Does anyone know the depth of the '84-'86 fuel tank and the depth of the larger '87-'88 fuel tank? I am investigating installing a capacitive fuel level sender (NO moving parts!) and need to know the depth from the mounting flange to the bottom of the tank.
Our club's spare tank is in storage, and is not convenient for me to access. Perhaps someone else has easy access to one. How exact of a measurement do you need? (Best guess is "about 11 inches.")
[This message has been edited by Raydar (edited 07-03-2016).]
What you need is float travel of each tank setup to match Full and Empty. Big difference to total tank height.
From the plane the mount flange at top of FP assembly you want distance to float full and empty. Some here have sender/fp Assembly for spare parts. Draw a line. Lay down the sender on side w/ flange at the line. measure distance line to float full and empty.
Why? If new sender is set too "empty" then the Fuel Pump can go dry and wreck the pump. Running any pump dry is a quick death to them. (Some pump don't care but most can tell so rule is never run any pump dry.) If new sender is set too "full" then might you never see Full on gauge. Fuel Nozzle at stations should shut off close to real full level of the tank.
Warning: Never Trust a Fuel Nozzle at a filling station to say tank is full because often does not shut off properly. You may think is a tank etc having problems but is just nozzle issues. (Some nozzle designs just don't work well with some to a lot of cars.) Worse if you overfill for any reason, including iffy nozzle, you run the risk to push liquid fuel out of the vent line and poison the EVAP can. Fuel expanse quite a bit when you full up from underground tank an station vs. tank in car in summer heat then add Fuel System heats the fuel too. Very possible w/ 84-86 tanks w/o extra expansion tank.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
No, What I need is what I asked for. And am still asking for.
imacflier, I found this post here where mcaanda says the tank height on his 88 is 10 inches. Haven't seen anything anywhere about the 86 and earlier tanks yet, but I have an 86GT and my fuel sender is definitely bad, so I'll let you know what my tank measures when I get around to it. No idea when that will be exactly though.
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Originally posted by theogre:
What you need is float travel of each tank setup to match Full and Empty. Big difference to total tank height.
Ogre, you need to know the tank height to know how long you need a capacitive sender to be. There is no float or anything, most of them have a way to set the full and empty points separately and are (sometimes) trim-able to the exact length needed, but you have to get in in the ballpark first as you usually can't cut more than a few inches off. Even if he isn't planing on using a trim-able one, you can get them close to the exact length needed normally. Like this VDO sender from summit that is 90-0 ohms and 9.1 inches long so would work with the Fiero gauge and probably be correct for an 87-88 tank.
:edit: Upon further inspection that sender would probably make the gauge read in reverse since I believe it is at 90 ohms when empty and 0 when full instead of the other way around like the Fiero gauge needs. Either way, a sender like that would need the tank height, not the sweep height of the current float style system.
:edit2: I guess you could always get a FuelLink SN34 and then use whatever sender you want since it can take any sender input and convert it to any gauge output. Looks like it would be easy to set up with that VDO sender as it already has a setting for taking a 90-0 ohm sender and convert it to 0-90 ohm built in.
[This message has been edited by difluoroethane (edited 07-04-2016).]
Actually, here you go. Classic Instruments actually makes a tube type sender that is 0-90 ohms in various lengths. Could probably get the 8 or 9 inch sender for the 87-88 tank and I would guess a 7 or 8 inch for a 86 or earlier depending on the tank depth. That should put the gauge reading empty when you aren't quite sucking air yet. I'd much rather have the gauge tell me I'm empty when I actually have a bit left then be out before it hits the E!
[This message has been edited by difluoroethane (edited 07-04-2016).]
Thank you very much indeed. I had not seen those capacitive tubes at Summit. I must find the manufacturer and determine is they are trimmable or not. Not badly priced either. I have sourced some which are trimmable and have original lengths of from 4" to about 12" with zero and full adjust.....but also .5 to 5 vdc and would require an interface board to drive a gm fuel level guage.....means the cost would probably be about the same either way.
