Low Voltage from 5V supply - JeepForum.com
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post #1 of 17 Old 10-10-2019, 06:19 PM Thread Starter
USMC_XJ
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SOLVED: SEE POST #14.

Still working on a 96 4.0/auto. Friend of mine hit a bump and the jeep died. Tried starting it and nothing. I checked gas, and it was fine, I re-did the battery connections because of some cheap fix garage, and still nothing.

We did get it started after it sat for a while, but its back to being dead. Fuel pump primed for a bit, but now the relays don't click. I jumped the 30/87 and the fuel pump turned on, sitting at 43 psi on the rail. Rules that out. So, I know the fuel pump and the ASD are ground controlled by the PCM, which uses info from the CPS and other sensors. I checked resistance across B and C of the crank position and it read fine, infinite resistance. However, I know these can read fine and still be bad.

So, this leads me to my question: When I was probing power to the sensors, I noticed that the violet/white wire, which is the 5V supply from the PCM, was only at ~2.6V. I read this amount at the cam sensor, crank sensor, and TPS. So, I know this comes directly from the PCM. Is that at fault? I can check to see what power is leaving the PCM and I will triple check all the grounds. Also, I can't check for codes because it keeps saying data link error. I do know this could reference a bad CPS. But the low volts are a red flag.

New battery, new battery terminals, good grounds, cranks fine, and I checked all the fuses and relays and they're good. Guess it's limited to a CPS, cam sensor/distributor sync pick-up, or bad PCM. I did grab a PCM from a junkyard 96 (dang 1-year specialty). I will test it tomorrow.

Any ideas? I am open to suggestions.

Thanks


1994 Cherokee Sport - 4.0 HO - AW4 - 4WD

Quote:
Originally Posted by Rob99
The next time you want to tell a story but not get people's opinions, rather than post it on an internet forum, open up Microsoft Word, type your story there, then click on the little X in the top right corner and then hit yourself in the head with a sledge hammer.
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Originally Posted by bigsquat
If he finds the yj section im putting round headlights on mine.
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post #2 of 17 Old 10-10-2019, 09:07 PM
2oldjeeps
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get loads off 5v line. see if it goes up to 5v. could be overloaded and current limited? guessing...

99wj,143,000 miles
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post #3 of 17 Old 10-10-2019, 10:06 PM Thread Starter
USMC_XJ
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While cranking, it got up to 2.7, but no where close to 5. I am going to test the sensors outputs tomorrow and swap in a different computer.

1994 Cherokee Sport - 4.0 HO - AW4 - 4WD

Quote:
Originally Posted by Rob99
The next time you want to tell a story but not get people's opinions, rather than post it on an internet forum, open up Microsoft Word, type your story there, then click on the little X in the top right corner and then hit yourself in the head with a sledge hammer.
Quote:
Originally Posted by bigsquat
If he finds the yj section im putting round headlights on mine.
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post #4 of 17 Old 10-10-2019, 10:18 PM
StarfishPrime00
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I would need to pull up a diagram and will, but if it's a 5v reference and your getting 2.7 I would check your pcm for a loose connection, possibly high resistance!
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post #5 of 17 Old 10-11-2019, 11:50 AM
2oldjeeps
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get loads off 5v line. see if it goes up to 5v. could be overloaded and current limited? guessing...

99wj,143,000 miles
00xj,177,000 miles
10hummer3,74,000 miles
98xj,130,000 miles
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post #6 of 17 Old 10-11-2019, 12:11 PM
StarfishPrime00
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What how could it be overloaded?
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post #7 of 17 Old 10-11-2019, 01:24 PM
jtec
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I think they are suggesting you remove the sensors on that 5v circuit.
I would remove the TPS, probe voltage on 5v reference wire then unplug the other sensors as you read the voltage.
Do you have a good diagram (OEM) of all the sensors on that circuit?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #8 of 17 Old 10-11-2019, 05:28 PM Thread Starter
USMC_XJ
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I've been trying to find a 96 factory service manual, but no luck other than the $100 ones on eBay. Which I might do. Most manuals are either the 95 or 97. Which doesn't help since 96 is a one off.

So, we got it started today. And now it is back to it's old self. Drove it around the block, and then it started dying. Good pressure to the rail when I jump the fuel pump. Also put a new crank sensor in with no luck.

Something new, it dies mainly when you put it into drive. When we got it running, it ran really strong , but as soon as you put it in drive, dies automatically.

