Where to start with inconsistent starting issue

[absenytx]

2018 JLU 3.6L - started having problems starting over last fall.

- Aux battery was original, realized it was basically dead.
- Until we had time to replace the aux battery, I removed the necessary fuse and disconnected the aux battery.
- This cleared starting issues for awhile but we still had one or two fluke instances where it wouldn't start.

In January, we had both main and aux batteries replaced. Until recently, the vehicle has started fine. Then this week we have had two instance:

- Once in the morning my wife was leaving for work and she came back and said the Jeep wouldn't start. Then I went out, depressed the pedal, and the Jeep started. She had struggled to get it started four or five times before coming to get me.

- Now today, two days later, she starts the vehicle fine in the morning, but at five pm calls from work because she cant get it started. I go down, try all the tricks like pushing break pedal harder etc and I can't get it to start.

- Remote start never seems to work when we run into this problem.

- Jumping the vehicle finally got it started.

I have read through every post on this thread as it seems we have this same problem. Anytime the thing wont start with the push button, the brake is very firm:

https://www.jlwranglerforums.com/fo...r-being-left-overnight-with-push-button.4623/

I dread taking this to the dealership because its the classic case of a problem they can't reproduce and of course it happens inconsistently for us at the most inopportune times.

Would the fact that a jump helped in starting it today suggest we have yet another battery problem? The fact that it wouldn't start two days ago, but then would start when I tried suggests some type of other failure (or in the process of failing) part in the starting system.

Alternator tested good back in January.

Can anyone point in the direction of some diagnostics I can run/try over the weekend to try and solve this before resorting to dealership?

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[jludave]

Would the fact that a jump helped in starting it today suggest we have yet another battery problem?

Most likely.

1st. Change the batteries in your keyfobs.

2nd. Have both the main and aux batteries load tested. Yes, I know you had them replaced in January, but you never know.

3rd. Just for sanity, have the starter tested.

 

[absenytx]

Most likely.

1st. Change the batteries in your keyfobs.

2nd. Have both the main and aux batteries load tested. Yes, I know you had them replaced in January, but you never know.

3rd. Just for sanity, have the starter tested.

Thanks, will get started on these this weekend. I think I will just manually remove the aux battery and main battery and take them in for load testing. I didn't change the aux battery myself because we were living in the tundra with no garage and it was zero out. Now I have my attached garage so I'm going to dig in and get my self versed on removal of that battery anyways.

 

[absenytx]

Nice to finally have my tools and a garage to work on this thing.

Removing fuse box to get to Aux battery is indeed not that bad. Like all things, just need the right tools and the time to do it.

Felt really good ripping that damn thing out.

Voltage on both batts removed from vehicle read 12.38.

Will load test them tomorrow.

I also have the high amp fuse bar out and did a continuity check of two through seven and they all beep.

I find it funny that the dealership that replaced the aux battery (which on the invoice said it was a Mopar Xyz something something don't recall, but clearly it's not) just had an Oreilly's super start brought over from the store in town

The main battery was an Oreilly's I warrantied earlier in the summer. I don't have a problem with Oreilly's batteries because they have been great about the warranty, but maybe I should have a problem and they aren't good for this vehicle?

I'll take all suggestions - glad to be wrenching on this vehicle with the right facilities and a nice weekend to figure it out.

 

[absenytx]

Here is the update:

- Key fob batteries replaced
- Both batteries load tested and passed

Started with a bit of strangeness the first time (shit, already worried, but figured new fob batteries, who knows whats up)

Let it run for twenty minutes. Tried to restart, no go.

Going to start looking into Starter motor removal/testing/replacement and see what tomorrow brings.

 

[absenytx]

Realizing starter is really hard to get to, I tried to troubleshoot further so that I didn't go down the rabbit hole of trying to remove the starter.

Also checked all grounds etc...

Bought my own load tester and a really good battery charger (15 amp for AGM)...Charged both main and aux battery to 100% over five hours...then load tested. Battery was showing in the "weak" (around ten volts) for a 500 CCA and this batt is supposed to do 760 CCA's.

Once again jumped it to start so I could get it back in the garage and sure enough it fired up.

