Distributor doesnt keep timing

Tiny
DAVIDV2
  • MEMBER
  • 1999 CHEVROLET TAHOE
  • 195,000 MILES
1999 Chevy Tahoe. Distributor keeps reading out of time without being moved. I set #1 cylinder top dead center and adjust timing. Truck runs good for a week and then starts rough idle again(distributor goes back to being off time with scanning tool). Any ideas? I have done this twice already. Could the distributor be bad? Any suggestions would be appreciated.
Saturday, November 19th, 2011 AT 10:26 PM

9 Replies

Tiny
BILLYMAC
  • MECHANIC
  • 2,204 POSTS
Hi yes the distributor could be bad. It could also be a bad timeing chain or knock sensor.
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Saturday, November 19th, 2011 AT 10:28 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Did you disconnect the EST wire before you time the ignition switch?
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Saturday, November 19th, 2011 AT 10:31 PM
Tiny
DAVIDV2
  • MEMBER
  • 5 POSTS
Thank You for your reply's.I Did not disconnect EST wire. Would this cause it to change after running good for a week?
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Saturday, November 19th, 2011 AT 10:36 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
The timing is not adjustable in any way on this engine. The base timing is engineered from the factory with the Crank sensor and the computer controls everything after that. Don't even bother putting a timing light on it because the readings will make no sense at all to you. All turning the distributor does is throw the injectors and secondary ignition out of synch. If you have moved the distributor, you will need a professional scan tool to get it set right again. If it's wrong it will set a P1345 code and put the check engine light on.
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Saturday, November 19th, 2011 AT 10:56 PM
Tiny
DAVIDV2
  • MEMBER
  • 5 POSTS
Thank You, Yes, the scan tool is saying distributor is out of sync a week after setting distributor, even though distributor has not moved. It is not throwing a code only causing rough idle.
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Sunday, November 20th, 2011 AT 12:23 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
How far out is it. It will set a code at I believe 4 degrees of offset.
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Sunday, November 20th, 2011 AT 12:25 AM
Tiny
DAVIDV2
  • MEMBER
  • 5 POSTS
Thank You for your reply's. Not sure how far out it is. I am taking back to friend mechanic next weekend and will post results.
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Sunday, November 20th, 2011 AT 1:42 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
You just said the scan tool told you it was out of synch. You would have had to read the data to know that. Was it really checked? It can't move on it's own.
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Sunday, November 20th, 2011 AT 1:47 AM
Tiny
DAVIDV2
  • MEMBER
  • 5 POSTS
I did not read it myself. The mechanic told me it was out of sync.
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Monday, November 21st, 2011 AT 1:32 AM

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