1989 F-250 three pump system.
Bucking and back firing through the intake on the rear tank and pings over 3200rpms on the front tank.
Where would you start looking? Rear pump or the selector valve?

 

No selector valve on your system. Just an electric switch to switch tanks/ gauges
Just low pressure pump in each tank, high pressure pump in the rail

There is a can where all 4 lines go together, and into 2 lines coming out, this is the system that keeps the tank you are pulling from, from filling the other tank.
It fails over time. They are getting hard to find and expensive

When they fail, they shut down the fuel pressure.
you can put a fuel gauge on your rail, and check, but I'm sure that is your problem
Eventually it will shut down the fuel completely, none will pass through

I have one I bought foe my 89 as a spare, not going to use it. PM me your address if you want it, I'll see what I paid for it, it's yours if you want it

Here is one I took apart
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With the symptoms I was thinking it was the reservoir assembly, of course the most expensive part. The rear pump is about 10yrs old don't know the age of the front pump and the high pressure pump is about four years.
Amazon has a reservoir assembly for $190

 

Lift pump only really needed when tank gets below 1/4 tank. Then the truck will just plain old run out of gas


I know I paid wsy less than that, I have had it a few years.
At the flea market now, I'll get back to you tonight

 

Not the reservoir, the rear pump is bad.

Yea I get to drop the rear tank!
But I was having a cross flow problem so hoping the new reservoir fix's that problem.

 

I have a pump here too....
But would be cheaper to just get one off Rockauto

Also. Make sure to pull the tank, and check see if the top of the tank is rusted through, may be a better Idea to buy a new tank with the pump already installed.
You can still run your truck with the tank removed.

Oh yeah, the FDR will fix the fill the tank your not running on problem.

 

Not too worried about rust. I don't drive on the beach and ODOT just started salting the roads in the Portland area.
I'm going to take the old fdr apart just to see what the inside looks like.

 

Post pics. Mine both times I replaced was full of gunk and rust

 

Update.

What I thought was pinging was the fan clutch giving up!

 

Man, your truck must be talking to mine!
Fix one thing, they want another!

 

Sorry for the delayed response.
It's paying me back for making it sit!