1985 c30 350 V8 "Ursula", sub-project: Fuel System

[ThunderLizard]

Patient:  1985 Chevy c30 Custom Deluxe, Big Dually, Dump Bed.  5.7L Gas Engine, 4 speed manual, 42K original miles. 
Goal:  A reliable, fully functional, heavy duty farm/work/towing truck that I’m comfortable letting my wife or sons drive.
Fuel system symptoms:  Truck is running!  In fact, it starts right up and sounds great.  2 tanks, don’t know which it’s using.  Fuel level gauge isn’t working.  Fuel line set-up is confusing and seems non-standard. 

I bought this truck from my sister. 

Me:  Which tank are you putting gas in?
Sis:  I can’t remember.  I haven’t used it in years.  I think the driver’s side tank.
Me: Does the other tank work?  Does the switch work?
Sis:  I don’t know.

So, I’ve been working on this truck for a couple of months.  I’ve driven it through the fields and a little on the rock roads to check-out the steering and brakes.  I’ve put maybe 5 miles on it.  I haven’t put any gas in it.  It looks like there is gas in both tanks.

The fuel gauge is pegged all the way to the right, past full and doesn’t move when the switch is toggled. 

I used my circuit tester at the fuel sender unit, and the switch does switch power to the right or left fuel senders.  Did a functional test on the switching valve, and it doesn’t make any noise when the switch is toggled.  It doesn’t seem to have any power, based on circuit test light. My tank switching valve has one wire. 

So I started doing the research, and everything I found talked about a 6-wire harness for the fuel switching valve and fuel return lines.  Uhh, my truck doesn’t have any fuel return lines.  I’ve got fuel hoses all over the undercarriage that don’t go anywhere.  There is an un-connected hose right at the fuel pump that goes back to the tanks and is un-connected at that end too. 

What should I think about replacing?
1.   Tanks?  They aren’t leaking.  Should I clean them out?  What are the tricks to accomplish a clean and flush?
2.   Fuel Senders?  These are pretty expensive for “professional” units.  Do they go bad?  Is this likely why my gauge isn’t working?  Should I just replace them?
3.   Switching Valve?  No brainer, I’m going to replace this, but should I change to a 6-wire/fuel return set-up?  Or just replace with a similar one-wire type?
4.   Fuel gauge?  I don’t really know how this works.  Any resources would be appreciated.  Is the level determined by a voltage or .  Sorry for my ignorance. 
5.   Fuel lines?  Are there different types?  What should I use for a heavy duty work truck?

Thanks!

[ThunderLizard]

Thought I would try to throw some pictures up here.  Wouldn't work last night, but I'll try again. 

[English]

Probably not much help, but while you're waiting for someone more knowledgeable to come along...

I have dual tanks, and everything works fine. So all I can do is tell you what should be happening.
The fuel gauge displays the level of the tank currently in use. The needle does not drop to zero when the ignition is switched off.
When you switch tanks, the needle moves accordingly, but again, only when ignition is on. Switching tanks with ignition off will not move the needle.

A needle that's pegged to the right could be a faulty gauge or faulty sender.

I'm sure I read somewhere that the dual tank system naturally defaults to one particular tank. So if your switching system doesn't work you will be stuck with that one tank.

[BBM3]

Someone reduced the fuel system to it’s simplest configuration.
The return lines are not strictly required but desirable. My ’75 as built does not have return lines and my vent lines are vented to atmosphere with vent caps like yours.

Your fuel selector valve is aftermarket. If you want to put the return lines back into service you will need a new 6 port selector valve, fuel pump with return, wiring, and probably a switch.

The single power lead to the selector valve should show 12 volts when the switch is in the AUX (LH tank) position.
Looking at your third picture the cleaner black fuel line on the left should be connected to your RH main tank and the dirtier line on the right should be connected to the the LH AUX tank.

The fact that your fuel gauge reads over full (I’ll guess 3 o’clock) indicates a bad ground(s).
The fuel gauge receives a ground signal through the switch from the senders. The black / yellow spliced wire in the third picture should show somewhere from about 5 - 60 ohms from empty to full respectively. That butt blue connecter splice should be replaced with a water proof connection and the wires checked to insure water hasn’t wicked through and corroded the wire strands.
The other wire is a ground that should be connected to the sender and a clean connection to the chassis.

Let me know if I can help with trouble shooting tips. I just went through all of this on my truck and everything now works.

[ThunderLizard]

English and BBM3 - Thanks for the responses.  You guys have given me good jumping-off points for when I finally get back home and can get me hands dirty.  I'll definitely be replacing the fuel selector valve and re-doing all the wiring. 

BBM3 - Is there any advantage to going to a fuel return system?  What are the advantages?
For me, it seems, simple and cheap is better than spending more money to replace parts that seem to work OK (fuel pump).  However, I do want this truck to be reliable and durable.   It appears that someone (probably my dad) stripped all emissions control out of this truck.  He likely did this to increase simplicity and possibly performance.  This truck, in its first life, was a back-up Porta-Potty pump truck.  When you are 4-hours from the shop, with a tank full of honey, you definitely want any field repairs to be as simple as possible.  But, if there is a good reason to go back to a fuel return 6-wire set-up, I might just go ahead and do it.

