Intermittent issue - Jerking and Tachomter

[dkrusich]

I have had an intermittent problem with my 99 Yukon for the last couple months. The Yukon will start jerking after driving a few miles. Once started it will keep going until it sits for a few hours. then it may happen again the next day or not again for a couple weeks. Here is a video http://www.youtube.com/watch?v=gT9CWkz27qM

I have had it in 2 shops including a GM dealership service center. They drove it 25 miles and could not get it to jerk or act funny in any way. There are no codes except a pending crankshaft position sensor from long ago. We replaced it to be sure and it did not stop the issue. You can see in the video that only the tach is affected by this - what is the tach connected to that would cause this?

So far I have replaced the: torque converter solenoid and pump, transmission with reman from GM, crankshaft position sensor.

After thousands of dollars and weeks in the shop, I am very frustrated. Any help you can provide will be greatly appreciated.

 

[SunlitComet]

The tranny fuse powers the tranny solenoids and such as well as the tachometer and speedo. Based on your desription I would suspect at first that the power connection is flaking out in the wires, ignition switch or fuse block. When the power is cut off the tranny will do all sorts of weird stuff and it will vary with what gear you are manually selected in. It will also cause the tach to fail. As for the speedo it may just take longer for a power cut to effect it. Or it could not be a power issue. However the the tranny goofness and tach do share the same power supply line.

 

[dkrusich]

Since my initial post:

I did manage to get a code during an episode of jerking and loss of power. P0441 - most likely a secondary issue since I am not sure an EVAP solenoid could cause these types of problems.

I have replaced the ignition module and it did not solve the problem. the jerking/bucking issue is becoming more frequent almost daily.

What about a throttle position sensor? Anyone have any idea if this could cause the drivability issues?

 

[SunlitComet]

TPS? Yes it can but not so much on jerking issues. Look into the evap issue thoroughly you may have it a part leaking and effecting the mixture of fuel/air going in the engine and causing the bucking issue.

 

[dkrusich]

Finally isolated the issue to the crankshaft signal dropping out. I had already replaced sensor, this time I replaced the connector. The original crank sensor connector was covered in oil. So far the truck is running good again. Keeping my fingers crossed that this was the problem.

 

[SunlitComet]

Cool Beans.