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CJ fuel low lights

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keithmckinley

Joined: 11 Aug 2008
Posts: 434

Posted: Sat Apr 25, 2015 3:43 pm Post subject: CJ fuel low lights

I have a scratchy schematic but can anyone tell me the mechanism by which the low fuel lights trigger on the CJ through the transmitter. I seem to have a bad ground in the circuit but it's strange it would be occurring on both tanks apparently simultaneously. Especially since I see a separate ground for each sending unit. Anyway, with under 10L in each tank I'm not getting any lights. positive power to lights is there and they test when I intentionally ground them.

pfstelwagon(at)earthlink.
Guest

Posted: Sat Apr 25, 2015 4:34 pm Post subject: CJ fuel low lights

Where do you apply the ground when you test them?  These aircraft are 

getting  old and corrosion is sneaking in, you may be seeing a poor ground 

condition between the outer wing where the switch in the tank unit is 

located and the center structure.  Incidentally I got my schematic from Doug 

Sapp, excellent quality.



Frank

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clouddog22(at)gmail.com
Guest

Posted: Sat Apr 25, 2015 6:20 pm Post subject: CJ fuel low lights

Frank, any chance you could send a copy of the schematic to me

 Email is clouddog22(at)gmail.com (clouddog22(at)gmail.com) thanks. Greg, On Apr 25, 2015 7:37 PM, "Frank Stelwagon" <pfstelwagon(at)earthlink.net (pfstelwagon(at)earthlink.net)> wrote:[quote]--> Yak-List message posted by: "Frank Stelwagon" <pfstelwagon(at)earthlink.net (pfstelwagon(at)earthlink.net)>

 

 Where do you apply the ground when you test them?  These aircraft are getting  old and corrosion is sneaking in, you may be seeing a poor ground condition between the outer wing where the switch in the tank unit is located and the center structure.  Incidentally I got my schematic from Doug Sapp, excellent quality.

 

 Frank

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keithmckinley

Joined: 11 Aug 2008
Posts: 434

Posted: Sun Apr 26, 2015 6:08 am Post subject: Re: CJ fuel low lights

when I tested to ground I did it right at the bulb socket and the frame. Anyone know where the ground for the Fuel level transmitter initiates?



Also, is it a pain to pull the transmitter to bench check it?



I'll contact Doug to purchase his...Thx

pfstelwagon(at)earthlink.
Guest

Posted: Sun Apr 26, 2015 8:58 am Post subject: CJ fuel low lights

Per the schematic there is a connector or terminal block in the route to the 

sensor.  Pull the wing straps and look at the wiring that crosses the gap. 

The final ground point is at the sensor per the schematic.



Frank

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keithmckinley

Joined: 11 Aug 2008
Posts: 434

Posted: Sun Apr 26, 2015 9:12 am Post subject: Re: CJ fuel low lights

Thanks Frank. I think I may pull out a transmitter and check it if I can;t find the ground. I seems there is a separate switch that triggers the lights..

wlannon(at)shaw.ca
Guest

Posted: Sun Apr 26, 2015 9:46 am Post subject: CJ fuel low lights

Hi Keith:



The switch in the fuel sender unit enables a ground circuit in each side 

(wire # -14Y3 & - 15Y3 , L & R).    Very surprising that both sides are 

affected.   I can"t recall right now exactly where those wires go to ground 

but possibly at the wing joint?    In any case seems highly unlikely for 

both sides to fail concurrently!    Possible it's not a ground problem but 

that power to wires 14Y4 and 15Y4 has been lost at a common source.



Walt

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keithmckinley

Joined: 11 Aug 2008
Posts: 434

Posted: Sun Apr 26, 2015 1:32 pm Post subject: Re: CJ fuel low lights

Thanks Walt,



The front left light light distributes the power from the bus and it checks out as well as all the lights downstream. I did probably misspeak though because I only check these lights during an annual if I happen to be low enough on fuel to make it worth while to drain the fuel down to get them to work. Otherwise I never get anywhere near the level to trigger them (well 90% of the time). Since both sides are inop I'll likely have to pull at least one transmitter. That won't happen for a bit so if anyone has any ideas in the meantime......



Keith

keithmckinley

Joined: 11 Aug 2008
Posts: 434

Posted: Sun Apr 26, 2015 1:39 pm Post subject: Re: CJ fuel low lights

On second look....even though my schematic looks like it was done in crayon, it looks like I could pull off the cannon plug and ground the  #4 pin and see if I get lights and also see if I get anything on the meter taking the #3 pin to ground...



Cheers

Keith

Ttail

Joined: 24 Jun 2013
Posts: 120

Posted: Sun Apr 26, 2015 6:58 pm Post subject: Re: CJ fuel low lights

Interesting I have the same issue with my CJ both lights are inop.

mark.bitterlich(at)navy.m
Guest

Posted: Mon Apr 27, 2015 5:32 am Post subject: CJ fuel low lights

Betcha a nickel Doug Sapp might have another.



Hey... Just a thought.



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gill.g(at)gpimail.com
Guest

Posted: Mon Apr 27, 2015 10:28 am Post subject: CJ fuel low lights

Low fuel lights are powered directly from the instrument switch.  Front and

rear cockpit lights are paralleled and are ground at low fuel level by a

switch on the tank float level.  So grounding is done independently in each

wing, so it seems unlikely that grounding is an issue.  I would check to see

if you have power to the lights with instruments powered up.



Gill



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keithmckinley

Joined: 11 Aug 2008
Posts: 434

Posted: Mon Apr 27, 2015 12:39 pm Post subject: Re: CJ fuel low lights

This thread has come full circle.



In the previous posts I explained I have power to all 4 lights. They test good to ground. I believe, it will be an easy check pulling the cannon plug to determine whether the issue is in the sender itself or a bad ground through the sender



I'll post what I find.



Again thanks for the comments all



K

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