No one really likes to test a component of an ignition system while the engine is running. Too easy to get hurt, and seriously hurt, by either high voltage or by the prop spinning. Testing the mag and electronic ignition on a bench machine is recommended if possible. As for the 3000 rpm's, that is just what I test them to on my machine.
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Troubleshooting ideas?
- Thread starter Tweetr
- Start date
Fuel flow can be perfect and the spark plugs will be wet if there is no spark after 30 ish seconds of cranking. If the mag is old, it probably won't fire the plugs until above 400 or 500 rpm's. So far, everything points to the LSE being bad. That is the only sorce of spark likely to start the engine. Maybe he can find someone at his ffield that has an impulse coupler mag/harness and just try it. He said there are mechanics on the field.
Long shot here...but. A friend had a similar problem with his 200HP O360 RV-4, though it ran strong on the ground, but quit when he leveled out..2 times, and made dead stick landing back at field. I solved it quickly by finding his fuel pick-up tube B-nut backed off allowing the pick-up to draw air at just the right attitude and fuel level. I lifted his tail while we ran the boost pump, and the sound went from cavitation to pumping. Have you checked connections other than the line you found?
Sorry, late to the game on this thread. I am not familiar with the “lse” ignition but I have dual p-mags on my 7 and just had this exact issue! Went through everything you have done and was pulling my hair out trying to find the culprit. Turns out, in my situation that 1 silly screw on my power buss had worked loose and that screw fed the power to the mags for start.
Battery was fully charged, volts on the buss where 13 plus, volts checked anywhere else were all good, starter would crank all day, but volts at the mags themselves were only 8.4v due to the loose screw on the terminal.
The pmags would fire just fine when I was pulling the prop through by hand doing the spark tests but when you hit the starter, the 8.4 volts dropped below the threshold of 8v and that is when the pmags go into “safe” mode. They will not spark below 8 volts.
Like I said, the spark test was good, timing, fuel, checked continuity of wires, changed plugs, shot glass test, pulled snorkel looking for rags, flow tested pumps and tank lines… very time consuming. Just 1 simple screw on the power to the mags up under the dash. Hope it helps.
Toolman
Certainly a possibility, but OP said he pulled the plugs and observed them sparking while cranking, so can't definitively call no spark as a cause. Sure, wet plugs are a real problem, but he has confirmed spark. He needs to work that into his routine. As I said, crank no start is tough. Some variables could be preventing a spark at other times even though the test was good. Hopefully he buys a timing light to more easilly confirm spark as he goes through the variable elimination process.
Observing raw fuel spewing out of the tail pipe during cranking puts excessive fuel delivery pretty darn high on the list IMO. That is a symptom that simply CANNOT be ignored! You will never get a kick with constant flooding. I am still comitted to finding out if the servo is dumping too much fuel, but that is just me and the OP has to decide what is best. When dealing with CNS, I am always sticking my nose in the tailpipe. Flooding is a fairly common cause of CNS (as is no spark) and you must be able to figure out whether you are too lean to kick or too rich to kick, once getting a positive spark confirmation.
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Yes, that's the direction I'm thinking. During the hard starting problems I had first thought it acted like it was flooded. I would use a flooded start procedure (crank with throttle full open and mixture ICO, then slowly advance mixture), but with limited success. Hard starting first start of the day beginning a couple of months back was my first symptom.
Interesting. I was hoping to find people with similar problems. The LSE specifies operation down to 5.5 volts, and starting down to 6.5 volts. I keep charging the battery between all these tests so as to start out with a fresh charge. I will keep an eye on the voltmeter while cranking to see whether it's dropping low enough that it might be a culprit.
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It occurs to me that I can isolate voltage drop as the problem pretty simply by attempting a hand start on the electronic ignition, bypassing the electric starter.
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This is exactly the kind of experience I was hoping to see. Thanks! I'm down to the long shot category.
When you say B-nut on the pickup tube, you mean on the fitting on the inboard fuel tank rib, right? I did take the inboard forward wing fairings off and torque all the fittings inside the wing roots. I didn't find any loose and I don't see any staining. I also have been attempting starts on both tanks, thinking a problem like that would be unlikely on both tanks at once. So far no "aha!" moment on the fuel delivery lines, except for that short tube from the fuel selector outlet to the electric boost pump.
I'm flattered that you think I have that much spare time and energy for something so silly! No, I have a real RV-4 stranded in a real hangar away from home and I'm really frustrated trying to get it home.
No, do not do this. If you electrical system is that flakey that it cannot power the Lightspeed during start, fix that first.
In the meantime, connect a temporary battery to power directly to the Lightspeed to eliminate this as a possible cause.
I still think the next move is to disconnect the Lightspeed (or just pull the Lightspeed breaker), pull the P lead off the mag (so you have a hot mag), put a label on the key switch that you do have a hot mag and try to start the engine. Put the P lead back on before touching anything in the engine.
In your video I note you are way over priming the engine.
Carl
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I’ve been following this thread, reading all the posts by OP and the troubleshooting suggestions. Wonderful “think tank “ of ideas.
