EFI return line, use emissions return?

[Superelbert]

OK, bit of a strange heading there.. let me expand.

I'm running a megasquirt EFI on my mild 318, works a treat. But after installing electric fans, average underhood temperature has incresed (fan not running all the time), and on hot days I get issues with fuel boiling in the rails as I only have a local "recirculating" pressure regulator bleed-off in stead of a proper return line to the tank.

Now, there IS allready a return line in my car. In one end, it ends up uinconnected on the firewall, and in the other end, it is connected to this tubular thing poking up in to the boot. That tubular thing is allso connected to my fuel tank with several hoses. I believe this tubular thing is some sort of fuel vapour condenser, and the line was probably connected to some fuel vapour recirculation system not fitted to my model.

1:
Anybody familiar with what's just been described?

2:
Assuming the line is originally some sort of vapour recirculation line, would I be OK to use this as a fuel return line?

The reason I'm considering this is:

1:
The line is allready there

2:
it would save me the hassle (and danger!) of welding on an additional tube to my fuel tank.

I'm as allways gratefull for anny input fro you guys!

 

[BillGrissom]

It is too hot in Norway!

You could use the emissions hose. I have seen where people return thru the filler tube. It is probably too small (1/4"D) to be a proper return line, so you probably need to keep your existing bypass line to regulate pressure. The new return line would just aid cooling, by getting more fresh fuel to the pump inlet. I would be concerned if any rubber lines in the part that loops up thru the trunk. It would be pretty scary to have a fuel spray in the trunk.

Perhaps a better approach is to run a new 5/16" return line. If you are currently using the factory tube for supply, run a new 3/8" supply and use your factory tube for return. You could then do away with the bypass T. Get a new sender with 3/8" supply and 1/4" D return tube (~$45 new on ebay). I did above in my 65 Dart (lookup post). My problem is that I run 9 psi on the return side with a Walbro external pump (225 lph I think, but could be 190 lph). Most EFI systems suggest <5 psi. The main restriction is probably the 1/4" fitting on the sender. Next time I have it off, I will swage the entrance for a smoother transition. A 1/4" return tube should work if shaped more like a venturi. Not a problem now since I have a Carter 2 bbl carb on until I get around to EFI.

Excellent that you got the megasquirt working. I haven't heard of many Mopar success stories, but we are mostly a knuckle-dragging carb twiddling bunch.

 

[Superelbert]

"Too hot" is a luxury not seen to often in Norway, but on some summer days it can be!

Anyway, thanks for your answer Bill, this was most enlightening!

Apparently, it's been too long since I've been crawling under the old Dart now, forgot entirely about the sending unit back there, or at least that this is where the fuel line exited from!

An obvious solution would be to remove the sender and tig-weld in an extra tube for a return line if all else fails. Looked on E-bay as you suggested, but could only find senders with the one fuel exit pipe.

As for using the filler tube, its just a straight filler tube with no vents or connections, so that's an option I don't have.

The existing return pipe is corroded and has holes by the tank, so I'm replacing it with a fresh copper alloy tube instead. This tubing has an 8mm internal diameter, which I think should be OK for the return.

Good point about keeping any pressurized line out of the trunk!!

The Megasquirt has been very easy to work with and there's tons of info and help to be had on the web.
Seing some of the stuff you guys do, I'm surprised that not more people have gotten in to the Megasquirt thing!

And if you upgrade from narrow band to wide band O2 sensor, the thing will literally tune it self! Magic!

 

[67Dart273]

I'd use it. Might not be as big as the system "wants" but it's a heck of a lot better than a recirculating situation.

So far as TIG welding in an additional fitting, you don't necessarily need to TIG it. I actually added a 1/4 return line for my 67, which had none, for a vapor return system. I simply took the CO2 regulator output from my MIG, and filled the tank with CO2, then oxy/ acetylene gas brazed (hi temp silver braze) a 1/4 line into the tank. I believe you can also buy repop tank senders with a return line in them.

What year is your vehicle?

Here's a shot out of the 72 shop manual, which you can download here:

http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download

Go to page 25-14

 

[Superelbert]

Ah.. after reading your thread on EFI fuel supply, I noticed that you had a TBI/carb redundance thought...

Now this is a clever one I read about long time ago..

Use the intake manifold for a 4-bbl carb. fit it with injector bungs.. and use the carb as a throttle body! all you need to do is to attach a potentiometer to the butterfly-axle for throttle position sensor, and there's your throttle body!

Then you can just switch the fuel supply to the carb on and off at will! you will of course need one regulator for running carb and one for EFI respectively.

Now, my EFI has never failed, so personally, I consider such redundancy.. redundant, but it's still a neat approach if you want to do things on a budget.

 

[BillGrissom]

The one I got looks like this one:
http://www.ebay.com/itm/63-76-Mopar...t=Vintage_Car_Truck_Parts_Accessories&vxp=mtr

If the link doesn't work, seach "Dart fuel A-body".

