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390 will not start after annual

J

jfisher

Active Member
Just finished the annual on my 14 and rolled it out for a test flight, but engine would not start. It cranks just fine, but only a couple brief hints of wanting to fire during each 10 - 15 second crank. Tried several times to prime and start. Tried flooded start procedure. All with same results. Just dosen't want to fire.
I'm pretty sure it's getting fuel as the boost pump showed 3.5 GPM and fuel pressure got up to 28 psi prior to start.
I've got dual P-mags with AF Performance FM-150. Both fuel tanks are full. Wing root Holley fuel filters were cleaned and spotless. Safety wired the fuel value to on position. Re-checked ignition harness and P-mag timing.

This is my 3rd annual, and the engine has never behaved like this. Very frustrating. Any ideas?
 
You've got basically the same set-up as I do and it typically fires-up after the first few revolutions, so I can understand why you're frustrated. Not sure what the scope of your annual was. You seem certain fuel is getting the engine so it's likely the ignition. If it were my bird, I would first confirm the p-mags are delivering a spark to each plug using the pull-through test (described in the manual). If not, you'll need to track down why (breaker, ground, etc).
 
Check that the P-mags have power on when you try to start. Fuse? Circuit breaker? Ground wire on P-mag connector connected to engine and fuselage?
 
What did you or the mechanic touch that would affect either fuel or ignition? All the spark plug wires on correctly?
 
Cleaning the wing root filters empties the system of fuel. Perhaps the shutoffs are off? Perhaps a fuel pump test is in order?
 
RV6-KPTW said:
Cleaning the wing root filters empties the system of fuel. Perhaps the shutoffs are off? Perhaps a fuel pump test is in order?
Click to expand...
I was thinking fuel, too but OP said he’s getting fuel pressure and fuel flow. Others commented on possible ignition/spark ideas. What about air? Is the air filter installed correctly? Did you leave a rag in the air path somewhere?
 
You could remove the fuel line from the fuel servo and make sure fuel flow is consistent dumping into a container whereas you had the fuel system apart and filters drained.
If you have the cowlings already on, I would have recharged the battery overnight and tried starting the engine again the next day.
 
Were the Pmags pulled for the shaft inspection? Likely were but perhaps check if ignition wires installed in correct positions? Did you time them to TDC or slightly past?
Sounds like spark to me.
 
That is a mystery. I was gong to say that the pmag timing wasn't reset but you verified it? I'm assuming you timed at TDC and not 20 deg BTDC (an easy mistake for those used to conventional mags).
 
georgemohr said:
That is a mystery. I was gong to say that the pmag timing wasn't reset but you verified it? I'm assuming you timed at TDC and not 20 deg BTDC (an easy mistake for those used to conventional mags).
Click to expand...
Even though the root filters were drained, serviced and reinstalled, there would be some fuel between the firewall bulkhead fitting, the boost pump to the selector valve. At leat enough to maintain the prime on the pump, so the engine should have fired.
 
If it's wanting to fire but just cant I'm going to say that theres a 25% chance that the P-mags aren't timed correctly, the harness is loose or you've got a wire swapped etc. and a 75% chance that you've got fuel filter in backwards, shop rag left in the snorkel, something like that.

Start with the P-mag timing, since it's the easiest thing to check. Then make sure it's getting air, then finally, break into the fuel system.
 
As desert rat mentioned, check that you have the Holley wing root filters in correctly. I put one in backwards and in would not run.
 
Is there an inline fuse somewhere between the battery and the PMAGS? I am not familiar with PMAGS as I have an Electroair on one side and a non impulse mag on the other. I start on the Electroair and it’s wired direct to the battery through a switch. During one annual I was doing something under the electrical panel near that switch and accidentally hit a hot wire with screwdriver and saw the spark. At the time I thought it wasn’t a big deal.

Same exact symptoms- good fuel pressure, engine cranked but did not fire. There is an inline fuse for the Electroair back by the battery and sure enough it was toast. Replaced the fuse and the engine fired right up. Don’t know if the PMAGS have something similar but this sounds like a spark/wiring issue to me as well.
 
Pmag install manual specifies a 3 amp circuit protection on the power line (per mag). That can be a fuse or a CB, builder's choice. I used a CB and I think most do.
 
Last edited:
OP said in the original post:

"...only a couple brief hints of wanting to fire during each 10 - 15 second crank..."

There wouldn't be any spark at all if the P mags weren't getting power. They have to be spinning up around 700 RPM to self excite and cranking them with the starter isn't going to do it.
 
Turn on the power tonthe PMags.
Go look for a red or green (or hopefully NOT flashing amber) light.
No lights= NO power.
(Fuse? Loose wire/green connector at the PMags).

Then with engine set with a cylinder (say, #1) at TDC, look for a green light.

If red and you cannot get to green within about two teeth on the flywheel, you probably have a timing problem.
 
jclark said:
...

Then with engine set with a cylinder (say, #1) at TDC, look for a green light.

If red and you cannot get to green within about two teeth on the flywheel, you probably have a timing problem.
Click to expand...

One note, this is an angle-valve Lycoming, so the proper pmag timing is actually 5 deg AFTER TDC.
 
I have to rotate my P-mag to pull out for gear inspection. Didnt pull the wiring first.
Wouldnt start after inspection. Turned out one of the wires had pulled out of the connector block.
So, check wiring?
 
i had a no start problem on a 390. it was way too rich. pull a bottom plug after a start anc check for too much fuel. as stated above maybe something happened to the pmags.. pm if you need troubleshooting
 
Thanks for all the replies! Will start with making sure the P-mags have power, then the pull through test. I did pull both P-mags to inspect but didn'y remove the wiring harness block. Maybe I loosened a wire in there. I did time them 5 degrees after TDC just like before.
Will keep this thread up to date with my troubleshooting.
 
OK I found the problem. I timed the Pmags using the wrong TC mark on the ring gear. There is a TC mark on both sides of the ring gear. I timed the Pmags using the mark on the prop side of the ring gear by mistake. Have since re-timed the Pmags to the 5 degrees after TC line on the INSIDE of the ring gear. My bad.
Hope I didn't bend anything in the engine.
 
I strongly suspect you didnt hurt a thing. That outside TC is intended to line up with an index on the starter (believe it or not...).
 
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