Rule #1 of troubleshooting: What changed?

Start with those spiders and anything that was touched in the process.

I had a similar problem and shop said it was carbon arcing inside the mag.

I agree...I think...it's the only thing that makes sense.
But I don't understand why less fuel didn't reduce TIT eventually. It continued to climb until the engine stopped (about 02:49, it's only a blip on the data, I should have kept it there longer). It also needed more fuel or less power to keep temps "normal"...which I'm having a hard time finding in the data.
Those things make me question what seems to be an obvious fuel issue.

I had a similar problem many years ago (1978) with a C402. Short version is that the airplane set outside over the weekend in heavy rain. The sumps were drained during preflight with no water at all. Flew back to NC mountain airport, no issues, then hit moderate turbulence during descent, right engine stated surging with major fuel flow fluctuations. After a couple of minutes the engine operated normal. We hit more turbulence then left engine stated surging. Needless to say, we changed destinations to a flat land airport. We maintained altitude until closer to airport. Now both engines were fluctuating and unable to maintain altitude. We landed safely at airport and right engine quit during rollout, then after turning around, the left one quit and we had to be towed to the ramp. We had the fuel system gone through with no problems found. We also found out form the FAA that there had been several instances with these same issues that turned into accidents.
The airplane sit out all weekend in rain while on a trip. The day before departure, the temp fell to below freezing, thus no water found when draining sumps. All of the flight was conducted in well below freezing temps. When we hit the turbulence, ice was dislodged and restricted fuel flow at the fuel bowl outboard of both engines.
The problem was determined to be bad o rings on the fuel caps which let water enter the fuel tanks where it froze before the preflight.

Sorry to write so much but it was necessary to explain the problem.

Looks like the fuel flow is leading the EGT to me. So look at the fuel system. There is significant rises and fall in fuel flow that need to be determined if you didn't do that yourself.

Andrew

A deteriorating engine air filter being ingested by the turbocharger and then contaminating the upper deck can cause momentary loss of MP and FF havoc. I have experienced it twice with 421's.

Mike

Several years ago I flew a Ram 414. I don't think it is a Ram specific problem, we went to TBO and had them overhaul again....

One one occasion it was cruising normally and surged, it did it maybe a half dozen times, but it was so quick I couldn't tell which engine it was. I think it was passing some water, and I was faithful at slumping also.

One other roughness was at altitude, probably 20-21,0000. I suspected a mag, when I descended to 15K and it smoothed out. When we got on the ground there was a pressurization line off one mag, causing it to arc at altitude.

My only ram problem was the third overhaul, they used Cermichrome cylinders that broke in immediately, and continued to break in....wore out quickly! ( around 1991... )

Jeff H.

Threads like this amaze me how knowledgable this group is...

Jack,

Nothing like an intermittent problem to have you and your mechanic pulling your hair out.

Some questions:

When you did your inflight mag check, did you see all EGTs go up (pretty much together)?
When did you last do a mag grounding check?
What did CHTs do prior to and after the issue?
How is the oil flow managed for the spider heater option?

Some thoughts:

An ignition/magneto problem will cause high(er) EGTs.
ROP, a fuel problem will cause high HGTs

CHTs ought to drop if the problem is ignition related and rise if the problem is fuel related (ROP).

Please let us know what you find.

Sorry for insisting, but as noted before, it is not spark, compression or air. From the problem description it is fuel delivery. Something is starving the engine all at once - air, water, ice, or a problem with the lines going to the engine like a vacuum being created by clogged vents. A good way to isolate the problem is to run it on cross feed when it starts acting up.

Jack

Can you drain fuel and add fresh fuel?
Can you go up and duplicate?

I think that was mostly me.

I agree...I think...it's the only thing that makes sense.
But I don't understand why less fuel didn't reduce TIT eventually. It continued to climb until the engine stopped (about 02:49, it's only a blip on the data, I should have kept it there longer). It also needed more fuel or less power to keep temps "normal"...which I'm having a hard time finding in the data.
Those things make me question what seems to be an obvious fuel issue.

Plane stays in a heated hangar. I pumped 208 gallons into it from an underground tank two days before the flight. It was outside while I pumped the fuel and immediately went back in the hangar. Sumped the tanks in the hangar. Fuel pump unit is finicky about water, if it senses water it shuts off.
OAT at time of take-off was 5f/-15c. Problem started at 1:45 and continued intermittently until power was reduced for the approach at about 3:45. Last 30 minutes of flight was above freezing.
Fuel cap o-rings were replaced last October. It hasn't sat out in rain or snow since annual in October.

Mag check - yes, all EGT's climbed together
Grounding check - it's been a while...40-50 hrs maybe
CHT's - interesting question. Just finished comparing the last 3 flights, about 6 minutes into this last flight the CHT's started climbing higher than previous 2 flights. 10 degrees at first and then as much as 50 degrees higher in each flight segment, consistently across all cylinders. So all CHT's on this last flight were 10-50 degrees hotter than normal.
EGT's were about the same, 10-20 hotter than last flight, 10-20 cooler than flight before that.