Bottom line I'm going to warranty this Oreilly main battery, bet my money back, and do a Mopar or something better.

 

[absenytx]

Hmmm battery local dealership has is actually only 650 CCA's I feel like this is a step backwards and the thing is well over $300.

Any solid battery recommendations? I have had great luck with Interstate in the past, but kind of hard to get sometimes.

 

[Rhinebeck01]

Hmmm battery local dealership has is actually only 650 CCA's I feel like this is a step backwards and the thing is well over $300.

Any solid battery recommendations? I have had great luck with Interstate in the past, but kind of hard to get sometimes.

I'm only addressing your Main battery ?

DO, buy an H7 AGM Main battery...

Read here:
https://www.jlwranglerforums.com/forum/threads/??-main-battery-replacement-talk-jl-jt-?.100534/

• Interstate MTX-94R/H7 80 Ah AGM 850 CCA
• Odyssey Performance AGM94R H7 L4 850 CCA
• Super Start Platinum H7 SSB94RPLT 800 CCA
• Napa P/N 9894R H7 800 CCA
• Batteries+ X2 Power H7 Group 94R SLI94RAGMDP 840 CCA
• EverStart Platinum AGM Battery, Group Size 94 H7 800 CCA (Walmart 4 yr. warranty)
• Optima YELLOWTOP AGM YEL94R DH7 Group 94 880 CCA
• DieHard Platinum AGM Lead Acid Battery, Group H7 850 CCA
• Motomaster Eliminator AGM Group Size 94R (H7/L4) 800 CCA
• Duracell AGM 94R H7 800 CCA (Sam's Club)
• Weize Platinum AGM Battery BCI Group 94R - H7 850 CCA
• 94RAGM ACDelco AGM Group Size 94R H7 850 CCA
• FullRiver FT850-94R 850CCA

 

[garyji]

This!!


G.

 

[AcesandEights]

I like to start at the beginning, and work my way backwards.

 

[absenytx]

Amazing thanks for the great replies and recommendations! I've had good luck with Interstate and a local shop has the Interstate MTX-94R/H7 in stock.

 

[OrneryBear]

Why on earth did you go in through the top by removing the fuse box? You're troubleshooting a non start issue, why use the method that introduces the risk of introducing yet another electrical issue. Should have gone in through the fender/liner which is zero risk to vehicle function.

 

[absenytx]

Yeah I just don't like messing with rivets/clips and that sort of thing, plus I Just wanted to learn how get to it from the top and I wanted to test the high amp fuses anyways which I had been concerned about for awhile.

When I had this issue six months ago it was zero degrees out and I didn't have a garage so there was a lot of impatient and potentially not correct management of battery cables etc so I needed to get back in there and do some checks anyways.

When the small battery goes again I'll probably try the fender method.

The tricky part about this has been failure of two of the same types of batteries over one year, but they both always passed load tests at the stores, so, a bit of a wild goose chase.

 

[absenytx]

I installed the MTX-94R/H7 Monday afternoon.

It Started fine all Monday afternoon, all day Tuesday several times, then started this morning and wife went to work.

On her way home, the auto stop/start shut the vehicle off at a major intersection and it would not re start . She usually shuts it off, but forgot to this time. This is 45 miles from our house so I was of no help.

She was thrilled.

I have been relieved as the mechanic and it was towed to the dealership.

 

[absenytx]

Dealership actually did a very thorough electrical system diagnosis and gave me a three paragraph write up of their methodical check.

Original responder @jludave had it nailed with his #3 suggestion. The Starter was shot.

Dealer tested all grounds including all connections at starter motor, load tested batteries, high amp fuses and PCM, all passed...Even "Rotated engine by hand" to ensure it wasn't seized. I knew it wasn't but I appreciate the check.

The starter motor however massively failed the bench test. I love wrenching, but I didn't have the time or confidence or "other vehicle" availability to make that attempt and get my wife to work and back, so pay up it was. Bottom line had to put the issue to bed and I am confident it is resolved and we can get back to enjoying this really nice condition '18 Rubicon with pretty low miles.

Again, appreciate any and all help/tips/advice given here.

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