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Unread 05-24-2011, 11:58 AM   #1
pub
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Won't start

Hi,

My ZJ Laredo has run perfectly for ages, but just wouldn't start yesterday. I had driven it for 40 miles or so, stopped for an hour, and then it didn't start.

It turns the starter motor fine, but when I checked the contacts on the connector for the ignition coil there's no current.

Having read on the forum, I tried cleaning the ECU connectors, but nothing either.

Any suggestions gratefully received!

PUB

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Unread 05-24-2011, 12:33 PM   #2
ratmonkey
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swap asd relay, then check crank and cam sensors. most likely failure point is the crank sensor.

rarely throws a code when it pops up as a no start condition. sometimes it will prevent the ecu from turning on at all and connecting with a scanner though.
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Unread 05-24-2011, 01:07 PM   #3
pub
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Hi,
Thanks ratmonkey, I tried the ASD relay - but no joy.
I've seen the crank sensor mentioned in a few threads but it seems strange that it would fail catastrophically while parked for an hour.
I was thinking about hot-wiring the ignition coil through the ignition fuse to the battery, and putting a switch in if this works. Any thoughts?
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Unread 05-24-2011, 01:08 PM   #4
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Could it be the immobiliser?
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Unread 05-24-2011, 08:21 PM   #5
ratmonkey
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Quote:
Originally Posted by pub View Post
Could it be the immobiliser?
The security will allow it to start and idle 3 seconds at a time every time you try to start it with security tripped.
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Unread 05-24-2011, 08:30 PM   #6
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Quote:
Originally Posted by pub View Post
Hi,
Thanks ratmonkey, I tried the ASD relay - but no joy.
I've seen the crank sensor mentioned in a few threads but it seems strange that it would fail catastrophically while parked for an hour.
I was thinking about hot-wiring the ignition coil through the ignition fuse to the battery, and putting a switch in if this works. Any thoughts?
ECU controls spark. If you have no trigger signal this will not work.

You need to check a few more things. Check fuel pump (see if it runs when you turn the key to "On". Check fuel pressure at the fuel shrader valve.

See if you have spark at all. Check injector pulse. If you have no spark and no injector pulse you have a bad CPS.
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Unread 05-25-2011, 12:20 AM   #7
pub
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thanks all, I'll give these a try.
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Unread 05-25-2011, 01:36 PM   #8
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The local dealer want 80 for the CPS sensor (about $130) - seems steep.

All the other parts places only have aftermarket sensors (50 ~ $80) - and there's plenty of people on the forum saying to use only the MOPAR ones.

Is it a false economy buying the cheaper ones?
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Unread 05-25-2011, 03:29 PM   #9
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cheaper sensors fail more often and are quite often bad out of the box. some are even reversed polarity causing even more odd issues to arise.
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Unread 05-25-2011, 04:39 PM   #10
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Pub,
When you try to crank it over, do your gauges move when you turn the key to the on position?
Mine weren't and when I unplugged the crank sensor, they came up like normal.
I had the same problem last week. I did use an aftermarket sensor, and it's working as it should. If it fails again, I'll put a Mopar sensor in.
Hope it all works out for you.
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Unread 05-26-2011, 04:32 AM   #11
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Hi rehab,

Thanks for the reply. The dials are working as normal, the oil pressure & battery gauge read as normal, but there's no power at the ignition coil.

I found this thread about diagnosis with a great post from CJ7-Tim:

won't start no spark

so I'll get the multimeter on the sensor and go from there..
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Unread 06-15-2011, 09:52 AM   #12
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Hi all,

I finally got around to testing and then replacing the CPS, as you suggested, and it fired right away. Thanks ratmonkey and TallyZJ for you're help.

On to the next problem now..... (the alarm has started going off and won't disarm no matter what I do. Better start another post ......)
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Unread 06-15-2011, 10:15 AM   #13
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use the key in ALL the door locks. sometimes the driver's door switch goes bad but the hatch or pass side is good.
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Unread 06-16-2011, 02:14 AM   #14
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I've read all sort of different things about how the alarm system actually works. The remote is working and will lock unlock all the doors and arm / disarm the immobilizer. But is it actually the key in the door that disarms the alarm? I had disconnected the battery because it kept going off, locked all doors with the key, and it seemed to have disarmed. I started driving and after 10 miles it started going off as I was travelling!
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Unread 06-19-2011, 04:05 AM   #15
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fixed alarm

I managed to fix the alarm problem - hood closure switch was the problem!

When I finished fixing it I shut the hood and the glass fell out of the passenger side headlamp and smashed!

This is supposed to be my DD.
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