Intermittent no crank no start...running low on ideas

[rainman]

Originally Posted by awg

Good post,, and leads to what I had a couple of times, and took a little time to diagnose too

A failing starter solenoid..the internal points burn and wont always pass full current

In this instance, the damm thing will pass any test, but fail under load

all you get is a click at the relay..but if there is 12V at the solenoid terminal, that will be the problem

even though you can get a replacement solenoid, the most realistic fix is replace starter

if the problem is intermittent, run a test light into the cabin

if you have ever read or heard about hitting the starter with a hammer when it will not start-the condition described above were hitting it with a hammer works.

anything is possible, but interpreted that he was not getting the loud solenoid throwing out "clunk"...

[Roler]

Rainman, I'll check that. I think I had measured voltage at the solenoid and getting about 12V but I don't think I tested under load, which is of course is what's needs to be done. So will look into it tomorrow.

I do however can get it to start normally when I jump 30 and 78 on the starter relay 'sockets' though, which would suggest enough voltage and normal working solenoid?

Anyway will go at this tomorrow and will let you know.
Thanks for all the input so far guys, much appreciated.

[awg]

Originally Posted by rainman

if you have ever read or heard about hitting the starter with a hammer when it will not start-the condition described above were hitting it with a hammer works.

anything is possible, but interpreted that he was not getting the loud solenoid throwing out "clunk"...

you are correct about the hammer

the solenoid can be dicey, you can get a clunk or no clunk when its on the way out

the diagnostic is, as you stated, if every time the OP gets 12V at solenoid terminal, but on occasion, no crank, then (imo) he should replace the starter motor

Not sure this is the OP issue, but I have had this a fair few times on various vehicles, including XJ, at least twice

[Roler]

Intermittent problems, nothing is more annoying to diagnose..

Went at it again this am, started right up a few times and only had one no crank no start. When I went and did some other measurements, tried again 3 minutes later and has been starting since.

I did have 11.6V or thereabouts t0 the solenoid terminal when cranking. WHEN it starts, is goes too fast to be able to see the exact maximum on the multimeter (dont have the min/max function), but I saw at least 11.6V

Went over all the engine bay grounds once more, cleaned the battery to chassis ground. All read about 0.02-0.05 Ohm with key off.
With engine running the grounds on the fenrwalls and firewall read 15 Ohms, the engine block grounds (near dipstick and ignition coil) all read about 60 Ohms; that is with engine running.

As mentioned, the voltage drop tests to the starter motor were 0.16V power side and 0.22V ground side, so that should not be an issue.

So, like you said Rainman, is it still between relay and starter solenoid?
When I wanted to check the voltage at the solenoid terminal immediately after the no crank, it cranked up again with 11.5V....so I still don't know. Would only be able to tell if the no crank recurs and I'd be able to check then.

Oh, btw the tapping on the solenoid didnt make it go away either.




Maybe still the ignition switch?

- Does anyone know the wires layout at the ignition switch?
The FSM mentions to measure resistance between the ignition switch B(+) terminal circuit and the output circuit or something but I have now idea which ones they would be (no picture in the FSM either).
I tried searching but not convinced I found the correct one

[Roler]

See pic, the starter relay area at the PDC seen from underneath .
Apparently the yellow wire carries voltage from ignition switch to coil side of relay.
The bigger brown wire corresponds with terminal 87 (accidentally calling it 78 before) do that's were the high current from 30 should be going out thru? Does that go to the solenoid terminal then?

[Roler]

Originally Posted by awg

Good post,, and leads to what I had a couple of times, and took a little time to diagnose too

A failing starter solenoid..the internal points burn and wont always pass full current

In this instance, the damm thing will pass any test, but fail under load

all you get is a click at the relay..but if there is 12V at the solenoid terminal, that will be the problem

even though you can get a replacement solenoid, the most realistic fix is replace starter

if the problem is intermittent, run a test light into the cabin

I guess that would be possble; the hell, if it passes all tests, how in the world would I ever be able to diagnose it then!?

[Roler]

Went out again to the Jeep (have some self isolation time) and no crank again, which persisted so I could do some more testing. Every disadvantage has an advantage.

Turning key to accessories and on position (not start): everything dash-wise comes on like normal, start relay clicks
Turning key to start: no crank, verified NO voltage at the terminal on the solenoid

So next, went to the starter relay with probe wires setup in the sockets for the relay terminal and the relay put snug 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 was not 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
[/B]

So I would think:
1) Either no power from 30 to 87 for whatever reason despite good working relays
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

And I can still crank and start the Jeep by jumping 30 and 87!!!


I have ran out of ideas.