Right nacelle.

My recollection is that there is no filter (except what may be internal to the transfer pump) in the line between the nacelle tank and the main tank.

I would take a close look at the transfer pump as a culprit.

If you buy a replacement pump (McFarlane is a good source), I know people who open new pumps and clean them before installation. Contamination in new pumps is pretty common.

IIRC, I believe the internals of the spider are brass. There is a cone shaped divider that disperses fuel based on flow rate. If you had shavings in the injector lines, I'd look closely at that divider. They were just worked on, right? The fuel filters should have caught anything in the tanks.

At least call Dave at Great Planes to discuss the possibility...

They don't see how any fuel was getting through the injectors on the left side. Those lines had a lot of junk in them, worse than the right side for some reason.
Yes, they're confident that was the problem.
I just can't come up with a good explanation for the source of the random debris, or the timing of it coming through the system.

Jack,

I saw your similar post on the twincessna.org forum, as well as this forum, so for the benefit of all, I will post this on both.

It seems that you are suspecting that foreign debris in one of your fuel tanks was the cause.

I had a similar experience in the 414A RAM VII with oil heated fuel manifolds.
204 gal. total/no wing locker tanks installed.

At FL 250, the RH engine stumbled, surged, then one cyl showed no EGT.
RH engine was firing/running on only 5 cylinders.

After landing, both engines ran fine.

Mechanic suspected a fuel problem. Filters and injectors were clean, but my pre-flight sumping had previously been getting some trash from the RH wing.

The fuel manifold/flow divider was disassembled (it was a RAM overhauled part) and it showed some slight roughness on the poppet shaft, so it was replaced as a precaution.

The RH wing was de-fueled and inspected. The A&P (David at Gwinnett Aero at Lawrenceville, GA KLZU) found quite a bit of grit and trash. This was apparently from a previous corrosion repair on an internal tank area. The A&P dried out the RH wing and vacuumed out/cleaned this residue. The problem has not recurred since.

The consensus was that trash in the RH wing had blocked the injector to one cylinder. The actual bit of trash that caused the blockage was never found, but so much trash was discovered in the RH wing, that I was confident that the cause was trash in the fuel tank.

Eric

Don't the fuel strainers stop trash capable of clogging an injector?

They are supposed to, but some of the debris in my wing tank was like medium to fine dust from abrasive grinding wheels.
The theory was that it was fine enough, that it passed through the filters.

The A&P said that it doesn't take much to block an injector.

My wings now sump clear, and the engines are running great since that incident.

Thanks Eric,

It seems we have the same problem.
When they pulled the lines off the nacelle tank, prior to the transfer pump they found quite a bit more debris. They're in the process of flushing the nacelle tank and transfer pump now.
We haven't been able to get any more debris out of the main tank.
Filters are clean, injectors are clean and fuel is pumping clean at each injector line.
Perplexed about the source of the debris.

About 3 years ago, after a string of storms along the Texas, Oklahoma, Louisiana area, I started noticing a lot of crud every time I strained the fuel. I seldom park my airplane on the ramp, and it was very unusual to see this if the airplane spent most of its time inside a hangar when not flying. I never had the engine miss, but had our shop look into it anyway. This is what they found and what they got out after flushing out the fuel system.

Bottom line, I must have picked up fuel somewhere where they were getting water and dirt into their fuel tanks and were selling it like this.

In Jack's case, though, it looks like it was something left over from previous maintenance to the fuel system or wing locker tanks.

I think a lot of junk in our fuel tanks comes right out of the fuel nozzle. At self service islands I have seen guys drop the nozzle on the asphalt and cement, those tips of the nozzle hit. Before I fuel I have made it a habit to let some fuel out of the nozzle before I put into the tank of my plane. I know its not the most environmentally sound practice but its better then in the tanks.

I'm too cheap to dump fuel. I just swallow it and blow it into the tank through my nose.

OOPS...wrong thread...

Still working on this issue....
One of the consistent symptoms is the intermittent nature of the engine stumbling. It runs fine most of the time, then stumbles for a second or two (as I understand from talking to Jack).
So a question to those with knowledge regarding the design of the engine driven fuel pump on this GTSIO520: what type of pump is it, and it is possible to have a failure mode allowing the drive gear to slip on the shaft, or on the other end of the shaft (I don't know how it's made or what kind of pump it is) could the actual pumping mechanism be slipping?
Thanks to all who have contributed!

So they cleaned and flushed both tanks, cleaned all filters, flushed all lines. No more debris anywhere. Found and fixed a couple "while you're in there's" which added a few days.
Test flew yesterday, no change. Now it won't idle very well either.
https://www.savvyanalysis.com/flight/12 ... 1c0716b3fd
(pretty sure the #5 egt is a probe or wire problem, it was removed and reinstalled after last flight)

RAM wants us to pull the fuel pump, pressure regulator, throttle body, & fuel manifold and ship to their shop for bench testing. I hate to do that because they're just guessing and who knows how long it will take.

Somebody else thinks it's an upper deck pressure issue, they're going over those fittings and lines now.

Also going to pressurize the induction system, possibly something we overlooked there.

I feel your pain as a former 421 owner. Those GTSIO's are so complex that we rarely could get 10-15 hrs. without some sort of engine maintenance. I hope you find the culprit soon.

Wow. Mine were very reliable.