My 1988 Fords front tank hasn't worked in 2 years and I decided to replace it with a new tank and a pump in the tank. After finishing it I put 5 gals in it and it worked but the rear tank was pumping in to the front tank also. Confused in why.

 

If you trace the fuel lines from each tank one is a supply line and one is a return line. They go to the back of the fuel tank selector valve which is mounted inside of the driver side middle of the frame rail behind the high pressure pump.

When you select a fuel pump the fuel pressure from that pump moves a valve for the return port and the supply port.

You can unbolt the selector valve and bench test it with 10 psi of air.
That should be enough for the ports to switch. As far as I know a Ford OEM tank selector valve is the only unit that is plug and play.

Many years ago that valve sold for $75.00

Below is a thread that describes the fuel lines and the Ford part number.
https://www.ford-trucks.com/forums/1...tor-valve.html

 

Today I switched the switch to the front tank again and went under the truck to listen to the pumps. Both pumps are running at the same time. Switch to the rear and just rear pump runs.

 

Either the tank selector switch is defective or Bubba has done some rewiring.

Here's the schematic for the tank selector dash mounted rocker switch.
The selector switch has 6 wires going to it.

When you flip the switch to the front tank.

Yellow/White wire which goes to the gas gauge makes connection with Dark Blue/Yellow wire to display fuel level of front tank.

Red/White wire which is 12 volts makes connection with Red wire to power the front in tank fuel pump motor.

Flip switch to rear tank.

Yellow/White wire makes connection with Yellow/Light Blue wire to display rear tank fuel level.

Red/White wire makes connection with Brown/White wire to power rear in tank fuel pump motor.

Your mission is to determine why you have 12 volts on the Brown/White wire rear in tank pump motor when the selector switch is selected for the front tank. Should be zero volts.

 

Today I put a new switch in for the front and rear tank. The one in the cab. Tested the wires and all is good there. Still when flipped to the front tank, gas is coming from rear tank and filling the front tank and overflowing it. Just not sure what could be going on. Thanks

 

Another thing I did today was I cut the power for the rear pump and I still have gas coming out of the front tank fill. So the rear must not be pumping at the same time. Weird but could it be the selector valve?

 

You say when the front tank is selected gas is overflowing from the front tank because fuel from the rear tank is being pumped into the front tank.

You have cut the wire to the rear fuel pump and the problem still exists.

That would indicate the fuel supply valve in the tank selector valve for the rear tank is not completely switching to the front tank.

The high volume low pressure pump mounted on the frame rail is pulling gas from the rear tank. The extra returned fuel is going back into the front tank.

If the truck runs normal using the front tank, remove the selector valve and test it using about 8 psi of air.

Or buy a new tank selector valve.

 

I'll keep you updated, I have a selector valve on the way. Thanks for your advice. Well get it.

 

bingo the selector valve was bad, thanks to all.

 

My 1988 clutch is acting up. I bled this clutch many times. Its good when you drive the truck, Or when its cold. But when the truck is hot it won't disengage and go into gear. Works fine when cold. And the clutch lets out at the floor and works at the floor.

 

Assuming you have the Mazda M5r2 have you verified the fluid level?
The rubber caps on the rear of the shifter cover were known to leak and
eventually the trans would run dry.

Some people have reported excessive play where the arm of the clutch pedal rotates and have installed bushings. I'm not positive but I thing the factory used plastic bushings.

I had a problem on my 88 where the clutch slave was good but eventually the clutch wouldn't release completely.Turned out to be a weak clutch pressure plate. I guess the release springs wore out.

Read this thread about the firewall cracking. If you have someone press on the clutch pedal look under the hood and see if the plate the clutch master cylinder is bolted to pulls away from the firewall.

https://www.ford-trucks.com/forums/1...omparment.html

 

Yes I have a 5 speed. The firewall looks good as well as the bushing under the dash. Works good when not as hot. Seems like the clutch gets weaker on the disengaging part when it get hotter. It will disengage but you really have push it hard to the floor. Is is normal for the clutch to let out right on the floor?

 

No that is not normal. Cracked firewalls on the older Ford Trucks are very common.

It's possible the clutch master cylinder is bad and bypassing fluid. Do you see any fluid leakage
inside the cab where the metal push rod attaches to the clutch master cylinder?

When you have the problem.

**********Do this test in a clear area so you don't hit or damage anything because the truck could move forward *******************

Put the parking brake ON.

Shift the transmission into 1st gear and press the clutch to the floor.

When you crank the engine does the truck lurch forward?

If it does the clutch is not releasing and my guess is the clutch pressure plate is bad.

 

Had my wife push on the clutch pedal so I can check out the firewall. Yes it is separating away. Now would this make my clutch work the way it is?

 

https://www.ford-trucks.com/forums/1...omparment.html

You can probably find the small reinforcement bracket at the junk yard.

At one time this company sold the large firewall reinforcing kit.

http://www.terrapinmfg.com/product.php?cat=Ford

Here's the Technical Service Bulletin describing the firewall cracking problem.
http://www.terrapinmfg.com/TSB%2090167%20Clutch.pdf

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