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Mag Check Issues after Installing New Cylinders

Dan Langhout

Well Known Member
So I am about out of ideas. I have an Aero Sport Power IO-375 (Precision Airmotive Silverhawk FI / Lightspeed electronic ignition top and Slick impulse mag bottom) with almost 600 hours since new. Oil consumption rate has never been great (~ 7 hr/qt at best) and in the last year or so it had increased to 3-4 hrs/qt. I decided that at this annual, I would replace the ECI Nickel-Carbide cylinders with genuine new Lycoming Nitrided cylinders. Did the cylinder swap and now have about 11 hours on them - all following the recommended break in protocol (75% power etc, etc.)

Problem is, ever since the cylinder swap, The magneto really doesn’t pass a mag check at full rich mixture. EGTs all climb, but can be erratic. This is a change from the previous 600 hours. Leaning the mixture improves it significantly. In flight mag checks look good. The engine runs fine on either ignition (at least as well as any engine runs on one ignition). Of course the mixture is leaned normally during the in flight check.

Given that the mag check on the Lightspeed was still fine, I made the assumption it was some sort of mag ignition system issue. Short version is after swapping plugs, a new ignition harness, and even swapping out the mag, the issue is still there. Lower plugs basically come out black and somewhat wet looking.

Beginning to think the problem may be with the Silverhawk injection running too rich under typical run-up/mag check conditions - but that would certainly be a big co-incidence in that it just happened to develop the problem at the same time as the cylinder swap.

In looking for what items were “touched” during the cylinder swap, all spark plugs and leads were obviously moved, and the individual injectors and injector lines were removed and re-installed. If trash got into the injectors while they were out, I would expect lean issues - not rich issues. The magneto itself and the rest of the injection system were not touched (other than removing the “snorkel” where it bolts to the front of the fuel servo).

My next steps will be to do some of the recommended trouble shooting procedures for RSA type injection systems (injector volume flow test, etc.) but failing that - I am at a loss.

Any ideas?
 
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Is the vacuum line to the Lightspeed clear and attached properly?

Is idle mixture adjusted for 50 rpm rise at idle-cutoff?

How many GPH do you show on takeoff?
 
Is the vacuum line to the Lightspeed clear and attached properly?
It always has been. The Lightspeed box is mounted to the aft face of the subpanel and has yellow tygon line feeding it from behind the sensor manifold block on the firewall. Assume I would be looking for oil? I would have to get behind the panel to check - no reason to expect it to have changed since the last time I looked. In any case, mag check on the Lightspeed only is fine.

Is idle mixture adjusted for 50 rpm rise at idle-cutoff?

It rises - but I haven't specifically checked to see if it is 50 RPM

How many GPH do you show on takeoff?

I believe this has changed. Think I saw over 18 GPH on full power climb out after take off. I think I recall it being in the 17 GPH range previously - but I confess to not having specifically recorded either one.
 
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Sounds like your idle mixture is correct. I would just lean it manually for now and maybe revisit in the winter especially considering hot density altitude conditions currently.
 
Changes in ignition behavior caused by mixture variation is one of the reasons I always lean to highest RPM during the EOR mag check. I usually don't get any rise at SL, but at my home airfield (2600 MSL), I will see a 30 RPM rise at 1600, and considerably more at higher airports like Tehachapi or Big Bear. This leaning often has a dramatic effect on the "mag drop" value. If I left the mixture full rich at EOR for the various altitude airports I frequent, my mag drop would be all over the map.

Don - you may very well have a better/different seal integrity with your new induction tube gaskets which drives a different mixture behavior. I wouldn't get too excited about a different feel between old and new unless you have an obvious problem (mixture setting, seal integrity, etc).
 
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Thanks . . . . .

. . . . . for the responses. My biggest concern is that it was a total change from the pre-cylinder swap behavior. At full rich ground run up it really bucks and snorts when running on the Mag alone. Does fine on the Lightspeed. I may follow the advise here and just fly it some more - leaning it on the ground for taxi and run-up.
 
