home.

In Enid an excellent mechanic checked timing and compression and could see no obvious isues. By that time it was 10 pm Saturday night and we called it quits for the night.

Shame on me for not checking some of the things suggested in this thread. I found some problems and thought I had found THE problem.

I can't get back to Enid for two weeks due to family commitments so will have the mechanic pull the fuel controller and flow divider and send them to get checked at AFP.

I think there are two other sources of the trouble. In a post I made in another thread I posted that my fuel pressure is about 28 psi. Yesterday the pressure was about 13 and has been for quite a while. With the boost pump on I only get about 1 psi rise in pressure. I changed where I sensed fuel pressure a couple of years ago and chalked up the change in pressure to that change but really don't know if they are related.

For a fuel injected engine with RSA system is 13 too low? Perhaps Don will comment but perhaps I have an obstruction in the fuel system. Since it happens even with full fuel and either tank I don't think it is a vent line issue but will check that too.

Lastly when I go back up I will close off the alt air door. I have the original FAB system with a spring loaded door and perhaps as several people have suggested the door is opening in flight.

Any other ideas?
 
Fuel filter

Check fuel filter behind the connection to the throttle body/servo. You will see nothing but try to blow through it then back flush with aerosol can of carb cleaner on a white paper towel. Repeat that cycle several times and note the change in apparent back pressure when you blow through it.

It is a very fine filter and the stuff it catches is scarcely visible to the naked eye though you wil note darkening on the white paper towel.

The source of some of the debris in my filter was the electric pump slowly wearing out.. Has that breaker ever blown?
 
"Special Delivery" posted this in a different thread and I wanted to record it on this thread.

Just tossing this recent personal experience into the pot... cold starts were becoming less predictable over a two week period. Then one day at full power on take-off came the cough and sputter of fuel starvation. Run-up was ok and idle was ok... but when the engine needed a volume of fuel, it just wasn't there. Don answered the phone on this particular Saturday and after we field checked the flow divider (removed cover) it was found that the shaft from the spring load to the diaphragm was in a severe bind. Sent the RSA and divider in for service... RSA checked ok but divider required complete rebuild. I mention this in the off chance that you might want to check your divider before it goes to Don.
 
The Plan

Here is the plan. Please critique.

1) Pull fuel servo and flow divider and send to Don at AFP

2) get a new hose to replace the 10 year old one that connects the servo and divider

3) install a new fuel pump.

4) (re)test fuel tank vents.

I tested the fuel tank vents once before in two ways. First, I took the tank filler caps off and gently blew through each vent. In neither case did air flow very easily but it did flow. Then at the December condition inspection when the root fairings were off I disconnected the vent lines at the wing root, hooked up a short, L-shaped length of tubing to the tank vent, and blew through that. The air flow seemed about the same as when I blew through the vents on the bottom of the fuselage.

I suspect the main cause is low fuel pressure caused by a failing engine driven fuel pump

What confuses that issue is turning on the boost pump does not clear the problem.

And what confuses that issue is when I turn on the boost pump I only get about 1 psi rise, and the pressure does not go to 25 psi which is the relief valve setting on the boost pump. Perhaps the boost pump is bad too?

Questions? Ideas? Comments?
 
Bubblehead,

I had the same indication on my fuel flow on Saturday
at Hicks. Ernie and Jay helped me diagnose it.
I had a Fuel sender that had the post rotating.
Turned on the Boost pump read 13 would rise 1psi and
move the post with wire and jump to 27.
Ordered new fuel sender.

Engine was not running rough. RTB'd

Is your diaphram spitting fuel out of the fuel pump
to the ground from small overflow tube ???

That would indicate a problem with the mechanical fuel pump.

Hope this helps a little bit.

I would check fuel flow to mechanical pump first, then check it from
there to divider.
 
say a 10 year old hose? I hope it was teflon-
Y'know, I still see 40-70 year old 303/111 hoses between the carb & gasco to this day (I change 'em as soon as I get my hands on 'em and the owners not looking). I don't know how they got by so long. I've taken them off and just had them snap when you bend them. Nice huh?
For the OP's problem these suggestions all sound good, but the first thing I'd do is tee in an analog pressure gage. Then you'll know at least if your problem is upstream or downstream. Divide and conquer.
 
I would start off with replacing the 10 yr old hose and then verify fuel pressure with a separate gage. Fuel pressure issue should be corrected before any further troubleshooting.

Go from least expensive to most expensive, one step at a time otherwise we won't learn much from our trouble shooting experience.
 
