I have a 1982 crossfire 305. My car has always ran great and performs even better. Recently my fuel gauge stopped working so I changed the gauge and still nothing. The problem was the floater on the fuel pump sending unit was broken so I pulled the pump out the tank and repaired it. Upon completing, the fuel pump was not turning on, tested the pump and its good, checked voltage at the pump and its 8 volts while the battery is showing 12.5 volts. Does anyone have a clue why my voltage just suddenly dropped at the fuel pump power wire out of nowhere ?

 

ANYBODY....PLEASE.

 

I now know the fuel pump requires 12 volts to operate, which is why it is not turning on with the 8 volts that I am getting somehow.

 

Are you saying:

You could drive your car (the fuel pump was working) but your fuel gage was not working.

You replaced your fuel gage => and could still drive your car (the fuel pump was still working) <=.

You pulled the fuel sending system, repaired the float, reinstalled the sending system and now you cannot drive your car (the fuel pump is not receiving enough voltage to activate).

In other words you could drive the car AFTER replacing the fuel gage but NOT AFTER pulling and replacing the fuel sending unit ?

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For what it is worth see this post:
https://www.thirdgen.org/forums/elec...t-working.html

It discusses the wiring. The ground is in common with both the fuel level voltage and the fuel pump motor. Probably should check the quality of that ground just to cover all bases.

 

EXACTLY . And I have replaced the fuel pump twice before (in the past) and never had any problems.

 

Without having the fuel pump system out of my car and in my hands I assume the variable resistor that is hooked up to the float has three connections:
+12
Wiper
Ground

If that variable resistor is allowing appreciable current to flow between +12 and Ground then +12 would be lowered to something less than +12.

The only thing that would come to mind is that the variable resistor has degraded or there is a wiring problem between those leads. If you move the float UP and DOWN does the voltage to the pump motor change? If so then, again, there is a wiring problem in there somewhere. I wish I had my assembly out to look at it.

 

Well I have read the link you provided and it is very helpful, I am going to get started right now on some wire tracing. One question I have thought is that it doesn't mention anything about a drop of voltage in the threads. I will post my findings ( if any) after my troubleshooting.

 

Where is the variable resistor located ? I'm not sure how much voltage is required to run the fuel pump, I'm assuming its +12v, cuz when I hook it up directly to the Battery (+12v), the pump goes on. When I wire it up at the tank, I get +8v and when I turn the key to attempt to start the engine voltage drops even further to +6v.

 

Hey I just had a thought:

If your purple wire gets shorted to ground (somewhere) then it would pull the +12 down due to high current across PART of the variable resistor and your meter would be grounded thus showing EMPTY or at least looking unresponsive. That is a possibility.

 

I think there is a variable resistor located at the pivot end of the fuel float. That moving arm should be changing a wiper on that variable resistor. That wiper sends the sensed voltage to the fuel gage. The extreme ends of the variable resistor have +12 on one side (the pump is also hooked up to that) and the other side is ground (and the pump is also hooked up to that.

Assuming you have the wires PROPERLY installed then a short of the purple wire to ground is a real possibility.

 

My wires are different, they are black (ground), beige (power), and brown (floater/gauge). I am getting readings from my meter so its not unresponsive and where is the variable resistor located ?
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For more detail, I have the fuel pump separated from the sending unit and have the pump directly hooked up to power and ground wires and it is not coming on (voltage low).

 

Also, if the purple wire is shorted to +12 you would likely pull the +12 volts down at the pump. And in this case your fuel meter would be fed the voltage that exists after it has been pulled down (eight volts in your case). So in that case your meter WOULD be showing some reading but your +12 voltage to your pump might be too low.

 

I'm not using the sending unit at this time. I have the pump hooked up only (process of elimination) .

 

Are you saying that you have the Fuel Pump assembly pulled out and laying on the ground? If so, You should unhook the power to the fuel pump and check some things for me as sort of a sanity check.

 

It is out, but not on the ground, I have an access door for the fuel pump made so its inside on top of the tank.

 

OK. I just installed an access hatch in mine last week. I replaced the rubber connection hose between the pump and the hard line. That has to be reated as 'submersible' meeting a rating of SAE 30R10 similar to NAPA H213 hose.

But that variable resistor related to the float is in PARALLEL with the pump motor so if things are not right with the variable resistor or the wiring for it then it will influence the voltage at the motor windings.

Do you want to run some sanity checks?

 

YES ... and the only reason my pump is hooked up directly is because even with the sending unit in play , the voltage readings are the same.

 

Well I have to know exactly what you have there because I am envisioning too many setups.

Are you saying that you have the fuel pump motor completely removed from the sending unit wiring?

Or do you have the fuel pump motor connected to the sending unit wiring?

... If you have the fuel pump motor hooked up to the sending wiring harness are you is it plugged into the connector behind the back seat or it is hooked up to a battery or power supply that is at the end of the sending unit electrical connector?

