Possible injection system problem

Bubblehead · #1 10-04-2010, 04:00 PM

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.

molson309 · #2 10-04-2010, 09:21 PM

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?

Bubblehead · #3 10-05-2010, 06:08 AM

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.

David-aviator · #4 10-05-2010, 07:07 AM

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.

Bubblehead · #5 10-05-2010, 09:02 AM

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.

molson309 · #6 10-05-2010, 05:46 PM

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

Bubblehead · #7 01-22-2012, 08:20 PM

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?

zav6a · #8 01-22-2012, 08:37 PM

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?

rocketbob · #9 01-22-2012, 08:55 PM

Quote:

Originally Posted by Bubblehead

For a fuel injected engine with RSA system is 13 too low?

Way too low. Surprised it runs at all, if the pressure reading is correct.

Bubblehead · #10 01-23-2012, 05:07 AM

"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.