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-   -   EFI wiring question/philosophy (https://vansairforce.net/community/showthread.php?t=176167)

svyolo 10-19-2019 07:28 PM

EFI wiring question/philosophy
 
I am wiring up my SDS fuel injection. I was planning on using some automotive style (Delphi) multi-pin connectors on the cold side of the firewall to connect everything to the engine. I could just unplug them if I wanted to remove the engine. Lots of cars do it similarly where they have plugs mounted on the engine so the engine can be replaced as a complete assembly, wiring intact.

I am wondering how practical or necessary this is on an airplane. Is the value this adds worth the additional failure points induced?

I have a lot of experience with DC wiring. I can crimp, and I can solder. I have done very large amounts of both. But I have never owned an airplane.

I ask this here instead of the electrical section because it is specific to EFI.

Thanks for any answers/opinions.

Toobuilder 10-20-2019 07:49 AM

In my opinion the only way this would be useful is if you planned to change engines quickly for some reason. This would also require that you had a second engine (and harness) built up and ready to install at a moment's notice.

In reality, the engine harness is a "lifetime" install. I hard wired mine from the engine components to the ECU. As long as the engine side harness can be separated from the engine without cutting wire or metal I think you have as much engine change/maintenance utility as you need.

svyolo 10-22-2019 08:01 PM

I was also considering putting a fuel pressure switch on the pressure side, and if fuel pressure drops below a specific level, lets call it 30 psi, the second pump automatically turns on. Has anybody else done this?

Mike S 10-22-2019 08:26 PM

Quote:

Originally Posted by svyolo (Post 1381438)
I was also considering putting a fuel pressure switch on the pressure side, and if fuel pressure drops below a specific level, lets call it 30 psi, the second pump automatically turns on.

Consider if the low pressure was due to a leak in the engine compartment.

Consider if there was a fire from that leak.

emsvitil 10-23-2019 04:46 AM

Quote:

Originally Posted by Mike S (Post 1381444)
Consider if the low pressure was due to a leak in the engine compartment.

Consider if there was a fire from that leak.


A compromise would be to have the low pressure switch on a toggle so that you could have the 'automatic' feature only be on during takeoff and landing.

You'd also want a warning light if the 'automatic' feature has been activated.

You would need to use a latching relay so that the backup stays on until you turn it off.

Toobuilder 10-23-2019 07:43 AM

Quote:

Originally Posted by svyolo (Post 1381438)
I was also considering putting a fuel pressure switch on the pressure side, and if fuel pressure drops below a specific level, lets call it 30 psi, the second pump automatically turns on. Has anybody else done this?

My second pump is wired to and labeled to my former "boost pump" switch. No harm running both pumps at the same time, and more importantly, no need to unlearn decades of muscle memory and training.

airguy 10-23-2019 08:04 AM

Quote:

Originally Posted by emsvitil (Post 1381483)
A compromise would be to have the low pressure switch on a toggle so that you could have the 'automatic' feature only be on during takeoff and landing.

You'd also want a warning light if the 'automatic' feature has been activated.

You would need to use a latching relay so that the backup stays on until you turn it off.

And there goes the way of Boeing - overengineering a simple task.

If the fuel pressure drops, you'll know it by the engine coughing, no lights needed. Flip the switch and move on. No need to add more points of failure.

Ralph Inkster 10-23-2019 09:09 AM

Thoughts on installing the wire harnesses on the engine & having reasonable serviceability later. Consider not using grommets to pass the harnesses thru the baffling, instead create a plate/grommet affair large enough that the full harness & connectors (coil connectors, injector plugs for example) could pull thru if you ever have to take the engine off.
Others may help here with description failure symptoms of hi press/hi volume electric pumps they have experienced.
What we experienced in the one unit (not sold by SDS) that went bad on us is no loss of pressure but caught a lot of brass debris in the down line filter(gascolator). We caught this one before catastrophic failure and because of the down line filter didn’t experience any injector issues. Our 45 psi fuel didn’t drop & if it did, say to 30, we feel the engine would have told us we had an issue much before it degraded to that level, with power loss in progressing lean running. First item on our check list for power loss is second fuel pump than change tank, as mentioned above, a long learned response. I wouldn’t automate this for reasons mentioned by other posters.

svyolo 10-23-2019 03:14 PM

I will just put it on a switch. And no big connectors on the wiring harness. Thanks for all the input.


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