hi..total newb here. but trying to get a new digital fuel guage installed.after tons of reading and searching i found the area in the back seat where i think the wire for the fuel tank are coming out. there are 3..black,pink,and whitish. i followed them and discovered that two of them were cut,,and the black one was grounded to a bolt under the backseat. so i hooked up my guage power,,then i tried to splice the sender wire from the gauge to the pink wire that i found cut..guage reads full..same thing if i try the cut whitish wire.so im stumped. i already tried seeing if it would work if i gronded the black wire better. still same result. how does a sending unit get its power? or could the whole sending unit just be trash? i should add..that all the tune port was removed from the car,,and it operates on carburator now..so im not sure if that makes any difference..please help! im desperate to try and get my fuel gauge to work! any help is greatly appreciated!..ps would i need a special type of sending unit? i have a 1986 iroc....no tune port.

 

also..i should have mentioned.that the even the old fuel gauge never worked since i have owned the car..some people are telling me that there is no way for me to get a fuel gauge to work..is this true?

 

Highly likely you in tank unit is faulty then
( gauge sender doesn't care what engine you have now or had before )

read
http://www.aa1car.com/library/fuel_gauge_diagnosis.htm

 

 

i have been working on this the last couple days..i finally was able to get to the wire coming straight from the fuel tank. it appears the previous owner had cut a hatch out right over the top of the fuel tank and riveted it in place. i opened the hatch and was able to see 3 wires coming directly off of the tank. (sorry,,newb) there was a circle shaped piece there,with some metal gas lines coming from it. the 3 wires were pink,black,and a tanish colored one. the tan colored one was cut off right at the tank!(only about an inch 1/2 long) the pink one ran under the carpet(cut too) and the black was bolted down under the seat at the end.but i didnt see a purple wire anywhere. i just found out,,he installed an external fuel pump that bypasses the one that is on the unit in the tank.I was told that since he took the tune port off,,that the(original) fuel pump in the tank would have flooded out the engine?? so..im just guessing that the tannish wire is for that pump?( was told i cant use it anyway) thats all i know for sure right now...no purple wire though..so im not sure if i can properly test it...any ideas on how to get a fuel gauge to work with this setup?...ps i am in the process of buying a brand new sender unit..just getting some facts first. would i have to buy a sending unit that does NOT have a fuel pump on it?? NO ONE that i asked around where i live can give me a straight answer as to whether i can get a fuel gauge to work or not..lol..ANY help from anyone on here is sooo greatly appreciated. this is frustrating me lol.

 

Follow NINA 's advice and check between the pink and the black then

Pump is usually available separate to the sender ; one would hope the OP has removed the fuel pump altogether ( the reason for the hatch )

Before you buy a new sender , see if you can fix it up

Instructions for a Vette but sender fix the same
http://forums.corvetteforum.com/c4-t...h-article.html

 

The hatch cut out on the rear hump area means the original/previous owner was too lazy to drop the tank to repair a failed fuel pump correctly. My guess is that he also screwed up the sender unit as well. At some point you will come to the realization that to really fix this will entail dropping the fuel tank to either repair what the previous owner hacked up or repalce the sender unit entirely. Don't worry, we have all come to that same point in our lives where the only thing left is to drop the tank.

If I get a chance later I will look through my service manual and see what kind of wiring diags I can find. Hold on.

 

awesome,,thanks alot!

 

Looking at my '86 service manual, the black wire from the fuel sender unit is ground. The pink wire goes to the fuel gauge in the instrument cluster. Zero ohms indicates empty and 90 ohms indicates full. There is no other wire showed in the diagram. So I'm at a loss as to what the tanish wire is for. Wait. Hold it. Tan wire? When I put in my crate motor the mechanical fuel pump was deleted and an in-tank fuel pump was installed. I have a tan wire that comes from my oil pressure cut off switch - located near the dizzy - that cuts off 12 volts to the in-tank fuel pump. That could be what the tan wire was/is for. Check to see under the hood if you have a tan wire attached to a oil pressure switch. I think I have a pic of mine some where. Let me post it in a few.



.

 

Here it is. See that tan wire on the right next to the orange wire? That's the oil pressure switch cut off. It goes to a relay that kills the 12 volts when the ignition is turned off or if the oil pressure goes below threshold.




.


This is a pic of the sender unit connection under the gas tank. I had the tank out a few months replacing the fuel pump and snapped a few pics of the under belly. You can see this is a two wire connection. I don't remember though if this connector is original to the car or if it was replaced when I put the crate motor in. Sorry.

.

 

Thanks alot for the help. looks like this will be my weekend project. So,,the way i understand it,,is,, i only really need to have 2 wires connected correctly to get this sender to work??the pink(gauge) and the black(ground wire)...since im not using an in tank fuel pump currently anyway(using an external fuel pump)..can i just disregard that short tan wire that is 1 1/2 inches short..coming from the tank? ( 99% sure it is for the unused fuel pump in the tank ) i dont see what else it could possibly go to. not sure if the PO removed that original(in tank) fuel pump or not,,till i pull out the sender to see....if so,,,then all i have to do is hook up the sender wire,and ground wire...and if the sender is functional...it should give me a reading?? or ...is it essential to have that in tank fuel pump hooked up for the sender to work?...thats mainly what i dont understand. (sorry,,noob) lol...thanks alot for all the help guys!!i really appreciate it.

