Fuel related issue on rear engine
 

The io360CB in the rear--long in years, short on hours (10ish vs. 100ish)-- doesn't like to start. My IA decided to give it a go with the low aux pump on, but to no avail. We moved on to the high, and lo and behold she started, and quickly at that. But not for long. Short form: I had to manually meter the flow through judicious application of the high pump--on ... off ... on ... off--in order to maintain some semblance of a smooth idle.

That IA surmised either rear engine fuel pump, or the flow divider. The IA that's currently working on it said that the quasi-success of the aux pumps should rule the flow divider out, and so it must be the engine pump.

Having said all of this, I think my question is likely more academic than practical. It is:

Do these engines not have fuel pressure regulators like their automobile counter parts? Hard to imagine they wouldn't, but if they do, why would I need to back off the aux pump to keep it running?

My (sorely missed) 1971 Benz 280SE with mechanical fuel injection had such a thing. Even if the pump pressure for some reason exceeded normal, it wouldn't become an issue until something actually leaked or ruptured. But until that point, the injectors would received their holy 56-60 lbs/inch as the engineering gods intended. Not more, not less.

Any thoughts appreciated.

-Gray-

How to start every time in all conditions
 

Works HOT, COLD, and in between.
Even heat soaked engine.

STEPS
1. Throttles CLOSED
2. Props FORWARD
3. Mixtures RICH

4. Boost pump HIGH -

5. Throttles - move from CLOSED to OPEN then CLOSED again - about 3-4 secs for cycle
Pushes slug into injection system of fresh cool fuel under pressure

6. Boost pump OFF

7. While starting, slowly move throttles FORWARD until it fires (every time)

My theory is it puts a slug of cold fresh fuel into injections system

Thanks Dave.

Actually, my issue isn't a starting issue per se.

As I mentioned, we briefly failed to start it, but applying the high pressure pump quickly resolved that. What puzzled me was that the engine wouldn't stay running unless I then applied an on-off-on-off routine to the electric pump switch. It seemed I was, essentially, manually metering the fuel flow--as if there were no fuel pressure regulator in the system.

So now I'm wondering if I have two problems: 1) a failed engine pump, since I can't start or run the engine without the HP electrical pump, and 2) a failed fuel pressure regulator since I can't keep the engine running without the on-off-on-off routine.

I'm assuming of course that there is a fuel pressure regulator, but wondering also if that's a bad assumption.

Thanks again.

Sound like a dead mech fuel pump
 

The electrical one is fueling the engine, meaning the mechanical one is not.

Mine is turbo, so the fuel adjusts with both altitude and RPM.

My famous drain problem was fuel leaking past the inside of the fuel pump,
back UP the turbo/throttle pressure sense line that goes to throttle body,
into all the intakes.

All said, sounds like a dead mechanical fuel pump.
Prepare for a $1,000 or so OH.

Yeah, I figured that the rear pump was failed.

But why does the electric pump appear to flood the engine? Or at least it acts like it does--again, I have to turn it on and off with the just the right rhythm to keep the engine going. I would think that a fuel pressure regulator would take care of any excess pressure that the electric pump provides, so that I don't have to turn it back off to keep the engine running.

I likewise had failed pump(s) issues. This is my learned understanding: there is an orifice (not a regulator per se) built into mechanical pump. In fact, after new engine pump installed, part of check out process is checking fuel pressure and adjusting orifice on it if necessary, with the bleed orifice being the "regulator" of fuel pressure. It appears the electric boost pump on high provides flow for 75% power (not idle) "blowing through" a failed engine driven pump via a bypass valve in the event of a failure. At idle, high boost electric pump is thus flooding the engine providing flow for 75% power (bypassing the "regulating orifice") rather than only providing the fraction of that fuel flow necessary sitting on the ground.

check this out:

http://www.kellyaerospace.com/articl...inuousFlow.pdf

Thanks for that. Lot's of information in there. I notice however that it does show a separate fuel pressure regulator, but it doesn't say this applies in its entirety to the 360.

With regard to the situation that made me wonder about all of this:

Since posting, my IA says that persistence has gotten him to the point where "something worked itself out" and the engine runs fine, but idles a bit rough. I've long since conclude that nothing works itself out in cars, computers, or relationships--and I'm inclined to carry that mindset forward into aviation. Off the pump goes to QAA for replacement/overhaul.

Fuel Issues
 

Have you contacted Continental? I have found that their technicians can really help.

Was not aware they were able to offer help. We're pretty confident that rear pump is not trustworthy at this point, so we're sending it out regardless. But no guarantee that all will go well after replacement, so I'll definitely keep that in mind.

Thanks for the tip.

you might find this AvWeb article interesting (this is focused on the 360 engine whereas the prior takes in all manner of injected continentals):


https://www.avweb.com/ownership/cont...uel-injection/

Thought I'd follow up on this.

Fuel pump and distributor were rebuilt. Though only 100 hours on that engine, that clock was reset about 15 years ago. Am told that diaphragms can stiffen up over that length of time, especially with low use. The fuel distributor was a preemptive strike based on similar concerns.

Started easily and ran very well after.