Hello,

I'm converting a 1981 Corvette C3 to LQ4 engine.

Here is the original fuel system.



A (yellow): Fuel feed
B (blue): Fuel return
C (orange): Fuel vapor line

I'm keeping the original tank (with Walbro inline pump)

I think the answer is NO but do I need a fuel vapor line back to my tank with LQ4/injection system? Can someone confirm

 

On mine (74 Corvette) I used stock tank with internal pump, pressure regulator on the fuel rail. I ran new supply and return lines and closed off the vapor system. But - my pump module had a fitting I used for a tank vent. I think your fuel cap is not vented and you need some way to vent the tank, but the vapor system is for environmental controls and not necessarily needed.

 

I don't see why you would need that. Just cap the outlet for the vapor line at the tank, run your normal feed line, and use the Corvette filter/regulator to run the return back to the tank.

If you are keeping the truck intake and fuel rails, there should be a regulator at the rails, in which case you can skip the Corvette filter/regulator and run the return from the rails...but make sure to put a filter somewhere.

 

Thanks guys!

 

Though you can get away with it as long as the tank is vented someway.. to allow air and vapors to escape and to allow air in as the fuel is be used. A vent cap can allow this to happen.

But as a suggestion.. if you park inside.. you have a very high chance of smelling Fuel Vapor as they escape from the tank (fuel expands and push out the vapors). If the Garage is connected our under the main living area.. you might even smell the vapor in the house.. This is one reason why a Charcoal canister is used or even suggested.

This has been talked about many time.. just do a search on the subject.

BC

 

Interesting tip!

 

You don't need the vapor system. It doesn't hurt to keep it and as stated, might eliminate some smell and will function as a tank vent.
Since you'll be getting an LS1/6 intake you'll need the LS1 purge solenoid if you want to keep it. The truck solenoid plugs into the intake. The LS1 is a separate piece that connects into one of the intake vacuum ports.
If you buy a harness or have someone program the ecu, have them leave it in, most remove it.

 

I didn't get the purge solenoid with my LS1 intake but thanks for notifying about that option gary

 

I think I have a few, cost of shipping and their yours if needed..

I don't run the Solenoid myself..but I do run the vent line into the Canister to handle the flumes... I thought about making a smaller canister (like a fuel filter size) and filling it with Charcoal.

 

That's nice from you bczee but I'm living in Belgium. But next time I do a global order from USA I will pm you so you can send to my forwarding address in USA.. might be in several months!

 

Theoretically, running without a purge solenoid and charcoal canister vented to the atmosphere would result in an unmetered vacuum leak into the intake. I'm not sure how much air gets through a canister, but that could vary depending on the canister design. Running the canister vent to metered air (after the MAF, like the PCV) would allow for metered air at least.
In the case of using the purge solenoid, it only opens only in not critical situations. ie open loop.

 

I thought the canister hole was supposed to be blocked if not present, thus no vacuum intake leak ?!

We have no emission control tests here in Belgium regarding 25+ years old cars

 

The canister needs air drawn through it to remove the vapor/fumes. I think the early corvettes were open to the atmosphere.