Flat on its face

[myk]

Took the Charger in for some warranty work on the re-wire job, and I mentioned that at very, very high RPM the car falls flat on its face with the engine cutting out; I didn't have this problem before I started running an electric fuel pump rated from 4-6# of pressure.  With that in mind, the shop would like to install another pump that's rated from 4-8# of pressure instead.  They'd also like to eliminate the vapor-return line because they claim that the vapor-return line bleeds off pressure that the fuel pump is trying to maintain. 

Does any of this makes sense to you guys?  The pump swap won't cost me anything as it's all on their dime, so I'm not worried about them trying to pull a fast one on me. I thought that 7# was the highest you could go on a carb'd engine without a fuel pressure regulator?  Will losing the vapor return line have any negative impacts?  I'm willing to bet that the problem is the fuel pump, but I don't think I need to lose my vapor-return line because of it, so I'd like to hear what you guys think.  Thanks in advance!

[ws23rt]

You mention the problem at very high rpm that you didn't have before changing the fuel pump.  This looks like where the problem lays.

A 4-6# pump tells the pressure but not the flow.  If your engine needs more than the pump can give that may explain the cutting out.

I have felt cutting out in my old hemi RR at high speed full throttle which was the stock fuel pump wasn't keeping up with the demand.

I am not familiar with your pump system but if they say the return line bleeds off pressure and that is what is starving the carb that still leads back to flow as the issue.  

Nixing the vapor-return line feels wrong.

[jlatessa]

Check your vapor return canister to see if the 1/4" return orifice has the called-for restriction;
.060" per Ma MOPAR but smaller can improve your pressure and volume.

Joe

[myk]

Check your vapor return canister to see if the 1/4" return orifice has the called-for restriction;
.060" per Ma MOPAR but smaller can improve your pressure and volume.

Joe

Well, if I allow them to nix the return line they're going to plumb in a filter with no vapor return fitting.  Usually I have an opinion on mechanical issues but I've never thought about fuel pressure before.  Guess I shoulda' stuck with a mechanical fuel pump lol...

[Dino]

I see no reason to get rid of the return line.  That seems wrong to me.  I'm installing one on my car that never had one because they do have an actual function.  Let them replace the pump and call it a day. 

[66FBCharger]

If they are concerned that the vapor return may be the problem, have them pinch the rubber return line off with some hose pinch off pliers and see if it makes a difference.

[myk]

If they are concerned that the vapor return may be the problem, have them pinch the rubber return line off with some hose pinch off pliers and see if it makes a difference.

Yes I misquoted them; they just want to cap it off and see if that's the issue.  Apparently they don't want to "eliminate" the vapor line either.  Personally, I think it's the pump, as I'm not seeing how a vapor return line setup contributes to fuel pressure loss...

[Dino]

If they are concerned that the vapor return may be the problem, have them pinch the rubber return line off with some hose pinch off pliers and see if it makes a difference.

Yes I misquoted them; they just want to cap it off and see if that's the issue.  Apparently they don't want to "eliminate" the vapor line either.  Personally, I think it's the pump, as I'm not seeing how a vapor return line setup contributes to fuel pressure loss...

It could if the separator itself was faulty so them capping it for testing purposes is just a good process of elimination.  Nothing wrong with that.

[myk]

I see.  Well they're dragging on my car because they're not making any money off of it, but another idea that got tossed out is the MSD; any chance my MSD 6 box could be causing that high RPM cutting-out?  How does one test an MSD box anyway?  There are no other driveability problems at all...

[Paul G]

Why do run an electric pump? Is there a need for one? I have removed them on two different cars to get rid of problems. Went with a mechanical pump both times and have no issues.

[myk]

I was completely set against an electrical pump as well, but the day I saw someone else trying to start/move my car at a car show last year in addition to the insistence of my trusted shop, I decided to install an electric pump to make the car harder to steal.  Honestly, I see nothing wrong with a mechanical pump and I ultimately prefer one, but...at least it's much easier to start?  You're right though, an electrical pump just introduces a "branching tree" of reliability problems when something goes wrong.

Anyway they installed a new pump and it's not cutting out anymore...