All good suggestions

The servo and flow divider are leaving for Airflow Performance tomorrow. A new hose is on order, along with a new fuel pump.

I love the analog pressure gauge idea and will do that on the new fuel pump to verify pressure.

I think the spring on the alt air door is weak but no way of measuring it so will wire the door shut for the test run. Or maybe test run and then wire shut if there is still rough operation. I inspected the air filter and all is good.

Need to test the vents but it would seem if any air moved when I blow on it then it would be keeping up with fuel flow. The problem happens equally on left tank as right. Maybe both are a little restricted but it should not take much air to flow to keep the tank pressure at ambient. 8 gph is only 3/4 gallon every 6 minutes.

Keep the ideas coming but I think the fuel pump is the culprit.
 
I think you're on the right track, but before sending a bunch of parts off and replacing stuff, I think I would have verified that fuel pressure. The RSA needs about 20psi, but can handle more. I wouldn't think that it would affect individual egts, so you may have multiple things going on.

I believe it is a good idea to correct what you know is wrong and then go from there. There are times when it is just not possible to measure what is going on, but an analog gage to confirm the fuel pressure would go a long way in isolating the problem.

Assuming you confirm low pressure, then you can go after filters, fuel pumps etc.
 
Consider sending the injectors and fuel lines and have them flow (checked) and matched.
 
The injector bodies and orifices were replaced with new 2 years ago. I did not think about sending the lines with the servo but we did do the flow check of the nozzles and they met the flow requirements per the AFP documentation.

I wish I had thought of the analog pressure gage check on Saturday night.

Don at AFP said in an email to me that the flow transducer should be between the servo and the flow divider. I think I will temporarily remove it from the system until we get the engine running right.
 
Flow check?

While you have the system open, you may want to pump gas into a container using the electric fuel pump to get an idea of flow or possible obstructions in the lines/filter.
I.E. Record how long it takes to fill a 3 gallon can.
 
Don at AFP said in an email to me that the flow transducer should be between the servo and the flow divider. I think I will temporarily remove it from the system until we get the engine running right.


Verify and fix the obvious- the 13 psi fuel pressure.

The shotgun approach to trouble shooting can be expensive and unfulfilling....ask me how I know :eek:

IMHO, don't waste time futzing with the flow transducer unless you reinstall it immediately. For now, maybe look inside to verify it is clean, but don't pull it and not have the data it offers. It is a valuable diagnostic tool, and all I think anyone can say about location is the transducers are more stable and accurate between the servo and flow divider- however there are probably thousands installed before the servo working just fine.

The fuel system behavior sounds to me like air in the system. If the pumps can't get a full charge of liquid, they aren't going to achieve target fuel pressure. Seems unlikely both are going bad at the same time, more likely both are fuel starved at the same time (assuming your gauge is correct at 13 psi). I'd look for upstream restrictions, loose fittings, fuel selector seals..... that type of thing, something that would let air into the system.
 
Not shotgunning

I've been troubleshooting this logically for about 2-1/2 years. The problem persists despite finding and fixing issues like cracked intake tubes, defective intake tube o-rings, and ignition wire insulation worn off in 2 spots.

My bottom line now is I am tired of being a test pilot. I will re-qualify the injection system and the ignition systems so that I eliminate them as either the primary or as contributing factors in the problem.

AFP has bench tested the servo and it is in spec although bushings are pretty worn. It is now in line for rebuilding. The hose between the servo and the fuel divider is old and Airflow Performance is making a new one.

The Magnetos are on their way to Ly-con in Visalia (as suggested by Don at AFP) for a "stress test". They were rebuilt 3 years/300 hours ago but depending on what Ly-con finds they may get rebuilt again.

I will eliminate non-essential components from the fuel system (flow transducer) and the intake system (alternate induction air flapper) to eliminate any contribution they make to the problem.

I will measure what I can (compression checks out fine) correct what I suspect (bad fuel pump, although I admit a mechanical gauge would have been a smart check.)

The hoses from the firewall to the servo are only two years old but we are pulling them off and inspecting them, and will replace them if they look like they are obstructing fuel flow.

We're going to check the fuel tank vents again to make sure air flows through them at an acceptable rate, although I don't know what rate that is! I will probably go blow in someone else's vent tube with the fuel cap off and get a feel for what good is then compare it to my airplane.

I know this is going to cost me some $s but I am sick of flying with a knot in my stomach. We're going to fix this! I appreciate everyone's suggestions. It has been very helpful!
 
