Gas tank becoming pressurized???

[twobjshelbys]

I know new vehicles have all this evap recirulation stuff (charcoal canister, etc). (Trust me, I got to know a lot more about this system than I ever wanted to because of a problem with my 2004 Dodge Ram, but that's a story for another time.) But does this vehicle? I seriously doubt it. If it does it will have a purge valve controlled by the ECU. I doubt anyone installs those in older Cobras. Heck, my Cobra didn't even have a PCV.

[C5GTO]

Originally Posted by sunman

The emissions connection on the fuel tank sender is connected to the charcoal canister then to the purge solenoid then to throttle body vacuum port. To vent the tank. Check the line, is purge solenoid working?
You are pumping gas to the cap with return line also, that’s dangerous. Nobody does that.
Increase in elevation possibly makes problem worse.

This Cobra has no emissions equipment installed. No charcoal canister, no purge solenoid, etc.

[C5GTO]

Originally Posted by Morris

Show us a photo of the inside of the LeMans cap.....

Maybe all you have to do is put a check valve in your line and drill some holes in the sealing part of the open cap

The fuel tank has to vent to the Atmosphere

Here's what it looks like under the LeMans cap with the screw-in cap in place and removed.





I do understand now that the fuel tank needs to be vented to atmosphere. Upon reflection, it was vented (poorly but still vented) when the screw-in fuel cap could only be partially screwed down as the o-ring seal on the cap never seated. When I ground away some of the plastic part of the cap, the screw-in cap now sealed and thus no more atmosphere venting.

It sounds like at a minimum, 2 things are required to address the situation:

1. Add a dedicated port/line in the gas tank that exits at tank bottom for the fuel return
2. Make the fuel tank venting so it goes to atmosphere.

It also sounds like the fuel pressure regulator should be re-located to a cooler location to minimize the fuel vaporization that's occurring at that point in the system.

To add the return line port, I'll need to drop the gas tank...UGGGH...never a fun thing to do.

I assume the check valves that are installed in the gas tank vent lines are there to stop gas from running out the vent in the case of a roll-over. Please confirm or if they serve a different purpose, please specify.

Another question, if gas tank venting like what is shown in in Morris pictures is installed, is the vent port on the filler neck below the screw-in cap now superfluous? If it is, I'm guessing it's better to remove it versus just plugging it up. Thoughts?

If there's other obvious things I'm missing, please bring them up. I do appreciate all the help you guys have been on this issue

[sunman]

Change the return line and see if you still have a problem.
That’s a vent/splashback line connection so gas is not to top of neck and splash out when you open cap.
I’m one of those guys with canister and purge solenoid.

[Morris]

Originally Posted by C5GTO

Here's what it looks like under the LeMans cap with the screw-in cap in place and removed.





I do understand now that the fuel tank needs to be vented to atmosphere. Upon reflection, it was vented (poorly but still vented) when the screw-in fuel cap could only be partially screwed down as the o-ring seal on the cap never seated. When I ground away some of the plastic part of the cap, the screw-in cap now sealed and thus no more atmosphere venting.

It sounds like at a minimum, 2 things are required to address the situation:

1. Add a dedicated port/line in the gas tank that exits at tank bottom for the fuel return
   
   I don’t think this is needed right now.....maybe later
   
   
2. Make the fuel tank venting so it goes to atmosphere.

Correct


It also sounds like the fuel pressure regulator should be re-located to a cooler location to minimize the fuel vaporization that's occurring at that point in the system.

To add the return line port, I'll need to drop the gas tank...UGGGH...never a fun thing to do.

I assume the check valves that are installed in the gas tank vent lines are there to stop gas from running out the vent in the case of a roll-over. Please confirm or if they serve a different purpose, please specify.

Correct

Another question, if gas tank venting like what is shown in in Morris pictures is installed, is the vent port on the filler neck below the screw-in cap now superfluous? If it is, I'm guessing it's better to remove it versus just plugging it up. Thoughts?

No ...the vent needs to be above the stant gas cap....then drill a couple of holes in the top part of the LeMans cap like the photos above


If there's other obvious things I'm missing, please bring them up. I do appreciate all the help you guys have been on this issue

Check the responses above....

[sunman]

Holley Sniper instructions have pictures of fuel return line install to bottom of tank.
Google up on YouTube “how to properly install a EFI return line”.

[eschaider]

Joel,

Something to consider on the fuel return line;

If you put it at the bottom of the tank, fuel will run up the return line and force the return circuit to overcome the pressure this fuel presents to the returning fuel. When that happens, it will cause an artificially rich condition because the fuel pressure regulator can not return all the fuel it needs to.

