electrical guru's please read

[jackal264]

ok so i'm in the process of building a custom gauge cluster. every thing is done except for one gauge. the fuel. for fuel i'm running an autometer digital gauge with a range of 0 - 270 ohms. an s14 sender unit (float) sends a signal between 5 and 84 ohms.

my situation is this:

when the car is off or the key is set to acc the sender is reading perfect. (i pulled the float to test this already) when it's in the tank i'm getting a reading of 20 ohms which represents a 3/4 tank of fuel. (5 ohms is full 84 is empty fyi)

the problem comes when i tur the car on. as soo as i do this the signal is lost and the resistance goes through the roof and the gauge will read 100. what i'm trying to figure out is why the signal is doing this.

what i have tried:

so far i've tested the float by taking it out of the tank and checking to make sure it within spec

i've also ran direct grounds from the float to the battery and have run signal direct from the float to the gauge.

i've tested the autometer gauge on a circuit that is constant and the gauge works.

i've plugged in my stock cluster and that appears to work.

so this is where i'm at.

there are only two options left. either the float it somehow screwing up the signal when power is applied or the stock gauge has some sort of resistor on the board to deal with this change in signal when power is applied. however what i don't understand is that when the car is off the stock cluster continues to receive a signal and continues to read that signal (the signal that is within spec) and if there were a resistor i would assume the gauge would not read accuratly when the car was off, but it does.

i'm now trying to get access to another float so i can completly eliminate that as a problem. when i opened up my tank the float was not on it's bracket which means it was flopping around. so there is a slight chance it is causing the problems but it still reads within spec so i think it's fine.

what i'm thinking is that it might need some kind of resistor to be put in parallel with the signal wire?

hopefully someone has some knowledge to share with me.

[Om1kron]

you know a lot of people seem to have an issue with this when trying to get some aftermarket fuel gauge sender thing to work. Personally I would contact BROADFIELD in regards to the matter, him and one other guy on the boards are the only two people I know that have posted working gas gauge conversions to digital from analog.

The other guy's work can be found in the "post your gauge clusters" thread...

You'll know it when you see it.

But yeah Dousan has a stack cluster in his car and never bothered wiring up the fuel sender signal but since it's a track car he just add's gas, and if the car dies, add more gas.

lol.

[GSXRJJordan]

ok so i'm in the process of building a custom gauge cluster. every thing is done except for one gauge. the fuel. for fuel i'm running an autometer digital gauge with a range of 0 - 270 ohms. an s14 sender unit (float) sends a signal between 5 and 84 ohms.

... shit that doesn't matter ...

Which Autometer gauge do you have? The 0-280ohm has 5 presets, one of which is 0-90ohm.

... or you could just run one that's 0-90ohm.
http://www.autometer.com/img/products/4314_d.jpg
link: Auto Meter (http://www.autometer.com/cat_gaugedetail.aspx?ref=search&gid=3090)

Short-sweep electric is cheap, full-sweep electric is not.

Just because I'll know you'll ask - there is no resistor that you could put in there to "magically" give you the right resistance readings, because you'd have to compensate the top end (drop 90ohms to 280ohms) by adding a ~200ohm (+- 5%) resistor... then all your readings would be off, and the lowest you'd read would be 5+200 = 205ohms.

Get the right gauge, it's not like it's hard to get.

[jackal264]

yeah i contacted geno750 he did something similar but said he used the stock fuel gauge board. i'll try broadfield and see if he has any ideas.

[jackal264]

Which Autometer gauge do you have? The 0-280ohm has 5 presets, one of which is 0-90ohm.

... or you could just run one that's 0-90ohm.
http://www.autometer.com/img/products/4314_d.jpg
link: Auto Meter (http://www.autometer.com/cat_gaugedetail.aspx?ref=search&gid=3090)

Short-sweep electric is cheap, full-sweep electric is not.


we did a custom program. when the float was out you just flip it over set that as empty then flip it back set as full and then your done. plus i've tried all the others just to see if we did something wrong. so i doubt its that but thx for the input.

oh and i'm running a digital gauge. the cobalt digital fuel
http://autometer.com/cat_gaugedetail.aspx?gid=3805&sid=69

[GSXRJJordan]

... so i doubt its that but thx for the input...

OOhhhhhh, if I had $1 for every time someone told the electrical engineer that he was wrong, I wouldn't have a S-chassis anymore.

Alas, that's a nice gauge, so I looked up the manual and gave it a read. Make sure you disconnected the stock fuel gauge (running a new wire back to the *GREEN* float signal wire would be the best idea). The black wire for the gauge can be run to the *BLACK* wire coming straight off the top of the fuel pump too, just to be sure you're reading the same ground - at this point, I'm guessing that you're not getting a good ground somewhere (at the gauge or at the pump sender).

Apparently, if you just leave the other black and brown wire alone, it'll be set for 0-90ohm, which would be fine, but I'm guessing you did the whole "custom calibration" thing... just to make sure you've got it, after you calibrate it and put it back in "operate" mode, with the float out of the tank, run it from one end to the other (car off, then again with car off but ignition on). If you've grounded the gauge to the ground on the float, and it's the ignition on that throws the reading all over the place, double-check pump wiring (could be wired wrong, pulling 12V through the ground which the sensor shares).

I'm curious now, keep me posted lol.

[Om1kron]

OOhhhhhh, if I had $1 for every time someone told the electrical engineer that he was wrong, I wouldn't have a S-chassis anymore.


I would also like to throw in...

and a degree, and your dream job, and you would be paying cash for an m3 as well like that one guy you envy and is stupider.