I'm going to keep updating this thread as I work though the fuel system. So stay tuned for the next episode. 

[BBM3]

Am I glad I didn't insult the person that worked on your truck. 
I just got done insulting the unknown person that beat the snot out of my front driveshaft when they replaced the u-joints.

One of the advantages of having return lines it to keep cool fuel flowing through the supply lines to the pump and reduce the possibility of vapor lock.
Of course return lines are mandatory with high pressure fuel injection.
 

[ThunderLizard]

BBM3 - No worries, insult away.  If there is one thing my dad taught me it is to try to have a thick skin.... and there is more than one way to fix stuff.   

I did a little bit of Internet research and all the information I found pretty much backed up what you said.

One Mr. RB69SS396Conv on a Chevelle discussion board said:
The fuel pump pressurizes fuel to send it to the carb. If the engine isn't using much fuel (sitting still idling for example) the fuel in the line will be mostly just sitting there, getting hot. Then when it gets to the carb it is already EXTREMELY hot; sometimes so hot, it boils furiously into a foam and spews everywhere, including flooding the intake with fuel. Modern fuel, with high ethanol content and intended to ALWAYS be under high pressure (keeps it liquid) near the engine, is even worse about that, than pure gasoline.

Fuel pumps don't seem that expensive.  How hard are they to change out?  Am I going to be fighting seized bolts on the engine block?  I never seem to have very good luck when it comes to tough extractions. 

[BBM3]

Your Father sounds like a wise man and he certainly did no harm in the way he reconfigured / simplified the fuel system.

If you don't have a problem getting fuel to the carburetor with the current setup I would drive it and focus on getting the rest of the fuel system working.

To add my 2 cents too the quote in blue:
The fuel line(s) between the tank(s) and mechanical pump are under vacuum / lower pressure which will lower the boiling point of the fuel and may further lead to fuel vaporizing before the pump.

Replacing the fuel pump is easy but again, if your truck runs maybe you will want to consider insuring that your current selector valve, senders, gauge, wiring, and switch are working properly before messing with the unused return lines.

[ThunderLizard]

UPDATE -
So I found a few evenings to work on the fuel system.  I installed 2 new in-line fuel filters, a new tank switching valve, replaced some of the fuel lines, re-did the grounds for the fuel senders, and ran new wires for the tank switching valve and the right fuel sender.  I also replaced the fuel tank selector switch.  The switch I got was $23 from NAPA.  This seemed very high, but it was the only one I could find in town and I didn't want to wait to order one off the internet. 

My plan is to fill up both tanks, add Sea Foam, and monitor the new clear fuel filters to see how much junk comes out.  Depending on what I find, I might consider replacing or cleaning/coating the tanks.   Trying to stay on the cheap side for this sub-project. 

Good news: The truck is still running well after all my work.  Tank switching valve is switching between the 2 tanks.  The fuel gauge is working for the right side tank. 
Bad news:  When switched to left tank (primary tank), the fuel gauge pegs all the way past full.  Not sure why yet.  I'm not certain how to get to the back of the gauges.  I've watched some videos, but all of them skip the part where the actual gauge cluster is pulled.  I haven't yet figured out how to get the cluster off since I don't see any obvious screws or bolts holding it in.  I could use some advice on this.  I get the cover off (easy) and then the gauge cluster feels kind of loose, but won't come out.  Do I need to remove the speedometer cable somehow or something?

Anyway, I'll continue to update here for those that are interested. 

Some pictures:

[ThunderLizard]

OH YEAH, and I found a receipt in the glove box that says this truck received a new engine in 1998!  BONUS! 

[BBM3]

Good news: The truck is still running well after all my work.  Tank switching valve is switching between the 2 tanks.  The fuel gauge is working for the right side tank. 
Bad news:  When switched to left tank (primary tank), the fuel gauge pegs all the way past full.  Not sure why yet.  I'm not certain how to get to the back of the gauges.  I've watched some videos, but all of them skip the part where the actual gauge cluster is pulled.  I haven't yet figured out how to get the cluster off since I don't see any obvious screws or bolts holding it in.  I could use some advice on this.  I get the cover off (easy) and then the gauge cluster feels kind of loose, but won't come out.  Do I need to remove the speedometer cable somehow or something?

Good progress!

1) Primary tank is normally righthand (passenger side). Doesn't really matter other than it is best if the primary tank is the one that supplies fuel when the selector valve is de-energized. Better to not have the valve energized most of the time.

2) The fuel gauge indicating over full 3 o'clock is normally caused by a bad ground at the sender to the chassis.

3) Sounds like your fuel gauge is working since it works correctly now for one tank. The fuel gauge uses a single feed from the switch. The switch on the dash chooses which sender to send fuel level resistance to the gauge.

4) If you want to remove the fuel gauge you do not need to remove the entire cluster. Remove the lens and the fuel gauge can be removed from the front after removing the three 1/4" self tapping screws.
I'll bet your gauge is fine since it works works with one tank.