Puzzler- intermittently won't start, till you slam back hatch?

jeep
grand-cherokee

#1

2010 grand Cherokee with intermittent starting problem. Put key in, turn it- nothing. Maybe hear some clicking noises, but not always. Have regular lights on the dash, etc. Replaced the starter, as per jeep, but still have the problem. Battery is good.
So I started trying different things when this happens- locking/unlocking doors, slamming the back hatch door- narrowed it down to back glass door- opened/closed it- put key in, vehicle will start. Crazy. So I unplugged back glass latch- I haven’t had a starting problem since (3 days), but this must be a fluke…? Starting problem happens more when I open/use back hatch…trying to not use it too much!
It still happens that when I put my key in to start, I may have to hold it over for up to 10 sec before it fires up…or sometimes it starts instantly.
I am pretty sure it’s a grounding/shorting problem, perhaps somewhere in and around my back hatch, but any tips would be appreciated. Not sure how to go about tracking this one down.


#2

I see quite a few have wiewed this post, but no replies…so I’ll give it a shot.

I wonder if you would find anything in the owners manual about the ignition being disabled if the hatch is not shut.
This may be a safety feature and the mechanism that senses that the hatch is open is not working like it should.

The next item I would look at is that there may be corosion at the battrery posts and when you slam the rear hatch the connection gets a jostled enough to make a better connection.

I would check to be sure that the cable clamps on the battery are tight. It wouldn’t hurt to remove both clamps and use a tool to clean the clamps and posts. A little dielectric grease when you reinstall the clamps might help to keep the corosion down.

http://shop.advanceautoparts.com/p/kd-tools-terminal-battery-brush-kdt201/25980576-P?searchTerm=terminal+brush.

Make sure they are tight and plug the hatch sensor back in.

Yosemite


#3

I appreciate all of the tips, but unfortunately I have tried them all already. The battery is new, the cables are cleaned spotless with noox, and according to my Haynes manual, there is nothing about the rear hatch that disables the starting circuit…when the vehicle will start- you can have the hatch open/glass open, etc and it will start…


#4

I have not much to add and agree with Yosemite but you might check the ground wire from the engine to the body just to make sure that is intact. The other thing is that it might be time to take a look at a factory service manual instead of Haynes. They would have all the trouble shooting charts and wiring diagrams to try and see what the relationship is. If you hadn’t replaced the starter I would have said just slamming the door might be enough to jar the starter.


#5

I understand that you cleaned the cable clamps with “Nook”…whatever that is, but did you actually take them off the battery to clean the posts and the clamps contact areas.

Sorry to question you, but some people just scrub the corosion off the outside and never actually do any good.

Yosemite


#6

OP can rule this out by trying to start with the hatch open (after slamming shut if necessary).


#7

If he slams the hatch shut it proves that either the hatch has something to do with it, or it was a coincidence.

So we are back at square one.

I like the idea of it being a chassis ground.
The battery cables may be too coroded under the insulation to carry the high laod needed for starting. This would allow for the light loads to be carried for the idiot lights, key buzzer, etcetra…but not the load to the starter.

Yosemite


#8

Maybe ignition switch.


#9

A short would blow a use before killing a starter, would think. To test it you can pull the fuse, then see if it starts, if not try the slam method, if it starts you know it is not the circuit.


#10

One idea: The long crank problem may be another cause, from the fails to crank one. In other words, you got two separate problems going on there.

I’d focus on the no-crank problem first. It might be your replacement starter motor is bad, and slamming the rear door is just jiggling it enough to get it working again. Next time it fails, see if whacking it – the starter motor, not the door – with the end of a broomstick will cause it to resume normal cranking.

fyi, The no-crank problem is quickest resolved usually by starting with a couple of voltage measurements at the starter motor.


#11

Who said ignition switch? Insightful? Might be something to think about although I’m not sure if you would get the “click” yet with a bad switch. At any rate I did have a problem with one of my Rivieras that I’d go to start it and nothing. Then turning the key way over to the start position and it would finally activate the starter motor. Turned out it was just the switch mechanism on the steering column that was out of adjustment so that turning the key to push the rod to slide the switch was just too shallow to activate the switch. Took about 10 minutes and I brought the new switch back.


#12

Not sure why the connection to the rear hatch but most hatches have a harness running to them with a rubber or plastic boot/bellows protecting the wires. You can pull this back to inspect the wiring inside.

Live long enough and you’ll see many strange things. Wouldn’t be the first time I saw a car with a bad ground where the circuit was finding an alternate ground path through some other circuit. Perhaps the normal chassis ground is bad and it was finding a path through the tailgate wiring. The repeated flexing of that harness finally caused the intermittent failure of this alternate ground. Or, excess current helped it to begin failing. Once you rule out the normal and it defies logic, start looking at the strange and unusual… :wink:


#13

My wild guess is that you have an intermittent connection in the gas pump connections. The pump is back there.

Second wild guess would be a faulty “inertia switch”. It’s a safety device designed to protect you in the event of a serious accident or rollover.