some interesting car trouble

[Sledgehammer427]

Hey, I hope there are some car gurus out there who can help answer my question.

I drive a 1995 Oldsmobile Cutlass Supreme SL with a 3.4 liter DOHC V-6 (the biggest fitted to these specific cars) and the 4-speed Hydra-matic transmission

I love my car and it means the world to me, but the transmission has been having some issues that are really irritating and I'm afraid of what it might mean farther down the road (no pun intended)

Now, for the trouble. It only does this when the engines warmed up and I've been driving it around for a while (lets say, a 5-6 mile run into town to get McDonalds for the family, it would do this on the way home)

When it goes into overdrive, it will stay there, but any amount of accelerator I add will make the Overdrive try to kick out (upshift) and it isn't happening, so it rhymically pulses from accelerate to overdrive and I'm not gaining speed at all and it's not very comfortable to sit in and experience.
I know how to fix it as I'm going along, I just jiggle the gas pedal for a couple seconds, it stops pulsing and I accelerate to the speed I want, and I can set the cruise control and as long as we don't go up any hills it won't do it until I want to accelerate again.

it ONLY does this in overdrive, in-town driving is fine.:hmmm:

I swapped the transmission filter and put new fluid in it, I've run some store bought "transmission conditioner" through it and I checked, there are no metal flakes indicating some nasty grinding going on in there.

I'm at a loss at what it can be, anyone have this happen before?

[UnderseaLcpl]

I'm no expert on automatic transmissions, but it sounds to me like a problem with the vaccum modulator or pipe. If you can find a technical manual for your vehicle, I'd suggest locating the pipe and checking for leaks. The vaccum modulator measures engine load and manipulates the throttle valve, and if the vaccum pipe is leaking, you're likely to get sudden shifts in power output as the vacuum builds up and then bleeds away.

Again, I am no expert, and I'd recommend getting a second opinion, but that's my suggestion.


In related news, I hate automatic transmissions.:stare:

edit- I just got off the phone with my brother, who is more knowledgable about these things than I, and he says there could be a computer problem as well. What it might be or how one would go about fixing it, I have no idea.

[Sledgehammer427]

I'm no expert on automatic transmissions, but it sounds to me like a problem with the vaccum modulator or pipe.
I got the Haynes manual but I never took a really good look through it. I'll have to do that. sounds like you could be right.

he says there could be a computer problem as well.
hmmm, if there was something wrong with the ECU wouldn't there be more messing up? It's accumulated a lot of mileage (previous owner lived in wisconsin, the I-Pass holder tape is still under the mirrir) so I assume it must be wear on something else. It's hard to say at this point.

In related news, I hate automatic transmissions
+1, I want to find a Getrag 5-spd manual for this car eventually. it's bloody fast as it is, I can cover 0-60 in about 9 seconds, that's not bad for an all-metal Olds. I want to get a manual in it so I can manage my mileage better. my first car was a stick shift and it's kind of an affair.

[UnderseaLcpl]

hmmm, if there was something wrong with the ECU wouldn't there be more messing up?


Sorry boss, I wouldn't know. The extent of my knowledge of automotive computers is the awareness that they exist.:oops:

There's bound to be someone else with more automotive knowledge about, though. Perhaps they can shed some light on the subject.

[VonHesse]

Just got off the phone with a buddy of mine that's been rebuilding automatic transmissions for twelve plus years, and he suggested that while it may be any number of things, it sounds likely to be a sticky "overdrive valve body" due to the fact that it corrects itself after jiggling the gas pedal.

Unfortunately, there's no way to be sure what is really wrong without taking the transmission out and visually inspecting all the bits and pieces.

If it is a sticky "overdrive valve body," it would be caused by a general build-up of gunk in the transmission, but just changing the fluid (while helpful) won't clean the gunk off of the valve body. He recommended that before you pay to have the transmission torn apart and rebuilt, that you try using a transmission flush/cleaner on it. That will actually clean any gunk or residue off of the parts, and if it fixes the problem, you've saved yourself $1,000's of dollars on a repair bill.

Again, it could be any number of things, but that was his recommendation.

Good luck.