2000 GMC 4.3L, V6 Ignition Timing

[R Crane]

Still trying to diagnose my vibration problem. From all I've read it is probably the motor mounts. Does anyone know the correct way to check the timing? Does anything have to be disconnected, plugged, etc ? I am familiar with older cars, but have never tried the newer fuel injected type. I'm pretty sure that my timing if probably too advanced and this might be causing the idle to be too high. Also, the starter drags slightly when starting vehicle (like a weak battery).

[GMCTech]

The timing is not adjustable in the 4.3. The distributor is in a locked position. The only way to time it would be to remove the distributor and move it physically one or more teeth. It is relatively impossible for the motor to "jump" timing.

The timing adjustments are completely computer controlled, and if there is a timing problem it is probably related to something else causing the computer to adjust timing.

I'd have it scanned by a competant tech. paying specific attention to timing adjustments and streaming data (O2 sensors, MAF, IAT, etc.)

What conditions is your vibration apparent in? Just curious.


Hope this helps.

[R Crane]

The vibration is most noticeable when vehicle is stopped with transmission in drive. If a/c is switched on at this time it becomes even more obvious. If you move trans. into neutral, while holding foot on brake, the noise/vibration diminishes somewhat. Also, I have noticed if you apply heavy pressure on the brake pedal during this time that you hear an increase in the vibration.

[GMCTech]

I'd have to agree with those that have told you motor mounts.

Hope this helps.

[R Crane]

I took my van to a very reputable mechanic and he believes that he has found the problem. 1st, he removed the serpentine belt and started the engine with all of the accessories disconnected. the vibration did not change! Next, he dis-connected the exhaust pipe from the engine with no change. Lastly, he dis-connected the torque converter from the engine and still no change! After all of this, he found out from one of his internet sources, that the problem is most likely with the balancing shaft. Neither of us had ever heard of this. Starting in 1994, GM starting putting this just above the camshaft to allevate vibration problems with the older V-6 engines. My van only has 71,000 miles on it. The balancing shaft has two bearings that it rides in. My mechanic thinks that the gear may have been installed a few teeth off from the factory? He said that if the bearings were going bad, there would be oil pressure fluctuation and this isn't the case. I am thinking about tackling this repair. According to the repair manual, it can be done without removing the engine. However, if the rear bearing is bad for the balancing shaft, then the engine has to be removed. Has anyone had any dealings with this repair?