If you plumb the return line to the top of the tank or near the top, the return line does not need to push against the fuel weight in the return line and tank to return. The engine likes its fuel delivery better when it is closer to stoich.

[sunman]

The return line is at the bottom to prevent aeration of the gas. EFI 101.
The flush cap EFI fuel cell I’m putting in the trunk has pump, emissions connection and bottom of tank return built in.
Gas in the return line increases pressure, no don’t think so…and there’s a vacuum line vent to the throttle body.
I had my harness redone stand-alone by Dr K and am using everything hooked to it. Not the EGR pump tho
This is an 86 Mustang GT California motor with all emissions parts and no miles. I’d sell it, some dude in Cali lookin for this

[Morris]

You guys are way off base......

Joel has a kit car that was built many years ago and is using old technology.....

All he needs to do is vent the tank in a way that is safe and won’t let fuel out if the vehicle rolls over.....

[sunman]

This Ford EFI systems and modern gas tanks are sealed. Mustang II front suspension is hot rod industry standard.
I suggest you consult Holley for return line info.
I’ve run this type 5.0 EFI since Reagan and Bush were in power, going big block with Sniper now.

Morris and Ed your galleries are wonderful and the cars are unbelievable.

[eschaider]

Originally Posted by sunman

The return line is at the bottom to prevent aeration of the gas. EFI 101.
The flush cap EFI fuel cell I’m putting in the trunk has pump, emissions connection and bottom of tank return built in.
Gas in the return line increases pressure, no don’t think so…and there’s a vacuum line vent to the throttle body.
I had my harness redone stand-alone by Dr K and am using everything hooked to it. Not the EGR pump tho
This is an 86 Mustang GT California motor with all emissions parts and no miles. I’d sell it, some dude in Cali lookin for this

The bottom of the tank return line positioning will richen your AFR and it will not be linear across the engine's operating range. Additionally, the AFR change will vary as the fuel level in the tank goes up or down.

I run a three pump fuel system with between 750 and 1350 lph delivery capabilities. If the fuel is aerated it produces no adverse fueling considerations that need to be attended to. My pumps and all OEM manufacturers pumps draw from the bottom of the tank not the top.

The gas in the return line is not what creates the back pressure for the return line. It is the fact the return line fuel is entering at the bottom of the tank and has to push against the weight of fuel already in the tank. Same as ocean diving. The deeper you go the higher the pressure from all the sea water above you. In the gas tank it it no different.

Most significantly, it will change your commanded AFR, and the change will vary by the amount of fuel in the tank at the time.

Ask me how I know — been there done that ...

[sunman]

Pressure of water at 1’ deep is .445 added psi over atmospheric. Gas is lighter. The tank is 9” deep.
The ECU controls AFR. The tank has about 5# pressure. Vapors are vented to throttle body not 3’ from your head. You understand it will pump vapors out all the time if vented.
OEM tanks have bottom return lines.
This is great easy EFI hook it up correctly and use your code scanner.

[twobjshelbys]

Originally Posted by sunman

Pressure of water at 1’ deep is .445 added psi over atmospheric. Gas is lighter. The tank is 9” deep.
The ECU controls AFR. The tank has about 5# pressure. Vapors are vented to throttle body not 3’ from your head. You understand it will pump vapors out all the time if vented.
OEM tanks have bottom return lines.

What ECU??? As stated, this is an old technology engine. No electronics, no emissions. Purely mechanical. Nothing but pumps and gravity.

[sunman]

Joel said he has early 90s Ford EFI. He’s got a ECU if he’s got EFI.
He’s got throttle position sensors, air flow sensors, O2 sensors and everything but the canister and purge solenoid.
Pumps and gravity? No but its not real complicated the code scanner does all the troubleshooting
The question is where to hide the canister. Oh wait, I know, chrome paint

[eschaider]

Sunman,

Have you tuned an EFI engine and tested your theory against ECU reported/recorded AFR or lambda targets? Have you measured the varying impact across the engine's part-load, part throttle driving rpm? When you do, you will find data that is both surprising and also nonsupportive of your argument.

You are dealing with relatively low differential pressures at the injector at part throttle / closed throttle. The reason for this is the vacuum present in the manifold at low engine speed and small throttle openings.

Ford's pressure compensated fuel pressure regulator adjusts fuel rail pressure for observed / measured manifold vacuum in these low throttle opening high vacuum situations to preserve the base fuel pressure differential across the injectors. If you have a manifold vacuum of 17 inches at idle and higher cruising speeds when you take your foot off the throttle, you are changing fuel rail pressure by more than 8psi.

