No cranking/starting when warm

[JefCooks]

Hey everybody 

I have a 92 4x4 4.0 AW4. Sometimes (randomly) my truck won’t start, it won’t even attempt to crank. It’s been happening for several months at this point, but I don’t drive the truck much so it feels quite frequent. It’ll start fine at home but if I go somewhere and the engine warms up, it won’t turn back on after shut down. 2 months ago I cleaned the NSS and it hadn’t happened since then but then happened yesterday. The headlights don’t dim when I’m trying to start it so it’s not a bad starter. The lights and fuel pump kick in when the key is turned so I don’t think it’s the ignition switch. The grounds don’t look terrible, but which ones should I inspect closer? Any other insights? Thanks everyone!

[scguy]

Do you have a multimeter? Get a helper and when it's not cranking, check voltage at the big wire and the small wire at the starter solenoid while your helper turns the key. You should have over 10V at both. If you have lower voltage on the big wire, check your battery terminals. 

 

[JefCooks]

Ok, I’ll try and get it to happen later today and keep you posted. Thanks. 

[Eagle]

Starter relay?

 

[WahooSteeler]

Have you given a close inspection of the battery cables, particularly the negative? If you've never changed them out they have been known to have the sheathing rub through. 

[JefCooks]

The cables all look good from what I can see, no corrosion and solid attachments. My plan was to check the voltage as previously suggested and jump it to see if that’s it. 

[hassyfoto]

The resister wire, made into the harness was the problem on my MJ. I had the exact same issues. I replaced the dizzy, and just about everything else on the ignition system before I found the problem. I had to cut out the resister wire (about 3 feet long) and replace with standard wire. I added a in-line resister fuse ( from local auto parts store- its about 6 inches long). I have not had an issue since. 

You can tell the resister wire when you unwrap the harness running next to the block. It's a softer rubber type of wire sheathing as compared to normal more rigid sheathing normally found on most wire harness components on the vehicle

[JefCooks]

Just to close up the thread, I figured out the problem and repaired it. The next time it wouldn’t crank, I checked the battery o nextions and fuse, all good. Then I got under the truck and tried to jump the starter solenoid. It sparked, but didn’t spin. Bingo! While under there I found the heater core valve had a very slow drip right onto the solenoid. So, got a new starter & solenoid and am going to replace heater hose with the 97+ direct run hoses. I was baffled that it was the starter given that it was intermittent, but I guess the coolant would cause a temporary short??