. . . . . for the responses. My biggest concern is that it was a total change from the pre-cylinder swap behavior. At full rich ground run up it really bucks and snorts when running on the Mag alone. Does fine on the Lightspeed. I may follow the advise here and just fly it some more - leaning it on the ground for taxi and run-up.

Most problems don't miraculously go away, I suggest you continue to troubleshoot until you get it fixed.

To start, if the mag has never been in for service with 600 hrs on it, that would be the first thing I'd do.
 
Most problems don't miraculously go away, I suggest you continue to troubleshoot until you get it fixed.

To start, if the mag has never been in for service with 600 hrs on it, that would be the first thing I'd do.

I installed a brand new mag this past November at 520 hours (in too much of a hurry at the time to finish the disassembly/inspection process on the original one). As part of the troubleshooting this week, I finished the inspection/setup of the original mag and swapped it back in. No change in symptoms.
Beginning to think the problem is rich mixture. Problem with all of this is the coincidence with the cylinder swap.
 
Dan,

I suggest you continue troubleshooting but just want to make an observation. I just got back from flying the RV-6 and the density altitude at DCU was nearly 3000' (going to be higher next week!). I noticed both of my ignitions during ignition check (Surefly and Slick) were down about 20 rpm from where they were in cooler temps. I suspect they were seeing richer mixture than before, enough to impact the check rpm.

Get out to 3M5 at daybreak some morning and see if the mag is any better behaved. Nice time to fly, too. :)

Of course this won't explain why you didn't see this issue the past couple of summers........
 
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Dan,

I suggest you continue troubleshooting but just want to make an observation. I just got back from flying the RV-6 and the density altitude at DCU was nearly 3000' (going to be higher next week!). I noticed both of my ignitions during ignition check (Surefly and Slick) were down about 20 rpm from where they were in cooler temps. I suspect they were seeing richer mixture than before, enough to impact the check rpm.
.

Good point here.

Many often forget that the warmer the air gets, the less oxygen there is in given volume of air. Therefore, without temperature compensation, which our systems don't have, your air fuel mixture (which is really an oxygen fuel ratio) gets richer and richer, at any given mixture setting, as the ambient temps rise. This is why modern EFI systems use an IAT (intake air temp), as well as a barometric sensor (typically measured at startup only via the MAP sensor). Richer mixtures burn faster and therefore will be less impacted (i.e. smaller RPM drop/EGT rise) by the retarded effective timing seen when one mag is shut down.

Larry
 
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Leaning the mixture improves it significantly.

In flight mag checks look good. The engine runs fine on either ignition (at least as well as any engine runs on one ignition). Of course the mixture is leaned normally during the in flight check.


Any ideas?

The EI will fire a bad mixture better than the mag, making it look like the mag is defective------possible red herring there.

My thoughts are that you already found the issue, but you have no idea how/why it is too rich.

How did the intake flange gaskets, and the intake coupling rubber hoses look when you took the engine apart?

Did you just remove the cylinders with the engine still on the plane, or take the engine off the plane. If the latter, could you have gotten the mixture cable installed differently------might not have had full travel before, but now does?

Good luck
 
It could be you had some small intake leaks (not unusual for a Lycoming) with your original set up, that have been cured with the new gaskets and your replacement cylinders.

I just replaced all of the intake gaskets and hoses on my wife's Decathlon; it sure idles better when hot than it did before the new gaskets and hoses.
 
How did the intake flange gaskets, and the intake coupling rubber hoses look when you took the engine apart?

The intake flange gaskets actually looked really good (green ECI gaskets). I have the Superior cold air sump which uses the red silicon coupling hoses - also in really good shape. I put it back together with new Superior intake flange gaskets because there has been anecdotal evidence on this forum that they do better than the others.

Did you just remove the cylinders with the engine still on the plane, or take the engine off the plane. If the latter, could you have gotten the mixture cable installed differently------might not have had full travel before, but now does?

IMG_0142.jpg

Changed them out with the engine on the plane. None of the control cables to the fuel servo were removed.
 
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