Intermittent Starting Problem 2012 Journey 34Y

[LOG]

My 2012 Winnebago Journey 34Y has an intermittent starting issue.
Sometimes it will start instantly just by turning the key. At other times, it will not turn over without using the battery boost switch.
The two starting batteries are 950 CCA each. The batteries test as 1900 CCAs
and 84 percent starting capacity. The battery terminals are clean and tight.
Has anyone had this problem and what fixed it.

[Morich]

It may be simple or a total headscratcher!
But on thing to keep in mind is that the RV is just the parts that are added to a stripped chassis and the starting part is just what we find on the normal truck, with a few connections added for RV things.
So the main idea for starting is the chassis battery, cables from them to the starter solenoid and then the starter itself.
Treat the issue the same as what you would do on a truck!
You've covered some of the idea but maybe a good look at the battery is needed as it leans toward not enough power when you can get it to crank by adding the coach batteries to the sytem?
Is it the battery not holding a god charge or is it possible there is a bad connection somewhere between the chassis battery and the starter? Bad contacts in the starter solenoid, so that it is only passing some of the voltage on to turn the starter?
One frequent problem is just dirty cables, so you checked the battery end, but did you check the end at the starter and any connections along the way?

Also it is easy to miss checking the negative battery cable on both the battery and where it connects to the frame ground. that frame ground is often down behind and out of sight where we forget to check that point.

what I am saying is that it "might" be something hard like a bad ignition switch but most cases are just dirty connects where we are not thinking to check! dirty cables act just like weak batteries because it only lets part of the voltage go through the dirty spot!
Cheaper/easier to make sure connections are good before buying new battery!

[LOG]

It seems my starting problem has been narrowed down to the following items:

Ignition switch, Batteries, Battery Cables, Starter solenoid, Starter, Battery Ground Connections, Battery Positive Connections and other unidentifed problems/areas.

[Morich]

Yes, that is the problem with intermittent problems!
Most will have to just start at some point and check the cables and connections first and then once we have assured those are not the problem we can move to the other problems.
But what are your other options?
Most who have owned and repaired a car for very long will have had this problem and found no magic to cure it!

On the newer vehicles with lots more electronics the problem is much harder to sort out as there are lots more things we can't find , let alone fix!
On a 2015 Ford Focus, it took at least 10 trips to three different dealers and six months before we gave up and sold the car. During that time, they changed the transmission control module (TCM) three times as that is what the computer said as second choice after the battery which they all suggested changing but agree it was not the battery after they put new ones in. In changing the TCM, they broke a piece off which ruined the transmission .
They said the transmission was a $7000 dollar hit on the extended warranty. It was the only time I had every bought an extended warranty but it saved me that time.

Part of being a repairman is butting the head on the wall at times!

[Ray,IN]

After all the cleaning cable/wire connections and retightening them; before reattaching the battery cables, test them for internal resistance. If it is a bit high, then under load resistance might increase to troublesome levels.
This chart show the ideal resistance per foot, by wire size: https://www.engineeringtoolbox.com/w...ges-d_419.html

[Morich]

When I've looked for starting problems, I ran into the problem of it being a chassis problem where the diagrams on my model did not show the route or connections from the battery to the starter. That left me missing a point where a second cable joined the main run with no drawing to know it was there.
At first the starting problem seemed to show if it was cold, so that the battery seemed a suspect, but as the weather warmed and the problem got more frequent but would still start if I used the boost switch, I knew by then that my battery was good, the cables that I had checked were good but it still acted like a weak battery!

I finally found there was a connection on the frame just behind the front wheel that was well hidden under road oil and mud! Once I cleaned it, things got better!

[dickb46]

I've been lambasted for saying this before and told it doesn't exist...but the low tension wires from the ignition switch go back to a starter relay just above the frame rail on the passengers side at the front of the engine that sends power to the starter solenoid.
The ignition switch doesn't go straight to the solenoid.
Sorry I'm up for lambasting again... but that's why were here
dickb

[dickb46]

Sorry, the relay was $27.00

[dickb46]

My symptoms were.. turn key nothing over and over then engaging