G’day people, its been a while, good to still see some familiar names though, hope everyone is keeping well.

Bit of a read, to catch up on the issue at hand:

Xj doesn’t get much action but has been parked for longer times before without issues. Now, for the first time in ages, the Jeep (97 XJ 4.0, auto, 190K km, RHD) doesn’t want to play. Spent two weeks now reading up and testing all kinds of possibilities, and now running low on ideas.

The issue: Intermittent No crank-No start, which is a pain to try and diagnose

So here a summary of what has been done and checked so far:

· Brand new battery, 650 CCA

· Voltage drop testing batt to starter: (+) side 0.16V and (-) side 0.22 V (a tad high but nothing dramatic) (I jumped 30-78 terminals at starter relay to get it to crank)

· Have 12 V at the starter B- terminal, about 11.5V when cranking

AT THE PDC:

Starter relay clicked, didn’t trust it, bench tested it, energizing pin 85 and grounding pin 86 gives continuity between pin 30 and 78: all ok

For good measure changed it with the fore-sure-working cooling fan relay, still no crank-no start


WITHOUT relayin place:

With key off, have power at terminal (receiving end for) pin 30 and ground at terminal (for) pin 78

With key on, 12.06V at terminal for pin 85 and 0.17V at terminal 86 (!?) (see below, the NSS grounds through this, mine is only 5 years old)



WITH relayin place:

With key on, have 12 volts at terminal 86 (extra wire in the terminal/receiving end ) which tells me the ignition switch is working.

NO change in voltage wiggling the NSS with this. NSS grounds via terminal 86 and with good ground should see 12 V. (there is a good Youtube about that)



At the PDC I can crank the engine when jumping terminal 30 and 78 (with key off) and crank and run the engine when key on and jumping 30 and 78.


Yesterday I took out the key cylinder, ignition switch actuator pin assembly and ignition switch. Actuator pin assembly not broken, ignition switch not damaged/cracked/melted at the connector, connector itself clean and intact, nil corrosion or loose wiring. I couldn’t find info on actually testing the ignition switch itself except a post about measuring continuity over input and output but I could not find that specific post anymore (plus there were about 8 or 10 pins in total on the switch)

Today, took apart the PDC, thinking maybe the pin “sockets” could be loose as was the case with another XJ having similar issues. Pin terminals all solid within their place, no wires damaged or loose



So now, I’m a bit low on ideas for what’s next; mechanically everything appears to be able to work, and it can be cranked and started. Just not in the way it should haha.

I get voltage at pin 86 so everything from key to that point seems to be working as it should, and jumping 30 – 78 cranks and starts the engine so from that point it seems to work too. It seems very " relay/relay socket"….but I have nothing suggesting that in my checkings/measurements!? I must be overlooking something

Why intermittent? Because every now and then during the past weeks of testing, it would start up normally. Just to die again the next time.

Hope to get some advice /ideas!

Cheers

 

After two days of checking and testing, went out again to the Jeep and no crank again, which persisted (has several normal starts earlier today) so now I could do some more testing. Every disadvantage has an advantage.

Checked all grounds, all read about 0.03 Ohms of thereabout (engine off)
Turning key to accessories and on position (not start): everything dash-wise comes on like normal, starter relay clicks
Turning key to start: no crank, verified NO voltage at the terminal on the solenoid (battery terminal has battery voltage)

So next, went to the starter relay with probe wires setup in the sockets for the relay terminal and the relay in place
With key on , verified power at 86 and 30 (30 is always hot but thought maybe the relay in situ would disturb something, but this proved not to be the case).
When cranking NO power at 87

I tried three different other relays from the PDC, that all work, but still no power to 87.

