'89 GMC Timing


Old 10-06-06, 07:44 PM
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'89 GMC Timing

5.0 litre motor would ping when I pulled anything heavy. I just bought a 4,000lb trailer so I had the timing retarded a couple of degrees to get rid of the ping. Now it is very sluggish. I noticed when the mechanic did it he didn't disconnect the ignition wire or use a timing gun. Does the wire just need to be disconnected when you are using a timing gun or should he have done it even though he just did it "by eye"? Thanks.

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Old 10-07-06, 06:38 PM
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When timing with an induction timing light you would hook the light to the battery with two cables and the wire with the induction clip would go on the #1 cylinder plug wire.

I believe I would first get an accurate setting on the timing. Then I would make sure the spark advance was working properly. Both can checked with a timing light. If setting to recommended specs was giving you a ping or spark knock, you may try going to a higher octane fuel for pulling the trailer.

Retarding the timing is a solution to the problem to a point, then I would start looking at some other remedies.

Hope this helps,

Old 10-07-06, 07:43 PM
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Also, when doing a timing advance, you usually have to run higher octane fuel. Minumum of 91.

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