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Unread 05-03-2010, 01:16 PM   #1
sprowley
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1997 TJ Wrangler 
 
Join Date: May 2008
Location: Madison WI
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WEIRD electrical issue!!!

I am not going to guess what the cause is because I'm totally stumped. Here's all the symptoms I've noticed:

-Battery is testing better than new.

-Won't start occasionally. Today, not at all. Bump-started 3 times.

-Voltmeter reads lower than battery tests. I theorized that I had a bad stator or spot on the rotor in the starter motor which would explain the random failures due to position of the rotor. When in the bad spot, it would draw much more current, and only occurred when the motor wouldn't start. Before a successful start, the voltmeter would read correctly.

-Today, with 0% electric start success, volt meter always read low, no matter what position the rotor was in. (I put it in gear and pushed it to turn the starter motor - worked earlier this week).

-Today, bumpstarted 3 times. After being driven and shut off, voltmeter would read correctly when powered back up. This time it wasn't an indication of starting ability, and when power is left on the voltmeter will quickly drop from about 12.5v to 9.5v. Appears to be a heavy draw on the battery somewhere.

-When put in reverse gear, voltmeter drops 2v or so. This occurs anytime - whether the meter reads high or low, whether the engine is running or not. When put back in neutral or any other gear, voltage returns to its previous reading. This part COMPLETELY baffles me.

I think that sums it up. That last point dumbfounds me. Why would that happen, and only in reverse?

I *think* my starter motor is bad and that is the cause of these symptoms. But I am not sure, I don't know if that explains the low voltage readings before a bad start attempt or the rapid decline of voltage I saw today. I also don't know how that could explain the reverse gear voltage issue.

Please help me pinpoint the cause so I can fix this quickly. This is my daily driver and my wife and I rely on it for work.

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Unread 05-03-2010, 01:50 PM   #2
Weavis
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The only point I might help on would be the reverse voltage drop - reverse lights coming on is going to make it drop a bit. As for the other issues...good luck! I'm dealing with all sorts of electrical issues on top of tons of other stuff myself. Hope you figure it out and post up when you do!
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Unread 05-03-2010, 01:53 PM   #3
sprowley
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Quote:
Originally Posted by Weavis View Post
The only point I might help on would be the reverse voltage drop - reverse lights coming on is going to make it drop a bit. As for the other issues...good luck! I'm dealing with all sorts of electrical issues on top of tons of other stuff myself. Hope you figure it out and post up when you do!
I thought about that but all the other accessories don't have that effect - and the radio, blower motor, and headlights draw a lot more than the little reverse bulbs would. Though, I guess anything is possible right now.

I'll definitely post up my solution.
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Unread 05-03-2010, 02:17 PM   #4
idaholtby
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You need to check the voltage with a test meter (DVM) at the battery and at the output of the alternator when your rig is running. If these voltages do not match, then it sounds like you may have blown one or both maxi fuses in the PDC. If these voltages do not match, then check F2 and F6 (both are 50amp maxi-fuses in the pdc[directly located in front of the battery]) These fuses are on the output of the alternator and will prevent the battery from charging if they are blown. In effect, with these fuses blown, you are only drawing upon the battery and the alternator is completely removed from the circuit.
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Unread 05-03-2010, 02:28 PM   #5
sprowley
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Quote:
Originally Posted by idaholtby View Post
You need to check the voltage with a test meter (DVM) at the battery and at the output of the alternator when your rig is running. If these voltages do not match, then it sounds like you may have blown one or both maxi fuses in the PDC. If these voltages do not match, then check F2 and F6 (both are 50amp maxi-fuses in the pdc[directly located in front of the battery]) These fuses are on the output of the alternator and will prevent the battery from charging if they are blown. In effect, with these fuses blown, you are only drawing upon the battery and the alternator is completely removed from the circuit.
I've tested the battery after trying and failing to start, and it reads 12.5v 560 cca. I also know the alternator is working because the voltmeter will read higher after the vehicle is started.

I just started it 5 times as if nothing was wrong, after I made the initial post. WTF? Why would it not turn over at all sometimes, then start like it's brand new others? The battery is fully charged and when it does start, provides lots of power and engine starts in about 2 seconds.
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Unread 05-03-2010, 02:35 PM   #6
idaholtby
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Quote:
Originally Posted by sprowley View Post
I've tested the battery after trying and failing to start, and it reads 12.5v 560 cca. I also know the alternator is working because the voltmeter will read higher after the vehicle is started.

I just started it 5 times as if nothing was wrong, after I made the initial post. WTF? Why would it not turn over at all sometimes, then start like it's brand new others? The battery is fully charged and when it does start, provides lots of power and engine starts in about 2 seconds.
O.K. then, what are the symptoms when it does not start? Does it make a clicking noise, or nothing at all? Does the engine turn over and not start or do you not even get that far?
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Unread 05-03-2010, 02:39 PM   #7
sprowley
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Quote:
Originally Posted by idaholtby View Post
O.K. then, what are the symptoms when it does not start? Does it make a clicking noise, or nothing at all? Does the engine turn over and not start or do you not even get that far?
When it doesn't start, I get nothing. No clicking, no slow cranking, nothing. I do have power to all accessories though, which behave as though nothing is wrong.

