I have a 99 blazer 4x4that hasa 4.3with a 4L60E. The truck has 156,000 miles on it and from what I have learned and been told this would happen. It started about a month ago when the truck is going down the road at 40 mph(like in a 40 mph speed zone) it starts to bog severely the rpms drop to around 1,000-1,200 and almost feels like its only got about 20 hp. Now in the last couple of days when you take off from a stop sign the rpms raise between 2,000 to 3,000 rpm but the speedo comes up real slow. Then it will do it if your going down the road at like 40 ish the truck will bog real hard when you change lanes and step on it like to pass someone. It is more prone to this after its set all night or been setting for 40 mins. or more. In the last couple of days I am noticing it is just starting symtoms after its run awhile. I started thinking maybe the cat because I know that its the original one and I know when they get clogged it can cause symptoms especially when it only doeswhen its cold (running not outside temp). Now its started after its been running so now I am starting to think its the converter not locking up. I change all my fluids regularly and flush the trans regular and pull the pan to inspect. I just cleaned out the valvebody and changed the filter and fluid (the fluid wasn't burnt and smelled ok - normal in color). I also used a bottle of Lucas Trans treatment because of the mileage. So what do you guys think?

 

howdy muddyblaze, my 99s10 4.3 has 260.000 plus miles so i dont think its the cat. it sounds like a clogged fuel filter or aclogged pressure regulator in the plenum. the pressure regulatorscan have a smallleak and gobad, i wouldstart with the fule filter first and see if theres any improvement.

 

Ok, I will try that. I forgot yesterday I found out by accident I put it in 3 instead of drive and it quit doing it and as soon as I realized it I was at exactly 40 mph and put it in drive the trans shifted then the rpms dropped like it should then it sharply dropped to 1,000-1,200 and did what I call a dance (reminded me of a vehicle with a cam when you watched the tach. So at the next light put it in 3 and took of at about 45 when the truck would normally hit OD I manually shifted to D no rpm drop (as opposed to what it should do).

 

so your sayin from third to drive at around 45-50 its not shifting into drive or comming out of 3rd gear and the rpm's are not dropping.

 

If you were to put it in drive to take off at exactly 40 mph its like the truck has instantly acquired a fully loaded trailer and the rpms drop from like around I think 1,500 rpms to like 1,000 rpm and the tach starts bouncing from 1,000 to 1,200 and sounds as if it lugging the engine down (while its doing this if you give it gas the speedo will climb very slowly, but the rpms don't raise) once its at 50 it takes off and is fine. It also like for example I left school the other nightand there is a light about a block up the road that stays green for like a minute, so I stepped (by no means hard, I was at 1,500 - whats normal I guess taking off) and itshot up to 3,000 rpm but felt as if I was standing still and the speedo seemed to be stuck in time for about 2 seconds. I then took and startedlet my foot off of the gas, then when I stepped back on the gas it was fine.

EDIT: it also does it sometimes when I am passing at around 40 and accelerate.

 

ok around 40 its a sluggish feeling in the trans andit fills like you lost a gear under normal load, and when you give it more gas it sometimes throws the rpm's up and fills like it went to a lower gear. and if you let off the gas and step back on the gas it gose back to feeling ok. and it dose not do it consistantly or is it doing it morethe more you've been driving.
i had the same syptoms 6 mounths ago had to replace the tranny.
you can get the tranny inspected at a shop you trust probably free
just to be sure of the diagnosis .

 

Thats what I am thinking. And I am doing it quite a bit just about everytime I go somewhere and about twice per time I drive. Right now I am only trying to baby it, you know not flooring it when I don't have to and taking off easy from stop signs. I drive very sensible anyway but now I am more cautious. I don't want to blow the trans just drivin up the road and all of my normal offroading is suspended until I can get it fixed. I think I a could do it myself and I done other trans swaps and trans rebuilds before but I think I am going to go with a reman istead of a rebuild (better warranty). I'm all about saving money, so while everyone else I know has their projects done. I am little by little building a much better and more reliable vehicle because I believe it better to spend on the higher quailty stuff rather than the cheap crap.

 

Just had the same problem with a Buick. After $90, I finally checked the plugs, replaced and checked to make sure all injector wires are snapped in, #5 was not, after snapping it back in all the feeling that the trans was going to drop was gone, kinda makes an old mechanic feel like a fool

 

ITS FINALLY FIXED FOR NOW!!!!

Yeah, my buddy and I narrowed the symptons down to the lock up / unlock control solenoid and one of the shift control solenoid so luckly they still make them I posted the link below incase anyone else has this problem they will know what they need (So you also know what they look like).

http://www.eatmyshifts.com/pl_4l60e.htm#Solenoids

You can purchase them separtely of in a kit will all of them. (I know how my luck is I bought the kit).

This is what it will cost #60L. Fits 1996 to 2002. Cost $256.00
This is what is in the kit.
4L60E transmissions. Complete electronic kit including wiring harness, lock-up solenoid, 2 shift solenoids, force motor, 3-2 solenoid, PWM solenoid and pressure manifold. All as needed.

I was going to buy a new trans when I start my project but I think when comes time I just put a better converter and a shift kit along with replacing the worn parts. (I think it is a better and more cost and time efficent way to go).

Zach