Not starting - Starter or flexplate? Something else?

Hey guys, 96 XJ 4.0 auto 242 with about 400K on the clock.

It sounds like the starter is not meshing with the ring gear. Turn key and just get whir of motor, no cranking - except occasionally will catch if
I keep cycling the key repeatedly. Barely starts to inch around, and sometimes then starts turning the engine and starting up.


This started happening a couple of weeks ago and got worse fairly quickly to the point of not engaging the ring gear at all.

Had the starter completely rebuilt last week. (also, someone broke the magnets trying to give it a few taps from the bottom - don't know how they got my hammer.)

New (rebuilt) starter is in - same thing. Started with difficulty for a few days now just spins without engaging the ring gear. pulled it out and jumped it with the battery and the bendix seems to pop out normally. Looked at the ring gear teeth and the do not really look worn.

Turning the engine 45 or 90 degrees by hand and trying again made no difference to whether the gear engaged, gear on the starter does not look too bad either.

Not sure where to look from here - any ideas on how to figure out what is at fault?

Pull the starter and look at the teeth on the flywheel were the starter should be engaging it. If they look fine then the issue is with the starter and the gear on it is not extending out to engage the flywheel when you try and start it like it is supposed to.

Or maybe the issue is with the battery, or cable feeding power between the starter and the battery. Loose/faulty/dirty connection causing less juice flowing to it then what it needs to get that starter gear spinning fast enough so that the gear extends out as far as it needs to.

Flywheel teeth look ok behind inspection cover I think

tried running a line direct from the battery to the starter - no change so I don't think it's wiring.

when starter is out on the bench, the bendix gear snaps out nice and hard every time

It's like it is just not reaching when mounted.

Did you notice any shims between the starter and the block? My best guess is the starter is either to close or far away from the flywheel. Also, running the starter on the bench and on the vehicle are completely different animals. There's no load being placed on the bendix or solenoid. Many a starter will work great on the bench but in the vehicle not so much.

Sounds like low voltage/amperage, either from the battery or the cables or maybe even the solenoid wire.

There is an over running clutch in the starter ( a one way clutch), doubtful that is your issue on two different starters.

The solenoid is actually dual purpose. It closes a set of contacts to power up the starter motor, the contacts compress on a spring and the solenoid then closes even farther to completely seat the drive gear. Low voltage/amperage to the solenoid and the piston may not seat all the way. The motor can spin up and the drive gear may not seat all the way into the flex plate teeth.

Batteries can be tricky, one cell goes bad and the other cells may over charge a bit and give you a decent volt reading, but the amps are way down. A quick test is to volt test the battery while cranking, if it dips below around 9 volts you likely have an issue. The only way to know for sure is to have the battery load tested, many of the parts stores have a load tester. With a seriously sick battery sometimes a jump doesn't even help much.

My solenoid wire was rubbing on the block and rubbed all the way through the insulation. And/or the short piece of wire coming out of the PDC to the solenoid wire connector right next to the PDC (91 up models) is really anemic. A likely spot for issues.

The most common cause of what you are describing is dirty battery terminals. I wipe mine down with solvent, the terminals and the inside of the clamp, just to make sure there isn't a film of oil or grease on there. Then I either sand them shiny with 3 M pad or 220 sand paper and then tighten them down. I do it every time I disconnect a clamp from the terminal. To small a thing to ignore, that can cause big issues.

Quality control and reliability has gone way down on most batteries in the last decade. I've had many battery issues, even from top of the line batteries. They are making them worse now on days, not better. Twenty years ago I could get a Sears Die Hard battery that might outlast the truck, not anymore. I've had some really odd battery issues, like a battery totally failing, right down to the last volt, from one start cycle to the next maybe five minutes apart. I'd never seen that before, the battery just developed a *completely* open internal circuit from one minute to the next.


The only other possibility I can think of at the moment is maybe your flex plate bolts have come loose or the flex plate is cracked and/or warped. But this seems kind of unlikely. I'm out of ideas.

I've never had to shim a Jeep 4.0 starter, fairly common in Chevy. You can try loosening the starter bolts a couple of turns, pulling on the inside of the starter to kind of cant it away from the block and see what happens when you try a start. Really unlikely this is your issue, but heck anything is possible.

Never put my final outcome on here and just noticed I left it hanging when looking for something in old posts.

The starter rebuild was not done well, they did not change the drive gears.

Took it back to the starter guys when I discovered I could turn the worm gear in both directions.

New drive unit in starter and everything worked great.