Than you, respectfully.

heh

Jeff is the man, listen to him.

[jackal264]

OOhhhhhh, if I had $1 for every time someone told the electrical engineer that he was wrong, I wouldn't have a S-chassis anymore.

Alas, that's a nice gauge, so I looked up the manual and gave it a read. Make sure you disconnected the stock fuel gauge (running a new wire back to the *GREEN* float signal wire would be the best idea). The black wire for the gauge can be run to the *BLACK* wire coming straight off the top of the fuel pump too, just to be sure you're reading the same ground - at this point, I'm guessing that you're not getting a good ground somewhere (at the gauge or at the pump sender).

Apparently, if you just leave the other black and brown wire alone, it'll be set for 0-90ohm, which would be fine, but I'm guessing you did the whole "custom calibration" thing... just to make sure you've got it, after you calibrate it and put it back in "operate" mode, with the float out of the tank, run it from one end to the other (car off, then again with car off but ignition on). If you've grounded the gauge to the ground on the float, and it's the ignition on that throws the reading all over the place, double-check pump wiring (could be wired wrong, pulling 12V through the ground which the sensor shares).

I'm curious now, keep me posted lol.


i also called autometer and every one i've talked to says a ground issue but i'ts also what i thought at first to but i can't see how it is because atm i'm running a ground wire from the float to the battery (my battery is in the trunk) and a signal wire right to the gauge from the float. i'm also running a ground from the gauge to the battery. i'm starting to think more and more that there is a possibility the float is creating some type of fault but only when power is applied.

spent almost 5 hours on this the other day. gonna go spend tonight

autometer told me to run a ~40ohm resistor on the signal wire and run the other end to ground. it that reas on the gauge then i will have an issue with the float and maybe the float it just pooched even though it is within spec according to nissan.

[GSXRJJordan]

i also called autometer and every one i've talked to says a ground issue but i'ts also what i thought at first to but i can't see how it is because atm i'm running a ground wire from the float to the battery (my battery is in the trunk) and a signal wire right to the gauge from the float. i'm also running a ground from the gauge to the battery. i'm starting to think more and more that there is a possibility the float is creating some type of fault but only when power is applied.

spent almost 5 hours on this the other day. gonna go spend tonight

autometer told me to run a ~40ohm resistor on the signal wire and run the other end to ground. it that reas on the gauge then i will have an issue with the float and maybe the float it just pooched even though it is within spec according to nissan.

There's no reason for the float to need to ground to the battery - both the signal wire and the ground reference from the float can be connected directly to the gauge.

The float does not get +12V, that's why I asked if turning the ignition on (meaning giving the fuel pump +12v) is what causes the foul up, because if the fuel pump is grounding through the gauge, that'll cause all sorts of problems. Give the fuel pump it's own ground, and get the float wired directly to the gauge.

[Om1kron]

why the hell did you ground it to the battery... have you tried grounding it directly to the chassis.

i'm just throwing it out there, i'm no electrical engineer by any means. But would the alternator charging the battery with the car on cause any resistance changes on the negative battery post?

[GSXRJJordan]

why the hell did you ground it to the battery... have you tried grounding it directly to the chassis.

i'm just throwing it out there, i'm no electrical engineer by any means. But would the alternator charging the battery with the car on cause any resistance changes on the negative battery post?

First of all, resistance with relation to what? All resistances are measured in relation to battery/chassis ground, which has nothing to do with the alternator.

But to answer your question, no. lol

[jackal264]

There's no reason for the float to need to ground to the battery - both the signal wire and the ground reference from the float can be connected directly to the gauge.

The float does not get +12V, that's why I asked if turning the ignition on (meaning giving the fuel pump +12v) is what causes the foul up, because if the fuel pump is grounding through the gauge, that'll cause all sorts of problems. Give the fuel pump it's own ground, and get the float wired directly to the gauge.


as it stands right now the float and pump are on separate grounds. one thing to keep in mind is that the gauge itself puts 5 volts through the signal wire. either way i'm off to go try a few more things today i'll let you guys know what happens.

[jackal264]

so after a couple hours tinkering my friend and i finally figured it out. for whatever reason the gauge doesn't like the preset ranges and didn't like the way the manual said to set the gauge. we ended up buying an 8 ohm and a 82 ohm resistor and setting the custom values with a resistor on the signal wire and then strait to ground. after doing that the gauge worked like a charm.

http://i114.photobucket.com/albums/n248/Jackal_364/CIMG1933.jpg

[GSXRJJordan]

^^^ You forgot a boost gauge :down:

Glad you got it working - So you used the "-8-" mode to custom calibrate it to 0ohm-90ohm, then just plugged it in? Lol, it's hilarious that its the only way you could get it to work, but more power to ya :)

[jackal264]

^^^ You forgot a boost gauge :down:

Glad you got it working - So you used the "-8-" mode to custom calibrate it to 0ohm-90ohm, then just plugged it in? Lol, it's hilarious that its the only way you could get it to work, but more power to ya :)


boost is mounted somewhere else.

and yeah i actually called autometer back and their tech didn't even know why it worked when i programed it with resistors and not with the preset ranges.

[GSXRJJordan]

forgiven! :keke:

What was the total cost, using those gauges? I know the cobalts are pricey!

[jackal264]

well i had oil temp/press and water temp and boost before. the fuel was like 130, tach and speedo were like 175 each but that all in cnd dollars. the cf was like 40usd but i have a bunch left and then just misc other stuff. when it's all done and installed i'll post my setup in the gauge setup thread. i did a lot more then just the main cluster.