When it does start, it fires right up. Good spark, fuel, starter only turns about 3 times before it fires up.

I put it in gear and gave it a push once, which seemed to move the starter enough and it fired right up after that. That trick didn't work today though.
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Unread 05-03-2010, 02:46 PM   #8
idaholtby
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Quote:
Originally Posted by sprowley View Post
When it doesn't start, I get nothing. No clicking, no slow cranking, nothing. I do have power to all accessories though, which behave as though nothing is wrong.

When it does start, it fires right up. Good spark, fuel, starter only turns about 3 times before it fires up.

I put it in gear and gave it a push once, which seemed to move the starter enough and it fired right up after that. That trick didn't work today though.
Given your last description, I strongly suspect that your starter is at fault. Next time this happens, try smacking the side of the starter with a dead blow hammer and see if she starts. I have experienced this several times in the past. What happens is that the brushes in the starter become wore to the point that they no longer make sufficient contact to rotate the starter motor. The "jostle" from a dead blow hammer allows for sufficient temporary contact in order to start. If this is the case, then replace the starter. You can have it tested, but it would likely work on the bench because it was jostled in the process.
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Unread 05-03-2010, 02:54 PM   #9
mudbug89
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it sounds like starter to me also check the cables are not loose going to starter and make shure your ground cable from battery to block is tight,but all roads are leading to starter good luck
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Unread 05-03-2010, 02:54 PM   #10
sprowley
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Quote:
Originally Posted by idaholtby View Post
Given your last description, I strongly suspect that your starter is at fault. Next time this happens, try smacking the side of the starter with a dead blow hammer and see if she starts. I have experienced this several times in the past. What happens is that the brushes in the starter become wore to the point that they no longer make sufficient contact to rotate the starter motor. The "jostle" from a dead blow hammer allows for sufficient temporary contact in order to start. If this is the case, then replace the starter. You can have it tested, but it would likely work on the bench because it was jostled in the process.
That was my thought too. I have 175,000mi on the odometer and my title says its odometer reading exempt.... and it's the original starter motor. Sounds like I'll just go replace it then, no harm in having a good new part!

I'm still concerned about the reverse gear voltage drop... could this be a bad ground that only matters when those lights are turned on? I'm really baffled by it.
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Unread 05-03-2010, 03:08 PM   #11
idaholtby
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Quote:
Originally Posted by sprowley View Post
That was my thought too. I have 175,000mi on the odometer and my title says its odometer reading exempt.... and it's the original starter motor. Sounds like I'll just go replace it then, no harm in having a good new part!

I'm still concerned about the reverse gear voltage drop... could this be a bad ground that only matters when those lights are turned on? I'm really baffled by it.
As far as the reverse issue, I suspect it is seperate and unrelated. This may be due to a short in the wiring or the lamp(s) it'self. One thing at a time. Fix the starter, then address the remaining issues.
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Unread 05-03-2010, 03:12 PM   #12
sprowley
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Quote:
Originally Posted by idaholtby View Post
As far as the reverse issue, I suspect it is seperate and unrelated. This may be due to a short in the wiring or the lamp(s) it'self. One thing at a time. Fix the starter, then address the NEXT issues.
There, fixed it for ya!

I guess I assumed the reverse issue was related because I hadn't noticed it before and did while working on the starter issue. BUT you are correct - correlation is not causation!
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Unread 05-03-2010, 03:19 PM   #13
idaholtby
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Originally Posted by sprowley View Post
There, fixed it for ya!

I guess I assumed the reverse issue was related because I hadn't noticed it before and did while working on the starter issue. BUT you are correct - correlation is not causation!
Agreed my friend
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Unread 05-03-2010, 05:04 PM   #14
WebWheeler327
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Try a neutral safety switch. I had similar problems and thats what it was. It might be stuck in a certain position. If it is stuck or sticking it will not let the vehicle start but everything eles will work. It is also connected to the reverse lights which might explain that voltage drop. The switch is cheap and only takes a few minutes to change.

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Unread 05-03-2010, 05:58 PM   #15
idaholtby
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Quote:
Originally Posted by Red88YJ View Post
Try a neutral safety switch. I had similar problems and thats what it was. It might be stuck in a certain position. If it is stuck or sticking it will not let the vehicle start but everything Else will work. It is also connected to the reverse lights which might explain that voltage drop. The switch is cheap and only takes a few minutes to change.

The O.P.'s profile shows that the rig has an AX-15, in which case, this is not a possibility. If it was an auto, then this could be an issue. The manual equipped YJ's will allow starter engagement whether the clutch is engaged or not, no matter what gear the manual tranny is in at the time it is tried. The possibility of an auto transmission ecm being installed on a manual equipped rig is a possibility, but the O.P. has not indicated this.
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