Hmmm...some tubes are not only trimmable buy bendable....mebbe I will get lucky!
1. You Q gives you new sender fits the tank. 2. My info gives you some data on fuel level in the tank. Regardless Cap sender doesn't have a float.
Without 2. you are guessing to setup any new sender.
Say Tank is 11" and Float measures above are 1" Full and 9" Empty. Flip number as if measure from bottom... Now fuel level is 10" Full and 2" Empty as read at the gauge.
You want New sender to read very close to same.
If you can't adjust full and empty properly then no better than OE setup w/ accuracy problems. Worse if you set gauge empty to very low gas lever could let pump to run dry often. GM and others made Empty on gauge to be sooner then Real Empty for the tank to protect the pump going dry.
Why? If you allow FP to running dry then you will fry the pump because fuel Flowing thru the pump is coolant and lube to most units. Every second the pump sucks air can/will do permanent damage. You might get away running out of gas a few times but damage is this there waiting to fail.
Note: Tank Spec's is Completely Dry to Full. In the Real World, Most Tanks has 1 to 2 gal (more/less depending on tank shape etc.) because pump pickup can't suck the tank dry. Most vehicle systems can't, not just Fiero, and that's on level ground.
Example: I ran out of gas 1 time, 87 Fiero, Spec is 11.9 gal Per Owner Manual... Took ~10.5gal to fill. When I see Gauge = Empty takes ~9.5gal before most nozzles shut off. If I "top off" might get ~10. (Ran out at time means pump sucked air when you hit a bump or change road grade a little. Just made it to a gas station ~3/4 mile away when engine first started to cough.)
Thank you very much indeed. I had not seen those capacitive tubes at Summit. I must find the manufacturer and determine is they are trimmable or not. Not badly priced either. I have sourced some which are trimmable and have original lengths of from 4" to about 12" with zero and full adjust.....but also .5 to 5 vdc and would require an interface board to drive a gm fuel level guage.....means the cost would probably be about the same either way.
Hmmm...some tubes are not only trimmable buy bendable....mebbe I will get lucky!
Thanks again,
Larry
No problem, I've been looking into doing the same thing with mine as the fuel gauge is pretty much useless on my 86 with how inaccurate it is. Those senders I linked at Summit are actually not capacitive but resistive and would work with the stock gauge without having to make any sort of interface board. They are also not trim-able or bend-able, but would be very easy to use if you could find the correct length to use. All the capacitive senders I've seen run on a volt range (usually .5 - 4.5 volts or so) and would not work with the Fiero gauge without making something to change the voltage output to resistance. They would work fine with an aftermarket gauge made to read a voltage range though.
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Originally posted by theogre:
Actually, You need both.
1. You Q gives you new sender fits the tank. 2. My info gives you some data on fuel level in the tank. Regardless Cap sender doesn't have a float.
Without 2. you are guessing to setup any new sender.
Say Tank is 11" and Float measures above are 1" Full and 9" Empty. Flip number as if measure from bottom... Now fuel level is 10" Full and 2" Empty as read at the gauge.
You want New sender to read very close to same.
If you can't adjust full and empty properly then no better than OE setup w/ accuracy problems. Worse if you set gauge empty to very low gas lever could let pump to run dry often. GM and others made Empty on gauge to be sooner then Real Empty for the tank to protect the pump going dry.
Ogre, for what it's worth, I'm not arguing or trying to say that you are wrong, and for a gauge to read perfectly you are absolutely correct. But with that said, and the inaccuracy of the default setup it should be very easy to ballpark a tube type sender and have your gauge read much more accurately than it did before while still giving you cushion at the low end of the tank being full, where you want to have it be slightly inaccurate to the safe side. As you said, you don't want the tank to be completely empty as you will burn up your pump. One of the reasons that most cars built now will go about 1/4 of a tank below the E before you actually run out of fuel.
