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99 lumina intermittent crank fail


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loneranger 
Copper - Posts: 572
Copper spacespace
Joined: December 28, 2008
Posted: June 28, 2009 at 6:02 PM / IP Logged  

Ok, I'm hoping some guru(s) can help me diagnose this issue.  The vehicle (99 Chevy Lumina LS) has VATS and a Python 1400XP with VATS over-ride (resistors).

About 2 weeks ago, a senior citizen friend of mine had a problem starting his vehicle.  He could not get the engine to crank.  An hour or so later, he tried again and the vehicle started, with no problems and operated fine.  Then the same scenario popped up again a few days later.  I went to his location and when I arrived the vehicle was operating properly.  I tried to recreate the issue while I was there, but it would not arise.  The scenario has happened a few more times, but I was not availvable when it did.  He needed the issue resolved quickly and wanted to replace the starter as a likely cause. I was reluctant, as I was not optimistic that the starter was the issue, but I accepted his wishes and replaced the component.  Of course, 2 days later the scenario repeated. However, this time I was able to recreate the issue.

Here are my findings when the vehicle is operating properly:

  • With the vehicle off and the key is turned to ignition or crank, the VATS security light is solid for ~5 seconds and then turns off.
  • The vehicle will crank at anytime.

Here are my findings when the vehicle is operating improperly:

  • With the vehicle off and the key is turned to ignition or crank, the VATS security light is solid and never turns off.
  • The vehicle will not crank at anytime.

Here is my initial test diagnostics:

  • The VATS over-ride's relay is working properly and the factory VATS operates at the relay's rest (30-87a).
  • The VATS security light blinks when the factory VATS cable is un-plugged (steering column), at ignition sequnce.
  • The VATS over-ride's resistors are within 1/2% of the factory key resistance at the VATS plug (steering column).
  • Both facotry and by-pass VATS resistance values are reading proper at the VATS plug (steering column).

The Python 1400XP can be ruled out as a culprit, simply by the fact that it has no intervention when it's not engaged.  My questions now become:

  • What causes the factory VATS light to stay solid at ignition sequence?
  • Is this pointing to a more seroius ECM issue?
  • Can it be diagnosed definitively?

I really hope someone can help me on this. He has already lost ~$200 on the starter replacement.

Ideal - cmon dude, add to topics in a useful manner, not stuff that is obvious.
Story - Phzzzt! Hey, what happened?! ... Isn't it obvious?
Moral - Never dismiss the obvious.
howie ll 
Pot Metal - Posts: 16,466
Pot Metal spacespace
Joined: January 09, 2007
Location: United Kingdom
Posted: June 28, 2009 at 6:11 PM / IP Logged  
Can't help you much except the usual clean all plug contacts, etc but welcome back, long time no hear from.
t&t tech 
Platinum - Posts: 2,601
Platinum spacespace
Joined: October 05, 2008
Location: Trinidad and Tobago
Posted: June 28, 2009 at 8:07 PM / IP Logged  
seriously, long time i haven't seen you on mr.loneranger, welcome back, sorry i can't help, cheers.
JW.ORG.
COMMIT YOUR WAY TO JEHOVAH AND HE WILL ACT IN YOUR BEHALF.
PSALMS 37:5
loneranger 
Copper - Posts: 572
Copper spacespace
Joined: December 28, 2008
Posted: June 28, 2009 at 10:15 PM / IP Logged  

Thank you for the replies.  I've been vacationing and very busy with side work lately.

I really don't know where to continue diagnostics at this point.  I really dont want to replace the ECM.  I'll try bypassing the factory key's signal to the VATS for a bit and see if that resolves the issue.  Obviously, that would point to bad contacts in the key cylinder or cylinder plug.  However, I would assume if the contacts were bad the security light would flash.  I guess I could try using an invalid resistance to the VATS and confirm it.  If anyone else has an idea, please chime in.  Thanks again.

Ideal - cmon dude, add to topics in a useful manner, not stuff that is obvious.
Story - Phzzzt! Hey, what happened?! ... Isn't it obvious?
Moral - Never dismiss the obvious.
loneranger 
Copper - Posts: 572
Copper spacespace
Joined: December 28, 2008
Posted: July 01, 2009 at 7:48 PM / IP Logged  
After quite a bit of diagnostic work and testing, I have solved the problem.  I will post the information I have gathered, along with a diagnostics tree, to help others who may run across this scenario.  It's not an un-common scenario, on older VATS(PASS KEY) equipped vehicles.
Ideal - cmon dude, add to topics in a useful manner, not stuff that is obvious.
Story - Phzzzt! Hey, what happened?! ... Isn't it obvious?
Moral - Never dismiss the obvious.

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