jrhope

Unfortunately not. Mileage is down to about 11mpg. Seems sluggish and still misses or bucks. No one can seem to pin point the problem.

Please if you are able to solve it, share what you find and I will do the same.

levi3

Will Do. I just dropped it off at Chevy. I was told they are going to download updates to the vehicle. From what you describe wehave the same problem. I will keep you posted.

Thanks,

levi3

The download did not work. The coil was also replaced. The distributor is being replaced again. They are thinking we may have gotten a bad one.

kinger

i have virtually replaced everything other than trans and tq conv and ecm -- from dist to u-joints - rebalanced tires twice !!! still no luck vibrates when slowly push on throttle at cruising speed over 45 up to 70 mph --i am about to drive this thing on lake before ice melts !!!!

jrhope

No news on my end. The last week or so I seem to have more power, yet I have done nothing but drive the truck. I am not sure about mileage as I havent checked. I also did some towing which is where I really noticed the power gain, however it was pinging bad.

Did the new distributor help? This was one of my attempts as well, but I went with remanufactured. Still stumped........

jrhope

Dont drive it into the lake. I like to fish from time to time. I would bet it is not your tranny or convertor based on my experience. I fell for this diagnosis only to find nothing was wrong. Both only showed normal wear and had many miles left on them. Please see my original post. I too am very deep into this problem, and it is very deep into my pocket as well.

Stick with it, and please share if you find the problem.

in2pro

Its shot in the dark but what about the throttle position sensor or the vehicle speed sensor?

jrhope

I had tested the TPS some time ago with an ohm meter and didnt find anything out of the ordinary. However i thought the method was kind of crude and always suspected a possible problem. After your post I decided to replace it. The old sensor apparently had a broken internal spring and was sloppy throughout the sweep of motion compared to the new sensor so it needed to be replaced, but I think it was working. No noticeable change and the buck or miss is still there.

I was able to squeeze out 15mpg on a recent tank of gas. That is the best I've seen in a while. Yet I filled up today and Im back to 13mpg. I have been as low as 11mpg in recent fill-ups. I need to mention that these are all under the same driving conditions so my mileage is changing for some reason.

About the VSS...Are there other common symptoms I should see? Will the VSS trigger an MIL? Cruise control and speedometer appear ok if related. Does the ecm monitor this sensor while in open loop? I ask because I only see or have this problem when engine is warm.

jrhope

I recently came across a data logger and tried it to see if anything stood out. I noticed that this buck that I feel coinsides with what is a seemingly drastic timing advance. According to the logger, I am advancing from about 10° under load to 37° when I let off the throttle or reach cruising speed in a fraction of a second. Is this normal?

Also, I clearly remember the shop telling me long ago when the fuel spider was replaced, that they had a hard time getting the cam and crank sensors to sync up. Now, my distributor is rotated in the "timing advance" direction more than what I am accustomed to seeing on other vortecs. Usually the distributor cap wire connections are about 90° to the centerline of the engine block, right? Assuming that it is properly set up and has no problems. If the base timing is not set correctly, would it cause issues with the timing advance function of the ecm or cause these symptoms I have?

shamrock246

it could be the crank sensor mine failed and call for enouph timing advance at start up to stall the starter and rip teeth off the flex plate i'll try to attach the TSBDR-04.pdf



Sean

97 4x4 burb