At the risk of repeating myself, I recently bought this truck and was told only the front tank was working so that's what I've been using. I noticed in the service records that the front tank was dropped and cleaned along with new pump and filter due to the truck sitting unused for an extended period of time. I'm sure the rear tank needed the same but only the front was done. The rear has gas in it, but I don't know how much. I have not flipped the switch, if the pump is working I don't want to pump bad gas or debris into the lines/injectors. I do want to drop the tank and either properly clean it or replace it and also replace the pump. Before I do any of that I would like to establish if the current pump still works as this will tell me everything is fine electrically. Also if the pump works I would like to disconnect the fuel line at the filter and use it to pump the gas out of the tank before removing it. Is this possible? I'm hoping to do that, drop the tank, clean it, install new pump, reinstall tank and be good to go. If I were to flip the switch to the rear with key off and then turn key on without starting the truck, I should be able to hear the rear pump cycle on if it's working. I would then flip switch back to the front and start truck as normal. Would this introduce bad gas if I never started the truck using the rear tank?

 

That will introduce bad gas. Best bet is to pull the supply lines off the fuel selector valve off that run to the rear tank, point them towards a bucket, and KOEO to see if the pump works.

 

I assume that's the "Y" piece that the lines from both tanks run to. I noticed that it was not nearly as accessible as the filter. Could I just disconnect at the filter instead? In normal operation gas from the rear tank can't enter the front tank can it? The filter is only about 12" forward of the Y.

 

Does it look like this:




Or this:



Either way, I'd remove it before the selector valve. That much less trash to wear out the valving later.

 

Looks like the lower pic. I assume that pic was taken with the tank dropped?

 

I dont believe so. I drive a RCSB And I was able to completely change that out in about 20 minutes, there's plenty of room to work around it. Just trace the lines that run to the back tank, and use a flathead screwdriver or small pry tool to pop up the clip and pull out. Try not to exert to much perpendicular force on the fittings, they may crack/break at the housing and you're in for a world of hurt after that.

 

Bad information in this thread above.
You do not have the selector valve that is in the photos above.
There is no way to separate the fuel lines going to the tanks.
Also you do not have the type of fuel line connector that you "use a flathead screwdriver or small pry tool to pop up the clip and pull out".

Your fuel lines need a special tool to disconnect the fuel lines from the filter and the tanks. You will need two tools at the tank as the two fuel lines are of different sizes, 5/16" return line (gray) & 3/8" supply (pressure) line (blue).
To disconnect a fuel line squirt WD40 into the connection to lube the "O" ring and then twist the fuel line connection to break the "O" ring loose. Then shove the tool in as you push the fuel line further into the connector. Hold the tool all the way in and pull the fuel line out of the connector.

Fuel line disconnect tools:


The "T" between the two tanks:


Fuel line clip to release:
/

 

Just looked under the truck and the T in your pic is what I have. I do have fuel line removal tools also. Do you think I can proceed as above and disconnect the line at the filter and purge the tank with the pump if it still works? If not, I'll just siphon the gas out.

Thanks for chiming in

Edit: What prevents gas from entering the front tank when using the rear tank? Is there a check valve somewhere that's not pictured?

 

Seems like a bad idea to use an expensive fuel pump to empty out a tank filled with fouled or dirty gas. Much better to use an inexpensive siphon to do the job. Might take a little longer, but you won't damage the pump.

I did this last weekend to empty both tanks on my '89. Used a $5 siphon kit that had a simple squeeze bulb in the middle. No check valves in that bulb to fail or get dirty, so you squeeze and then hold your finger over the end of the hose to get it started. Took some time, but worth it.

 

You can not remove the fuel lines from any point without the tool or you will mess up the clip inside the fuel line.

Maybe but you might clog up the sock at the bottom of the Fuel Delivery Module (FDM) inside the tank.

The high pressure pump check valve inside the FDM.

Yes inside the FDM.

The FDM that is inside the tank:


Your fuel system:


/

 

Thanks greatly for the pics and help. I will just siphon prior to dropping the tank. I believe the pump is original and has 130,000 miles and I will be replacing it regardless of condition.

 

There is a FILTER for a reason. I say dump a bottle of dry gas in it and RUN IT.

Hell, the fuel pump may not even work

 

Ordered new tank with pump preinstalled from rock auto. Hopefully get it installed this weekend. $200 for the kit, comes with new straps too.

 

Just got the old tank out. Before I completely dropped it I disconnected the fuel lines and tried to activate the pump and it didn't cycle. I assume each pump has it's own relay and the previous owner may have removed it. Which relay should I check and is there something else I should look for, like a fuse maybe?

 

the switch might be bad...


make sure you wired the new tank correctly too. a lot of those pump/tank combos require the dissection of the harness and rewire.




wait.....you tried to run the old pump that you think is bad??? switch to the rear tank, ground the fuel pump test port (google to find it) located by the air filter, and check for voltage at the rear tank with voltmeter. if voltage is present for the pump (use wiring diagram for pump color) then your pump is bad and you need to continue replacing it.