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Guest Anonymous

fuel injection safety questions

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Guest Anonymous

1. can the return line be the same I.D. as the delivery line? Or does it HAVE to be larger? I'll go to the junkyard to look at examples sometime, but if there are any engineers in the audience I'd like to hear your thoughts.

2. running high-pressure lines inside the car vs. under the car. The reading I have been doing suggests that I must run the lines under the car. Of course I already spent the time to run them inside the passenger compartment. I'm using continuous runs of 5/16 steel line from the in tank fuel pump in the trunk to the rubber hose that joins this to the fuel rail. So it would seem really unlikely that I could have a problem inside the car. But again I'm interested in the opinions of engineers in the audience regarding my current approach vs. tearing this out and putting it under the car.

I'd rather be unburned and alive then lazy and crispy so I may decide these are dumb questions to even be asking, but if there is someone out there with technical knowledge on these matters I'd love to learn (and I imagine some of the other folks would too).

thanks,

ben

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Guest Anonymous

EFI systems typically flow much more fuel per minute than is actually consumed by the fuel injectors, so that changes in demand do not cause big changes in pressure. The return side (the outbound side of the fuel pressure regulator) is at lower pressure than the feed side, so to maintain the same high flow rates, bigger lines are used to keep the fuel flowing more freely. However it's difficult to say whether you'll actually run into problems with same-sized lines, so I suppose I'd be tempted to leave it as is and work on the rest of the system. If you have trouble providing fuel at the proper pressure and flow rate, then it might be worth re-examining the return line size.

Regarding fuel lines in the cockpit, yes, clearly it's dangerous. Of course, driving the car is dangerous as well. If you are planning to install carpeting and all that stuff over the fuel lines, I'd say it's a bad idea to leave them in the passenger compartment, because it will not be easy to assess the condition of the lines. The biggest danger probably isn't the rupture of a solid piece of steel line during an accident, it's a leak forming from rust, friction with the rug, etc. Of course, with the lines bare and uncovered in the passenger compartment, you'd have to be careful that you don't damage them during the course of the normal use of the car.

I've certainly never seen a factory EFI setup where the lines were run inside the passenger compartment.

Mike

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Guest Anonymous

16-3757063.JPG

From the gaz tank, the lines go underneath the car, right above the passenger side half shaft where the fuel pump and filter are located, then back in the cockpit where it follows the transmission tunnel and into the firewall.

I decided to put the lines inside because I felt safer this way. In the case of a side impact, the fuel lines have no chance to be broken and spill. My fuel lines are Aeroquip braided lines. Why the pum is located under the car? Because of the connections, I did not want to risk and spill of gaz. Obviously, my car is a racecar...

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Guest Anonymous

I'm an engineer, and I agree that rust and abrasion are your biggest enemies. If that line sits under a wet mat or carpet, you won't see the rust either.

If you get a leak inside the car, the fuel pump will put a lot of fuel in there with you in a hurry. The spark from shutting off the ignition could set it off. I'd reroute that line.

While still a student I was cleaning my Fiat's carb. I forgot to reinstall the fuel line due to rapidly darkening conditions and tried to start the car. Having "improved" the car with an electric fuel pump I had doused the engine with gasoline before I hit the starter. WHOOOOSH!!!!! I hate that sound.

--Jerry

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Guest Anonymous

Go to the boneyard and grab a fuel pump interial cut-off switch from most any EFI F**D car. They're usually located in the trunk on the driver's side, mounted between the bracket that holds the trunk lid and the side.

These little jewels are either NO or NC and open(or close) on sharp impact. If you're so unlucky to have a rollover that doesn't stop your engine, this will keep the fuel pump from humming merrily along and filling everything in sight with gasoline.

Regards,

John N

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