Engine won't turn over, Battery at 100%, won't jump either
 

As the title says, my 2004 Sedan won't start.
With no warning today, the engine turned over a couple times but very sluggishly, then nothing. Like whah, wha-wh.
Battery test at AutoZone says 100% and it won't jump off another car. Just the same very weak turnover.
Starter or solenoid? Anything else I should check first?

Battery terminal connections? You might be having voltage drop along your cables to the starter or back from the start/block to the negative battery terminal. The FSM has a good no-crank debug process. You'll end up measuring voltage drop along your cables while you crank. Just making sure your battery terminals are clean and cables are tight is the easiest and free-est thing to do before you start trying to debug harder things.

Sometimes banging on the solenoid with a hammer or a something can clean up the contacts just enough to get it to crank normally which would point you to needing a new starter.

Good luck and come back and tell us what it was when you find it.

Thanks, what is the FSM? (I searched.)

Factory service manual. You can download one for your model by registering a forum account at https://www.nicoclub.com/infiniti-service-manuals. It's multiple files. Download them into one folder. Start with the .fwd pdf. It is the table of contents and is automagically linked to all the other chapters if you have them in the same folder.

Sorry I assumed because you had a few posts you'd been around long enough to see references to the factory service manual. Anybody with 1 post, I'd have included a link. Thanks to G2B for posting the link.

Here's a little screen grab of the troubleshooting tree from the starting and charging (SC) chapter. I would think it points you to the B terminal check on the starter whether you have normal or low starting voltage because the car doesn't crank normal. Basically you'd measure B terminal on the starter when you crank and if it's normal, you'd go to the next step and check the S terminal voltage (after the solenoid) etc. etc. Just follow the steps and you'll figure it out.
https://cimg8.ibsrv.net/gimg/g35driv...aa5446d4f8.png

Thanks guys!
This car has been so reliable I haven't needed the manual yet. Only has 95k on it.
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S terminal is the actual solenoid drive terminal. M terminal is the main current path after the solenoid. I goofed that up from memory.

I followed the FSM troubleshooting chart, which all checked out okay, so I pulled the starter and hit it with a set of jumper cables. Bingo. It barley turns over.

Now, buy a new starter from one of the parts stores, or get it rebuilt at a local shop, and thus wait a week?

If you can find somebody that rebuilds them maybe. I just put a reman bosch unit in mine rather than try to find rebuild parts myself of look for a place that would rebuild it. Around Boston metro west I don't think there are many places like that any more. Places like Providence you seem to find shops still rebuilding stuff like the old days because there are more people that are more cost conscious. But I don't see anybody doing it around here. Nobody turns rotors etc. etc. I think the labor dollars to do that kind of work just don't make sense any more. Everything is disposable Chinese crap now. There are rebuild parts available for things like alternators (had one of those die recently) so I assume starters too for you to diy it if you were into it. It would just take time to order and ship and then do the actual rebuild. Normally I like that kind of hobby work on my old cars, I guess I've just had a little too much of this hobby just lately (crank sensor left me stranded last week, against better judgement I rolled the dice on a local parts store replacement part and it's working for now so we'll see how it holds up).

There's an excellent auto electronics shop here in Portland OR, where I had an Alfa Romeo starter rebuilt a few years ago. (Auto Battery and Electric on Hawthorne Blvd. ) Very old school place, totally Portland, where diy and makers thrive.

But anyway, I decided to have a go at this one myself. Glad I did.
It was absolutely filthy inside, so much burnt oily gunk between the brushes and commutator that it was obviously shorting out everywhere. It smelled terribly of burnt oil and was packed with sludgey carbon. I took it apart, cleaned it up and after putting it back together, it spun up fine.

Here's a very nice video on rebuilding starters that I watched before I opened it up.

And some shots of my filthy starter:

https://cimg3.ibsrv.net/gimg/g35driv...d69d710231.jpg
https://cimg4.ibsrv.net/gimg/g35driv...b62bac6382.jpg
https://cimg5.ibsrv.net/gimg/g35driv...10cb2254bb.jpg
https://cimg6.ibsrv.net/gimg/g35driv...24652260dc.jpg

Great post. You inspired me to try that if any of my starters go out in the future. I remember my Murano starter failed at the solenoid to starter motor connection where the big braided wire was fused in half. So I'd at least have needed some service parts and not just a cleaning.

Make sure and post back if it goes flakey again in the near future. Not sure how worn the original parts were versus just dirty. If just cleaning the filth gets you a year that's one thing but if it lasts until the gunk builds up in 10-12 years again, that's worth it for sure.

I decided to replace the brushes, because they were pretty worn.
Found these on Amazon for $12. The haven't arrived yet, but the picture appears identical to mine, and they're returnable.
Everything else in my starter appears to be okay, just filthy.
If it works, I'll photo document, and do a rebuild thread for future travelers. Will link it here.

It’s great to see you tackling the starter rebuild yourself, Bockaroogaipan! Cleaning out the gunk and replacing worn brushes can definitely breathe new life into older components, and it’s always satisfying to fix things with your own hands.

Since you're already deep into the DIY approach, I thought I'd share a couple of other maintenance tips that might help keep your engine running smoothly, especially as it ages:

1. Carbon Buildup: Over time, carbon deposits can accumulate in your engine, affecting performance and efficiency. To tackle this, consider using a professional-grade carbon cleaning solution like the Hydrotech Engine Carbon Cleaning Machine available at Autozilla. It’s a highly effective way to remove stubborn carbon deposits and keep your engine in top shape.
   
2. Air Filtration: Ensuring that your engine gets clean air is crucial to its longevity. High-quality air filters, such as those from Bharat Filters, can help reduce the amount of contaminants entering your engine, which is essential for maintaining performance, especially in older vehicles.
   
3. Convenience: For easy access to these products and more, you might want to check out the Autozilla app. It’s a handy resource for finding all the parts and tools you need for maintenance and repairs. You can download it here: Autozilla App on Google Play.
   

Good luck with the rebuild! It’s always inspiring to see fellow enthusiasts keeping their vehicles running smoothly with some DIY know-how. Don’t forget to share your results with the community—looking forward to your rebuild thread!