IO-320 Fuel Pressure

I've noticed in the past 4-5 months (approx. 30 hours engine time), my fuel pressure has dropped from 24-25 psi mechanical only/ 31 psi with electric boost pump to 18 psi mechanical only/28 psi with electric boost pump in cruise. This was really brought to my attention when trying 91 MOGAS for the first time but thats for a different thread.

http://www.vansairforce.com/community/showthread.php?t=132326

My troubleshooting consisted of checking every fitting from tanks to fuel servo, all were tight. I also checked the filter in my gascolator (mounted in cabin, under tank selector) and it was clean. I checked the flow by taking the hose from the inlet to the mechanical pump and running it into a bucket. With full tanks, it was flowing .25 GPM with just gravity, no boost pump. Turning on the boost increased the flow as expected. This seemed to prove adequate fuel supply so I just replaced the mechanical fuel pump. I got a pressure increase, but not as much as I was expecting. I'm now running 22 psi on mechanical only and 31 psi with the boost pump on in cruise. The pump says 25-30 psi output.

I'm not too familiar with aircraft engines but, after looking at how the mechanical fuel pump is actuated, it makes me wonder if there is possibly something wrong with the drive. One possible problem I can see occurring is the cam (or the actuating rod for that matter) on the left mag drive being worn to a point were its not pushing the pump lever down enough. Not sure if this has happened before, just throwing out ideas. Has anyone heard of this occurring in the past? I would hope its not the case considering its only 90 hours on a new Superior IO-320 but who knows.

Have we investigated the pressure sensor to make sure it is correct?

I have had to replace several of them on fuel and oil pressure.

I'm betting it's the OP sending unit.

Fuel pressure sensor

While I haven't completely ruled that out, when I tried running the 91 octane and had pressure readings intermittently down to 9-10 psi, the engine began to lose power so I'm reasonably sure the sensor is reading correctly. They weren't lying when they gave a 12 psi minimum fuel pressure spec.

Problem solved

I figured I would post the resolution to my fuel pressure problem.

So on the return trip of a 5 hour X/C, I switched fuel tanks while cruising, and the fuel pressure began dropping and the engine started to lose power. I switched on the boost pump (I don't normally use the boost pump for switching tanks) and fuel pressure recovered as well as engine power. Once home, I decided to dig a little deeper into this issue as it seemed to be getting worse.

I pulled the left mag and found a 1/4" gap between the cam and fuel pump drive rod. A call to Aerosport confirmed my suspicion, the engine had to come off and be sent back to them for repair. Not something I anticipated doing with 93 hours on a new engine, before my first annual but it could have been worse.

I received the engine back last week and have about 5 hours on it and its running great.

To be clear, this is a Superior built engine, purchased from Aerosport Power and this post is not intended to speak ill of either company. I could not be happier with how this problem was resolved so smoothly. I wouldn't bat an eye about buying another Superior built engine and when I start building an RV-10, Aeropsort will without a doubt be getting my IO-540 business.

Elwell81 said:

I figured I would post the resolution to my fuel pressure problem.

So on the return trip of a 5 hour X/C, I switched fuel tanks while cruising, and the fuel pressure began dropping and the engine started to lose power. I switched on the boost pump (I don't normally use the boost pump for switching tanks) and fuel pressure recovered as well as engine power. Once home, I decided to dig a little deeper into this issue as it seemed to be getting worse.

I pulled the left mag and found a 1/4" gap between the cam and fuel pump drive rod. A call to Aerosport confirmed my suspicion, the engine had to come off and be sent back to them for repair. Not something I anticipated doing with 93 hours on a new engine, before my first annual but it could have been worse.

I received the engine back last week and have about 5 hours on it and its running great.

To be clear, this is a Superior built engine, purchased from Aerosport Power and this post is not intended to speak ill of either company. I could not be happier with how this problem was resolved so smoothly. I wouldn't bat an eye about buying another Superior built engine and when I start building an RV-10, Aeropsort will without a doubt be getting my IO-540 business.

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Did they tell what the problem was? Assuming either the pushrod or lobe on the camshaft wore down (given that it worked fine initially). I am curious which it was.

Yes

I knew what the problem was before I pulled it of the airplane. Apparently when that fuel pump rod gets installed upside down, it wears down very quickly.

Elwell81 said:

I knew what the problem was before I pulled it of the airplane. Apparently when that fuel pump rod gets installed upside down, it wears down very quickly.

Click to expand...

I wouldn't have guessed that. If it is installed upside down, the rod will slip right out and fall into the oil sump unless the fuel pump was installed on the accy case before installation. I guess some thick grease would hold it for a while if they put the pump on before shipping.

What a shame to have to pull and ship an engine for something so simple.

Larry