Hypothetical Fuel Return Question

[John D]

On a '98 XJ there is two lines coming out of the top of the tank. One is the fuel supply to the engine the other is a vent to the EVAP canister. Assuming you didn't intend to use your EVAP system anymore, what do you suppose would happen if you used the vent line for a fuel return to tank line?

I am setting up a higher pressure fuel pump and using the Corvette style fuel filter with return line. I was going to drop the tank and tap a bulkhead fitting for the return line when I noticed the EVAP line sitting there.

Also, if I wasn't going to use the stock in-tank pump, is there an issue with just leaving it in there attached? Can I pull fuel through the stock pump without it running or will it block the flow?

What are your thoughts?

John

 

[5-90]

The EVAP port should just be a blank port through the access plate - probably no trouble using it as a fuel return, since you don't need to pick anything up.

Electric fuel pumps are usually a "vane" type - they don't freewheel. You may be able to draw through them, but I doubt it. Better off fabricating some variety of pickup (a tube going down with the ability to attach the in-tank sock filter should serve.)

Why for do you intend to not use your EVAP system? Leaving aside that you can't really seal the fuel system totally (thus the EVAP system - catches fuel vapours and introduces them for combustion,) the EVAP would also contribute slightly to fuel economy - anything that isn't run through the cylinders and burned is wasted, and fuel vapours make an excellent "primer" for fuel/air mix anyhow - so you're also going to get a slight increase in combustion efficiency.

I also believe that the fuel tank access plates are a fairly standard size, so there's nothing really stopping you from using an earlier one - or another ChryCo or GM using the same style of sensor - with the three ports you'd need to have feed/return/EVAP. Just a thought...

 

[Shorty]

if I wasn't going to use the stock in-tank pump, is there an issue with just leaving it in there attached? Can I pull fuel through the stock pump without it running or will it block the flow?

What are your thoughts?

John

electric pumps are generally designed as "pushers" as opposed to "pullers."
I think you would experience severely shortened life out of a pump that's trying to "pull" fuel through a dormant "built in" restriction. The optimum installation would include a higher pressure pump in the tank with some sort of pressure regulator to set system pressure where it's happiest and a return line from that point to the tank. I'm not sure the Corvette filter has anything more than a vapour return built into it, but if it, indeed, has a built in return line, you would need to match the injector size to the engine needs at the pre-determined pressure.

edit: I know someone will reply "I've run a XXXXbrand pump outside my tank pulling through the original for a million miles and it works better than any other upgrade I've done" but the principal behind electric pumps still doesn't change. I've run dry rotted tyres before, but that still doesn't make it the best option...

 

[John D]

That's the reason I don't intend to use the EVAP system, sounds funny probably, but with eveything else I have had to figure out making the EVAP work seems a bit daunting.

Anyway, since you say I should pull the pump I will just drill a bulkhead fitting while the tank is out and plug and leave the EVAP vent line. Who knows, maybe I'll get back to the EVAP some day and try to make it work.

Thanks,
John

 

[Shorty]

"vette throughout??

I guess the injectors will be fairly well matched to the rest, huh??
What, if anything, is stopping you from installing the GM pump and sender (with a little modification) into the XJ tank-- or for that matter, the entire GM tank under the XJ?

 

[John D]

Its actually a 5.3L, I used a LS1 intake/H2O pump and I fabbed the alternator/tensioner bracket.

Time, $'s and convenience is why not on the vette tank/pump.