This forum was so helpful when I pulled the oil cooler lines off my blazer last week and screwed the filter to the block... but I'm on to a new issue: NO OVERDRIVE! (4th) This is a 1996 blazer 4wd with over 200k. I had a junkyard tranny (4L60e) put in it a couple months back so I understand I could just be dropping another transmission, but how could I really have that bad of luck!? I'm seriously hoping this is some other issue as I WILL NOT put another transmission in this vehicle. Fluids fine and no leak. Allow me to give list of symptoms:

It did have overdrive for a little while after tranny was replaced. It slowly started to go. I noticed that it would hop into OD in the same place in the road everyday, if it was a long drive (not done often as I have a civic for longer trips) I might lose it again but after stopping for errands or what have you I would get it back for the trip home.

There was one instance weeks ago where the gas pedal stuck, another instance last night where after it hesitated to crank it sounded like it reved way up for a second before settling into an idle.

Now that I have it back on the road after fixing oil leak i also notice that when going down highway in 3rd (cause 4th doesn't work), i'm babying it doing only 50 to keep under 2500 rpms... when I let off of the gas the tachometer starts to decline slowly as it should then drops fast down to about 800rpms and bounces back up to 1000 rpms until I reapply gas. Sounds like it lost power in the downshift, almost feels like it's dragging.

it is sluggish at initial take-off but switches gears fine with no jerking 1st-3rd and reverse.

Oh yea, no CEL but my CEL isn't flashing on at start up to show it's working (just noticed this) so I will take it to auto zone for a scan hopefully tomorrow.

Can anyone tell me that they have had these issues before and it wasn't a failing transmission? bare with me, as I am a female who has only recently really started working on her own vehicles. I'm pretty good where knowledge is available, hoping to gain some more direction with this post.

TPS?
TCC?
I even read that ignition switches can do funny stuff to tranny. (or i'm way out on the limb)
if there is anything you can point me towards first that would be SO HELPFUL!!!

 

Your 4L60E is a 4 speed trans. From a standing start, the transmission is in first gear and you should feel 4 distinct shift points as you gain speed, the last one being the torque converter locking up. Once in 4th gear, depending on % of engine load, the torque converter will lock up, usually around 40mph, or slightly above.

When cruising at ~60MPH, holding steady with your right foot, just barely tap the brake pedal while watching the tachometer, you should see the rpm increase ~150-200rpm. If it increases, lock up is working. If you have the GU6 rear axle, (3.42:1 ratio) 70mph, in lock up, should be very close to 2000 rpm.

Really need to get the DTC's retrieved. If there's something screwy going on, it will set a code in memory.

 

ok, thanks! I will give it the brake tap test dealio on my way to get codes read tomorrow, though i do think i remember seeing it tach up slightly when hitting brakes at those speeds before. The oil pressure gauge and rpm needle drop bounce simultaneously when I let off the gas like I mentioned above. I took a video of it which I will post tomorrow if I come home with no other answers. I don't have a voltmeter or ohm-meter yet.. will advanced be willing to check out the TPS for me. even if there is no code i feel that's proably still worth checking too. I'll post codes tomorrow if I get any! Thanks again! By god, I'm going to figure this mf-er out.

 

Not sure if they can check TPS data, usually they just have code readers, and they can't access live streaming data. Keep in mind though, if there is a problem with a sensor, the PCM will detect it, and set a DTC in memory and turn the light on. Don't let them talk you into any new parts until it is properly diagnosed.

If you're at 2500 rpm at 50mph, you're probably right about it being in third gear. You've got 4th and OD that it's not even getting to! Might be a problem with 2-4 servo. You can actually get at it without pulling the trans out. While you're out driving, pay close attention to how many shifts you feel. Lockup kinda "slides in" with light throttle, and it can be tough to feel, easier to see it on the tach.

Post the DTC's, if there are any

 

well, i finally had some time to drive the blazer and take it to get scanned. It failed the stomp test if I did that correctly. No codes... but again, no check engine light at ignition. I guess I need to figure out how to get the CIL to light up again and then re-scan. I'm bummed... of course when you want codes you can't get them. It seems to do totally fine all the way up to third and like 45 mph then it begins to wind up. Sounds hung up when you let off acceleration at that point like it doesn't shift back down. I didn't do the stomp test at 60 mph because I would have been at like 3500 rpms and I've been trying to baby it so we at least have a second vehicle for short runs if necessary until I can get it fixed/replaced.

 

had my nearby mechanic plug it up to a computer while i drove. it shifted fine as usual up to 3-4 shift. He tried to command 3-4 shift and got notta, tried to force lockup, notta... tried to change shift points, notta. Meanwhile, while running at 50 mph my tachometer read about 2700 rpms... his computer said it was like 4400 rpms... but in all the other gears the computer read the same as my tachometer... ssooooooooo since i still don't have a blinking CEL at sttart up to show me it's working or anything saying their are codes... I'm starting to lean towards a malfunctioning PCM. Thoughts?

 

Did he mention anything about the 2-4 servo? Gotta get the codes retrieved and post them here. Very doubtful the PCM has a problem, when they're replaced, it's usually due to misdiagnosis. Typically if a shop can't diagnose a problem, they recommend replacing the PCM in an effort to scare the customer away. Not saying they never fail, but it's extremely rare.

 

i'm so lost on how to get codes when I can't even get my CEL to work. I changed fuses, and tried to scan anyway, but it's not telling me anything and it won't flash on when I turn the key. He didn't mention servo, but remember I'm a girl... he's not going to talk to me like that cause he thinks it's so over my head. this is my moms car and a few years back she had a rebuilt trans put in with a junkyard PCM. I know, PCMs are unlikely to fail, but anything outta the junk yard makes me wonder how long it will really work. meanwhile... what do you make of the non matching RPMS? The scanner said well over 4000 when trying to get to that 4th gear shift while my tach said much less... they matched up again between the tachometer and scanner when I came back down from that shift point. Thanks for your help, you're the man.

 

The CEL alerts you if/when there's a problem. It should come on with the bulb check, but if it doesn't, you should still be able to retrieve the codes. Older, (OBDI) vehicles flashed the CEL to indicate the trouble codes, yours does not.

When the scan tool indicated 4400 rpm, and the tach showed 2700 rpm, and engine speed was allowed to drop, did the scan tool show a smooth decrease in rpm and the tach stayed at 2700 rpm?

 

okay well, since i tried to scan anyway with no working CEL and got nothing I guess there are no codes. grr.
I was not looking at the scanner since I was driving, but he said at the 3-4 shift point it wasn't matching, reading way high on scanner... once I dropped in speed the rpms on tach decreased to their normal 2100-1800 range depending on how fast i was going. I don't know if it just fell off on scanner or if it smoothly decreased there too. I'm sure I can go find out tomorrow if that's pertinent info... i'll just make him do it again.