 

The fuel pump is hooked up to the Beige (power) wire and black (ground) wire. The sending unit itself is out of the picture, for now. Only working with the fuel pump.

 

It is really critical that I understand exactly what you have on your end because misunderstanding exactly what you have set up there will just make things much harder or maybe impossible.

Are you using the three wire connector hooked up to your fuel pump motor?

Is that connector plugged into the connector behind the back seat for a source of power?

 

Yes. Never even messed with anything behind the back seat yet.

 

If the connector is plugged into the connector at the back of the rear seat how are you taking voltage readings?

 

From the source 3 wires that lead to the fuel pump.

 

So you are saying that the brown wire that normally goes to the gage is not even hooked up at this time?

 

Its is not hooked up at this time. Even with it ALL hooked up the way its supposed to be, I still get a +8v reading right at the pump.

 

Sorry my keyboard locked up and I had to reboot.

It is not a good idea to be working with a live circuit near an open gas tank. Can you move the motor and fuel sending unit to a place away from the open fuel tank?

 

Yes. while testing I have extended wires that are away from the tank opening, plus i cover the opening as well.

 

OK. The variable resistor we mentioned is in parallel with the pump motor so even if you do not have the brown wire hooked up to the connector behind the back seat it IS influencing to circuit at the pump motor.

So here is what you can try:

If you have power going to the pump take these voltage readings and write them down and let me know what they are:

Take a voltage reading between the brown wire of the fuel sending unit and the black wire of the sending unit. Use your ground probe on the black wire.

Take a reading of the voltage between the beige wire of the sending unit and the brown wire of the sending unit. For this reading place your ground probe on the brown wire.

Take a reading from the beige wire to the black wire. This I think you state is normally +8 because of the problem but take the reading again.

Let me know what those voltage are in that order.

 

OK , I will post those readings. Is there another way to get a hold of you in case u r not online ?

 

I will be here quite a while. I am literally 'waiting for paint to dry'. If you have the time to work on this now I will hang in there until we reach some type of conclusion.

 

Cool, in process now.

 

OK, brown to black +0.5v. beige to brown +4.4v. and beige to black +8.3v

 

Now those reading were taken with the float in one position.

Try changing the float position and take new readings between the brown and black with the ground probe on the black wire.

Then take new readings between the beige and brown. Use your ground probe of the brown wire for this reading.

 

Standby...

 

Upon checking voltage I thought I'd test the ground wire for resistance (from where it ends on top of sending unit, to connector at back seat) and had a reading of 1.0 ohms. Is this normal or should it be around 0.2 ohms ?

 

Well that is a relatively short run of wire. I would expect that it should be really close to ZERO ohms. But it is also of interest to make sure that from the negative battery terminal to the end of the ground wire for the sending unit that this be very low. Again I would assume near ZERO ohms. This evidently passes 'through' a ground connection below the driver's seat. This should be a good ground that is not allowed to oxidize.

 

So should I need not be concerned about the ground wire at this point ?

 

Actually, right now I am trying to see what influence the variable resistor (on the float arm) has on the pump voltage. You mentioned that after you repaire d the float the problem started appearing. I am assuming the problem could be from something related to the float. Lets see those readings after you changed the float position and see how they look then you can go on to other things.

 

Actually, when I said I repaired the float arm, I did so by replacing the entire sending unit from that of a 89 Iroc (which has the purple wire ).
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I will get you those readings right now.

 

Now I am getting even more confused. Do you have a PURPLE wire that goes into your CURRENT fuel sending unit?

Do you also have your OLD sending unit laying around somewhere ?

 

Sorry took so long, was getting unstable readings for a while. I have brown to black at 0.2v and beige to brown at 0.3v. This is with the floater in a different position.

 

Yes I have both sending units, I am currently using the original for test purposes .

 

Number one, do you have a purple wire the exits the sending unit and connecting to the brown wire of the car harness?

 

I thought we were trying to diagnose you current system used in your fuel tank.

So currently you are using your ORIGINAL sending unit for this testing. Thus you are have a brown wire coming out of the sending unit and attaching to the brown wire of the car's harness.

Do you happen to have free long distance phone call capability? I think this is getting very confused now.

 

I Private Messeged you.

====== pause =====

Thanks for the phone call !! Hope to hear how it worked out.

 

I did what u told me over the phone and ran a wire from the Negative post on the car battery to the Ground on the Fuel pump sending unit....fuel pump now fires right up , indicating a ground wire problem somewhere. I will trace the ground wire and post my findings for all to see. Thanks for sticking with me on this one CamaroRider.

 

Problem was the absolute obvious... checked entire length of ground wire by means of a resistance with an ohm meter, all checked OK. The negative terminal that connects on my battery was loose, even though I had previously tightened it. Bought new terminal and connected it to my negative cable and on to the battery post and all is well.... the IMPORTANCE of a good ground !!!
Thanks once again CAMARORIDER !!! you the man !!!

 

any updates?