I have been chasing an intermittent no start situation on my 97 TJ 2.5L Automatic. About 1 out of 5 tries it will start completely normal, but the other 4 tries I get nothing whatsoever. So I’ve been chasing down the issue. I checked at the starter relay and incorrectly thought it was the ignition switch. But after putting a new switch in, there is no change at all. So now I am doing a deeper dive and tracing the wiring to hunt down a short or break or something. But I have a couple questions that I’m a bit confused on, and I’m hoping the experts here on the forum can help me out.
1. Based on the strange intermittent behavior, I’ve started to wonder if the PCM could be going bad. But I checked all the feeds into the PCM and the grounds, everything checks ok and behaves correctly when you turn the ignition to start. My question is, does the PCM have any direct control or connection to the starter relay circuit? Looking at the wiring diagrams, I don’t think it does. I.e. I should see 12V on the starter relay terminal when the key is turned to start, regardless of a good/bad PCM, correct?
2. Looking at the starter relay circuit, the FSM shows terminal 85 is the coil ground, and 86 is the coil battery. Looking at the diagram (and the numbers on the relay) 86 is on the right, 85 on the left. But when I looked under the PDC, I found the BR LB (which runs to the NSS and is grounded when in Park, I confirmed) on terminal 86. Is this backwards from what it is supposed to be, or an I reading the diagrams incorrectly? 1 out of 5 times it starts and runs fine, and until recently it was starting fine everyday. So it can’t be wired backwards, can it?? But please look at my pictures and let me know if I’m reading the diagrams wrong. 86 is the terminal on the outside edge of the box.
Thanks in advance for any help on this.
Dan
1. Based on the strange intermittent behavior, I’ve started to wonder if the PCM could be going bad. But I checked all the feeds into the PCM and the grounds, everything checks ok and behaves correctly when you turn the ignition to start. My question is, does the PCM have any direct control or connection to the starter relay circuit? Looking at the wiring diagrams, I don’t think it does. I.e. I should see 12V on the starter relay terminal when the key is turned to start, regardless of a good/bad PCM, correct?
2. Looking at the starter relay circuit, the FSM shows terminal 85 is the coil ground, and 86 is the coil battery. Looking at the diagram (and the numbers on the relay) 86 is on the right, 85 on the left. But when I looked under the PDC, I found the BR LB (which runs to the NSS and is grounded when in Park, I confirmed) on terminal 86. Is this backwards from what it is supposed to be, or an I reading the diagrams incorrectly? 1 out of 5 times it starts and runs fine, and until recently it was starting fine everyday. So it can’t be wired backwards, can it?? But please look at my pictures and let me know if I’m reading the diagrams wrong. 86 is the terminal on the outside edge of the box.
Thanks in advance for any help on this.
Dan