I recall paying ~$45, but probably shipping so above might be same price as above. I bought another one recently to try on my 65 Newport since I have a home-made sender adapter for return there (Holley Pro-jection). If it doesn't work on a C-body, I can use on the Valiant I got since. I recall the vendor was A1Autoparts or such.

If I ever remove it, I will try enlarging the swaged part of the 1/4" return tube, since that is a noticeable reduction and probably the main culprit in the 9 psi return pressure I measure in the engine bay.

 

[Superelbert]

67dart273, sweet!

Thanks a bundle for that manual shot! That wasn't to be found in my chilton manual!

At least schematically, that vapour/ liquid separator which it apparently is called, is definitively that tubular thing poking up in to the boot of my car! It's a '71 Swinger GT by the way.

Any brazing or welding on my fuel tank is something I'd go a long way to avoid.

Had a sobering experience weldign a hairline fatigue-crack in a motorcycle fuel tank once.. washed out thoroughly with hot water several times, filled with water, but a very small pocket of air still went BOPP! No damage done, but still..

But if I can weld something through the sender unit flange, I'm OK annyway!

If I remember correctly, the hoses for the separator might well connect inside the boot, which is a no-no in terms of hooking up a return-line to the thing. An alternative might be to simply block off one entry to the separator and hook the return line up to the corresponding tube on the fuel tank?? Hmm.. that should work..

 

[Superelbert]

Bill, the link worked!

If left with no other options, this would be a bolt-on solution! Having said that, the price is 61$ and 46$ to Norway.. then there is import tax and declaration fees... so modding my existing sending unit would be a more economic option.

But thanks a lot for the advice and link annyway!

I wouldn't be to concerned about swaging that 1/4 pipe, any restriction is more likely to come from the diameter it self rather than turbulence from an abrupt transition in diameter. A bit surpised you got as much as 9 psi backpressure in the return line, but as long as you still get the correct supply pressure to your carb, I wouldn't worry too much.

 

[67Dart273]

I don't know of an easy way----- ONE or more of the lines (don't know which) in the vapor separator drains out the bottom of the separator. Without knowing which one, you could end up with fuel trapped in the separator.

I'd be tempted to unhook the separator completely, cap all unused tank lines, and run the return tube into one of the tank ports you unhooked.

VENTING the tank is also an issue. The original cap on those systems is a "pressure vacuum" cap, which by implication has a "pop off" pressure for both inlet and outlet. I'm not sure if you can get by in finding a vented cap -- it may slosh fuel out the cap

Older cars, "non emission" like my 67, had a metal tube welded into the highest point in the filler neck, IE just inside the trunk way up high in the filler tube. This tube then went down through the trunk rubber gasket and dead- ended (open) inside the rear frame rail. Thus, other than the static restriction in the 1/4 vent line itself, the tank in essence sees no vacuum or positive pressure.

Vacuum in a tank (such as the pressure vacuum caps) can ALSO contribute to your vapor / boiling problems because the pump has to work that much harder to overcome the vacuum.

I dearly hope, by the way, that you have the pump mounted in the rear of the car?

Here's how the vent works in the earlier cars, out of the 67 manual:

 

[Superelbert]

Dart,

Good point about not knowing which line drains the separator! If I can't come up with any obvious way to tell, that pretty much excludes some of the options considered!

It seems I have some sort of aftermarket cap, I'll need to check if it has any valve functionality or is just straight vented, there is no vent line on the filler tube as you describe.

The big issue about not having a vented fuel tank is.. collapse, which I have so far not seen any sign of! Having said that, there is the charcoal cannister return line, both open in the engine compartment and with holes rusted under the car... definitively need to check the ventability of mu fuel cap before I block the entry of this line to the separator!

My high pressure pump IS in the engine compartment, but it's being fed by the mechanical fuel-pump in the engine, something that seems to work quite nicely.

 

[67Dart273]

Your pump situation is not good. The mechanical pump is already pumping against a vacuum, and not having a return is really not good.

I'd get a low pressure electric, mounted right near the tank. That way, there is very little "under vacuum" before a pump. The main line from the tank to the (now) mechanical pump sees some heat as it comes up past the engine, AND it is now under a slight vacuum, which promotes vapor/ boiling.

 

[Superelbert]

Dart,

Not quite sure I get you right, but to claridy, I don't have any Vacuum in my tank at this time, the open cannister return line allone will see to that. I allso think my filler cap is vented judging from the smell in that area on hot days!

Its a long time ago, but when I replaced the stock mechanical pump, I did go for a high capacity unit that would correspond to my expected horsepower output, so as with a carb, it can't really see why it wouldnt bring the correct volume of fuel to the electric pump like it would bring the correct volume of fuel to a carb.