John,
from what I know of, the common fixes with your issue have already been posted. Many are watching this thread, including myself. Wish I could help more. Since you did not know the hours/years on your spider it is good preventitive maintenance to rebuild it along with the other things of same.

You will have a nice rebuilt fuel system soon. Hopefully the culprit part will be identified when re-installed and tested.

Thanks for posting your issue and especially your progress. Your issue will help many be more knowledgeable on this issue. I have seen A&P's have much frustration with this same issue. Your thread brings out possible issues involved.
 
Thanks for the words of encouragement. They have helped me look forward in a more positive manner. I'll keep posting what is discovered along the way. Hopefully it will be of value to others.
 
It sounds like you'll have a bird you can feel confident in when you are done. That's key. Just don't forget the elephant in the room, that 13 psi indicated fuel pressure. There are a few of us wondering about that- expecting you should see 25 psi there or so.
 
nomocom - that one looms large with me too. I wish I had taken a reading with an analog gauge to verify the pressure before pulling the servo and fuel pump. When everything is installed we will use an analog gauge to verify pressure.

The low pressure with some under-cowl heat plus a small obstruction in a hose or the fuel flow transducer could be causing vapor which would make it go lean. OAT was about 50F when I had the problem so it would not seem to be likely, however all possibilities must be explored at this time.

Fuel pressure seems the most likely though.
 
It's hard to enjoy yourself when you fly behind an engine you are not 100% confident in.

Have you had any more luck with your troubleshooting?

Cheers,
 
You are in Texas .....Walt is in Texas

Threaten him with greenbacks.

Strip everything and while you are at it look at the cam etc and then put all the ancillaries back on.
 
Walt and I know each other well. He's done my static system checks and W&B and prop balancing and I trust him a lot. I will brainstorm with him about the problem.

The Fuel Injection system is now overhauled and on it's way back to Enid. The mags are at Ly-Con for testing and I hope to hear something yet this week from them.
 
John,
I'll probably be over to Hicks this weekend for the RV-1, I'd be glad to come over and brain storm with you.

We need to get this fixed :D
 
Thanks Walt. I'll be out there too. The plane is still in OK so nothing much to do this weekend.

See you at Jay's.
 
Heresy

Find a really good mechanic experienced with AFP and your mags. While we have a natural aversion, hiring a professional is sometimes warranted. After 2 1/2 years, I would say you are more than entitled.
 
Thanks for the good advice, Duane. Everything will be back in Enid next week and I'll be there with an A&P friend from Ft Worth early Saturday morning. The mechanic in Enid will install the new fuel pump, rebuilt AFP system and mags and is inspecting all the fuel hoses this week. No news yet on the magneto testing though. I will call Ly-con later today.
 
Here's another recommendation for AFP. I had AFP rebuild my Bendix FI last Fall.

My engine exhibited roughness at low MP, typically while in the pattern or taxing back from a flight. The problem manifested very slowly over a period several years and I kinda got used to it. Besides, the engine never quit. Then I went flying with a friend from the MN Wing after he helped me install a Dynon Skyview. He was not happy at all with the roughness and before the following week the FI was on its way to AFP. I did not have any prior records of FI servicing. I bought the plane in 2001 and it had been flying since 1997.

I sent AFP the throttle body, flow divider, injectors, and lines. The fuel pump was new from a recent engine rebuild. Don red tagged the injector lines, rebuilt the rest, cleaned and flow tested the TB and nozzles. I reinstalled the works and the engine now runs excellently at all throttle settings.

My only remaining nagging question relates to my WOT fuel flow. I have an IO-360 and I get a bit over 15 GPH (measured with a Shadin Econonflow). The spec says it should be 18 GPH. Don flow tested the throttle body and it will deliver 18 GPH with the corresponding air flow. WOT fuel flow has always been on the low side. I have learned to live with it.

Nancy
 
Nancy - excellent additional information. My WOT fuel flow has been low too, around 15 gph like yours. It will be interesting to see what flow I get when everything is back together, although I am planning on leaving fuel flow transducer out of the system for the testing. That would eliminate one potential source of the problem.

In talking with several people over the weekend including Walt Aronow a stuck valve is another possible source of the problem. All the cylinders compression check fine but the #3 cylinder, which shows problems first, had an oil-fouled lower plug and a little oil was in the bottom of the cylinder when we pulled the spark plugs out.

I've asked the mechanic in Enid to do the wobble test on the exhaust valve on #3. We'll see what he finds.
 
Welcome to VAF!!!!

