Troubleshooting a rough engine

[UnPossible]

Hey – I went for a flight this morning and my engine seemed to not be running as well as usual. It was hot here in Texas and I climbed out to 3,700 feet at 25 squared. #1 and #6 CHTs were just over 400 (which seems pretty normal). However in cruise at 23 squared, I could not run lean of peak without the engine stumbling – which is something new.

I have a Precision Silverhawk fuel injection system and two SureFly electronic ignitions.

When I got back home, I downloaded the data, and it looks like #5 cylinder EGT is quite a bit below the others (normally they are pretty tightly bunched). At this point I am thinking it could be a spark plug, an ignition or a fuel issue.

I started with fuel by removing each of the injectors and cleaning them (I did not see any debris, etc. in any of the injectors). While all the injectors were out, I ran a test to see if each cylinder is getting the same amount of fuel. I put 6 cups under each of the “spider legs” and with the throttle and mixture both wide open, ran the boost pump for 45 seconds or so.

What I found was a bit interesting….. cylinders 1,3 and 5 were getting less fuel than 2,4, and 6. Below is the data comparing the amount of fuel (by weight) relative to the lowest amount (#3).

1 4.1%
2 15.7%
3 0.0%
4 19.0%
5 5.8%
6 9.1%

I am assuming that it’s not normal for one cylinder to get nearly 20% more fuel (by weight) than another cylinder. If it was a clogged line, I’d expect one leg to be way lower than the others, but it seems strange for all of the odd cylinders to be flowing less fuel than the even ones.

At this point, I am wondering if I may have a problem with the flow divider. Is there a good way to flush out the divider? I’d love any thoughts as how to trouble shoot this further. Thanks.

 

[Avanza]

I have an IO-360 with a RSA5AD1 fuel servo, similar to yours and two sure fly ignitions. I had trouble with different fuel flows to the cylinders when leaning.
The standard fuel injectors are 0.028 on my engine and I changed them to
0.025 (smaller size). This have resulted in more even fuel flow to the cylinders when leaning. I recomend you to call Don at 864-576-4512.

https://airflowperformance.com/index.php/contact/
https://airflowperformance.com/index.php/product-category/nozzles-restrictors/

Good luck

 

[UnPossible]

Based on some of the comments I've received, I cleaned all the fuel restrictors and injectors and reran the flow tests three times. In the chart are the values averaged across three runs. The numbers represent the % increase in fuel flow compared to the lowest flow cylinder.


Fuel Lines w/ Inj and Nozzles
1 4.1% 13.1%
2 15.7% 27.8%
3 0.0% 0.0%
4 19.0% 30.7%
5 5.8% 19.3%
6 9.1% 25.6%

#3 Cylinder is getting the least fuel in both scenarios. What seems really strange to me is again cylinders #2, 4 and 6 are all getting significantly more fuel than #3, regardless of whether the injectors and restrictors are installed on the fuel lines or not. Cylinder #4 is getting more than 30% more fuel compared to cylinder #3.

I have received several messages suggesting that I contact Don at Airflow Performance in the morning and get his thoughts - which is my plan for the morning.

 

[UnPossible]

Test for image insertion

 

[lr172]

You need to disassemble the flow divider and clean it out and inspect it. There is a V slot for each output and gueessing there is some debris in the #3 slot. Could also be wear on the piston that moves up and down to select flow via the pistons position in the V. If this is beyond your skill set, send the divider to AFP and they will get it back to new condition.

I would also use compressed air to blow out the 1/8" SS lines. The blue die in the fuel can cake up inside the SS lines due to the extreme heat at shut down; The fuel evaporates, but the die does not and instead sticks to the lower wall. Do this a few thousand times and you have sheets of it that can break loose. If a piece breaks off, it can clog up that line.

Larry