503 DCDI issue

[j4flyer]

Guys I have a question for anyone familiar with this engine. My buddy has this engine on his aircommand. The engine is new with two hours on it. During the first runs the engine would develope 6400 RPMs. Lately it will go to 5500 after warm up then the rpm drops to 4100 and won’t rise. We’ve checked the wiring for shorts, made sure we had fresh fuel at 50:1 per the manual, checked the plugs for fouling etc. It seems that nothing we have done has brought the RPMs back to the 6400. Has anyone else experienced this issue ? I can shut down each cylinder with the switch and both will show a drop. Thanks

 

[rcflier]

Maybe you should have used the run-in procedure in the owner's handbook...?

 

[bryancobb]

Maybe you should have used the run-in procedure in the owner's handbook...?

That would definitely have been my FIRST action with a brand new engine. Tie it to a tree and do it exactly as the book says without interruption.

 

[bryancobb]

Then and only then can troubleshooting continue. The thing with the most "muscle" to affect the RPM is the prop. If you have a prop that has pitch that is ground adjustable, it sounds like that may have moved.

 

[j4flyer]

Maybe you should have used the run-in procedure in the owner's handbook...?

We did

 

[scottessex]

What are your EGT and CHT temps?

 

[j4flyer]

Scott the CHTs hang between 320 and 350. The EGTs are hovering around 1000 to 1100. We thought of a mixture issue but, everything seems normal. Our next step is to remove the muffler and see if we have a broken piece inside.

 

[Georgi]

Scott the CHTs hang between 320 and 350. The EGTs are hovering around 1000 to 1100. We thought of a mixture issue but, everything seems normal. Our next step is to remove the muffler and see if we have a broken piece inside.

Bob, if carb clean, floats are OK and needle doesn't stick, check carb boot for cracks. Then fuel pump. If you need gauges to check cylinders compression (like in

), I have them in my hangar.

 

[scottessex]

I have seen dirt dauber wasps pack a muffler causing it not to reach full RPM.

 

[j4flyer]

We’re still researching. The intake boots are new and compressions are good and equal. The engine will rev without the prop installed but, we didn’t do a lengthy test as I wasn’t sure if it was good for the engine. We’re checking the muffler and if it has no issues we’ll look harder at the prop. It’s an IVO prop that’s ground adjustable. While it was off for the above test we removed (after numbering each blade to hub location) each blade, inspected them and grease the adjustment cam. We reinstalled the prop and set the pitch again. We’ll see how it plays out.

 

[scottessex]

Make sure your jam-nut on the ivo prop is tight so the pitch can't change.

Underloaded (low pitch) prop gives low CHT and high EGT. Overloaded (high pitch) prop gives high CHT and low EGT
But from your numbers it does not seem that is the problem.

 

[j4flyer]

Make sure your jam-nut on the ivo prop is tight so the pitch can't change.

Underloaded (low pitch) prop gives low CHT and high EGT. Overloaded (high pitch) prop gives high CHT and low EGT
But from your numbers it does not seem that is the problem.

Scott thank you, I wasn’t aware of the cht/ egt correlation to prop pitch.

 

[j4flyer]

Guys just thought I would give an update. The problem turned out to be an intermittent short on one side of the ignition.

 

[Doug Riley]

J4: What components were shorting together?

 

[j4flyer]

One side of the dual ignition was shorting against the airframe. The wiring harness made a bend to allow the wires to go under the seat. At this bend one of the wires chafed. You had to look very carefully to notice the exposed wire. We discovered it while checking the fuel pressure. The harness was moved slightly to get to a clamp and the engine shuddered. We tried purposefully shaking the harness and we were able to duplicate the event. After this the gyro was completely retired.
When Doug bought the gyro the seller said it had flown. Once we got it to the Hangar we began an inspection. We found several things that allowed us to conclude the gyro had never been flown, much less recently. Since the gyro started easily and seemed to run well, we didn’t rewire it. Lesson learned