Now narrowed it down to NO power at terminal 87 when cranking


So I would think:
1) Either no power from 30 to 87 for whatever reason (good relays, no relay terminal sockets loose or displaced)
2) Or no ground for 87 to allow current from 30 to flow through


1) I tried several good working relays
2) there is good continuity (like 0.2 Ohms) between Solenoid terminal and Batt negative post in the key off state

I have looked into testing the ignition switch itself ( checked the FSM, but have no idea which terminals they indicate to check for continuity

With the key in the ON position, I can still crank and start the Jeep by jumping 30 and 87..


I have ran out of ideas.

 

Crank Position Sensor. Test it.

 

Replaced mine when I had stalling/backfiring issues years ago.
According wiring diagram (and its workings) I'd think CPS is not involved in initial "startup" crank (yes for allowing subsequent starting when PCM sees sufficient pulse/speed from the flexplate via the CPS and of course for running).

But can't hurt, testing everything by now..

 

The CPS is absolute involved in starting. No CPS, no spark.

 

[QUOTE=Roler;3632131]Yes, the NSS grounds one side of the relay coil. Have you measured the resistance at the relay socket to see if the NSS is providing a GOOD ground? You can deceived yourself by just measuring voltage and not see a high resistance connection, as is often the case with a dirty NSS. Have you tried bypassing the NSS yet?

 

But if the crank sensor is bad, it would just crank and crank and crank without actually starting, right?
At least that's what mine did. I'm not so good with these kinds of problems, but to me if you can start it via the PDC, then the problem would be between there and they key?

Mine sometimes won't want to start if you start it from cold and then shut it off before it fully warms up. Once the key goes to "start" the radio and everything shut off but it wont crank, sort of like when the NSS is bad/misaligned. Give it a few minutes and it will start. If the engine is fully warmed up it will restart the first time no matter how many times you want.

 

Yes absolutely correct!
BUT: not before it sees the flexplate move.
Therefore causing crank no starts
I have no crank (and therefore no flexplate movement), in which case the CPS hasn't had the chance yet to produce info for the PCM.

 

[QUOTE=lawsoncl;3632643]I came across that yesterday, good suggestion to check. I concluded sufficient ground to through the fact my NSS voltage was good, and therefore ground should be good.

 

Update: after 10 days got this eventually fixed. Biggest thing was, I was going from this Youtube which explained everything quite well actually.


HOWEVER: my starter relay pins were actually exactly the other way round. Power to 86, ground at 85 (I think that might actually be the normal setup?)
So once I discovered that (when I had the PDC flipped), it made a bit more sense.

It seems to have been the NSS. The first time I had replaced it about 7 years ago, it gave me the typical symptoms of not starting in P, still able to start in Neutral, and eventually didnt start in Neutral, as well as intermittent reverse lights.
This time different issues, and initially the tests that I did according the youtube, gave mixed results. Eventually grounding pin 85 to battery negative post made it crank, which was the clue.

Got a lot wiser in the field of wiring diagrams, car electrics and what not in the past 1-2 weeks for sure.

Now did the NSS jumper bypass which has tje Jeep starting, and will source a backup NSS before I attempt to take it off again. I remember braking off one of those weird aluminium threaded parts around the shaft in the past. If it remains in tact, I'll clean it up and check for shorts on the wires before I put it back on. .

Here the link to the entire thread of the forum here in OZ, for those interested in how this was approached and eventually solved.
http://www.ausjeepoffroad.com/forum/...d.php?t=158807

Thank you for all the input and suggestions.

 

Yes, power is normally to 86. Some of the relays have an internal voltage suppression diode across the coil that will pop if wired backwards. It'll still work afterwards, just without the protection diode. Also beware there are two different pin layouts. Bosch A and B.

 

• mine was chaffed right above the rear cat going to the down stream O2 sensor. The power wire for the Automatic Shutdown relay runs through every critical component of your xj fuel injectors, fuel pump, ignition, crank sensor, cam sensor, alternator, coil, PCM,O2 sensors. I’m sure I forgot something but you get the point get yourself a short finder of any type and start chasing but check around any where with vibration or heat first

 

Have you found a solution for you problem, it sounds like we have the exact same issue and I'm hoping for some insight.