Ford has a preference for a 39.15 psi differential pressure across their injectors. At idle, this can drop fuel rail pressure to 30 psi. On the highway, when you lift your foot off the throttle, the pressure drop is exaggerated because of the higher engine speed and, again, the closed throttle.

Any restrictions or impediments to flow in the return line will upset the fuel available to the engine at the injector when you tip in your throttle. The result will reduce the attractiveness of the car to drive. The engine can behave weak, non-responsive, and then surge with power.

This discussion is not about whose dog is bigger. It is just about the real-world experience working with these systems and what makes engines, tunes, and cars more or less drivable. If the OP wants to put the return line into the bottom of his tank, by gosh, that is his call, his car, and his money. He should absolutely do it! The information and experiences I am sharing are for knowledge. If he wants to discount them for any reason, that's his call and his right.

One of the more daunting challenges with the Ford OEM EFI systems is Ford's reluctance to share the programing tools and methodology they have used. Many aftermarket shops like HP Tuners, SCT, and others have done a pretty impressive job laying out the Ford maps, logic, and tuning parameters. The most important thing to remember is that they have used a trial and test approach that, while validating what they are working on, does not give the complete picture of all the variables the ECU is using and how it uses them.

The switch to an aftermarket ECU is a breath of fresh air for documenting how the EFI system handles differing engine situations. It also brings a wealth of engine protection tuning, data logging, launch, flex-fuel capabilities, and much more. The most significant barriers to using one are cost and emissions testing in your home state.

Some excellent low cost EFI systems leave little to want feature-wise in their implementations. Some are priced as low as $1,500 or less! If the emissions Nazis don't shoot you down, the aftermarket approach is the way to go. If they shoot you down, a good tuning software package like the HP Tuners offerings will help you get the most out of your OEM ECU but, and this is a big but, the now modified code in the OEM ECU may not pass emissions testing.

[C5GTO]

Oh boy, I love it when one of my challenges results in vigorous information/idea sharing! It's a good sign I'm dealing with a non-trivial issue and that I'm not an idiot for not already knowing how to resolve it. So please keep the information/ideas coming.

So the plot thickens...

I dropped the gas tank and it's clear now to see why I went with the rather hacky fuel return line into the tank vent configuration. This gas tank is very old school and was never meant to support EFI. It has the filler pipe welded on the side, a hole for a SAE 5 screw fuel level sending unit and a vent welded in place. That's it. I had to modify the sending unit to add on a fuel line to get the fuel out of the tank.



The tank hole for the sending unit is 1 1/2 inch and the Stewart Warner sending unit is located in that hole filling all of it. Back in the days when building this car, I somehow found a way to drill a hole through the sending unit to pass the gas line through. I was hoping there would be room for a second hole for the return line. No luck, it just won't fit even if siamesed with existing line.

I've done some Internet searching and haven't been able to find a SAE 5 screw sending unit that also has fuel out and return lines. I've found OEM sending units that have fuel lines incorporated into them but they are not SAE 5 screw mounts and I suspect they wouldn't fit through the 1 1/2" hole. I found a SAE 5 screw plate with 2 threaded holes for fuel line out and return but I suspect it would be very complicated (likely not possible) to graft on a sending unit and still have the works fit through the 1 1/2" hole. Did I miss finding the "magic" part? Do you guys know of a combination sending unit and fuel line in/out part that has a SAE 5 screw mount?

I also found a couple of fuel return line port kits that require drilling a hole in the tank. One requires you can get a large sized wrench to it to tighten the sealing nut and with a 1 1/2" hole I don't see that as working. It has an option for running the return line to tank bottom but this also requires getting a good sized wrench into the tank. So I've ruled out this option.

The other attaches like a Riv-nut so all wrenching is external to the tank. But given that, it doesn't support attachment of line inside of tank so return will be to top of tank only. I think this fitting might fit between the tank top and under the trunk floor with a special 90 degree AN fitting but locating it in just the right spot would be key.



Following the theme of keeping it simple, I've come up with another option. That is adding a fuel return port into the "S" bend filler pipe shown in picture above (shiny section is where overflowing gas dissolved the paint coating). Obviously, this doesn't get a return line to tank bottom but neither does the other viable return port option. It could be positioned so the return tube runs down the filler pipe and releases fuel below the tank top level. It's simpler in that it doesn't require a new hole in the tank with the possibility of getting shavings in the tank or having the new fitting leak. There's more space to work with out in the fender area than between tank and trunk floor.