If, for instance, the 87-88 Fiero tank is 10" from the top to the bottom of the tank, and the fuel pump pickup is at 9.5 inches from the top of the tank, putting the 8" sender in the tank that I listed before should be pretty perfect. They are built to where the float in the tube can't travel outside of the 0-90 ohm range. When the fuel gauge reads E you would still have 1.5" of fuel over the top of the pickup. Probably should have more cushion than that so you could go with the 7" sender instead for 2.5". The sender doesn't read 90 ohms when the float is all the way at the top of the sender but about 1 - 2" from the top (not sure on that specific sender as I haven't used one from Classic Instruments before, just similar units). That gives you the required space necessary for temperature expansion of the fuel. It would also mean that your gauge should read at full when the tank is actually full. IT may be slightly inaccurate in that the car may read as full for longer than the tank is actually full before the fuel level drops to where the float can drop, but I see nothing wrong with the gauge being slightly inaccurate at full so long as it shows E well before you would be in danger of sucking air or actually being out of fuel.
All the numbers are theoretical at this point as I have not been inside a Fiero tank to see where the fuel pump sits or how deep the tank actually is, but it should be very easy to find the proper length sender to work with our tanks if you don't want to deal with the stock style sender unit. I've built multiple trailer mounted diesel engine powered units for a company I worked at previously and used capacitive senders plenty of times in the fuel tanks on those units. Normally with a VDO or similar style gauge made to read voltage instead of resistance, but I see not reason ballparking things to the safe side with a resistance based unit would have any issues whatsoever for a Fiero. It doesn't hurt anything for the gauge to read Full for the first 50 miles or so before it starts to drop so long as it reads Empty before I need to start walking but not so soon that I'm filling up every 100 miles. Making sure the bottom of the sender is located higher than the pickup on the pump ensures that you won't run out of fuel anymore and a tube type sender will make sure the gauge stays accurate to the actual level in the tank much better than a standard float style.
What I need it the depth of the tank. Once I acquire the tube, I will put gas in the tank and run the fuel pump until it cannot draw any more. This sets true empty....given the inherent accuracy of this type of sender that would probably be sufficient....but for peace of mind add additional gallon. Adjust the fuel tube for empty (a simple screw adjust), then fill the tank and set full. At this point it is set accurately for the specific installation without having ANY information as to the float position or swing. AND a known reserve is set when the sender indicates empty.
The Float and arm are not the source of most the accuracy problems. The resistor in the tank, Iffy gauge, and/or wiring anywhere in the car are. Is why we tell people you can't trust a dash gauge.
If your new sender is using 0-90Ω to ground then still have most of the parts that screws up Accuracy. Sadly often including the New Sender... Many NEW "solid state" senders aren't more accurate vs old mechanical ones. Can be worse.
Example: 88 OP sender are electronic too. http://www.airtexve.com/sft...it_sens_bulletin.pdf Spec from Wells/Airtex... (Both Brands made by NGK SPARK PLUG CO., LTD.) PN 1S6635 Switch opens 2-7 PSI (Fuel Pump Switch) 80 PSI - 60-96 Ohms (Full scale should be ~90Ω) 40 PSI - 48-70 Ohms (Half scale should be ~45Ω) 8 PSI - 20-35 Ohms (Hi end here will read ~30psi) Less than 2 PSI - 5 Ohms max
OP Gauge is 0-90Ω, same as Fuel gauge, and Is why many w/ 88 and upgrades read high pressure w/ ~40psi real pressure. Main reason to use them isn't accuracy but can't dump Quarts of oil when they fail. Old mechanical units love to fail the diaphragm and do just that. If not caught fast, will dump entire oil load fast, meaning every drop the Oil Pump can pump in <100 miles. If really bad <20 miles.
[This message has been edited by theogre (edited 07-05-2016).]