My only remaining nagging question relates to my WOT fuel flow. I have an IO-360 and I get a bit over 15 GPH (measured with a Shadin Econonflow). The spec says it should be 18 GPH. Don flow tested the throttle body and it will deliver 18 GPH with the corresponding air flow. WOT fuel flow has always been on the low side. I have learned to live with it.

Nancy

Nancy, is with the boost pump on or not??

And, I see this is your first post-----Welcome to VAF:D
 
Thank you, Mike, for the welcome.

The WOT fuel flow is with the boost pump on. The boost pump does not affect the WOT fuel flow at all. Don explained to me that in order to get 18 GPH I need a corresponding volume of air. I tried opening the alternate air but that had no effect. The reason I ponder the low flow is:

1. Does this mean my engine is not developing full HP on takeoff?
2. On hot days (85F) I can see my CHTs approach 400F by the time I get to pattern altitude.

I read that the WOT fuel flow cools the engine. In cruise flight I run LOP and the CHTs will drop below 330F.

Be that as it may, my engine runs so much better after getting overhauled by AFP.

Bubblehead, I look forward to hearing how things go when you get the FI back.

Nancy
 
My experience

I had lots of problems trying to figure out my RSA running really rich at WOT, in-fact it was so rich I lost power at full throttle but recovered it at a LOWER throttle setting.

I had the servo flow checked and kept being told it was fine. Then I got in touch with Terrilee at Aircraft Fuel Specialties in MD. She suggested I have the verturi removed and the verturi and air chamber checked for oil contamination. The technician did this and found a small amount of oil behind the venturi, he cleaned it and I put it back on the engine.

Low and behold, problem gone away. Apparently this is not uncommon and won't show on a bench flow test. Terrilee said she has seen this on servos before when oil leaked into the intake and was sucked into the servo. There is a service bulletin from Precision Air motive referring to it but it doesn't describe my symptoms exactly.
 
Cautiously Optimistic

The plane is back at Fort Worth - Hicks and things seem to be working right. Here's what we found.

1) Manifold pressure sensor line from #3 cylinder was loose. That is probably why I was losing so much power and had to land in Enid. The fitting into the cylinder does not have an orifice, which surprised me since I used the Van's kit when I installed it. The line is now tight and will have an orifice in it very soon.

2) One coil in the Bendix 2000 series dual mag showed signs of significant distress, although it tested fine on the bench. The mag is now upgraded to a 3000 series with two new coils.

3) The spring in the Airflow Performance fuel filter was installed (by me) backwards. I don't think that would cause a loss of fuel flow. More likely it mean I was not fully filtering the fuel.

4) The cap on the fuel filter was a little loose, which might have allowed air to be drawn in my the fuel pump. There was never any fuel smell in the cockpit so no fuel leaked out, but perhaps air leaked in.

5) Airflow Performance tested the fuel injection system and found only minor wear problems. It's now rebuilt.

6) The hose from the servo to the flow divider was very old and is now new with fire sleeve to reduce chances of vapor lock.

7) The hose from the mechanical fuel pump to the servo has been rerouted to be farther away from the exhaust pipes, improving safety and reducing chance of vapor lock.

8) The mechanical fuel pump was replaced due to perceived low fuel pressure. I might have avoided this (see next item) but the pump was of indeterminate age and hours. Chalk the cost up to "insurance."

9) Fuel pressure was checked with an analog gauge and found to be about 28 psi, which is good. The Dynon SkyView, however, only displayed 16 psi. I checked the fuel transducer and found it was not the right model. I replaced with the correct model and now the display agrees with analog gauge.

10) Oil pressure was also checked with an analog gage, even though oil pressure was satisfactory. Found the SkyView was reading about 6 psi low. The transducer was the correct one, but was apparently defective. I replaced it with a new one from Dynon and oil pressure indication agrees with the analog gauge.

11) One CHT probe was bad. It is now replaced and CHT now reads correctly.

Everything was completed late afternoon last Friday. The skies were blue and clear, there was NO wind (yes, in Oklahoma) and nobody else was in the pattern. I explained to ground that I needed to stay in a position to make a landing if the engine started acting up, and the tower controller was very helpful. I flew for about 20 minutes without any hint of trouble.

Saturday morning I needed to take care of some business by car in Kansas, then I returned to Enid to face 30 mph winds but they were lined up right down the runway so I took off, climbed to 7500 feet, and used flight following to keep a friendly voice in the headset. 2-1/2 hours later I landed at Hicks with out incident.

Sunday I pulled off the cowling, checked everything for leaks, lose wires or hoses, etc., and after finding things were fine, buttoned it up and flew it hard for an hour. Everything was rock solid.

