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LS swap seems to be eating fuel pumps. Or is something else going on?

K30Blazer

K30Blazer

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When I swapped in my LQ9 I replaced the sending unit and put a walbro 255 in the tank. Fast forward to about 500 miles in and I run out of gas. Pump goes dead about 50 miles later.

I chalk this up to my dumb error but swap an AC Delco 62psi pump in. Now that one has gone bad. Started by just stalling while driving occasionally but now won't start and has left me stranded.

I pulled the pump and sending unit and noticed that the connector on the sending unit top (where the wiring terminates) to be charred from what looks like a short.

I replace the pump with another AC Delco under warranty and pull the charred connector out and wire positive and negative up directly. I have 12.4v at the pump and connectivity tests good all the way through.

But no priming and no pumping. Apart from a doa pump (unlikely) what else could I check? I know I am getting power but nothing happening.

At this point, apart from dropping a whole new assembly in (pump and sending unit) I am at a loss. I am also considering going to a higher end frame mounted pump as this is getting old real quick, but I like the security, protection and cooling of the in tank models

Thoughts?
 
Have you tested what the psi is at the rail? Just curious. Are you using the Vette filter/regulator or is yours a return style?
I would also pull the external filter off and blow compressed air back from the rail and from the filter back into the tank, make sure the line is good. Also make sure it's not messed up some place along the frame. What line did you use btw? Also, make sure the pump sock isn't smashed up against the tank bottom, that will make it work much harder.

My FAST system runs 45psi, I think that's about the same as an LS motor, right? So I've got a TBI tank, Delco pump, and the same psi as you.

Also, you sure the ground for the tank is good?
 
I actually just measured pressure about two days before this all happened 500 up to redline and I got 56 - 58PSi. Corvette filter is installed and everything is fine there. Pulled filter and it runs good through. Ground is good as far as I can tell.
 
Have you tried any different brand of pump? I used a delco pump on my ls swap and it was really noisy and gradually dropped pressure over a period of about 6 months till I had to cycle the key several times to get it to start and then it had low pressure which caused a lean condition. I read about others having problems so swapped in a Delphi pump. So far it's quiet and good pressure but I haven't had it long.
 
I'd check the 12V feed wire to the pump that powers that charred connector--often that wire develops a high resistance and wont send enough amps to the pump motor to activate it..
Many brands of new pumps come with a new connector and the instructions say you must replace it,and check the wire for ability to deliver sufficient amperage..an old headlight bulb can be used to determine this..
Quick way to test for that would be to hot wire the pump right at the sender to the battery positive using a long jumper wire..

My friend has had several GM's give trouble shortly after a new pump was installed due to the wiring having too much resistance,and the low voltage wont show up using a typical test lamp or digital meter because they dont put enough load on the wire..
I have seen one GM truck that would light the headlamp bulb up bright for about 20 seconds,then it would dim down,and you could feel heat building up in the 12V feed wire..the low voltage and amps likely smoked the pump motor quickly..
That truck ate 2 pumps ,the third one was installed with a new wire right to the fuse box and so far its still running.
 
When an in-tank pump goes bad, it sometimes can ground the electrical pump motor internally causing a short in the entire system. This can cause everything from melted wires to blown fuses.
 
Make sure the pathway has no out of whack resistance. Ohm the circuit from the relay outlet (87a) to the harness break out (87-91) in the left rear corner of the frame in front of the tank...
Generally a healthy circuit will see an ohm or less...
 
yea, it is a new Pacific Fabrication harness with relays etc. I will hook up my 12v to it and see what happens. At this point I am gonna try and get a new sending unit too. I did paint the tank so thought that might be part of the grounding issue, but there is a rubber o ring between the sending unit and tank, so I doubt that is the issue.

I guess the question I have is does the PSI (12 vs 60) from TBI to LS draw that much more amperage. If it does and the stock sending unit wiring is unable to keep up with the amps, maybe that needs to be addressed.
 
Ground is on the frame. As long as its clean and unbroken it should have anything to do with an oring or paint.
 
The wiring is fine. Dumb questions but maybe will jog some thinking...

Youre using the right size fuel line yeah? Just thinking a kink would really work a fuel pump.

I think youre using a tahoe tank or something like that right? How far off the bottom is the pump?
 
yea, fuel line is great. I had good pressure a couple days ago. Line is straight and perfect. I have a feeling I just got a bad pump. Ordered a new sending unit to throw in there too. I am using a stock tank which I cleaned out really well prior to reinstallation
 
Well not that it makes a huge difference but I went through 3 pumps in a vortec truck once. Never even ran the tank dry. Theres an amazing amount of threads about crappy pumps out there so its clearly a major issue. Guess you just have to find the one that works for you.
 
That's actually good to know. The last ac Delco I picked up on Saturday was doa. Never worked once. Ran power from straight from two different batteries and nothing. I ordered up a new one to see what happens.
 
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