Granted, as the return fuel now feeds back downstream of the mechanical pump, this limits the demand on volume, if adding a proper return line reveals mechanical pump capacity to be an issue, I'll see the O2 values leaning out on high load and install an electric low-pressure pump near the tank.

At the end of the day, I am convinced the issue is fuel circulating in a loop in a hot engine compartment with no return line to facilitate circulation of cool fuel or path of escape for vapour. Granted, a fuel line passing by the engine block does not improve matters, but I think the effect is relatively small.

Annyway, Thanks a lot for all high-quality information and comments provided! My options are certainly clearer now, just cant wait to do some wrenching during easter! (car comming outr of winter hibernation tomorrow! )

 

[cleverbob]

65 Bcuda, 318, Holley Pro-Jection, Thought I'd throw my two cents in.

Since I didn't have a return line available I added a 3/8 line as the new supply and used the original 5/16 line for the return. Punched a hole in the filler tube and sealed a 5/16 SS nipple with JB Weld.

A smarter way would have be to install the nipple in the sender unit, using something like silver solder to secure it.

The Pro-Jection Manual cautions you to measure the return pressure to insure the line will handle the return flow. My 5/16 line measured next to nil.

Fuel pumps are a whole separate story, as is too gas tank issues. If you want I'll write a separate post on those issues.

I'm currently modifying the gas tank, adding baffles and an in-tank fuel pump assembly, hoping to to solve the last two issues I've encountered. [dry pump, and low tank cornering]

 

[Superelbert]

Well, since I have a buddy with a really nice TIG welder, I'll porbably go for welding a pipe through the sender unit flange, allso saves me routing any pressurized line in to the boot.

But If I didnæt have the option of welding stuff.. hmm.. no telling what I'd get up to!

As my return line will be about the same diameter as the supply line, I hope I'll be okay.

Friend of mine got him self a custom alu tank welded up with baffles and all other niceties imaginable.. But then again, hes building a 1978 Opel Kadet with a 400+ HP turbo engine going in. As opposed to me he'll NEED baffling!

 

[67Dart273]

............... to claridy, I don't have any Vacuum in my tank at this time, the open cannister return line allone will see to that.)

Here's the thing.......

I was assuming you have the original pressure/ vacuum filler cap, which, as I said, has a "pop off" pressure both for outgoing pressure and ingoing ---vacuum

The return line / canister system has a certain amount of static pressure, even though it may be "open" so it DOES cause SOME vacuum IE "negative pressure" in the tank, as the fuel is pulled out of it by the pump

The fact that for now, your pump(s) are both up front means that at least the low pressure pump IS operating UNDER a vacuum on the suction side of the pump. Again, this is due to the pressure vacuum cap, and the restriction in the canister system, (which may also have limiting valves)

Even the older cars with an "open vent" operate with the suction side of the mechanical pump "under a vacuum" which PROMOTES fuel vapor/ boiling.

That is, ANY time you lower the pressure on a liquid, you LOWER the boiling point of that liquid. So here you have the original supply line from the tank being "sucked on" by the pump up front, which lowers the boiling point IN THAT LINE. Additionally, the line comes up front past the exhaust and hot engine, which promotes boiling/ vapor even more.

And of course, last, you have the recirculation problem.

 

[BillGrissom]

Dart,
My high pressure pump IS in the engine compartment, but it's being fed by the mechanical fuel-pump in the engine, something that seems to work quite nicely.

Unlike all the Holley instructions and other advice, you don't need the fuel pump near the tank. My mistake was following Holley's manual when I installed Pro-jection on my 65 Newport in 1996. I put their gear-rotor pump on the frame rail in front of the leaf spring, below the floor (no such space on an A-body). Besides making a racket, if failed at least once (pickup restriction), and that wasn't a nice place to get to for repairs. I then put a small electric rattle pump as a "pusher" there, with the gear-rotor low in the front engine bay. The rattle pump starved the main pump, so I put a Holley rotary vane pump in the rear. That worked until I got the brighter idea of getting a 15 psi spring for the vane pump and ran that alone, which worked for years. When it leaked (porous casting it seemed), I tried just the gear-rotor in the engine bay. Worked fine as I figured it should since gas just pours out of the open 5/16" supply tube. Ran that way since and did similar in my 65 Dart (see my post). In sum, you might try losing your mechanical pump.

 

[Superelbert]

Well, everything is relative.. and I did find that the ols cannister vent line to the engine compartment was for all purpose and intent blocked by internal corrosion. (no kidding!)
So had my fioller cap not been vented, I would probably have sucked the petrol tank flat a good while ago.

Obviously, since fuel is being sucked to the mechanical pump on the engine, there will inevitably be some pressure drop as a function of the flow VS cross section of the tubing. But I doubt that this is low enough to change the boiling point of the fuel significantly.

Anyway, I did install a new copper return line, ID 8mm, and now everything seems to work just fine, hopefully it will continue to do so when sumer comes with warmer weather!