Birty Dastards Jeep Club

Tech Forum => Workshop => Topic started by: keegantj on August 22, 2011, 07:55:28 PM

Title: No power to coil.
Post by: keegantj on August 22, 2011, 07:55:28 PM

Hello, my daughter has recently bought a 1997 TJ 4 litre. It has always taken some cranking before it starts. Once started, it runs fine . This morning it wouldn't fire up. Had a look tonight and there is no power to the coil. Can anyone point me in the right direction? Many thanks in advance, Tim.

Title: Re: No power to coil.
Post by: Tank on August 23, 2011, 12:01:26 AM

Maybe a crank position sensor or cam sensor,but could also be ecm,loose wire etc.Maybe a diagnostic will help?No expert so maybe others could advise further

Title: Re: No power to coil.
Post by: Jonny Jeep on August 23, 2011, 05:28:43 PM

Coil is powered by the ASD relay. ASD relay is only energised for the first two seconds when the ignition is turned on, or when the engine is cranking or running. If you are testing at any other time it will have no voltage.

There are online factory service manuals (FSMs) at http://www.jeep4x4center.com/knowledge-base/index.htm#service (http://www.jeep4x4center.com/knowledge-base/index.htm#service) that might be of help.

Title: Re: No power to coil.
Post by: scrw on August 23, 2011, 06:37:17 PM

Quote from: Tank on August 23, 2011, 12:01:26 AM

Maybe a crank position sensor

 :imwitstupid:

Same issue with an old XJ, duff crank sensor=no power to coil

Title: Re: No power to coil.
Post by: keegantj on August 23, 2011, 08:53:52 PM

Thanks for the replies. I have got the Jeep in the garage now so have had a good look tonight.The ASD relay is working perfectly, so I swapped it with an identical one. Testing the coil voltage tonight I seem to have 2 volts even when cranking. I have tried a jumper wire to give the coil 12 volts but there was still no spark. The cam sensor and CPS both have 5 volt feeds. Should I replace these just to eliminate them? Why don't cars still have points and condenser? Any ideas? Tim.

Title: Re: No power to coil.
Post by: Tank on August 23, 2011, 11:26:04 PM

I would say that just because the feeds are showing,its no guarantee the sensors are working,and even powering the coil wont work if sensors are down as the computers read loads of input and data at the same time.It may be a case of changing the sensors,even as a process of elimination

Title: Re: No power to coil.
Post by: bigjeepzj on August 24, 2011, 09:21:51 AM

hi
this link may help

http://www.lunghd.com/Tech_Articles/Engine/Cam_Position_Sensor_and_Sync_Pulse_Stator.htm (http://www.lunghd.com/Tech_Articles/Engine/Cam_Position_Sensor_and_Sync_Pulse_Stator.htm)

Title: Re: No power to coil.
Post by: Tank on August 24, 2011, 11:16:28 AM

Linky no worky

Title: Re: No power to coil.
Post by: bigjeepzj on August 24, 2011, 11:31:08 AM

Try it now
http://www.lunghd.com/Tech_Articles/Engine/Cam_Position_Sensor_and_Sync_Pulse_Stator.htm (http://www.lunghd.com/Tech_Articles/Engine/Cam_Position_Sensor_and_Sync_Pulse_Stator.htm)

Title: Re: No power to coil.
Post by: keegantj on August 24, 2011, 11:35:35 AM

Thanks for your replies. I think I will order a cps and cam sensor. Even if it doesn't work, it eliminates the usual culprits. I will post results as soon as I have them, Tim.

Title: Re: No power to coil.
Post by: bigjeepzj on August 24, 2011, 11:46:06 AM

think I originally posted it as an email  :banghead: :banghead: :banghead:

The link tells you how to test the cam sensor with a normal meter

but a better way is if you have an oscilloscope to check the pulse stream is good

Title: Re: No power to coil.
Post by: keegantj on August 25, 2011, 06:40:05 PM

Wooo hooo it's fixed. Turned out to be the cam position sensor, £58 well spent. Thanks for your pointers, much appreciated, Tim.

Title: Re: No power to coil.
Post by: bigjeepzj on August 25, 2011, 07:14:14 PM

Glad you got it working

Title: Re: No power to coil.
Post by: Tank on August 25, 2011, 07:18:53 PM

 :imwitstupid: :iagree:
Happy to help