So what have I learned? There were a lot of little things plaguing this engine over the last year or so and it took a loose sensing line to make it so bad I had to spend the money and time to get everything as right as I could make it. My flying budget took a big hit - basically 2012 gas and fun money is gone, but at least it looks like when I can fly I will be able to fly with confidence in the plane. Only time will tell, of course, but that is why I labeled this "cautiously optimistic."

So I need to say thanks to God for keeping me safe, to Don and Mike in Enid for doing great work on the plane, and to Ken at Airflow Performance for spending a lot of time on the phone explaining things to look at, many of which turned out to be contributing factors. Also a thanks to Will for the ride home in his Super Viking, Gary at Enid for his kind offer of help and words of encouragement, and Charlie for a ride to/from Tulsa in his great -6 to pick up the new coils. Oh, and Jay, Walt and others at Hicks for helping diagnose the problems and Jim for a ride to my apartment in Keller from Hicks.

At age 57 I am no longer surprised at how many people are willing to help a stranger. It has been the rule, not the exception in my life that people are willing to help. But I did re-discover that blessings are always found in times of trouble.
 
Bubblehead,

I am happy to hear you are back flying with solid engine performance. You have invested your money wisely.

You nicely articulated the blessing we receive from strangers and from our friends in aviation. I enjoy several hobbies, but flying is the one hobby where I rely on the wisdom and skill of many folks to supplement and guide my choices.

Did you observe your WOT fuel flow rate?

Nancy Jean
 
Here we go again

8.4 flight hours since fixing everything we could find or think or and the problem is back. I was on my way back to Hicks (near Fort Worth) from Midland, TX and just before starting a descent things started running a little rough. I delayed the descent but when I finally throttled back the EGT on cylinder #3 shot up and the engine started running rough again.

I switched tanks, put boost pump on - no change.

Richened mixture slightly, with no improvement. Leaned slightly, but no improvement. Decided to leave it alone and concentrate on arrival, which went ok except on each throttle reduction #3 EGT would go up for a lot, then drop to be in line with the other cylinders.

I pulled the cowl today to see if the manifold pressure line had loosened yet, but that was tight. I checked all fuel and ignition connections to #3 but they're good. I pulled the spark plugs but they look good.

So where do I go from here? Fuel injections and mags were rebuilt, engine driven fuel pump new, old hoses replaced, fuel filter checked and fuel tank vents are ok. Compression checked fine after the last occurance and the exhaust valve wobble test was passed.

I think i'll go back to drinking. I was better at that than owning/maintaining an airplane. It was a lot cheaper too.
 
Change the plugs on #3 and while the plugs are out have a quick look inside with a borescope if you can get access to one.
 
I like the boroscope idea, Bob. I'm sure someone around here has one.

On the plugs, should I swap them with the plugs from #1? If the problem moves to #1 it would tell us a lot.
 
My -8 has an early design filter and intake system that has a spring loaded flpper valver for alternate air in case the filtwr becomes blocked.

At some point Van's changed to a cable operated system.

Does anyone remember why the change was made? Could I be having the flapper occasionaly opening in a shallow descent putting hot, less dense air into the intake? It would seem that would make the engine go rich, lowering EGT, not lean.
 
My -8 has an early design filter and intake system that has a spring loaded flapper valve for alternate air in case the filter becomes blocked.

At some point Van's changed to a cable operated system.

Does anyone remember why the change was made? Could I be having the flapper occasionally opening in a shallow descent putting hot, less dense air into the intake? It would seem that would make the engine go rich, lowering EGT, not lean.

John,
One way to check that would be to temporarily install a small "lipstick" camera pointing at the alternate air door, so that you could record what it does during a decent. Maybe you could borrow one from a friend? Another "inexpensive" troubleshooting experiment would be to swap the $3 injector onto another cylinder to see if the high EGT stays or changes cylinders. Just a suggestion and worth what you paid for it.
Charlie
 
How about mag wires, were they checked/replaced?
I'll be over at Hicks tomorrow, give me a call.
 
Charlie - I can always count on your for good ideas. I have a small cheapie video camera that might work. I could also try a small piece of tape as a "Tell tale."

Walt - ignition wires were new about 200 hours ago and we recently visually inspected them again. When the problem started 2 years ago we found two areas with worn insulation. We replaced them and redid all the securements to avoid a repeat.

I won't be able to get to Hicks until late afternoon.

Do you have a boroscope that can get into a cylinder?
 
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