How to get the fuel sender level to be seen by the obdII (Page 1/3)
Tweeder MAY 27, 06:51 PM
I have the ultra guage and in it for calculating the dte it would normally use the fuel sensor level but my vehicle doesn't support that in the obdII it says. So how do I get it to recognize it or do I have to wire it to certain pins in. The PCM? I see in the wiring swap diagram, it shows blue pin 3 is "fuel level output control circuit", connector clear pin 69 says " fuel level sensor input" and those get deleted.

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86 SE Convertible 3800sc 4t65e HD.

[This message has been edited by Tweeder (edited 05-27-2014).]

hookdonspeed MAY 27, 08:41 PM

quote
Originally posted by Tweeder:

I have the ultra guage and in it for calculating the dte it would normally use the fuel sensor level but my vehicle doesn't support that in the obdII it says. So how do I get it to recognize it or do I have to wire it to certain pins in. The PCM? I see in the wiring swap diagram, it shows blue pin 3 is "fuel level output control circuit", connector clear pin 69 says " fuel level sensor input" and those get deleted.



clear pin 69 would need to be wired into the sensor line from the 3pin fuel pump connector on the firewall. not sure if the signal is compatible tho, should be, but the values are obviously going to be different as the tank size is not the same.
Tweeder MAY 27, 08:53 PM

quote
Originally posted by hookdonspeed:


clear pin 69 would need to be wired into the sensor line from the 3pin fuel pump connector on the firewall. not sure if the signal is compatible tho, should be, but the values are obviously going to be different as the tank size is not the same.



Can someone confirm what wire that I will need to splice and bring to clear pin 69? I'll ave to look but I think I can play with the tank size with hptuners

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86 SE Convertible 3800sc 4t65e HD.

phonedawgz MAY 27, 09:16 PM
The fuel level input needs to be from a 0 - 5v sender, not the stock Fiero one.

The fuel gauge output will then run to your dash. I am not sure if it will work with the Fiero dash gauge however.
Tweeder MAY 27, 09:45 PM

quote
Originally posted by phonedawgz:

The fuel level input needs to be from a 0 - 5v sender, not the stock Fiero one.

The fuel gauge output will then run to your dash. I am not sure if it will work with the Fiero dash gauge however.



So I would need a fuel setup from a Grand Prix then? Or just the sending unit. Why would I need to run it to the dash if there's one already there, wouldn't I run it to the pin 69 that way the PCM will see the level and pass the info through the obdII and into my guage.

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86 SE Convertible 3800sc 4t65e HD.

[This message has been edited by Tweeder (edited 05-27-2014).]

phonedawgz MAY 27, 11:10 PM
With more complex evaporation control systems, the PCM needs to know the fuel level to run the tests correctly. To do this, rather than have two senders in the tank, one for the PCM and one for the gauge, GM designed the dash gauge to run off of the PCM output. GM couldn't run the PCM by tapping onto the existing gauge sender since the the voltage received would vary depending on the internal resistance of the dash gas gauge itself, and because the wiring of the gas gauge will allow the voltage on the gas gauge wire to go up to vehicle voltage. PCM inputs need to be between 0 and 5v. Thus GM designed a potentiometer type sender for the fuel level. Then to keep the dash gauge going there the PCM had to have a gauge output signal.
Tweeder MAY 27, 11:36 PM

quote
Originally posted by phonedawgz:

With more complex evaporation control systems, the PCM needs to know the fuel level to run the tests correctly. To do this, rather than have two senders in the tank, one for the PCM and one for the gauge, GM designed the dash gauge to run off of the PCM output. GM couldn't run the PCM by tapping onto the existing gauge sender since the the voltage received would vary depending on the internal resistance of the dash gas gauge itself, and because the wiring of the gas gauge will allow the voltage on the gas gauge wire to go up to vehicle voltage. PCM inputs need to be between 0 and 5v. Thus GM designed a potentiometer type sender for the fuel level. Then to keep the dash gauge going there the PCM had to have a gauge output signal.



It looks in hptuners, i can play with the tank size. http://www.ls1gto.com/forum...wthread.php?t=399573
So with that, could I run a wire from the fiero sender (not sure which wire)or guage cluster to pin 69 and that will tell the PCM what the level is at and then calibrate the tank size through that? Or is the voltage thingy going to be my problem?
Also my guage is not correct right now it looks like it's about 1/8-1/4 tank off as I recently ran out of fuel while in my garage tuning.
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86 SE Convertible 3800sc 4t65e HD.

[This message has been edited by Tweeder (edited 05-27-2014).]

phonedawgz MAY 27, 11:52 PM
No you can't use the Fiero sender.

FYI also - while it looks like the other senders will just drop into the hole on the Fiero tank, the newer senders have a bigger hole in the tank.

[This message has been edited by phonedawgz (edited 05-27-2014).]

Tweeder MAY 27, 11:55 PM

quote
Originally posted by phonedawgz:

No you can't use the Fiero sender.



So what's the easy way around this? I do have a spare potentiometer from the tach swap if that helps.

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86 SE Convertible 3800sc 4t65e HD.

phonedawgz MAY 27, 11:59 PM
You will have to figure out how to get a potentiometer type sending unit into the tank.