Ct1987

So here is the story. I converted my 87 firebird from carb to Holley Sniper EFI. Works great... New intake manifold also.
To do so, I had to drop the tank and replace the 3 psi pump with a Walbro high capacity pump. Rather than putting the old one back, I elected to replace the tank and sender unit.
I had to modify the pump wires so that the Sniper could control the pump. I cut the gray and black pump wires that normally goes to the bulkhead switch and instead ran heavy duty wires from the pump direct to the Sniper unit.

The problem is that the gas gauge does not work. I have tested the purple and black wire coming from the tank sender unit and it reads 22 ohms. About 1/4 tank of gas. I have connected a 100 ohm variable pot connected to the purple and black wires on the bulkhead and with the key on, rotating the pot will change the gas gauge readings, so that works as it is supposed to.

When I connect the plug from the sender to the bulkhead receptacle, I get nothing, reads empty. I have checked grounds and they are all good. Since the ECM no longer works, I doubt it has an effect on the gas gauge.

Does anyone have any ideas?

Thanks in advance,

Louis

Jorlain

iTrader: (4)

Any chance the float got stuck when reinstalling the sending unit?

Ct1987

Hi Jorlain,

I don't believe the float is stuck. Its giving me a resistance reading of 22 ohms, so even it its stuck, I should be reading something on the gauge.

To confirm this, I will put more gas in the tank and see if the resistance goes up, that would confirm normal float.

Thanks for the input,

Louis

Abubaca

iTrader: (3)

So not to go off topic, but is the Sniper triggering the pump or a pump relay? Pretty sure you need a relay in there. Sniper doesn't have enough juice to adequately run the pump.

Aviator857

Set your variable pot to 22 ohm's and see what your gauge reads, then touch the gauge lead to ground it should go to E, then disconnect the lead it should go to F.

Then I would test the resistance through the bulkhead connector should be pretty close to 0 ohms, then test with nothing hooked up the bulkhead connector resistance to ground should be infinity.

If you have continuity through the bulkhead, the guage functions as described above, and the sender to ground is giving you 22 ohms then the gauge should move to this position.

If it is not then you may have a ground continuity issue. that is when you test the resistance of the sender are you grounding your meter to the car frame or to the tank? The tank may not be grounded to the frame.

But based on what you said I would bet that the bulkhead is grounding your sensor lead, or the harness from the bulkhead to the tank is pinched somewhere.

Ct1987

Hi, The sniper has a built in relay for the pump, its part of the harness.

Thanks for answering,

Louis

Ct1987

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Aviator, you are close to something. The tank, as I remember is not grounded to the frame. There is a rubber buffer between the straps and the tank. I do believe its a grounding issue also.

Will work on it when I have time. Thanks for answering,

Louis