Is there a reason that this is a bad idea? The return fuel would be taking the same path to the tank as when new fuel is added. The gold plated option is to retrofit the tank with an in-tank fuel pump/return system but I'm into a pretty major project at that point. I really don't like drilling/cutting into a fuel tank that's had fuel in it if I really don't have to. I don't have the same reservations for drilling and welding on a section of filler pipe though. I do understand that in addition the tank venting needs to be fixed or I'll still have fuel coming up to the cap.

Is the simpler option the better one here or am I missing something?

[sunman]

Great idea simple with a little line it will lay on tank floor. You have a code 85, canister problem. Solenoid has power to it and ECU grounds it to open at cruise. Pin 31 on ECU gray and yellow wire. Easy to add a canister, solenoid and vacuum fitting. Add a tee next to corner vent on tank for vacuum connection. Ford wouldn’t have it if it wasn’t needed.

[eschaider]

Joel,

There are any number of ways to fabricate what you are attempting to add to the fuel system. The simplest way to do this is go to an aftermarket hat, I'll show you what that is in a moment. The hand fabriccated solutions all suffer from various maladies and failure points over time. They are time consuming and sometimes expensive (when you are all done) solutions to the problem.

There are a number of EFI suppliers today that provide all the functions and functionality you are looking for in a fuel hat that replaces (bolts in?!) where the OEM hat used to be.

The first thing I might do, if I were you, is determine the year and model vehicle your existing fuel tank came from. Then I would buy a hat for that tank if available. In the case of Ford tanks I would look at using a SN95 series tank like a 2000 through 2004 (possibly earlier and later also) Mustang used.

The fuel pump hat manufacturer I have used and currently use is Fore Innovations. Fore makes a family of fuel hats that will accept virtually all of the high and highest performance fuel pumps avilable from TI Automotive today. TI makes the oem pumps.

The hats allow the use of one to three pumps and bolt right on where the OEM fuel pump hat did. In your configuration a single 255lph pump will probably be more than adequate. The nice part is if you later hop up you powertrain you can just add more pumps. The hats also contain mounting provisions for the OEM fuel level sensor and the return line facility for return style fuel systems.

Here is a link to the 03/04 Mustang style tank, pump hat, click here=> Fore Fuel Hat. Look at the blown up pics, roam around the site and check out the various supporting pieces he makes for EFI installations. The equipment is very high quality, all bolt together on OEM style tanks and a much easier, properly designed enhancement for your ride. BTW notice the fuel return in the top of the hat.

The base version of that particular hat is configured with two 255 lph GS342 Walbro pumps. Ford used two 190 lph (or so) pumps on the 390 HP 03/04 Terminators. Those fuel systems were essentially tapped out. Any additional power required bigger pumps or a Kenne Bell boost a pump. My guess is you are at the same or higher power level. Although a blown 390 HP will use more fuel than a n/a 390 HP, whatever you don't need can easily be returned to the tank. You will have a comfortable fuel reserve. Roam around the site. You will find a wealth of EFI equipment and some tools to make life easier — but most importantly the Fore stuff will get you away from those unreliable, nasty welded add ons you are currently saddled with.

[sunman]

This is a Pinto style tank made for Classic. Put a fuel cell in the trunk if you are going to spend any money.
$350 for a EFI tank ready to go.
Im putting mufflers where the tank was with C4 exhaust tips in lower valance panel.
Inspections? We don’t need no stinkin inspections in Oklahoma

[eschaider]

Kyle,

I think you said early on that you had an early 90's 5 liter engine. I just got a heads up from the DIYAutoTune folks in my email today about a plug and play version of their ECu for 96-98 mustangs. Yours obviously is an earlier implementation. That said if you get an engine and dash wiring harness out of a salvage yard car this ECU will work for you, click here =>96-98 Mustang P-n-P ECU

If the early 90's wiring harnesses are too hard to find get a early 2000's Mustang GT wiring harness and use the same ECU but packaged for the newer car and at the same price point, click here => 1999 - 2004 Mustang GT The software and electronics are identical only the pinouts on the OEM connector are reassigned for the particular year harness you are using.

This approach and one of the Fore hats for the fuel pump and fuel level sender / sensor capabilities will transform your ride into a very manageable very tuneable attitude adjustment car. The documentation on the EFI computer is stunningly complete and the Videos from Youtube give visual confirmation to the written word in the manual.

Replace your existing beat up fuel tank with a suitable OEM alternative, plug in the Fore fuel hat and install the MS3Pro plug and play ECU from DIYAutoTune and put your aggravations behind you.


p.s. One of the nice attributes of the MS3Pro PnP systems is their support for the OEM Ford dash instrumentation. It is always nice when the dash is not dark.