Swapped out the PCM, same problem. We are going to put a new cam sensor in next. Then I am out of ideas.

1994 Cherokee Sport - 4.0 HO - AW4 - 4WD

Quote:
Originally Posted by Rob99
The next time you want to tell a story but not get people's opinions, rather than post it on an internet forum, open up Microsoft Word, type your story there, then click on the little X in the top right corner and then hit yourself in the head with a sledge hammer.
Quote:
Originally Posted by bigsquat
If he finds the yj section im putting round headlights on mine.
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post #9 of 17 Old 10-11-2019, 07:26 PM
StarfishPrime00
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Is the car still dieing automatically when you throw it in drive? just wondering if your neutral safety switch is on its way out or if you have high resistance on those lines
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post #10 of 17 Old 10-11-2019, 07:46 PM
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did you disconnect the sensors and leave them disconnected as you went on to next?

I am thinking one or more is pulling the circuit dowm.

CKP, CMP, TPS, MAP.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #11 of 17 Old 10-11-2019, 08:31 PM Thread Starter
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Left it for the night. New cam sensor did nothing. Leaving it for the night. We did not probe anything because my multimeter decided it didn't want to work anymore. Getting a fresh start tomorrow.

Going to test the relay inputs with a multimeter to make sure they are pushing power from the ignition switch.

After it sits for a while, it will start and idle great. Park reverse and neutral are all fine. As soon as you put it in drive, it dies. And it doesn't matter which forward gear. D, 3, 2-1, they are all killing the Jeep.

After cranking it, it will not want to idle and eventually won't want to start at all, leading to the asd and the fuel pump not getting power. Was thinking a TPS possibly, but a bad tps shouldn't cause a no-start. I took the throttle body apart and cleaned it, evei looked fine. Maybe a map sensor too. Just tired of throwing sensors at it.

1994 Cherokee Sport - 4.0 HO - AW4 - 4WD

Quote:
Originally Posted by Rob99
The next time you want to tell a story but not get people's opinions, rather than post it on an internet forum, open up Microsoft Word, type your story there, then click on the little X in the top right corner and then hit yourself in the head with a sledge hammer.
Quote:
Originally Posted by bigsquat
If he finds the yj section im putting round headlights on mine.
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post #12 of 17 Old 10-11-2019, 10:51 PM
jtec
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what does the DLC look like? OBD1 or OBDII.

Should be OBDII and I would ask did you look for codes.

try this transfer case to N then shift to a foward gear - any change?

be careful shifting back to P, turn off in N.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #13 of 17 Old 10-11-2019, 11:50 PM Thread Starter
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Dlc is fine. It is obd 2. Had my reader hook up a couple different times. Now it is giving me a data link error when it doesn't want to start. When I had it running, everything connected and looked fine. It is 2wd.

1994 Cherokee Sport - 4.0 HO - AW4 - 4WD

Quote:
Originally Posted by Rob99
The next time you want to tell a story but not get people's opinions, rather than post it on an internet forum, open up Microsoft Word, type your story there, then click on the little X in the top right corner and then hit yourself in the head with a sledge hammer.
Quote:
Originally Posted by bigsquat
If he finds the yj section im putting round headlights on mine.
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post #14 of 17 Old 10-12-2019, 02:21 PM Thread Starter
USMC_XJ
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Found the problem. We cleaned and tested all the grounds, and started testing the harness. Came across a short in the harness by the tranny dipstick tube. Then I found the attached pic at the VSS sensor. Someone tied the wires together with bailing wire and it was shorting everything out. Getting a new harness all together from the junkyard now. Hope this helps someone else if they have this problem.
Attached Thumbnails
IMG_20191012_141019_1570908102663.jpg  

1994 Cherokee Sport - 4.0 HO - AW4 - 4WD

Quote:
Originally Posted by Rob99
The next time you want to tell a story but not get people's opinions, rather than post it on an internet forum, open up Microsoft Word, type your story there, then click on the little X in the top right corner and then hit yourself in the head with a sledge hammer.
Quote:
Originally Posted by bigsquat
If he finds the yj section im putting round headlights on mine.
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post #15 of 17 Old 10-12-2019, 04:02 PM
2oldjeeps
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you can spread the wires and tape them,good to go...

99wj,143,000 miles
00xj,177,000 miles
10hummer3,74,000 miles
98xj,130,000 miles
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