So now I’m placing my bet: 33.3% chance of correctness. (Air-spark-fuel)
My late Father taught me electrical theory in simple kid terms (I was lots, lots younger)
“An electrical circuit has a “goesinta” and a “goesouta” and the ignition for an engine is like asking a girl out; the correct timing and forcefulness.” (Paraphrased somewhat by memory)
So I think the symptoms indicates a failing electronic ignition and I would rig her up to start with a known good magneto to verify.
Not my $.02 cents so I’m betting a $100 and if I’m wrong it’ll go to Doug for the forum. (Maybe even if we are correct as this is a great brain trust). - cappy
So now I’m placing my bet: 33.3% chance of correctness. (Air-spark-fuel)
My late Father taught me electrical theory in simple kid terms (I was lots, lots younger)
“An electrical circuit has a “goesinta” and a “goesouta” and the ignition for an engine is like asking a girl out; the correct timing and forcefulness.” (Paraphrased somewhat by memory)
So I think the symptoms indicates a failing electronic ignition and I would rig her up to start with a known good magneto to verify.
Not my $.02 cents so I’m betting a $100 and if I’m wrong it’ll go to Doug for the forum. (Maybe even if we are correct as this is a great brain trust). - cappy
walkman
Well Known Member
Graduated baby bottles are best for visual comparison. Or even a gram scale and pre-weighing each bottle for tare weight to be really accurate.
Yes, The B nut inside the tank that holds the pick-up in place. there is the SB for this. I've also don't tank re-seals on a few with flop tubes, were the tube becomes so stiff it doesn't reach bottom. It's those internal tank/fuel systems you can't see that can elude resolution. I hope the thinktank can find an answer for you soon.
I think you are close to solving your problem...
I would put some 100 LL in a spray bottle and spray it directly into the air intake 2 or 3 sprays...and crank!
If it fires, you officially have a fuel delivery problem. If it doesn't you have an ignition problem.
The engine will fire or it won't.
Steve
There is a disk of some sort in the servo that gradually closes off flow as you move the mixture arm. If there is a problem in there, fuel could still be flowing at ICO and cause flooding during your start procedure. The test I gave you will show if this is the case or not.
My theory is he is getting too much fuel not too little. Both conditions cause a no start, but thr visible fuel coming out of the exhaust points to too mucc, not too little.
Everybody keeps talking about ignition, but he is blowing visible raw gasoline out of the exhaust. Am I the only one thinking this is a problem? I will step away now. You are free to DM me if you would like further advice from me.
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I agree.....
I truly belive in Occam. Simplest solution is usually correct.
Next thing I would do is isolate the power to the ignition by hooking up a second battery supplying power only to the ignitions.
If it puffs, it's firing at some point. If it were a car, I would be looking at a bad cam chain, but in this case, it still sounds like spark is not where or when it should be.
Next thing I would do is isolate the power to the ignition by hooking up a second battery supplying power only to the ignitions.
If it puffs, it's firing at some point. If it were a car, I would be looking at a bad cam chain, but in this case, it still sounds like spark is not where or when it should be.
Yep. We did that. Disconnected P-lead from the mag, pulled the Lightspeed circuit breaker, and cranked. No pops at all.
I just cranked with a multimeter at the battery terminals. 12.8 volts when I turn the battery on, and that matches my cockpit voltmeter. During cranking it drops to 11.1 volts.
That's a good idea and easy enough to try. We are looking for a spray bottle.
And you are confident the mag is working?
I just tried a start with the breather hose disconnected at the Christen air/oil separator. No change. Got two good chuffs on the first start attempt, then nothing.
No, I'm not entirely confident. The mag also has 1650 hours on it. The last mag check was normal, but of course it doesn't guarantee that it did not fail enroute. The last mag failure I experienced in a borrowed RV-10 was exactly like that: normal mag check, 3-hour flight smooth as buttah, then at my fuel stop the mag check failed utterly on the left mag. Just like shutting the engine off. So in my experience a mag can fail suddenly. We found heavy arcing inside the distributor cap.
Yes, send the mag off for a 500-hour check is on my list to try.
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While you are at it, buy a nice pMag to replace the LightSpeed (like I did 20 years ago).
Carl
STOP THE PRESSES!
We couldn't find a spray bottle, but we pulled the filter off, opened the butterfly with the throttle, sprayed Gun Scrubber into the fuel servo, and cranked.
She started right up! Ran on the first compression as it's always done on cold starts for 25 years! Ran on the Gun Scrubber until it ran out. I advanced the mixture on one attempt. I hit the electric pump on another attempt. 4 attempts total. In each case the engine wound back down as it exhausted the spray cleaner.
Fuel metering seems to be the culprit. By the wet plugs and fuel mist coming from the exhaust I think it's excessively rich. We're going to pull the fuel servo and flow divider off and send 'em to Airlfow Performance.
Sounds like you found the problem.
Funny story though. It sounds exactly like an arching dist cap. I spent a day on Boca Chica once. Yea. Back then no Star Base. Just miles and miles of nothin'. Dang car was arching and wouldn't start. Luckily someone had a can of WD40 and we sprayed the gajesus out of it. Started right up. Funny, he was old school. He had me spin the motor while he ran his finger around. Pop, pop. Didn't even flinch. Oh, there's the problem.