 

Some short answers:
- Whoever is telling you that you cannot get the fuel gauge to work is obviously an idiot. Stop talking to those people.
- Nina gave you the best advice: measure the resistance of the purple wire coming out of the tank. If the tank is full, you will see close to 90 ohms. If the tank is near empty, you will see closer to 0 ohms. That will tell you that the sender is in the tank and hopefully working.
If the sensor has been completely removed, it will read infinite resistance.
- With the key on, the disconnected fuel gauge will indicate full tank. If you ground the purple wire under the dash (good luck finding it :-D ), you should see the fuel gauge show empty. Keep grounding the purple wire along its way to the rear and you'll see where it is interrupted (IF it is).

Hope this helps.
Lou

 

okay. thanks for the tips. what im actually trying to do is,,not even bother with the stock fuel gauge.because the tank itself is not in any way even connected to anything under the dash. only the fuel lines are connected.when they removed the tune port,,the wiring harness went with it.so all i have is a fuel tank with 3 wires coming from it.ill attempt to check the pink wire,,because there is no purple wire. i have tried hooking the sender wire from the gauge up to the pink wire on the tank,,and hooking up the ground.. all directly to the tanks wires where they come out..and .even the new gauge is still pegged at full. if the sender was operating correcly..i should get some type of reading ,,right?

 

i think what alot of people around here where i live are telling me about not being able to get a fuel gauge to work,,think that i am trying to hook my gauge up to the old tune port wiring under the dash. i know that that wont work. im just trying to bypass all that stuff and run all new wires from the tank itself to my new gauge.,,im just stuck on that right now..i dont want to spend the cash on a brand new sending unit if it still wont work anyway. i am new to this..but am i just being paranoid about it? it should only really be a couple wires...right? and does anyone know...if im using an external fuel pump...and i get a new sending unit,,without a pump on it...and hooked up an aftermarket gauge correctly...would i be able to tell how much gas i have? this is a big learning experience for me..lol

 

You should get some ohm reading between 90 and 0 - unless you have no gas in the tank or if you're certain that that the tank is full of gas. The sender can't send out any other indication other than between 90 and 0. If you get infinite ohms, 1 meg, 10 meg, or some such crazy number then you can assume as Lou said above that the sender unit is not connected, or not working. If that is the case, either way the sender is going to need replacing.

As for the tan wire, I think that wire was/is for an in-tank fuel pump oil pressure cut off circuit related to the TPI(?) system. What was the car before, TPI? and what is it now, carbed? I'm still not entirely clear on that. In my '86 shop manual page 8A-20-2, the tan wire is for a low oil pressure cut off relay circuit for cars equipped with in-tank fuel pumps. My '86 was an LG4 carbed motor with mechanical pump and not an in-tank fuel pump equipped car. So I am trying to help diagnose this with what I had at one time and what I have now.

You said when you hook a new fuel gauge it reads full? What ohm reading are you getting off that same set up?


.

 

While searching for something completely different I found this schematic...

http://www.austinthirdgen.org/mkport...uges_part1.gif

...here.

http://www.austinthirdgen.org/index.php?pid=19

.

This schematic is the same one out of my '86 shop manual.

http://92b4crs.tripod.com/86wiring/dia-pics/81-1.jpg


.

 

thanks! those daigrams should be a big help!oh,sorry i didnt make it clear...but my camaro is carburated. it used to have tpi..but it was changed over. from what the PO told me...the in tank fuel pump wich was previously used with the tpi system had to be disabled/bypassed because he said that that fuel pump puts out too much pressure...and would constantly flood out my carb...so he had to put a mechanical fuel pump on it. outside the tank. i gotta go out and check that ohm reading probly this weekend. ill let you know what it says. all i remember was the needle was moving around when i had it on the sensor.

 

too bad there isnt a way to use that original in tank pump,,,and just adjust the pressure of it somehow to match up what i would need for a carbed engine. might save me alot of headache..lol

 

Sorry, my bad. Yes, your car has a pink wire. Purple was 91-92. I hate when Chevy pulls stunts like that, it's hard to keep track of wires.

Gauge pegged means that either the tank sensor reports full or there is a break in the line.
Like I suggested, ground the pink wire in the dash and the gauge should read empty. You can continue back to test the wire along its length.

 

It's called a Fuel Pressure Regulator. I am sure you can find one at any car parts supplier. Carb pressure is usually set at 6psi but can vary by as much as 2psi.

So yes, you can use your original fuel pump (if it is still in the tank, though).
The FPR will provide the desired pressure to your engine and divert all excessive fuel back to the tank.

