How does your speedometer work? A malfunctioning VSS sensor, especially at low speeds, can cause the PCM to start in 3rd. This can happen when high stall converters are used as well because the PCM sees a lot of slip and things there is a problem.

 

I sense nothing wrong with the speedometer. It is a standard gauge readout, as opposed to digital, and it appears to remain in step depending on how fast I am accelerating or slowing down. Thanks again.



Benjamin

 

i have the same issue. except the fact that my moms 2002 4x4 has been throwing all sorts of codes. maf sensor, cts and trans. shift solenoid b, oxygen sensors and catalytic converter have all been replaced and it was just recently that it started acting as though i was in 3rd gear. some moron put in etholene glycol in the resivior instead of the proper dex-cool so i've been flushing that system also. during the inspection i found that the ignition coil has a crack on its mounting area would that cause a problem causing all the sensors and transmission solenoid to throw faults? my other thought was the egr system but without the proper equipment its hard to properly perform the test procedure

 

To both of you with problems.

Pull the tranny dipstick and smell it, does it smell burnt, if so your tranny is toast.
Is the fluid red or black, red =good, black = bad.

Now onto the more realistic problem, with a little background. The computer controls the engine and tranny as one unit. It reads various sensors and makes adjustments to the engine and tranny shift points based on those readings. 9 times out of 10 when people report tranny problems its not really the tranny malfunctioning, its the engine. If you have either of the above conditions, burnt dark/black tranny fluid your in the 10th category.

The biggest problem with engine performance as you discribed is either a faulty ignition system (typically the distributor cap) or leaking spider injector assemble, another posibility is vacuum leak (vacuum hose or intake manifold).

One of those is typically the culprit, after that we get into things like EGR, MAF/MAS sensor, etc. Do you have an aftermarket air filter, like a K&N? Those things a natorious for depositing oil on the MAF/MAS sensor and causing all sorts of engine/tranny performance issues.

The key here is the moisture. If your truck runs better when its raining, typically that means you ahve a crack in teh distributor cap. The other option is you have a lose electrical connector on the tranny. Look for the wire pig tail on the passengers side towards the back, unhook it and make sure its dry, then reconnect it.

To check for a vacuum leak use a spray can of either, spray it around the engine compartment while the engine is running, if your rpms go up, you found a vacuum leak. False air is another posibility, false air is air that gets in the intake manifold by a means other than through the MAS/MAF sensor, like if the intake hose is disconnected or cracked by the intake manifold. The computer wont be able to compensate for tha false air and it causes performance issues.


As for the downshifting, nothing wrong with it like Kyle pointed out. The tranny has an overrun gear, when you down shift the tranny will spool up until it matches vehicle speed and then start to decelereate. And no you cannot get your tranny to shift gears while going too fast, you may be able to move the lever, however it wont downshift. As for upshifting, it wont shift any higher than you go with the shift lever. However you can blow up your engine downshifting too soon, or upshifting too late. Wathc those RPM's, that pretty red line isnt just a cute color to break up the look of hte dash!

Thses are not high reving engines, they gain most of thier power under 3,000 rpms. In most cases under 2,500 rpms. Sure red line is like 4-5K, however itll be sreaming bloody murder at those rpms.


I hope that helps.

 

thank you. i know that some of the vacuum lines don't look the best but i couldn't find a leak. i have not tried the ether yet but i will here in a few minutes. also i noticed that after running the vehicle and shutting it off roughly 5 minutes afterwards the fuel tank plinks (either expands or contracts and makes a sound) i know that has to do with the evap. system and i had to change the fuel pump about 2 months ago. i'm getting ready to replace the coil its got a hair line crack on one side. so hopefully that $40 part will help fix the issue i will check the rest and let you guys know what i found out. thanks again

 

OK , I had these same issues with my 2000 ZR2( Not *** dramatic ) . Low horsepower in low RPMs not shifting correctly. A post on here under ( Low Horse Power ) recommended cleaning Mass Air Flow sensor . I pick up a can of CRC MAF Sensor cleaner for 7 bucks , cleaned sensor as directed on can . Cured all power and shifting problems. It is an easy and cheap thing to try .

 

But the Blazer is not an Astro Van is it?

 

We had the catalytic converter replaced a few months ago like i sad in my previous post. Well the muffler shop put on the first cat with the heatsheild facing away from the transmission leaving the transmission vulnerable to the 900+ degree temps. They also bent the exhaust in a few places making it sit about 1/4 in away from the passenger side of the pan. On the blazer all the shift solenoids sit on the passenger side. Taking the blunt of the heat.
So I took it to the shop and moved the cat at least 3 in away and put another heat shield towards the transmission. I then dropped the transmission pan replaced solenoid 2-3. I then thouroughly cleaned all other solenoids checking each one trying to be sure no others were going faulty. After reasembly and a new filter I power flushed it with 4 gallons of trans fluid.
Now it shifts properly and the temp is correct instead of being the same temp as cat. If you are still having a problem with your blazer crawl underneath it with a temp gun and check the temp of your trans pan and compare it to the temp of your front cat if same temp I recommend doing the same except identifying the faulty solenoid. Good luck!!!

 

ok i read this and just had to have a laugh....now this issue could be a matter of opinion but heres mine.
1) in the DMV book it states that using the downshift method while coming to a stop is the right thing to do, but thats with a stik shift, but whos to say u can't do it with a auto without shorting its life span.
2) you say that an auto is not designed to slow down a 4000lbs brick and would mess the tranny up, but that same tranmission is designed to accelerate a 4000lbs brick from a dead stop with out messing it up?
3) i commonly use this method to slow mine down and keep my brakes life longer or to keep from warping rotors, its not technically using the transmissio to slow down its using the engine rpm to slow down. when u do this your basically just changing the gear ratio and using rpm's from the engine to match that gear ratio. correct me if im wrong on that but its how it seems to work to me.

 

Maybe some searching on Throttle Position Calibration/Testing could help. On previous generation (700R4) they used a Throttle Position cable that modulated line pressure to determine when to downshift. Since that is gone on an electronic trans, you will be running off the Throttle Position compared to VSS(transmission output speed). No VSS signal results in some weird stuff. Possible loss of any or all but first gear.
I have not done lots of work on these yet, but that would be a good starting point.

As far as using the trans to deccelerate, the only downside would be that the converter could be heating up fluid more and would create more heat. Heat is the mortal enemy of a transmission. As long as that's not causing you any problems, the computer should prevent any harmfull downshifting if speed is to high.