2 cylinders not firing on initial engine start

[BrianL29]

Hey all,

Strange problems started late November on my Bravo.  Latest in a series of them on my IRAN engine with about 40 hours on since then.  

When i start the engine, cylinders 4 and 5 do not fire up.  I let it idle for a while and typically no luck. I have to stop and start the engine 5-10 time and eventually they all fire.  During my re-starts I am doing a flooded engine start and trying to keep mixture as lean as possible and throttle close to idle and that seems to help.  

The first time this happened I remember accidentally trying to start with the mixture at idle. I stopped and tried again and had the throttle a bit too far forward and it roared to life a little harder than I would have liked. 

 The engine used to start on the first blade turn.  When it does catch quickly, then it does seem to start ok.  Lately it seems to crank for 4-5 seconds before it start and that is when those 2 cylinders don't light.  My engine has been buggy. I had broken intake valve springs at hour 20.  The crankcase seal pushed out around hour 27.  When it does start it runs smooth and EGT and CHT's look good.   

Any thoughts? Do you think the plugs are getting wet? I installed fine wire plugs mid October. I am tempted to put the old plugs back in to see what happens.     

[MikeOH]

When 4 and 5 "come on line" do they do so at the same time, or one then the other?  And, when they do, is the idle immediately smooth, or initially rough?  I'm wondering if you have sticking valves.  Which cylinders had broken springs?

[BrianL29]

Normally 4 comes on line first and then 5.  But I may have to restart a couple more times to get 5 going.  Its runs smooth as soon as they are all running.  Cylinder 3 had the broken spring.  

[MikeOH]

What were the symptoms when #3 had the broken spring?  Just speculating that might be the case here, though I wouldn't think it would ever run smooth!  Curious if you had an explanation for why the spring broke on a new engine?

[BrianL29]

When springs broke I landed fine pulled off the runway and the engine started shaking violently. I saw no EGT on #3. Obviously didn’t come back to life. We found both intake valve springs broken. Shop said that the new camshaft installed probably over compressed original springs and broke them.

My current problem seems to correct itself with time. I haven’t pulled valve covers but doesn’t feel like the issue.


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[GeeBee]

42 minutes ago, BrianL29 said:

Shop said that the new camshaft installed probably over compressed original springs and broke them.

I call BS! Sounds like a cam out of time with the crank

[EricJ]

1 hour ago, BrianL29 said:

Normally 4 comes on line first and then 5.  But I may have to restart a couple more times to get 5 going.  Its runs smooth as soon as they are all running.  Cylinder 3 had the broken spring.  

If you just leave it running while the two cylinders miss do they eventually come online?   If so, that sounds like sticking valves that just unstick as the engine warms up.   That's pretty common.   

[BrianL29]

I haven’t had both come on line by just leaving it running. I’ve had to stop and restart the engine. I’m guessing the longest I’ve let it run is maybe 10 minutes.

My savvy analysis indicated a potential valve failure on #3. I borescoped last month and everything looked good on that cylinder. I’ll have to check others.

Is it possible I’m getting too much fuel on initial start and soaking those plugs?

[Andy95W]

52 minutes ago, BrianL29 said:

Is it possible I’m getting too much fuel on initial start and soaking those plugs?

One plug? Maybe. Both plugs? Not likely.

What happens when you advance the throttle to 1500-1800 rpm?  What happens when you lean the mixture?

[BrianL29]

Engine shakes pretty good if I increase power that much. Leaning doesn’t change much. I keep it as lean as possible while I’m trying to revive it. 

[cferr59]

I had an issue like this after a cylinder replacement and after some troubleshooting found that there was no dry tappet clearance at all on the exhaust side.

[EricJ]

It's unlikely to be ignition related if the cylinders don't fire at all, since the ignition is redundant and it's unlikely that both sides would fail exactly the same.   So single-point-failure items like valves or fuel injection seem more likely.  

 

[Andy95W]

I’m with Eric.  It seems like it’s gotta be either no compression or no fuel to those 2 cylinders.

[MikeOH]

I'm completely speculating here, but it bugs me that you had that valve spring break on #3.  No way that was the 'new camshaft'; as @GeeBee said, that is BS.  I am beginning to wonder if the wrong valve springs were installed in some locations such that they bind.  That could explain #3 failing as well as your issues with #4 and #5.  Yeah, it's a long shot, but maybe the next time you start and have the problem, shut down and then pull the rocker covers on #4 and #5 and see if the valves are 'hanging up' (not closing)