 

Just a heads-up, this is an old myth that I hate seeing spread across the Internet.
The tan wire is the one and only fuel pump feed wire (grey on 1990-92). It provides 12V to the fuel pump from the Fuel Pump relay (controlled by the ECM) or from the backup oil-pressure switch.
The switch is not there to prevent the pump from running during low oil pressure conditions. It is there to provide 12V to the pump when there is oil pressure present, i.e. engine running. It is a backup for the relay to not leave you stranded on the side of the road when the $1 relay fails. It is a great feature on our cars and it saved dozens of us (without us even knowing) but it is often misunderstood. So I just wanted to clear up any confusion.

Since the car has a carb now and no ECM, the tan wire is likely without power anyway. To restore the in-tank fuel setup, the tan wire would need to be powered, probably from the same source that powers the current external fuel pump.

Hope this helps.
Lou

 

Re read your service manual properly
The OP switch has no relationship to the pump relay operation



The OP switch is wired in PARALLEL with the fuel pump relay so it keeps the pump running if the relay fails for some reason;
allows you to START and run your car so long as you have engine oil pressure.

and because the pump relay is operated by the computer, if the OP switch drops out due to low oil pressure ,
the pump ( and engine ) will continue to run because the pump is still getting power from the relay so you do not have low OP protection


Most likely the reason for the access hatch is that PO had to remove the stock pump because it is not recommended to have a external pump pull through a non running in tank pump.
He may have stuffed up the sender unit or wiring in the tank at the same time;
only one way to find out ........
AS BigBadLou stated above; the easy way of doing a carb swap is not to touch anything at the tank end
and just install a bypass reg on the stock fuel line in the engine bay to drop pressure down to carb psi

 

The oil pressure circuit on my '86 is not factory nor does it conform itself to any standard published shop manual. I have an entirely different application due to an engine change that required the mechanical fuel pump removed and an in-tank fuel pump installed along with a low oil pressure switch cut off circuit that engages a relay to shut off the fuel pump if oil pressure goes low. So what I said and how one normally operates may not jive to what is SOP. I appreciate your clarification. Can we now get back to help fix this guys fuel gauge problem?

 

So why confuse the issue by mentioning it if it is totally irrelevant to the problem in hand

We were til you took us off track with pump wiring on a fuel gauge problem

 

okay..i have been dreading having to do this part. but i have never attempted this before. i have to get my old fuel sender out of the tank. i can see 4 gas lines attached to a circular cap on the tank. each of these run a short lenth before bieng connected to a short piece of rubber hose,wich are clamped tight on both ends,to the rest of the gas lines. it looks extremley easy to disconnect these.and reconnect them. but im worried that fuel will spray all over the place..lol. or that something catastrophic is going to happen once i reconnect the lines.(like the car wont run). i have to get this thing out. but i need to consult with people who know what they are doing.this is probably a simple task..but im asking for advice and guidlines for this procedure before attempting this.(then..get back into the electrical part after this)Thanks so much for anyone who would be willing to take the time to help me out with this.best way to learn is by getting in there and doing it i guess. i dont have anyone to help me.

 

okay..i didnt realize that it needs no power.(the sending unit) why is this??? does it just operate on the power that flows through the gauge??? i am trying to just hook up the new fuel gauge straight to the tank...my wires under the dash wont work for this application. im trying to understand how current flows through the sender so that it operates,,and sends a message to the gauge...thanks for any answers!.

 

The sender is a simple variable resistor. The gauge uses power to deflect the needle and the sender resistance (in a bridge configuration with the gauge's deflection coils) makes the needle move left and right (or up and down on Firebirds) based on how much resistance is on the sender.

So yes, the sender has a little bit of current flowing through it from the gauge. Most resistance senders work that way (your coolant temperature, oil pressure etc).

That's why it's easy to test the gauge in the dash by usually disconnecting the sender wire or grounding it: that makes the gauge swing both ways and you can verify that it is still operational and has a connection to the wire you're testing. That's why I suggested before to ground the pink wire to see whether the gauge moves to empty (with key on).

Hope this helps.
Lou

 

Since you already have access to the top of the tank, this is not a hard procedure at all.
Usually you just label the hoses and release the fuel pressure before attempting it.
However, since you are not using your in-tank fuel pump, there is no fuel pressure in your supply line. There is probably no fuel pump in your tank either (otherwise you won't be able to use the external pump because the in-tank pump poses as a flow obstruction).
So it should be safe to disconnect all 4 hoses, there should be no pressure in them at any time.

Hope this helps.
Lou

 

yes..it helps alot! thanks for all the info. i did what you suggested (grounding the pink wire) and nothing happens.the gauge just stays pegged at full.i found a brand new sender for a decent price. so i should be getting this squared away pretty soon.

 

If the grounded pink wire didn't make the gauge go down to empty, you have either a bad gauge or wire. The gauges usually don't go bad so it is more likely that the pink wire simply does not go all the way to the gauge in the dash. Or it has a break in it. As I pointed out earlier, you can keep grounding the wire along its path to find the break.

Glad we could help and good luck with the in-tank assembly removal, it should be a piece of cake.

Lou

 

HOT DAMN! as of today..i now have a fully functional gas gauge in my iroc!! big day for me...lol. All possible because of the responses i got to my questions on this forum...Thank you guys sooooo much! i tackled the job with confidence..and it all went smooth! thanks again guys!