79 Eldo Gas Tank

[bcroe]

Every couple decades gas tanks have to come off and be reconditioned;
its time.  After running well for a while, the EFI 79 Eldo started going lean after
cold warmup enrichment ended.  That as seen on the wide band OX sensor I
added.  Its not the ECU, so something is restricting fuel. 

The whole thing is complicated by another project.  The plan is to replace the
2 fuel pumps with a single one mounted in the tank.  This would clean up stuff
in the frame and eliminate the annoying pump noise.  A common in line gas filter
replaces the complicated cartridge and custom molded hoses. 

A modified tank unit with the new pump is finally ready, and a beautiful RENU
reconditioned diesel tank (several extra gallons) is ready.  Just pull the old tank
and put them in, right? It only goes that smoothly if the tank was previously off
last week. 

After doing all the prep work and putting this job off a long time, its going ahead. 
Perhaps the hardest part is safely getting the old tank off.  My method is disconnect
everything, capping hoses as I go, then unbolt the tank and drop it onto plywood
fastened to my trans jack.  The tank was close to empty. 

First clamp off a hose on both sides of the disconnect.  Pull it apart with a drip pan
below, cap both ends.  Continue with all 3 hoses.  Unplug the gauge and pump wires. 
OK, then take out the front 2 bolts to release the tank.  But the snap in nut clips in
the body have rusted to the bolts.  The nuts break loose and are spinning out of sight. 

There are a couple other more accessible  bolts at the rear, so these were removed
and the tank dropped.  This allowed coming in with an electric saw to cut off the rusted
bolts.  With the pieces fished out of the body channel, new parts can go in. 

This car brings the entire wiring harness back to the tail lights, then some of the wires
double back to connect to the gas gauge, the 2 pumps, and the auto leveling rear
sensor.  The wires are lying right on top of the tank, which is is interfering with my nice
clean removal process.  One pump wire must go away, and a body ground is needed. 
I had already added a waterproof connector so pumps could just plug in. 

So the wiring needs some work, and needs to be held up against the body so as not
to interfere with work on the tank.  May drill for a ground and some Ty Wraps...

I have had issues with hose failures in the high pressure line.  Some of that hose
with stainless braid might be more reliable, if less flexible.  Now would be a good time. 

Anyway with the tank down, there is for the first time a clear view of all of the 3"
stainless steel exhaust system.  Its heavy, and there are 4 very much custom made
hangers to guarantee it will stay in place.  The camera got pictures of everything while
possible. 

Once the wiring is ready, the new hoses go in, and the frame pump is removed.  No
hurry, the idea is to make it a lot easier next time.  Bruce Roe

[bcroe]

I wanted a low restriction exhaust but also quiet, so the biggest pair of stainless
steel mufflers that would fit under the car are used.  A 3" pipe is pushing the
available space.  The trouble is, some hangers need to be not very close to the
frame.  This took some creative (but amateur) welding to support in front and
back of each muffler. 

Don't need so many hangers, you say?  After decades and 100s of thousands of
miles with SS, I have developed different rules.  First realize that unlike a steel
exhaust system, the parts never rust into a solid mass.  Instead they just keep
trying to wiggle loose.  And the hangers DO wear out, even if the pipes don't. 
So I have punched marks some 4" back from the ends of pipes, for inspecting
the current depth of engagement.  And lots of hangers take the extra weight,
trying to keep things stable and guaranteeing my laborsome system will never
fall onto the road. 

[Roger Zimmermann]

It seems that you have nuts in an unlimited supply!

[bcroe]

It seems that you have nuts in an unlimited supply! 

Yes long ago I discovered that the exposed threads of muffler clamps (or any under chassis
bolt) would soon corrode, making it impossible to get the nut off for the next service round. 
So the clamp had to be cut off and replaced.  This DID NOT fit into the plan here, of things
being easy and inexpensive to service.  I put antiseize on the threads and covered them with
nuts for protection: no more damaged threads.  At least a second nut is also much more
effective than a lock washer.  Remember stainless stuff doesn't rust together, so this is
standard on any high vibration stuff.  Bruce Roe

[bcroe]

The RENU reconditioned diesel tank is now installed, with a single high pressure fuel pump
in the tank.  It seems to be working properly.  I drilled the front tank bolt holes into the
trunk, so regular bolts could be dropped in.  A new tank wiring harness supports the single
pump setup, with plug in ease.  Guess the original tank heads for RENU. 

One thing that came up was pipe diameter.  The history seems to be, a 3/8" line was
used to a carb mechanical pump.  Then they decided to recirculate some gas so it
wouldn't just keep getting hotter and vapor lock, 1/4" return pipe.  Then they needed
a vent line for the emissions canister, and added a 5/16" line.  My thinking is, they
were all different so they wouldn't get switched connecting up. 

Well THEN, we got EFI in the 70s; started out with the same convention.  But a carb
car had the fuel mostly sitting in the 3/8" supply line when sitting in traffic.  So bleeding
a little back would keep it cooled down.  But the electric pump in the EFI car runs at
maximum volume all the time; all the fuel not being used is shunted back to the tank
by the fuel pressure regulator.  That means practically the whole pump output at idle. 

This inspires the idea, that the return line shouldn't be the smallest, like it was on my
79 Eldo.  AND the tank unit I used for the high pressure rebuild was set up that way. 
Logical, but what about the pipes in my car?  To achieve this, I reversed the functions
of the vent and fuel return pipes going forward from the tank.  But they need to be
reversed at the engine end as well.  Today I got into the nearly unaccessible spot with
my smallest tubing cutter, put in new hoses, and did it.  At least these lines have almost
no pressure to worry about.  I put bands of Red heat shrink all along the Return path, to
remind me of the change. 

I also just noticed, power for the rear leveling unit come from the pump power lead. 
More strain on the circuit, which so often fails.  And the book says there is a ground by
the tank for the leveler, pump, and gauge, BUT doesn't identify where it is.  I found a
ground wire between the tank and leveler, but not where it connected to body ground. 
Well now there is a super ground connected at that point. 
Need to buy more miniature hose clamps.  Bruce Roe

[bcroe]

I gauge the pressure at the fuel injector rail, and it says the new fuel system
and pressure are doing just fine.  Fuel pressure runs about 39 psi above
manifold absolute pressure (vacuum), max pressure with the throttle wide open
or starting, and dropping back some at high vacuum idle or coasting. 
Bruce Roe