electrical overcharging with delco alt, oil pressure, fuel, temp gages inop on 81 cj7 - JeepForum.com
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Unread 05-28-2012, 08:11 PM   #1
terre
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electrical overcharging with delco alt, oil pressure, fuel, temp gages inop on 81 cj7

The Symptoms: Last week all systems appeared to work normal on the final stages of a rebuild. But brake light switch was out of it's little clamp. After I worked that into the correct position, pushing my hands in over the top of the steering column and snapping on the plug. Ran engine to tune carb, remove extra vacuum lines and plug unused vac ports (environmental packaged removed) and afterwards the oil pressure gauge was in-op. It was determined the gauge is bad. Continued to run the engine the next day to continue to tune and check timing. Then the fuel gauge never moved from empty. Then the temp gauge also stayed on the cold position. During running I noticed the amp meter was sticking and tapping on it brought it up to 15 volts (it was 13.8 earlier) A digital volt meter confirmed 14.8 volts. Alternator was putting out max voltage of 15.2 The Ign Lps fuse was blown. Replaced fuse, checked others and ran engine. Fuel and temp gauge steadily worked their way to full hot and full tank. Then blew fuse. replace fuse again. removed power wire from fuel gauge to keep fuse from blowing.

Did I just loose my fuel and temp gauges?

The Checks: The Alternator at the napa store checks out "good". I pulled the brown wire from alternator plug (delco w/ internal reg) when ign on it has system volts. I made additional grounds from various places incuding direct from alt and wired to battery, check grounds, down to shinny metal and with screw and nuts to make good connections. Ohms checks throughout veh at .000 Checked as many connections as i can find. Battery terms very clean, and newer cables.

It still puts out max volts if I connect the clip to alt. It was working correctly last week. I disconnected brake lights switch w/ no difference. Also ran wire direct from ign coil to the brn wire position in the plug with identical results.

Oil pressure is in-op . Fuel and temp gauge will climb to full indication if I connect the red pwr wire to the fuel gage. But then will blow fuse if I leave it there. Volts are at max output of alt.

Any help greatly appreciated! this is eating my lunch. Will replace gauges after alt problem solved. Battery is new in very good condition.

instruments

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Unread 05-28-2012, 08:31 PM   #2
BagusJeep
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When you say Amp meter, I take it you mean Volt meter. T

Acceptable voltage output of the alternator at current air temperatures would be 13.9 to 14.9V. It COULD give that much voltage at lower temperatures so by itself I do not think 15.2v is the source of your problems.
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Unread 05-28-2012, 08:36 PM   #3
draperjojo
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My CJ is down for at least 2 more days or I'd fire it up and put a meter on it. The test sheet that came with my Delco alternator shows that my voltage setpoint was 14.7 volts at the factory.
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Unread 05-28-2012, 08:40 PM   #4
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Here is the test on the charging voltages.

Put the carb linkage on the fast idle cam (for this test you want it at fast idle to get the alternator moving). Start engine without touching accelerator, ensure all accessories are turned off. Place voltmeter across battery +ve and -ve terminals.

Once the engine is warm the needle will stop moving (electric choke etc will have turned off)

Now measure the voltage, specs are 12.5 to 15.5V. You should pass this and the charging system is delivering the right voltage.
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Unread 05-28-2012, 08:42 PM   #5
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The voltage will drift with temperature. It will not consistently give only 14.7 Volts.
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Unread 05-28-2012, 08:44 PM   #6
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Sounds like you have an issue with the wiring or equipment connected to the LPS fuse. This is generally what is connected to the fuse:

You don't have electronic engine control on a 1981 so the red wire goes to the oil pressure gauge and the instrument cluster (to feed the fuel and temp gauge).

It sounds like you have disturbed the red wire, probbaly at the oil pressure gauge, and it is shorting.
84-86fuseboxsch.jpg  
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Unread 05-29-2012, 02:21 PM   #7
terre
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First of all thanks for your help w/ this!
1. I kind of thought 13.8 +-, maybe 14.2 at highest volts would be about right for the voltage reg to put out w/ full charged battery. 15 ish volts will eventually fry the battery. ? (Yes it is the volt meter I meant, not amp.) It did indiacte about 13.8 last week.
2. Thanks for the diagram! on the fuse block the IGN LPS is 15 amps and goes to the inst cluster: Fuel gauge, linked to the Eng temp, AND the oil gauge? (EEC not installed) I've disconnected the "volt" meter and still have the same issue w/ the fuel and temp gauge. Both steadily rise to their max and peg. With the pwr wire removed from the fuel gauge, there is no movement.
3. There are two electronic boxes, help me identify which one is for what. On the RH fender behind the headlight area there is one smaller box with one flat sytle plug. Another is on the LH fender across from the canister, and under and next to the windshield wash fluid and says Motorcraft w/ 2 large round plugs. Which one is for what? Not an EEC?
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Unread 05-29-2012, 05:12 PM   #8
terre
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It's getting so that the space under the dash is bigger than it use to be.
I checked the red pwr wire from the IGN LPS for a short to gnd. Ckd OK. The alt is putting out 14.9 volts so according to the earlier post this should be OK. I think I will string a dedicated wire fro the back of the fuse block to the inst cluster: temp, fuel, oil gauges. I found on this forum the Oms for the senders and will check that later tonight. Am I right to think that it's either the sender(s) shorting out or the gauge(s) shorting ?

