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Unread 04-24-2010, 07:13 PM   #1
adman02
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1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 294
Temp/Fuel Gauges

I've been trying to figure out why my gauges aren't working. I've worked through John Strenk's gauges write-up, but I'm not sure what the results tell me. Here are my numbers:

Fuel
S to Grnd - 36.4 ohms
S to I - 21.6 ohms
S to A - 21.4 ohms
I to A - .6 ohms
I to Grnd - 15.6 ohms
A to Grnd - 15.2 ohms

Temp
S to A - 6 ohms

Fuel sender
64 ohms (tank is pretty low right now)

Am I right in concluding that my fuel sender is fine, but my fuel and temp gauges are toast?

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Unread 04-25-2010, 01:13 AM   #2
samini
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1984 CJ7 
 
Join Date: Sep 2008
Location: utah
Posts: 35
I got readings close to the same when going through my brand new gauges, went through all the trouble shooting as described be strenk and finally found out that the little dimples (grounds for the gauges) on the speedometer housing were not quite grounding. I discovered this because I scrapped them with a screwdriver and cleaned them up with a wire brush and viola! it all worked. Try that! and hopefully it works.
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Unread 04-25-2010, 06:50 AM   #3
adman02
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1979 CJ7 
 
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Location: Durham, NC
Posts: 294
Are the dimples you're talking about located inside the speedo cluster? I haven't taken mine apart, but did pull the unit out and clean up the outside with a brass brush. Then I ran a dedicated ground to the cluster. No change. Gauges still unresponsive.
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Unread 04-25-2010, 09:45 AM   #4
brian613
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1977 CJ5 
 
Join Date: Apr 2009
Location: doolittle, missouri
Posts: 475
the fuel gauge grounds through the speedo cluster by touching the speedo case. if the back of the fuel gauge is gunked up it wont ground. id put more fuel in the tank then take the speedo cluster apart remove the fuel gauge and clean the back of the gauge (in between the bolts) and then clean the inside of the speedo cluster where the fuel gauge touches
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Unread 04-25-2010, 07:24 PM   #5
adman02
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1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 294
Tore everything down, cleaned it (again) and put it back together again. Found a short in the system and diagnosed a bad temp sender. Rechecked my numbers and they now read:

Fuel
S to Grnd - 72.4 ohms
S to I - 21.5 ohms
S to A - 21.2 ohms
I to A - .4 ohms
I to Grnd - 51.1 ohms
A to Grnd - 51.1 ohms

Temp
S to A - 21.2 ohms

Put five gallons of gas in my 15 gallon tank, but the fuel gauge barely climbs to E. Now I'm thinking my fuel sender is bad. Any thoughts?
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Unread 04-26-2010, 09:13 PM   #6
samini
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1984 CJ7 
 
Join Date: Sep 2008
Location: utah
Posts: 35
Where was your short in the system? Did you do the Stenk diagnostics on the sender?
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Unread 04-27-2010, 04:33 AM   #7
adman02
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1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 294
Short was in one of two places
  1. Wire strands in the fuse box left over from a PO's "repair" job
  2. Missing bulb in the speedo cluster (wire that goes to the base of the bulb I think may have been shorting the circuit)

Haven't done the Strenk sender diagnostics because I can't reach the top of the fuel tank (no body lift on my jeep).

I have run dedicated grounds, so I'm pretty certain the system is grounded well. The sender is the only thing I haven't checked.
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Unread 04-27-2010, 06:21 AM   #8
ctm
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1990 YJ Wrangler 
 
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Location: Boston MA
Posts: 1,429
If your gauge "barely climbs to E" then it is functioning but not accurate. I had my gauges out a while back and I remember there are mechanical adjustments you can make. One or both of the gauges has a slot for a small screwdriver so you can move the needle to where you think it should be. If you don't see an adjustment you can always pull the needle off and move it a bit to be accurate. It may take several tries to get it right. I would start with 1/2 tank or a full tank of gas and go from there.
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Unread 05-02-2010, 07:29 PM   #9
adman02
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1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 294
Dropped the tank today to replace the sender and found out why the old one wasn't working...the float was half full of fuel. Sort of surprised as the float was brass and I couldn't really see any holes in it.

The new sender has a spongey foam float, so little risk of it filling with gas.
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Unread 05-03-2010, 02:11 AM   #10
pazur
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1981 CJ7 
 
Join Date: Jul 2007
Location: eastern Europe
Posts: 206
I don't like I to A .6 ohms. There should be no resistance when there is no current supplied to I. You may have sticked or nearly sticked contacts in the "voltage" regulator. correct me if I am wrong.
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