Sorry, I'm not convinced.. Too many decsrepancies.. You're testing model is not good. If you tell us that the engine is already over rich and you add more fuel with the gun scrubber and it starts, there is somethings you have not told us. If the engine dies after you stop spraying gun scrubber into the engine, then it not getting any fuel. I am confused but you seem to be on the right track. If the too much fuel is your guess, then a hot start proceedure would have cleared the problem in the first place. Like I said before, maybe you left the purge valve open and you were not getting enough fuel. In any case, keep us posted.
And, as Don Rivera points out, it could still be spark. The Gun Scrubber aerosol spray is easier to ignite than 100LL. If it is excessively rich, I would think I could get it running by sweeping forward from idle cutoff! So it's not 100% the fuel servo , but at least I have a path forward from here. If I get the fuel servo back in overhauled condition and it still acts up, I know where to go from there.
The whole assembly is going in to Airflow Performance for overhaul: fuel servo, flow divider with purge valve attached, and 4 injectors.
I'm just gonna say what I'm thinking...IF you're going to replace a mag....get a Bendix. If you're gonna replace LS...get P Mag or Surefly.
Not saying anything terrible about Slicks...just sayin. Bendix.
If this is from the fuel selector, it would have negative pressure leaking air in. That would be an issue causing air in the lines and lean operation.
I am agreeing with your theory...black smoke equals too much fuel...however...If you spray fuel directly in and get a snort...you have proven the ignition is alive...now you have a fuel delivery issue.
dave wolfe
Member
The only unintentional engine failure I experienced was caused by the idle mixture adjustment self adjusting itself too rich. This was on a 172 which had the injected 360 motor. Engine died in air.
Your symptoms match up. It was a problem that got worse over time.
Cessna had a SB on the topic shortly after my incident. It could just be a matter of adjusting the idle mixture to fix it.
Your symptoms match up. It was a problem that got worse over time.
Cessna had a SB on the topic shortly after my incident. It could just be a matter of adjusting the idle mixture to fix it.
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Do you have a link to the SB in question? I'm interested to read it.
dave wolfe
Member
I misremembered it was actually an AD:
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Okay.
As of yesterday we can put a period on this maddening troubleshooting.
Yesterday we reinstalled the overhauled Airflow Performance FM-200 fuel servo, flow divider, purge valve, and 4 injector nozzles. (I did not send in the injector lines because my testing showed full fuel flow through them.) After we torqued the last fitting and double-checked everything, I dragged it out for a start attempt, having changed nothing else yet except the AFP system.
She started right up on the first compression and ran smoothly up to max ground power. Started on only the LSE electronic ignition, having changed nothing in that system. Then mag check at max ground power was normal on both ignitions, on only the LSE, and on only the Slick mag. Normal-normal. Idle RPM is a bit high at 1050, but that's easily adjusted.
I conclude therefore that it was indeed the Airflow Performance fuel servo that caused my problems. For a month or two prior it had become hard to start on the first start of the day, so something had changed. The reason it finally started to quit on me during landing probably was that mechanical fuel pump also failing, dumping fuel overboard through the external drain line. Unrelated, I think, but that is what finally caused me to start the troubleshooting.
I called Don Rivera at AFP to find out what he did on the overhaul (which incidentally was several hundred dollars more expensive than the estimate.) He said he did not personally do the work, but that it looked like a normal overhaul to him, given the 25-year age of the FM-200. He said the standard overhaul kit was the reason for the higher price: about $410 above the quoted overhaul price-plus-parts estimate! He listed the parts changed. It sounds to me like just about all the guts are new! Including the diaphragms, rod ends, bearings, seats -- the motive parts of the fuel control! It all looks brand-new out of the box. I think all I have left of my original servo is the housing! The injectors, too, look brand new. I think he changed the airbleed screens and shrouds from the parts price and their appearance.
The overhaul was expensive, but apparently necessary. It now starts and runs as it always has: smoothly and immediately, cold or hot.
I'll still change out the Slick non-impulse mag for an E-mag. Get rid of those massive and expensive aircraft plugs, plus the Slick is 'way past its projected service life. I also changed the original LSE coils for their new-style tower coils. I used the LSE adapter plate to just bolt them on in place of the older style coils. Just in case. I couldn't tell any difference after replacing the coils, so those likely were not the problem. But I now have new coils anyway.
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I'm glad you got it back together and running after so much testing. Now is the time to find out what was the real reason it gave you so much trouble. A work order and parts description is not a cause. So that we can all learn something.
Yes, I agree. I'll follow up with Don Rivera. I don't think the fuel servo should stop the engine from running before engine TBO! I also had sent in the flow divider some 10 years ago for overhaul when I found it leaking from the top seal. They replaced the seal, and told me they changed to a different material that did not decay in avgas. They sent the old seal back to me with the overhauled flow divider, and it was noticably soft and decayed.
Don didn't have any further light to shed. Just the "normal overhaul" kit and parts list (that sounds to me like just about all of 'em!)
