2001 blazer 4x4 LT 128k miles

I think I have a tranny issue or something related going on with my car.

The previous owner said the tranny was rebuilt(at around 80k I think) but I am not sure who rebuilt it or how thorough of a job they did.

There are several things I have noticed:

1-There is a slight delay in shifting from 1-2. When the car is cold or when the throttle is lightly pressed, when its about to shift to 2 there is a delay, it stays on gear one, rpm goes up, and suddenly it shifts into gear 2. This only happens when im driving really slow or the car is really cold.

2-On highway speeds it rarely downshifts to gear 3 when I press hard on the gas. If I want to accelerate while I am already at 60-70 mph I have to either press the gas pedal to the floor or manually shift it to 3.

3- Delay in reverse engagement. When I put it on reverse there is a slight delay until it goes onto reverse. I can notice it well especially since i have front drive shaft ujoint issues. Theres alwasy a clunk when putting the car in reverse and I notice that it takes a while for that clunk and If I put it in reverse and press the gas before the clunking it feels like the car is in neutral.

4- This one thing I noticed very recently is that when im on gear 4 on freeway speeds sometimes I notice my rpm gauge moving up and down. Its usually at around 2k and it bumps from 1.8 to 2 randomly. The weird thing is I dont really notice a chainge in the sound of the engine and there is no shaking or rattling, just the gauge moving up and down.

Any input from anyone who has/had similar issues would be greatly appreciated.

 

I've only experienced number 4 and haven't got the slightest clue about it.

For me it seems to only happen under load (climbing a hill, accelerating slowly, pulling a trailer (not overloaded)) once at operating temperature on a day above say 65.

In those conditions, slight pressure on the gas pedal when the rpm is between about 1300 and 2000 will cause the rpm to fluctuate, which is noticeable as a pulsing sensation. I've discovered this to be the case in any gear when replicating rpm and load situations (different speeds of course for the different gear). This is alleviated by either forcing a lower gear to get rpm above 2000, or letting off the gas. She also idles fine in all weather and will not pulse or fluctuate under a firmer press of the peddle in those rpm ranges regardless of gear.

However with the north land getting cold again, I haven't been able to replicate for further diagnosis, so its going to be a while until spring when it gets warm enough to begin diagnosing it again.


That is unless someone has a definite answer to this issue. Could it possibly be not transmission related since my trans is shifting smooth without any complaints?

 

I have also experienced #4 recently with my '00 Jimmy. On a flat stretch of highway at about 50 or 60 mph, as I hold the gas pedal steady I feel the transmission shift down then up again. Also the rpm's will kick up a little then back down. I'd love to get input from other members on this one.

 

Check your trans fluid level, hot and idling in park. Add as needed. That might be your reverse issue. If not, the seals are drawing up and it takes a while for them to pop out and seal well. It will just get worse until the trans needs overhauled. Lucas trans additive might soften the seals and improve it for a while.



Your other issues may be a bad TPS. The computer uses the TPS signal to set the shift points, wrong reading and it shifts late, or doesn't downshift when accelerating. #4 sounds like the TCC lockup is kicking in and out. TPS or the brake switch can cause the computer to cycle lockup on and off.


Without test driving it myself while watching the datastream on a scantool I can't say for sure, but I would suspect these things.

 

Thanks everyone and I'm surprised that u guys are experiencing the #4 as well. I thought it was a rare issue that I was unlucky enough to have.

Anyways I think I'll change the tps as suggested, and hopefully it will fix all of those or atleast some parts.
Any possibilities that these can be caused by shift solenoids?

 

The shift solenoids just make the valve body engage the various gears, if they are bad you get wrong gear starts and missing gears.

I wouldn't start throwing parts at a problem hoping something will stick. You need to hook a scan tool to it and at least get any codes out of it. Autozone will scan it for free and give you a printout of the codes. Let us know what they are, if any, and we go from there.

 

I did, I scanned it with the blue driver. Only tranny code is about the neutral safety switch. My reverse lights turn on when I'm in neutral.

But just cuz there isn't a code it doesn't mean there is no issues. I had a vacuum hose blown and I had no codes

 

If the manual lever position sensor ("Neutral safety switch") is sending the computer the wrong signal, it can cause shifting issues. Thinks your in neutral instead of overdrive, for example. May just be out of adjustment, If you shift it into neutral a couple lines on the switch will align, if they don't then loosen the mounting bolts and move the switch until they do. One is on the main body of the switch, the other on the little rotor the shaft passes through. If they align and the problem is still there, you need to put a new switch in before you do anything else.

"Only tranny code is about the neutral safety switch." Were there other codes? The computer uses all sorts of sensor readings to affect shifting, such as the water temp, intake air temp, etc. Need to know all of the codes to get a complete picture.

Does your scanner have a datastream function? If so, you need to watch the following parameters while the problem occurs:

Gear selected (neutral safety switch reading)
Gear commanded (what gear the computer is telling the trans to be in)
TCC slip
TCC command, both the on/off and the PWM percentage
TPS percentage


The gear selected should match whatever position the shift lever is in.

The gear commanded should start off at 1st and change to 2, 3, and 4 as you accelerate. If the scanner reading shows an upshift and you have a noticeable delay (seconds, a half second is normal) then an internal component is likely slipping excessively during the shift.

If it is staying in 1st longer than you think it should (computer commanding the 1-2 shift late) make sure the TPS is not reading high. A typical light acceleration is usually 18-30% or so, much higher and the computer will delay the shift to give you better acceleration. With the key on engine not running, run the gas pedal through it's travel a few times watching the TPS percent. It should climb and fall steadily with pedal movement, if it doesn't, jumps around, or is way off from the amount of pedal you are giving it, the TPS is bad.

With everything warmed up, try a highway run and see if #4 comes back. If it does, watch the two TCC solenoid parameters and see if they are holding steady or fluctuating with the tach. Also watch the TCC slip, 0-30 rpm or so is normal when locked up, if it is jumping up higher with the tach that confirms lockup is disengaging. If the solenoid(s) are fluctuating, the computer is causing it, likely due to a bad sensor reading. If they are holding steady, you have internal trans or converter issues. If everything is holding steady,including the TCC slip, you have a wonky tach!

And look at all the sensor reading for the engine, anything obviously wrong like the water temp reading -40 when the truck has been running for 20 minutes. Also check the alternator voltage, too high or too low can make the computer whacky. If you have a good multimeter, also check for AC at the battery terminals. Engine off, you should read 0 AC volts, engine running anything more than a fraction of a volt can screw with sensor readings.

 

Besides that I have several other codes for the airbag and ABS system and one on the fuel level sensor reading. Because of that my fuel gauge readings arent accurate.

The only live data info I get from the scanner is mostly from engine sensors. I am not sure if there is any tranny live data but I will definitely look and see what I have. I might have the TPS readings.
I will update back

 

Checked my scanner, no live data for tps sensor or tranny live data. I checked fluid and added around to half a quart. It shifts better now but the reverse delay issue hasn't changed one bit...