Ever heard of a bad sender could draw too much current to burn the 15amp fuse? Two bad senders (temp,oil) ?
How about a bad gauge, will it draw too much to burn the fuse?
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Unread 05-30-2012, 08:48 PM   #9
terre
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Found this info for who ever gets into this situation again. Very helpful: What I did for the blown or inop gauges and the high volts from Alt.

The fuel gauge should have the following resistances ...See pic below

  • S to Ground 68-72 ohms S is on Pax side
  • S to I 19-21 ohms I is on drivers side
  • S to A 19-21 ohms
  • I to A Zero
  • I to Ground 49-51 ohms
  • A to Ground 49-51 ohms
The fuel sending unit wires are located on top of the gas tank where they are hard to get to without dropping the tank. The fuel sending unit should have a pink wire with voltage on the isolated center post. The other black wire on the sending unit with a tab style connector is a ground to the frame. Make sure it has good contact.
To be sure the problem is not the gauge, you can momentarily short the pink wire on the output of the sender to ground, and this should show up as FULL on your gauge. DO NOT hold it for very long in this position. If the gauge does not move from EMPTY either the wiring has an open circuit (no voltage, or no connection to ground) or he gauge is bad. If it does move, the sending unit is bad.
The sending unit can be checked with an ohmmeter to measure the resistance between the round sender post (pink wire) and ground. It should be:
Resistance
Reading
73 ohms
Empty
23 ohms
1/2 tank
10 ohms
Full
If the resistance falls in this ballpark (depending on how much gas you have in the tank), then the sending unit is fine. If it shows infinitely HIGH resistance, then the sending unit could be bad OR the wire from the tank to the gauge could be open.
The gauge can be tested with the resistances listed above. Run an appropriate resistor to the S terminal of the fuel gauge and to ground and check the readings.


The temp gauge has the following resistance ...
  • S to A 19-21 ohms S is on the drivers side
A volt meter can be used to measure the voltage between the A terminal of the Temp gauge and ground. It should be pulsing and averaging about 5 volts. If it reads 12 volts the Jumper Strip/Regulator is bad. If it reads 0 volts, it has been burnt out.
The sending unit can be checked with the following resistances between the post and ground...

Totally Cold
high resistance 300- 400

Slightly Warm
73 ohms
Beginning of Band
36 ohms
End of Band
13 ohms
Hot
9 ohms
If an appropriate resistor is connected to the S terminal of the temperature gauge and to ground, the above restances can be used to check the gauge. Use a resistor close to the specifications above to simulate the sending unit
Back Side of Speedometer with Fuel and Temp Gauge
The jumper/regulator strap runs from a voltage regulator inside the fuel gauge (terminal A) to the temperature gauge (terminal A). A voltage reading at terminal A of the temperature gauge should be approximately 5 volts. A 12V reading here means you have a bad regulator.

[IMG]file:///C:%5CDOCUME%7E1%5CREDDOV%7E1%5CLOCALS%7E1%5CTemp%5 Cmsohtml1%5C01%5Cclip_image002.jpg[/IMG]
The meter movement in all the gauges have a built-in dampening mechanism which keeps the needle from bouncing around. The dampening mechanism is basically some thick grease on the movement's pivot points.
The reason all the meters are dampened is because the senders do not have a very constant resistance. If you put a good testing meter on the sender while the motor is running you will see the resistance bounce all over the place. The dampening averages out the reading. This also is why it takes a few seconds for the needles to come up to position instead of snapping to a reading.
To be sure the problem is not the gauge, you can momentarily short the wire from the output of the Sender to ground. If there is no resistance, your gauge should read 80 psi. DO NOT hold it for long in this position. If the needle does not move from zero psi then, either the wiring (open circuit) or the gauge is bad. If it does move, the sender unit is bad.

It is very common for the sending units used with the 258 and 232 engines to be inaccurate. Make sure you have a good connection to the sending unit
t is easiest to test the sending unit by temporarily plumbing in a good mechanical gauge.
Pressure (PSI)
Resistance (ohms)
0
234-246
20
149-157
40
100.5-105.5
60
65-69
80
32.5-34.5

Volt meter:


From the passenger side, left to right in the picture ...

  • Volt Meter gauge GND terminal (Center) - Black wire (Ground)
  • Volt Meter gauge terminal (right) - Red wire (Ignition-on hot 12v)
  • The other wire goes on the LH side or passenger side.

Testing the voltmeter is easy, you just need a good 12 volt connection to the (+) post and have a good ground to the (-) post.

All in all somehow every one of the sender units is bad. The gauges check out OK.

HIgh Volts: I polished every ground I could find, removed the alt bracket and polished the contact areas, poliched the pwr cable conections from alt to battery as well, and the volts are down to 14.5 still slightly high but within limits. Interesting that I found some resistance in the wires at the firewall connection. Some wires were also pushing out and not making good contact. I put a small bolt in the firewall and connecting the under dash ground wires to that, then direct to the battery. Will test that later.

Thanks

T.
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Unread 06-04-2012, 03:26 PM   #10
terre
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For the fuse blowing: Found a pinched power wire going to the lamp of the oil pressure gauge. The wire bundle above the speedometer had the lamp pwr line pinched in the front panel and front panel top, only seen when the speedmtr is removed, had to of happen in Toledo, and after 30 years started to occasionally make contact. Fixed wire and fuse does not blow. Volts still high at about 14.6 but I guess that's the best I can make it after running some additional grounds. Possibly due to a strong or high battery. (new) With all electrical on, volts comes down to 13.8 when running on high idle.

Thanks again for the help.
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