Possible injection system problem

[Bubblehead]

Here is the plan. Please critique.

1) Pull fuel servo and flow divider and send to Don at AFP

2) get a new hose to replace the 10 year old one that connects the servo and divider

3) install a new fuel pump.

4) (re)test fuel tank vents.

I tested the fuel tank vents once before in two ways. First, I took the tank filler caps off and gently blew through each vent. In neither case did air flow very easily but it did flow. Then at the December condition inspection when the root fairings were off I disconnected the vent lines at the wing root, hooked up a short, L-shaped length of tubing to the tank vent, and blew through that. The air flow seemed about the same as when I blew through the vents on the bottom of the fuselage.

I suspect the main cause is low fuel pressure caused by a failing engine driven fuel pump

What confuses that issue is turning on the boost pump does not clear the problem.

And what confuses that issue is when I turn on the boost pump I only get about 1 psi rise, and the pressure does not go to 25 psi which is the relief valve setting on the boost pump. Perhaps the boost pump is bad too?

Questions? Ideas? Comments?

[Bruce]

Bubblehead,

I had the same indication on my fuel flow on Saturday
at Hicks. Ernie and Jay helped me diagnose it.
I had a Fuel sender that had the post rotating.
Turned on the Boost pump read 13 would rise 1psi and
move the post with wire and jump to 27.
Ordered new fuel sender.

Engine was not running rough. RTB'd

Is your diaphram spitting fuel out of the fuel pump
to the ground from small overflow tube ???

That would indicate a problem with the mechanical fuel pump.

Hope this helps a little bit.

I would check fuel flow to mechanical pump first, then check it from
there to divider.

[TS Flightlines]

say a 10 year old hose? I hope it was teflon-
Tom

[aerhed]

say a 10 year old hose? I hope it was teflon-

Y'know, I still see 40-70 year old 303/111 hoses between the carb & gasco to this day (I change 'em as soon as I get my hands on 'em and the owners not looking). I don't know how they got by so long. I've taken them off and just had them snap when you bend them. Nice huh?
For the OP's problem these suggestions all sound good, but the first thing I'd do is tee in an analog pressure gage. Then you'll know at least if your problem is upstream or downstream. Divide and conquer.

[Wayne Gillispie]

I would start off with replacing the 10 yr old hose and then verify fuel pressure with a separate gage. Fuel pressure issue should be corrected before any further troubleshooting.

Go from least expensive to most expensive, one step at a time otherwise we won't learn much from our trouble shooting experience.

[Bubblehead]

The servo and flow divider are leaving for Airflow Performance tomorrow. A new hose is on order, along with a new fuel pump.

I love the analog pressure gauge idea and will do that on the new fuel pump to verify pressure.

I think the spring on the alt air door is weak but no way of measuring it so will wire the door shut for the test run. Or maybe test run and then wire shut if there is still rough operation. I inspected the air filter and all is good.

Need to test the vents but it would seem if any air moved when I blow on it then it would be keeping up with fuel flow. The problem happens equally on left tank as right. Maybe both are a little restricted but it should not take much air to flow to keep the tank pressure at ambient. 8 gph is only 3/4 gallon every 6 minutes.

Keep the ideas coming but I think the fuel pump is the culprit.

[NDrv8r]

I think you're on the right track, but before sending a bunch of parts off and replacing stuff, I think I would have verified that fuel pressure. The RSA needs about 20psi, but can handle more. I wouldn't think that it would affect individual egts, so you may have multiple things going on.

I believe it is a good idea to correct what you know is wrong and then go from there. There are times when it is just not possible to measure what is going on, but an analog gage to confirm the fuel pressure would go a long way in isolating the problem.

Assuming you confirm low pressure, then you can go after filters, fuel pumps etc.

[Doug]

Consider sending the injectors and fuel lines and have them flow (checked) and matched.

[Bubblehead]

The injector bodies and orifices were replaced with new 2 years ago. I did not think about sending the lines with the servo but we did do the flow check of the nozzles and they met the flow requirements per the AFP documentation.

I wish I had thought of the analog pressure gage check on Saturday night.

Don at AFP said in an email to me that the flow transducer should be between the servo and the flow divider. I think I will temporarily remove it from the system until we get the engine running right.

[jdeas]

While you have the system open, you may want to pump gas into a container using the electric fuel pump to get an idea of flow or possible obstructions in the lines/filter.
I.E. Record how long it takes to fill a 3 gallon can.