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Old 03-09-2015, 03:33 AM   #1
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Default Backfire after changing plugs and wires

My son just bought a '91 *-10 Tahoe with a 4.3l in it. After changing the plugs, wires, and distributor cap (didn't change the rotor since it looked all right) he has a backfire. When I researched the firing order, I mostly saw on the net that it is 1,6,5,4,3,2 in a counter clockwise direction, with the #1 terminal at the front middle of the cap. After looking at the cap installed, none of the terminals sits exactly in the middle front and my son swore he took the #1 wire off the back of the cap (1,3,5 bank on the passenger side, 2,4,6 on the driver side). Does anyone know if there is a different firing order for a Vortec V6? The old cap as well as the new didn't have numbers or direction of rotation stamped on it. I can't find where the order is stamped on the engine or where the VIN plate is located either. It really sucks to see him go through all the trouble of replacing those nasty plugs and wires only to have the truck run worse than it was. Oh yeah, the 1,3,5 plugs he took out looked really fouled like they were running too rich. 2,4,6 looked fine, an ashy gray. I wonder what'* up with that, too, since he'* got throttle body injection. I checked what codes were stored and saw all he had was one for the EGR circuit. Found a vacuum line not connected to the EGR valve and was wondering if it came loose or was deliberately disconnected. Thanks
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Old 03-09-2015, 05:49 AM   #2
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Take the left hand side(drivers side) valve cover off. Remove sparkplug #1 and rotate engine to TDC at #1. When the rockers on valves #1 are both loose, you are now at TDC. This should now allow you to put the engine back into proper timing with the distributor.
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Old 03-12-2015, 02:05 AM   #3
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Thanks Mike. Fortunatetly I didn't have to go through all that like I did when I had disturbed timing on my Mitsubishi 3.0l in my '94 Dodge Spirit when replacing the timing belt. All the diagrams show the #1 terminal on the distributor cap for the *-10 4.3l to be dead center front when in reality there'* two terminals offset from center. I treated the one to the left of center first as #1 and then went around clockwise 6,5,4,3,2 and that didn't work. Took all the wires loose and treated the one to the right of center on the cap as #1 and the engine fired right up. Runs quieter and smoother and the miss is gone. I believe my son is happy now! Still can't find the engine ID plate though. I've been told it'* on a machined flat on the right side of the engine below the valve cover and above the water pump.
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