1999 Silverado shifting problem

[jbnms99]

I recently bought a 1999 silverado, it has a 5.3 and 105000 on the engine and tranny! I don't know anything about transmissions, I have never worked on them, but everything else! I also have 0 codes to pull. My problem is that sometimes when I start it up and go to take off it acts like it doesn't want to go. It really confuses me because it isn't every time. I can gas it and it will sputter at me a little bit but not the engine. As long as I don't keep a lot of torque on it, when it gets to about 15 to 20 miles per hour it will shift and come out of it. The next time I go to take off it won't do that. It will only do it about 1 time a week and only when it has sit for a little bit. I have plenty of power otherwise! Can someone please help me out with this. I really don't want to take it to a transmission shop all of my local shops are crooks and always tell you that you need a new transmission! I took one of my older cars there and was told that and my father in law did the same thing except he didn't get it replaced and it ran for another 100000 before the engine quit on him and not the tranny! Thanks!

[j cAT]

Originally Posted by jbnms99

I recently bought a 1999 silverado, it has a 5.3 and 105000 on the engine and tranny! I don't know anything about transmissions, I have never worked on them, but everything else! I also have 0 codes to pull. My problem is that sometimes when I start it up and go to take off it acts like it doesn't want to go. It really confuses me because it isn't every time. I can gas it and it will sputter at me a little bit but not the engine. As long as I don't keep a lot of torque on it, when it gets to about 15 to 20 miles per hour it will shift and come out of it. The next time I go to take off it won't do that. It will only do it about 1 time a week and only when it has sit for a little bit. I have plenty of power otherwise! Can someone please help me out with this. I really don't want to take it to a transmission shop all of my local shops are crooks and always tell you that you need a new transmission! I took one of my older cars there and was told that and my father in law did the same thing except he didn't get it replaced and it ran for another 100000 before the engine quit on him and not the tranny! Thanks!

this could be engine controls or transmission shift issues or both .

when cold this transmission will upshift late . after warm up it should up shift at 12 MPH with light throttle.

with the engine not wanting to go on throttle increase this may mean a fuel pressure issue . measure this pressure it must be 53-62 psi.

If low you need to find out why.

low fuel pressures will not throw a code.

you need a GM specific code reader for any of these drivetrain/transmission codes if any are there.

I would drop the tranny pan inspect for condition , replace filter and use the new dexron VI transmission fluid. DO NOT USE DEXRON III ! GM HAS DROPED THIS FROM ANY USE IN THESE TRANSMISSIONS.......

[jbnms99]

Thanks for the information, I really appreciate it. It isn't the engine that doesn't want to go, it feels like the transmission, but it will shift seamlessly everytime. When it is cold it shifts a little bit harder until it warms up but then everything is perfect. This problem is so hard to explain because it is intermittant. Not every time I start to go when its cold, just once in a while. I think changing the fluid would be a good start, I have never tackled this job before... is it hard to do? How much transmission fluid should I buy? I know it takes alot. I wondered if it could be the computer since it shifts seamlessly? Is there a way to test it. I don't think it is a fuel problem either because I can rev it up and it is fine doesn't miss a beat and when I am having it do this I can shift into neutral and the engine sounds the same! Once I get to 15 mph or so this problem goes away and even if I am only going a block, turn it off and start all over it doesn't do it! That is why I am so dumbfounded by it!

[j cAT]

the MAF sensor can cause these type of problems. the engine torque being varied can get the tranny shifting weird at times. also the fuel pressures.

using MAF CRC MAF cleaner follow directions and spray down the small sensing wires of the MAF.. only need a small amount. do not use any other product. you can not see any dirt on these wires. a film forms on these over time then the PCM does not get the correct air flow to the intake . this then messes up engine torque .

you should see a faster smoother throttle response and may see some MPG improvements.

with the 4wd deep pan this will take 5qts. the hard part is loosening the shift bracket to drop pan. you need a torx bit with a 1/4 inch drive socket to get into this area. also some penitrating oil to loosen the corrosion for removal..

the pros like to bend these...do not bend. the drain plug may be working for draining if too hard to turn donot continue to try and remove. My drain plug was loctited in place. after I removed this pan I used a torch and got this red hot and then it came off 6pt socket..with NO tapered edge.

[jbnms99]

Thanks, I will definitely try that! Now I just need to figure out where my maf sensor is and buy some cleaner!

[j cAT]

Originally Posted by jbnms99

Thanks, I will definitely try that! Now I just need to figure out where my maf sensor is and buy some cleaner!

maf is between the air filter box and the throttle body. has a connector to it. you will need to remove from the rubber duct to access these small sensing wires...do not touch them just give a small spray to clean..

[slo99sierra]

Here's a thread on another forum that is a "How To"
http://gmfullsize.com/forum/showthread.php?t=179148

It's a good read. Everything you need to know the change the transmission fluid.

What you are describing sounds normal to me though. I've read a lot about people asking about this it seems like delayed shift is normal because of the ATF and components being cold. However it is possible that the current ATF in it is getting bad.

[transman618]

Several things come to mind here. First of all does it only act up after sitting for a while?? Does it act up only when its cold/hot?? Checking the fluid level and condition is always the first thing to do. Make sure the vehicle is on a level surface, the engine/trans is hot and the gear selector is in "P". If this is all good, I would guess at possibly either a converter drainback issue or the low sprag or forward clutches are causing it. Any of these things would mean overhaul.


transman

[4x4junkie]

i was thinking possible torque conevrter issue, like not having enough fluid in the convertyer. Had a comaro that did the same thing was a 87 model, the issue i found when it finally went was the torque converter was draining back, the pump eventually got damaged and quit pumping back into the convertor and i had to replace tranny and convertor.