I have a 2001 4X4 LT Blazer....Vortec V6.....when driving, the truck will suddenly slow, the tach drops to zero and the speedo jumps erratically. Plugs are new, fuel pump is 1 yr. old.....I have had a bad O2 sensor for awhile.....Its the aft-cat sensor I believe. Cat is about 2 1/2 yrs. old. Thought it was the ECBM and unplugged it....apparently not the case.....When this happens the truck is very hesitant to shift out of first when leaving from a dead stop. Usually a "goose" of the gas will fix it. This usually only happens after the truck is warmed up. Could this be a vacuum leak, catylytic converter, fuel situation or ICM ? Really hoping swartlkk will reply as he seems to be the resident expert on these Blazers.....Getting really frustrated trying to fix this. As soon as a mechanic gets in and test drives it, the problem never arises......thanks all !

 

Sorry for the delay in response. Notifications were on the fritz for awhile. Do you notice your security light coming on at all during this problem period?

 

I posted a question quite a bit eralier about power loss and a jumping speedo....Hasn't done it since October but today it reared its ugly head again....Going down the road about 60 the speedo will jump erratically and it doesn't want to shift properly. Called my mechanic and he suggested it may be a hydraulic problem in the tranny. Anyone ever experience this? The truck is a 2001 4X4 with a 4.3...........Sunshell was replaced about a year ago...I think that is irrelevant......

 

Your speedo is entirely electronic. If your actual ground speed is not changing along with the speedo jumping, then you have an electrical problem, not hydraulic.

*Merging with your old thread on the issue*

How about the question I asked back in August of last year?

Has anyone checked the connections at the VSS sensor in the back of the transfer case? Or the associated wiring to the PCM?

 

The truck goes in to the mechanic on Friday...He says he'll hook whatever gauges he can up to it to check pressure...its up to me how far he goes into it.......I just spent $1500 on a new sunshell and gaskets...obviously NOT the problem but I had NO tranny trouble for 140,000 miles and after the tranny work this happens...maybe coincidental.....I'll keep you posted...What else can I suggest he check? Thanks !

 

i am having this problem and my security light has came on before but it didnt stay on

 

If the security light comes on while driving down the road, that is not a good sign. Most likely cause is a failing ignition switch in the column.

Another member just replaced his but it did not cure his problem so he is sending me his original one which should be good. I am going to tear it apart and hopefully document how it works.

 

No lights have come on at all...no "Service Engine Soon " or "Security".....not even any ODB codes......

 

Last year the upper ball joint on the drivers side broke resulting in a severed ABS sensor cable. The mechanic resoldered the connection hoping not to disrupt the polarity....well it lasted about a week and there is no ABS and my "ABS" light has been on ever since....Could that severed cable be the result of the jumping speedo and weird tranny activity?.....I was told that all those sensors HAVE work together......any clues?

 

Well I am going to replace the hub assembly with an intact ABS cable....hopefully that will do the trick.....