I have a 1999 Blazer, 143k and I did the MPFI upgrade and a new fuel pump/filter maybe 1k miles ago as it had a hard start problem. This is a different problem I just wanted you guys to know the short history.

I have noticed that while accelerating that the blazer seems to shift late going from 1-2. It feels like it's shifting a little too hard for a 20-30% TPS signal (Yes I checked the live data) The 2-3 and 3-4 shifts seems pretty smooth but the 1-2 just feels like for example a car that is being driven easy but the transmission is acting like its being driven hard. (Like a badly adjusted TV cable on an earlier car) The transmission feels like it's shifting late. Maybe I'm too used to V8 vehicles as I had a 99' Suburban before this and it was a lot easier to accelerate under light throttle. This Blazer seems to need at least 40% throttle to accelerate even briskly. Past 50-60% it does accel quite stoutly but I don't feel I should have to put the pedal down that much.

The revs don't seems excessively high (2500-3k) rpm for a 1-2 shift. Is that just the way Blazers drive? I'm not really a fan of it. My suburban with 220k shifted smoother than this Blazer. Do these Blazers really need that much throttle to accelerate normally? I wish I could drive another blazer to see if it felt the same. 2-20% TPS doesn't really accelerate very well. It would take awhile to get to 60pmh at 15-20% throttle. To get onto a road to do 60mph I routinely go at least 60% throttle maybe more if I need to get going quick. Is this normal?

Also seeing as this is my first 4.3L V6 vehicle (I do have a 4.3L V8, L99 Caprice) is it normal that the engine makes noises around 2500rpm? Like a balancing type sound if you know what I mean. The engine feels like it has a vibration and makes noise at 2500rpm. A very fast vibration like the balance shaft or something. It could be normal IDK I just have never owned a 4.3L V6. Every engine I have ever owned has been A LOT smoother than this engine and I feel like that can't be right. There has to be something wrong.

Sorry for the long post I'm just trying to explain myself thoroughly.

 

Could the very small vibration I'm feeling be the balance shaft spinning at a high rpm with the motor? It just feels/sounds like something spinning and it not being balanced correctly so at higher rpms it vibrates just a little bit and makes noise. It's not the "balance shaft rattle" it's more of a humming vibration. I'll see if I can catch it on video.

 

So many views but no replies?

 

Observant...

TPS giving a smooth voltage sweep from closed to open with no jumps or sticky spots?

Beyond that, you'll need to dig into the pan and possibly deeper into the trans. It shouldn't shift like you describe. It could be a problem with the 1-2 shift acccumulator (shaft wear, cracked piston, and/or piston cocking and getting stuck in the bore). It could also be a problem with the 2-4 band.

The 1-2 accumulator is the one that is in the large aluminum housing attached to the separator plate along side of the valve body and can be replaced without pulling the valve body. Sonnax makes a pinless 1-2 accumulator that would alleviate the concern for wear on the pin causing bleed by.

While you have the pan off, I would suggest replacing the two shift solenoids off the back of the valve body. This too can be done without dropping the valve body, but be VERY careful not to damage the wiring harness.

 

Well I drove the Blazer for over an hour yesterday and on the last leg of the journey it was starting the shift really hard. (Like the tranny had an extreme shift kit) Even my wife noticed and asked what was that? There are probably 5-6 stop signs I hit on my way hom and it shifted really hard at all of them. Every gear shifted hard. 1-2, 2-3, and 3-4. The lower gears more noticeable obviously but it was shifting VERY hard. I did read something online that that is a common failure. (The bleed by you spoke of) Does those shifts sound like the problem you described, solenoids? Thanks for the help!

The TPS is very smooth throughout the entire range. Moving it slowly it read very accuratly and didn't jump around at all.

 

It's probably time to get it to someone that can put a pressure gauge on the transmission and look at the line pressure during these events. It sounds like you may be losing pressure when it warms up which can cause harsh shifts.

More often than not, low pressure gets solved with a rebuild, but best to get it properly diagnosed before jumping to that conclusion.

 

So I took a video of the blazer doing a 5-70 run and its quite obvious there is a problem with power. (It drives weak so figured I would try to prove it) Well I watched a 98 blazer do a 0-90 run on youtube and I got about 9 sec 0-60 and 12 secs 0-70 on the 98'. My Blazer did 12 sec 0-60 and 21.85 seconds on a 5-70..... Something is VERY wrong here.... It does have a starting problem and it probably needs plugs and wires but plugs/wires won't hurt performance that bad. If they were that bad I'll bet the truck wouldn't even run... The truck doesn't miss under load either. I have to check fuel pressure as it starts hard sometimes after being driven. The fuel pump, fuel filter and spider injector assembly are all only mayne 2-3k miles old (New intake manifold gaskets at that time too). Any ideas other than a fuel system problem?

 

O I forgot to mention the PCM did store a P0102 (Mass air flow Circuit A Low) and a P0507 (Idle Air Control System Revolutions Per Minute Higher Than Expected). I did try cleaning the MAF. Also these codes did not throw the SES light. I only found them when I was watching the Blazer's live data on my cheap scanner.

 

Also today I got a new code that also did not throw the check engine light... Code P1870 which I guess is some valve getting stuck in the valvebody from what I found. I think I have seen people talking about kits to correct this problem before it tears the tranny up. (Good thing its my extra vehicle so I don't HAVE to drive it) ANyone know where to buy the kit to fix this problem?

 

Well I think I'm having the worn valve in the Valvebody problem the 4l60e is known for. Does anybody know the number that is stamped into the valvebody? I'm looking to get a rebuilt valvebody but I need the number that's stamped into the valvebody.