Bad Starter?

53flattie

Well-Known Member
Joined
Jan 6, 2006
Location
Easley, SC
I posted this over at JeepForum, but it’s not getting any responses (which is surprising)... Thought I’d get opinions here, before throwing parts at the problem.

I have a 2004 TJ Rubicon. The battery, terminals, and leads are all new, as of January. I’ve had no issues at all with the cranking or charging system until now. (And just to be clear, there was no problem with it before January - I simply replaced the battery because the old one crapped out. And I replaced the terminals and cleaning up the wiring because I’m a little OCD).

On Sunday of this week, I noticed it cranking a little slower than normal. It progressively got slower and slower until yesterday evening when it wouldn’t crank over at all. I put a volt meter on the battery (without the engine running) and it’s showing 12.95 volts. With the engine running, I tested the output of the alternator and it was producing 13.88 volts, and the battery was showing 13.86 volts.

In my opinion, this tells me the battery and alternator are fine. So why did it begin turning over slower and slower until it won’t turn over at all? Could the starter be bad? Deteriorated to the point that it’s drawing more current than the battery can produce?

Thanks!

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Measure the voltage drop while cranking.
 
Someone with more electrical knowledge than me will chime in, but on a few occasions I have had a starter give up the ghost shortly after a battery does, I suspect low voltage at the battery leads to higher amp draw and premature failure.

That being said, my YJ just decided one day it was done starting (no slow turning, no delayed start, just DOA) I checked the charging system everything looked good, pulled the starter and it was full of mud, new starter fixed it.

Recently my Ram needed all the connections at the starter cleaned to make it a reliable starting vehicle.
 
X2 measure voltage drop while cranking. That'll tell if you have a bad connection. Also turn high beams on for a minute or so then recheck the battery voltage without cranking the Jeep first. A fully charged battery should read 12.6 or so, your 12.9 shows a residual charge or surface charge still on the battery from where it was just running and charging recently. The lights on will drain the surface charge. Less than 12.6 is a weak battery. There's a chart you can Google that will show voltage to battery charge level, basically 11.7 or so is fully discharged.

You can turn on blower fan and high beams for 5 minutes or so as a poor man's load test on the battery too. If it drops much below 12.4 after cutting everything off the battery is weak.
 
When you measure voltage drop while cranking, measure with respect to battery ground, and then measure with respect to the chassis. That can isolate whether you have a major problem with a grounding point, which would affect current flow from the battery. I suspect you have a starter solenoid or starter motor going bad though.

But first as a quick/easy sanity check, it's never a bad idea to remove and clean the high-current starter connections and the high current chassis grounds. One of my Subarus had the same issue you're talking about, and it was a corroded ground connection to the engine block.
 
+1 on check voltage while cranking.
Its possible to have a failing membrane inside the battery and it produces voltage fine, but when load is applied the current allows the internal short which would present as low voltage.
Also make sure and check all your grounds. A weak ground can show same symptoms as well.
Specifically battery to frame and strap from engine to frame. Starter is grounded through engine block.You can have a great battery to frame contact but if the engine ground strap is corroded (or missing) it can cause issues
 
Check at the battery post not at the terminal . Had the same problem I ask grumpy after checking terminals had 13.8, he said check the post it was 10 volts.
 
lol fabrik8 posted while I was typing
 
Tim C said:
X2 measure voltage drop while cranking. That'll tell if you have a bad connection. Also turn high beams on for a minute or so then recheck the battery voltage without cranking the Jeep first. A fully charged battery should read 12.6 or so, your 12.9 shows a residual charge or surface charge still on the battery from where it was just running and charging recently. The lights on will drain the surface charge. Less than 12.6 is a weak battery. There's a chart you can Google that will show voltage to battery charge level, basically 11.7 or so is fully discharged.

You can turn on blower fan and high beams for 5 minutes or so as a poor man's load test on the battery too. If it drops much below 12.4 after cutting everything off the battery is weak.
Click to expand...

The only problem with measuring the voltage drop while cranking is that it won’t crank over right now.

I just checked the voltage again. After sitting all night and morning, the battery was showing 12.9 volts.

Turned on the high beams and fog lights. After being on for 5 minutes, the battery voltage was 12.38. After 10 minutes, it was 12.36.

Once I turned the lights off, the voltage on the battery went back up to 12.67 (without starting the engine).

That seems to indicate that the battery isn’t the problem. I’ll check the grounds. If I don’t find any problems there, the only other thing I know to do is replace the starter...?


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Halftrac said:
Check at the battery post not at the terminal . Had the same problem I ask grumpy after checking terminals had 13.8, he said check the post it was 10 volts.
Click to expand...

I have been checking voltage at the battery post, rather than terminals.


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I just tested the continuity to ground at all the grounding points (body, engine, starter body). They all show 0.3 ohms.


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I would go ahead and replace the starter
 
53flattie said:
The only problem with measuring the voltage drop while cranking is that it won’t crank over right now.



Once I turned the lights off, the voltage on the battery went back up to 12.67 (without starting the engine).

That seems to indicate that the battery isn’t the problem. I’ll check the grounds. If I don’t find any problems there, the only other thing I know to do is replace the starter...?


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Click to expand...

12.67 does indicate a fully charged battery, and since it recovered back from 12.38 and didn't drop more that's a good sign too. A voltage drop test will determine if you have a poor connection somewhere. And it can be done whether it cranks over or not.

Put the positive probe directly on the actual lead post, not the lead cable end unless you don't have enough helpers. Put the negative probe on the actual starter post. Set the meter on volts and try to crank. You may need 3 people to do this test. If you read more than 0.5v (actually I think it's 0.2 or 0.3 per connection, but this is close enough) there's resistance somewhere between the probes. If you get 12v or more it's a full on disconnect (take the positive cable off the post and try once you get it running again you'll see what I mean)

Repeat the process on the negative side. Positive probe on case of starter, negative probe on negative battery post. Any reading higher than 0.5v is a bad ground somewhere.

Best results is to test from actual post on battery because then you're also checking the cable to post connection. I've seen corrosion there not visible from the outside cause no starts before.

Check batt voltage while cranking or trying to crank. If it drops below 9 it's a dead battery, no drop at all most likely a starter solenoid not kicking out.

Make sure there's battery voltage on the big starter post and the small trigger wire while holding the key down. If the big wire goes dead it's a connection, small wire it's a switch connection, or safety switch (clutch, neutral, etc).
 
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