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  #1  
Old July 3rd, 2019, 12:24
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90xj06 90xj06 is offline
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Interesting Voltage Issue

88 Cherokee 4.0

Im having this interesting voltage issue. i have a REM device that reads the ECU data from the diagnostic output. and im getting a low voltage reading from that. it reads the voltage when the B+ Latch relay is closed and i would surmise that this should be battery voltage. but im showing it down to 11.5 volts occasionally. but mostly down to 12.5v with the a/c on. across the battery is 13.7v. also the gauge cluster also reads low. i have checked grounds and clipped a jumper to different parts of the body. nothing changed.

what i did notice if i probe the diag connectors for B+ and B+ ground. i get 13.7v on the positive side. and if i check the ground side im showing .8v to the negative side of the battery. and this makes me think i have a bad ground. i checked the ecu ground and o2 relay ground and all show 0v to ground.

im not sure what relay it really is but the second one from the left when removed causes the B+ ground to drop to .3v

i do still have the C101 Connector but im not sure if any of the circuits go through that.
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  #2  
Old July 8th, 2019, 11:50
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Re: Interesting Voltage Issue

A little more info.

with out the ac on as the temperature increases. the voltage gauge does start to dip down.
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  #3  
Old July 8th, 2019, 15:56
chickenbot chickenbot is offline
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Re: Interesting Voltage Issue

http://cruiser54.com/
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Old July 8th, 2019, 16:59
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Re: Interesting Voltage Issue

Not a specific answer but when I went through the harness and connectors on my 88 I found multiple issues. The contacts in the connectors are prone to oxidation, the oxidation causes some resistance. Multiple connectors and resistance can accumulate.
I was also shocked when I unscrewed the relay block and turned it upside down, mine was really nasty.
Meter error can also be a factor, impedance and inductance can cause some small errors in a meter reading.
I've found something as inane as your body oil (fingertips) can cause erroneous small errors. I periodically clean my meter probes and clean off oxidation before probing.
A side note some of the sensor voltages are tiny, the lower the voltage the more oxidation can affect resistance. And the opposite is true, the higher the voltage and the greater the chance of a circuit bleeding to the ground. Oxidation can be a conductor and a resistor.
Dielectric grease can help with bleed, won't help with oxidation. I've found the best results are elbow grease, tiny brushes like the one designed to clean between your teeth and a high-quality contact cleaner, My method is solvent, contact cleaner, scrub, solvent and reapply contact cleaner. I shy away from dielectric grease, it can cause issues if the contacts in a connector lose their springiness/contact pressure. Dielectric grease doesn't enhance contact it displaces moisture and protects against oxidation, A good contact spray leaves a protective coating you can't see and protects against flash carbon and oxidation. Finding a good contact spray and a really clean drying spray solvent/brake cleaner can be a process.
And lastly, before I forget any oil on a connector contact will cause some resistance any coolant coating will cause bleed. Coolant can dry almost transparent, but it attracts moisture, moisture and glycol conduct somewhat. The higher the voltage the better it conducts. The best way to remove glycol is very hot water and light scrubbing.

The Delco alternator regulator has a feedback function, don't count on a constant voltage.

I got anal about the health of my connectors, grounds and harnesses in my Renix. Mine eventually idled like a metronome.
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Old July 9th, 2019, 06:24
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Re: Interesting Voltage Issue

Quote:
Originally Posted by chickenbot View Post
Specifically Tips 1 through 5 before doing anything else........

Please post back your results.
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  #6  
Old July 9th, 2019, 10:51
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Re: Interesting Voltage Issue

ill have to go through the connectors again. i was thinking a corrosion issue on the relaybox or perhaps a bad ignition switch? i cant remember what jeep i was working on that had a slightly toasty one.

i do have the upgraded battery cable mod.

also i have tried to get c101 apart once. it was really stuck and gave up. but i think it was cold out too. ill try it again after parking it in the hot sun.
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Old July 9th, 2019, 12:11
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Re: Interesting Voltage Issue

I can't remember if the C 101 has the same tiny screw in the middle holding it together that the bulkhead connector has or not. A question for someone with a better memory than mine, I'm old as dirt.

I didn't even bother taking mine apart, cut the wires one at a time, crimped the wires together, soldered the crimp just in case, then covered with shrink tubing. Or to put it all in the right order, cut, shrink tubing over one wire, strip, crimp, then solder, then shrink the tubing. I always put a drop of super glue at the end of my shrink tubing after heating and shrinking, makes it 100% watertight.
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Old July 9th, 2019, 12:34
chickenbot chickenbot is offline
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Re: Interesting Voltage Issue

cruiser54's video about the c101 and how to eliminate it

https://www.youtube.com/watch?v=3sWyFoSEpzk
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  #9  
Old July 10th, 2019, 15:57
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Re: Interesting Voltage Issue

So I haven't had time to go through everything. But I did check my battery charging again. And I'm at ~13.8 checked voltage at the fuse box. And with the AC on I'm at 12.9 at the gauges fuse in the fuse box. And another fuse that I checked. I'm going to check the ignition switch next. And see what the feed voltage is.
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