Intermittent Starting (works every morning, then doesn't)

I have a '06 Jeep wrangler, it has an interesting problem,
It starts every morning, (10 days now) but won’t start again in the afternoon, evening,
I have validated the battery, the connections, put in a new starter relay, and a new starter for kicks, and nothing in the afternoon,

What could be so temp sensitive that would make this happen?

Thanks for your help.

Jeep Driver

When you say it won’t start, do you mean it cranks, but doesn’t catch? Or that it doesn’t crank? If it doesn’t crank, does it make any noise at all?

there is a faint noise for the starter relay buzzing in the power distribution block
The starter is not cranking at all , when you turn the key, the electrical systems blank out, like it want’s to send all current to the starter, but the starter never spins

That info really helps. It means the problem isn’t with the starter system at all. There is a faulty connection to power going the ignition switch. Check the voltage getting to the power distribution panel under the hood while the trouble is happening and trying to crank the engine. Make sure 12 volts is getting to those fuses. If they are okay then you need to check the ignition switch connections.

A mechanic would measure the voltages at both starter terminals during attempted cranking. If either is below 10 volts, with a known-good battery and starter motor, that’s a pretty good indication of a problem upstream of the starter. It could be anything from a fuse on the fritz, the ignition switch, the neutral or clutch safety switch, passenger compartment relays, or loose/corroded electrical connections. Any can be temperature sensitive, esp a fuse. Usually a temperature problem affecting the electrical system such as this would occur more at lower temperatures rather than higher, but not in this case apparently. But working backwards with a DVM from the starter motor would quickly identify the culprit.

It could be due to multiple problems too. I had a similar problem w/my early 90’s Corolla and found three separate problems: a faulty ignition switch; a faulty clutch safety switch; and faulty starter solenoid contacts.

thanks all, I have bypassed the clutch circuit, (it’s a jeep, there a fuse slot to put in a jumper, so that should be out of the equation), I have put a new fuse in the starter relay position, I couldn’t work on it this SAT, but tomorrow I’ll wire up a bypass to juice the starter solenoid so I can drive it until I figure out where I’m not getting the right amount of current.

Check the distribution panel fuses first for voltage and then check the ignition switch if the fuse power is good.

I vote for a battery and charging system test first, free at many auto parts stores. If it is the original battery you are due.

Here’s an update, (no more morning starts, the key turn, only cuts out the acc electricity)
New Battery, New starter, new relay, new fuse,
Compression starts fine, every time,

I tried putting current to the solenoid to engage the starter, and that causes it to crank (turn over)
but either it’s too slow, or something else is not on, as it won’t fire?

thanks for any help

You say the engine starts up doing a compression start so it seems the ignition system is working okay. The slow cranking could be due to a weak battery, or a problem with the battery cable to the starter. Since the starter has been replaced I will assume it is okay. You also stated that you bypassed the safety switch so power from the ignition switch should pass directly to the starter solenoid through the jumper. I suggest you get something to check the power to the jumper lead when in the START mode. If you see power there then is a faulty connection between the clutch switch and the solenoid. If no power is seen then there is a problem between the ignition switch and that point.

The other possibility is a bad connection from the negative of the battery to ground on the engine block. Clean and inspect that connection. @nd possibility parasitic draw killing the battery. If you have a guage, how many volts showing before you try and start? Third possibility, timing has slipped. too many options, head hurts.

It’s important when measuring the voltages at the starter during attempted cranking to measure between the starter connector (back probe, leave everything connected) and the starter case. Not just to the chassis ground.