i bought a 2000 blazer and now when it shifts from 1st to second at slow speeds it jumps like back to first then to second back and forth but if you give a gas it will shift fine and go about normal shifting and adcelerating it only does it at the first second shift at slow speeds the fluid is full and looks to be not burnt i havnt changed the filter yet iv only had it for a week and it started doing this about 2 days of owning it

 

i would check the vss against the abs wheel speed sensors for the vss running slow. tps could have a dead spot and a real tricky one is a map sensor reading(low vacume) caused by a vacume leak. if the map sends a low vac reading back to the pcm, the pcm thinks load is high and downshifts, thats what pops into my head. get a scan tool and watch these things, and watch all live data for anything outa range. could be a bad map switch in the trans too, not reading adequate pressure when 2nd gear is applied or trans fluid temp sensor reading too low which is also part of the map switch in the trans. tell us what u find and go from there

 

thanks for the info ill check what you said what is the vss and how is it checked? i drove it tonight and manually shifting it works fine and after a hour drive it didnt do it as bad

 

vehicle speed sensor, in the tail shaft of the trans or it 4x4 tail of the t-case. a scan tool is nice, but to start use your speedo, is it jumpy or does it fail to raise from 0 until your over lets say 15 mph? this isnt as easy find for a diy'r, no offense be prepared for some diag time. without a scan tool you will not be able to go to far w this one. also thinking, the 1-2 upshift solenoids internal windings may be getting weak, is this operating temperature sensitive?

 

ok im picking up a vss tomarro, the speedo i belive works fine never noticed it the tack is kinda jumpy where can i get a scan tool is it the same thing the auto zone uses? for check engine lights? thanks any help would be nice as i bought this for my wife and now she not to happy about the possibilty of dumping a lot of money in it

 

I believe that the tach runs off of the CMP sensor (camshaft position) which is located in the distributor.

You can test the TPS sensor with a typical multimeter by back-probing the wires at the sensor itself and monitoring the voltage. There will be a ground, +5V reference, and then the sensor return. With the key on, engine off, the sensor return should show ~+0.5V at closed throttle and ~+4.5V at wide open throttle. This sensor can also be monitored using a capable scan tool as trucktom stated.

I use the term "capable scan tool" a lot because there are many generic scan tools that only list the generic OBD2 (P0xxx) codes and nothing else. You need a scanner that can display live data. I know that the TPS values are in the generic OBD2 data set so a GM specific update/upgrade is not required. The scan tool that Autozone/Advanced/etc typically use may not be able to display live data and even if it could, the employees rarely know how to access those features.

 

i had to order the vss will be here in the morning . im thinking of just replacing the tps . where can i get/barrow a scaner if i have to buy one where is the best deal on it ? thank you guys for the help this forum has became i life saver i i just leanred about the 4x4 not working and looked it up on here was a big help but that is a small problem not as big as getting it driving right as its her dd now

 

Hey everyone, Im brand new to the site. Its really amazing but wildhawghunter and my problems are Identical. Just bought my 2000 with really low miles on her for my wifes daily driver and she is not happy. First problem was Multiple cylinder missfire come to find out I had a bad headgasket so had every gasket replaced on the engine, now its started with this. Take off and first gear is ok but when shifting to second the engine will rev high and low just as it would feel if it running out of fuel. If you get down on it, It will shift fine, no problem. I was also told that if you disconnect the battery for a certain time and it stops for a while it means something. Im almost positive we have the same problem. If you find out whats going on before me please let me know. Ive been told the speed sensor or the teeth on the distributor or the shift solenoid and also could be the tranny wiring harness. My wife is pissed, I hope we can help each other out. Appreciate your input

I forgot to ask, Do you have a check engine light on? mine doesnt

 

i hear ya on the pissed wife i put the new vss in tonight and nothing better what i did figure out was going down the road slow it shifts throught the gears fast at like 20 30 it was in over drive and it bogged down as its to low of a gear to go that slow i disconected the battery and nothing as to testsing the tps there are two sensors one has 3 wires and the other 2 the 3 wire one i think is the tps is on the other end of the butterfly if thats it witch wire do i test.

 

Only had a minute today, stopped by the backwoods mechanic and he said hes seen this in other blazers of this year also. He said that usually the number one problem is a loss in voltage in the tranny wiring harness, he didnt have time to diagnose so I scheduled an appointment with him hopefully this weekend. He said even if I can get up under and make sure all connections are tight that I will see a big difference in the way that it drove. And he also said that the problem might be the upper intake not tightened to the correct specs. I dont know if your has been apart but mines been down to the blocks for the repair to he headgaskets. And Im still curious does yours have a check engine light? As of the correct wire for the tps, I have a ford sitting in the driveway, 95 so im still learning on the vortec ordeal, But if you find out please keep me posted. I figured what Im doing this weekend is going to the junk yard and getting a little of everything. Im scared to death that something silly as a wiring harness is bad and Im going to end up ruining the tranny. But if this dont work out I got a chevy Ill sell you, On a good deal...Appreciate it