Engine Misfire at Altitude.

[hharney]

From my IA:

I’d send the suspect magneto to Wayland Bruce at Magneto ER (easier said than done on the front engine of a T337).

A few years ago I had a similar issue with the rear mags on a P337G and Magneto ER was able to pinpoint the problem and fix it quickly and inexpensively. The mags have been running for a few hundred hours with no more issues.

If the magneto itself checks good then the pressurized air line is the next suspect. Is that magneto getting hit with oil residue from the pressurized air? Make sure there’s a good filter installed in-line (RAM Aircraft sells them).

A lot of shops have a high-tension ignition lead tester. I’d doubt that the ignition harness is a cause, but if a tester is available, it’s a very quick and easy test to rule out the possibility.

[basloane]

Thanks Herb.

Is the organization ( and contact information ) you are referring to?

Magneto ER Inc. 2505 South Main St. Searcy, AR 72143 Phone: 501-268-9950

Regards,...... Barry

[hharney]

Barry
Bingo

[JimC]

Is it possible to get pressurized magnetos on a non-pressurized turbo Skymaster? I took my T337E up to FL180 for the first time yesterday and had bad misfiring, so I went back to 16,000 where it ran well. I'd like to be able to use all the FLs I can, especially eastbound.

[hharney]

Originally Posted by JimC

Is it possible to get pressurized magnetos on a non-pressurized turbo Skymaster? I took my T337E up to FL180 for the first time yesterday and had bad misfiring, so I went back to 16,000 where it ran well. I'd like to be able to use all the FLs I can, especially eastbound.

Sure, it wouldn’t be too difficult. You’d have to tap into the upper deck pressure line…the pressurized Skymasters have a nipple welded to the steel pressure line that runs between cylinders 1 & 2, then a rubber hose comes from that nipple to a tee fitting, then rubber hoses going to the barb fitting on each mag. You’d also want to add an inline filter (1396-2 from RAM Aircraft) just before the tee fitting to make sure you’re not pumping crud into the mags.
You’d have to remove one plastic cap on each mag and add a barb fitting. Also add a gasket between the ignition harness & the mag. Whelen Bruce at Magneto ER is very familiar with this stuff and could hook someone up with the necessary parts if he was given the mag model #’s.
I’m not sure how to do this legally, but I don’t think the actual work would be that much.

Craig Griswold, Director of Maintenance
Griswold Aviation llc
1243 S Kalamazoo Ave Ste C
Marshall, MI 49068
(269) 213-6746 office
(269) 330-2908 cell

[JimC]

Are there any other T337 owners that are regularly flying at FL180 or higher? How do your mags do? What did you do to get them to run smoothly?

[Kim Geyer]

we do
I make sure the plug gaps are good and the mags are in good shape and timed correctly.
we use to have some issue with occasional misfire but we started using tempest spark plugs and it not much of an issue anymore
as far as pressurized mags I think ram aircraft can fix you up with what you need. I went through the TCM parts manual and ordered all the hard lines and fittings for pressurized mags but never needed to put them on
Kim

[B2C2]

I have a 1969 T337D, non pressurized and no pressurized mags. I have tempest fine wire plugs and GAMI injectors. I have also replaced all the ignition wiring and rebuilt the magnetos. The airplane flys nicely LOP with this setup. I occasionally have experienced bumps when operating at altitude above about 17K LOP. The highest I have flown it is 21K and it was the same experience, occasional ignition bumps, but not rough operation. I have found going to ROP stops this. You don't mention if you are running LOP or ROP but you might want to see how this effects the performance.

[JimC]

I'm still ROP. I haven't upgraded *anything* yet - I don't have an engine monitor, and I have the plugs, wires & mags that came with it when I bought it 4 months ago. It does run well LOP at 13K or so.

I ran a different continental TSIO up to 25K smoothly with pressurized mags, so I know that the pressurized mags make a big difference.

PS - How do you have a 1969 T337G? The model number & year don't match.

[B2C2]

Oops, sorry its a T337D. edited my below post to reflect this

[B2C2]

I was thinking about this and was wondering how Cessna gave a service ceiling of 30K feet for the T337D. With non pressurized magnetos this seems unattainable. Did they offer these as an option on the plane when they sold it? otherwise it seems like there is no way to achieve that altitude in operation.

[Dan schultz]

Try the fine wire plugs

Dan
67S

[B2C2]

I have them. I actually have good performance up to about 19K but I have never taken it up any higher than that, Based on what i have been reading 30K feet without pressurized magnetos seems a stretch, but maybe that's not the case?