Setting up the fuel system on a 231

[hubcap]

Does anyone have a digital or hard copy of how to set up the fuel flows on a 231 with the TSIO-360-LB engine with the Merlin upper deck pressure controller and the Turbo Plus Intercooler?

I know the system is pretty complex and there may even be tribal knowledge necessary. 

Thanks!

[Z W]

Only guidance I know of is in SID97-3G, attached here, which is now a part of Continental's M0 I believe.

When my fuel flows got all set wrong after a fuel pump replacement, nobody local could figure it out. Took it to Don Maxwell for annual and they dialed it in perfectly. I talked to them about it and they have some kind of a Bluetooth-connected pressure sensor that hooks up to an iPhone they use to set the pressures to spec. They knew to set the fuel flows a little higher at max power for better cooling. So, tribal knowledge is a good way to describe it. There may be even more of it for your Merlin/Turbo Plus setup.

The fuel system setup procedure can be tedious. It has to be tested with the cowling on, so the cowling has to be removed, the settings changed, cowling reinstalled, then tested, then repeat as necessary until it's right. I suspect some shops lack the patience or time available.

SID97-3G - Continuous Flow Fuel Injection Systems Adjustment Specs and Instructions.pdf

[exM20K]

4 hours ago, Z W said:

they have some kind of a Bluetooth-connected pressure sensor that hooks up to an iPhone they use to set the pressures to spec.

That’s pretty slick, and a whole lot better than bringing hoses, gauges, and raw fuel into the cockpit.

-dan

[jlunseth]

The SID alone is not enough.

There are instructions in the STC for the Turboplus. In very general terms, the Turboplus makes the induction air denser. There is a table in the STC instructions that tells the A&P what MP to use as max power during the setup procedure. It varies with OAT and is in the neighborhood of 36-37 inches. According to the STC instructions the A&P is to use the SID, but adjust the SID procedure per the STC. If you were to use the SID straight up you would use the factory MP setting of 40", which is way too high for an engine with an intercooler. I used to have the STC but don't think I have a copy any longer. You could contact Turboplus, they can send you one.

It is somewhat difficult to get mechanics to understand the process and the importance of getting it right. They are fairly persistent in just defaulting to the SID. So the fuel flow is set to 24 GPH at 40" of MP, but you use let's say 36" as your full power setting because you have an intercooler and then what you see is insufficient fuel flow at full power which is actually 36", not 40. The fuel flow is supposed to be 22.5 - 24.0 at max, but most A&Ps, following just the SID, set the fuel flow wrong and you will see 19-21.5 at 36". The consequence is an inability to keep CHTs under 400+ in a climb, especially in the "high, hot" conditions out west.

Many of us (231 flyers) try to get our A&P to set the fuel flow to about 25 GPH at max power (max power as defined in the STC table), which gives us a little extra fuel to work with in the summer. You could ask Paul Kortopates, he understands it pretty well. This means that on the ground you may want to reduce the fuel flow a little to stay under 24 during takeoff, but it sure helps with summer temps and climb outs.

Edited Friday at 06:33 PM by jlunseth

[hubcap]

On 6/11/2025 at 5:28 AM, Z W said:

Only guidance I know of is in SID97-3G, attached here, which is now a part of Continental's M0 I believe.

When my fuel flows got all set wrong after a fuel pump replacement, nobody local could figure it out. Took it to Don Maxwell for annual and they dialed it in perfectly. I talked to them about it and they have some kind of a Bluetooth-connected pressure sensor that hooks up to an iPhone they use to set the pressures to spec. They knew to set the fuel flows a little higher at max power for better cooling. So, tribal knowledge is a good way to describe it. There may be even more of it for your Merlin/Turbo Plus setup.

The fuel system setup procedure can be tedious. It has to be tested with the cowling on, so the cowling has to be removed, the settings changed, cowling reinstalled, then tested, then repeat as necessary until it's right. I suspect some shops lack the patience or time available.

SID97-3G - Continuous Flow Fuel Injection Systems Adjustment Specs and Instructions.pdf 3.17 MB · 4 downloads

Thank you for the information, but it doesn't cover the TSIO-360-LB engine.

I believe that is for the engine in the 252 and Encore.

[Z W]

The SID covers the TSIO-360-LB:

Here are the adjustment specifications from the document for the LB and GB engines in a 231:

 

I'd defer to what @jlunseth said about modifying it for your STC'd wastegate or intercooler. And I'd try to make sure your mechanic has access to the STC documents and any instructions in them.

I also can confirm the drawings of the fuel pump and adjustment mechanism locations don't exactly match what are in my plane. But, I spent a lot of time on this a couple years ago and came to the conclusion this was all the factory / manufacturer guidance available. If anyone else has more I hope they'll post it here.

Good luck.

[hubcap]

16 hours ago, Z W said:

The SID covers the TSIO-360-LB:

Here are the adjustment specifications from the document for the LB and GB engines in a 231:

 

I'd defer to what @jlunseth said about modifying it for your STC'd wastegate or intercooler. And I'd try to make sure your mechanic has access to the STC documents and any instructions in them.

I also can confirm the drawings of the fuel pump and adjustment mechanism locations don't exactly match what are in my plane. But, I spent a lot of time on this a couple years ago and came to the conclusion this was all the factory / manufacturer guidance available. If anyone else has more I hope they'll post it here.

Good luck.

Thank you. Those are the correct numbers for the LB, but I believe there is a step by step process to set it up correctly that I need as well. 

[Fly Boomer]

7 minutes ago, hubcap said:

Thank you. Those are the correct numbers for the LB, but I believe there is a step by step process to set it up correctly that I need as well. 

I think the SID is attached above.

[jlunseth]

I did a search on my old posts and found the Turboplus instructions for setting fuel flow:TSIO360 Fuel Setup - NEW 08.pdf

As I said earlier, some of us try to get the fuel flow set a little higher.

Please note that the max power MP in these instructions will generally be higher than the 36-37" most of us use to set full power in flight. The fuel setting process is conducted on the ground with the aircraft not moving and therefore very little air is passing over the intercooler to cool the induction air. The intercooler becomes more efficient as the aircraft picks up speed during takeoff and flight, and air passes through the scoop and over the fins of the intercooler. At cruise at altitude it is not uncommon to see a differential temperature (Compressor Discharge Temperature minus Induction Air Temp) of 100-125 degrees. So the higher max power MP in the table in the instructions is not directly applicable to in-flight power settings.