Question: Question for the master techs...fuel pumps

[boomdriver]

What is the function of the brown square "thing" that the wires pass thru in the fuel level/pump sending assy inside the tank?

I ask because of a strange thing that happened...

My old sender was bad, level sender broken so I got another...salvage part, pulled it from the donor car myself. Same yr etc...

After installing I ran it briefly to test and ck for leaks. All ok. Later after a 3 hr pressure leak down test, the pump refused to run.

After much cursing and testing I discover that somewhere between where the pump/sender assy plug thats on top of the tank and the pump itself, the power signal is broken, So I exchange the intank section of wire harness with the brown box, and all works well.

I test the "bad one" and it has continuity, but it will not run the pump.

So, whats its purpose? :confused A resistor of some sort? a diode? I cannot find anything on this in the FSM elect book...

 

[LLC5]

Can you post a picture?

 

[boomdriver]

Can you post a picture?

I'll have to go dig the old one out of the trash....

if you've ever changed a fuel pump on a C4 you know what I'm talking about.

The 1" X 1.5" X 1/2" rectangular brown/tan ceramic box that the 3 wires for the pump and level sender pass thru inside the tank. This "box" is just under the mounting plate for the assembly. Its top has the 3 wires in a small plug that fits on a bulkhead electrical plug that is the transition from outside to inside tank. It is part of the pump/level sender assy. Part of the wiring. Purple to the sender, blk/gry to the pump.


3 wires go in....3 wires go out. Whats it do? and why?

 

[LLC5]

I'll have to go dig the old one out of the trash....

if you've ever changed a fuel pump on a C4 you know what I'm talking about.

The 1" X 1.5" X 1/2" rectangular brown/tan ceramic box that the 3 wires for the pump and level sender pass thru inside the tank. This "box" is just under the mounting plate for the assembly. Its top has the 3 wires in a small plug that fits on a bulkhead electrical plug that is the transition from outside to inside tank. It is part of the pump/level sender assy. Part of the wiring. Purple to the sender, blk/gry to the pump.


3 wires go in....3 wires go out. Whats it do? and why?

You're right, I haven't actually replaced a C4 fuel pump or sender card, but some of the parts do cross over.

My guess would be that it is a junction block for the fuel pump and sender card for assembly purpose. The in tank senders and fuel pumps that I have replaced allow for replacing them seperately if desired.

 

[boomdriver]

You're right, I haven't actually replaced a C4 fuel pump or sender card, but some of the parts do cross over.

My guess would be that it is a junction block for the fuel pump and sender card for assembly purpose. The in tank senders and fuel pumps that I have replaced allow for replacing them seperately if desired.

I can;t see that....

the block is inline, below a plug that detaches from the underside of the top (plug-in) and below is the plug to the fuel pump. The 3rd wire is a permanent attachment to the sender (proximity sensor). The sender is spot welded to the pick up tube and return tube which is welded into the top plate. Pump mounting is able to be changed but the rest is pretty much a one piece unit. That explains the cost of around $450 thru some outlets. Just recently that has come down to $200 in the aftermarket.
Its not some modular piece, and has no label. Why its inline with no obvious purpose is baffling....especially after finding that it has something to do with the power to the fuel pump...

If its a resistor and I blew the old one, I need to know why and then what to do about it.

 

[boomdriver]

Pics as requested..

The part in question show installed then removed from sender/pump assembly.





Anyone? best guess?

 

[Schrade]

I don't see in any of vetteoz' schematics a '3-in, 3-out' device.

Do you see nothing in your own FSM?

With 3 wires, I'm guessing potentiometer. That can be checked with a multimeter, with ohmage set at minumum. (if the thing works tho')

 

[boomdriver]

I don't see in any of vetteoz' schematics a '3-in, 3-out' device.

Do you see nothing in your own FSM?

With 3 wires, I'm guessing potentiometer. That can be checked with a multimeter, with ohmage set at minumum. (if the thing works tho')

its in every c4 sender/pump assy that I've ever seen. Its not described in the FSM, at least where I have looked...

The later ZR1 assy does not have this part.

The potentiometer is welded to the return tube halfway down the assy, seen in the photos. Top rt corner pic 5.

 

[LLC5]

It looks like a junction block for the wires that can be clipped onto the sender assembly. The only way to know for sure is to cut it open and look.

 

[Schrade]

What's the verdict? Did you break it apart yet?

If not, do it with gloves on, because if it's what I think it is, it has mercury in it...

ed.:
Instead of breaking it apart, put your multimeter on it, turn it upside down, and see if you still have continuity...

 

[boomdriver]

What's the verdict? Did you break it apart yet?

If not, do it with gloves on, because if it's what I think it is, it has mercury in it...

ed.:
Instead of breaking it apart, put your multimeter on it, turn it upside down, and see if you still have continuity...

A mercury switch?
To break the fuel level signal when the gas sloshes around?

After talking with vetteoz, he likes the resistor theory, and I have heard of that before. I know somewhere there is some kind of dampening device to slow the signal or break it when radical changes take place so the gauge in the dash does not go nuts and be impossible to read...

I'll still test it as suggested and if there is not an informative result, then I'll slice it apart.

That'll be later or tomorrow....today is committed to polishing an aluminum air box cover...and a set of runners. Anyone want some polished & enlarged runners? not so cheap

Interesting that I've been looking at the brown thing for 25 yrs and never really questioned it.....

 

[Schrade]

Check valve stops fuel flow in rollover.

Switch is needed to kill pump power in rollover ... ?

Switches and gasoline don't mix well, unless they're SEALED in

brown square "thing" that the wires pass thru

:confused

 

[boomdriver]

Check valve stops fuel flow in rollover.

Switch is needed to kill pump power in rollover ... ?

Switches and gasoline don't mix well, unless they're SEALED in :confused

Good point !

I tried testing the wire upside down, rightside up....made no difference, so its not full of mercury. Rule that out.

Tomorrow I';ll slice it open with the dremmel cutting blade and see exactly whats in there.

Will let ya know.

 

[kvetty]

fuel pump wiring

Hey, guys, along this same line, I am putting a 1990 intank pump in a 1980. my question concerns the wiring for the pump in the tank. It looks like it is exposed to the fuel? No liquid tite plugs? IS that right?

 

[K & B Special Products]

Pics as requested..

The part in question show installed then removed from sender/pump assembly.





Anyone? best guess?

Our supply of GM service parts do not have the part you show on the sender. Apparently it is not needed anymore.
On the last post, I would not try to put a 1990 pump in a 1980 Corvette.

 

[G Winter]

Our supply of GM service parts do not have the part you show on the sender. Apparently it is not needed anymore.
On the last post, I would not try to put a 1990 pump in a 1980 Corvette.

I agree.
The 80 is throttle body, which I think is quite low pressure. The 90 is 43 lbs min. The line
on the 80 might not be set up to take that.


Glenn