Acceleration problem - is it so tough?

Vehicle: 1999 Buick Century
Mileage: 40K
Engine: 3100 V6
Transmission: automatic 4T60E w/vacuum modulator

The car has been checked by my regular mechanic twice, a transmission shop and a Buick dealer service shop in Richmond, VA with no success.

The problem is more noticeable when car warms up.
Once I reach wanted cruising speed of 35 mph or above (and the car changes to third or fourth gear), the car has a poor response on a slowly, steady press on gas pedal.

For a second it seems that RPM sound goes up and then it drops down with dull sound ( the car has no RPM gauge on dashboard). At that point I keep pressing pedal slowly but car does not accelerate or needs eternity to speed up.
Sometimes I do not even feel that RPM goes up even for that second.

At that point,
If I release and press pedal lightly once or twice, it will eventually “pick-up” and response.
If press faster or harder, it will downshift and speed up like a champion but I do not want to race.

Air and fuel filters, transmission fluid and PCV valve has been replaced - problem persisted.
So far I tried test-swapping used TPS, MAF, MAP – problem persisted
Fuel pressure within specs (40 psi in idle) and fuel pressure regulator holds vacuum.
Spark plugs and wires are original but they should be good at 40K, (GM says the should last up to 100K).
Poured a bottle of injectors cleaner in tank - problem persisted
Swapped vacuum modulator with aftermarket part – problem persists.
No SES light came, no malfunction codes set.

I love the car, it has low mileage and hopefully should give me years of service but I am desperate now. :disappoin

Any help would be greatly appreciated.

Roaddirt

I know it is tough, but there is no dumb sugggestion in my situation so please fell free to post any suggestion.
I replaced (again) trany filter and fluid with no immprovement. Reason is you can never be sure if a shop replaced filter and I wanted to eliminate plugged filter as a cause.

you are making thing hard to answer. try to hook up fuel pressure gauge and test drive and monitor fuel pressure.
see if you can check the exaust system.
roaddirt.i do not what to say

I myself do not know what to think. Every time I read something I start suspecting something else and try to test it but some things like checking if catalitic coverter is plugged or driving the car with fuel pressure gauge connected are beyond my knowledge.
How for God's sake I can drive with fuel pressure gauge connected in engine compartment and be able to monitor it? Hose is one foot long and Schreder port is half of an inch from running serpentine belt.
And I do not have scanner that could monitor fuel preasure readings either.

Food for thought...it is possible that the problem is normal. With the usage of overdrive and the lock up convertor, it is possible for the engine to be unable to respond well until the trans downshift or the convertor disengages. I am not sure that you are not trying to fix a normal condition. Ray

Well...I was thinking about that as well. I also have 1995 Olds Achieva with the same OD, 4T60E trany, and it does not do that. I has always driven it in OD and it runs "normal" like any other car I owned before.

I do not know if the 4T60E trany get some more electronics and more computer control since 1995, causing it to work different. I think have heard something about that though.

But again, this is something I never felt with any car before. If you do not press hard and downshift, the acceleration from cruising speeds above 35 MPH is so painfully slow that nobody would want to drive this car. I cannot believe somebody would design the car to run like this.

Did anybody heard anything about electronic control changes to 4T60E since 1995?

Every year there are updates done to the GM transmissions. Are you sure you have a 4T60E trans and not a 4T65E trans. GM has phased out the 4T60E trans in favor of the 65E since about 1996 or 97.

My User Manual says 4T60E. I also found info on Internet that Century 1994-2003 has 4T60E transmission.

"The 3100 V-6 engine is mated to a 4T60E four-speed automatic overdrive transmission, with an electronically controlled capacity clutch. It provides nearly imperceptible upshifts and downshifts and computer-controlled torque converter lockup for increased fuel economy."

Hey guys I am new here. Looking for answers to the same problem on my 98 Century. I will tell what I have so far 3 weeks with a good mechanic and he has no answer. I checked wiring to and replaced knock sensor. No help. Changed modulator valve $12, No help. My scantool showed EGR not ready or failed. I checked the EGR per instruction in Haynes and the EGR valve showes good but the harness plug did not. I left the EGR unpluged and the car is running great and the scan tool showes ERG passed???? Scantool also showes 4 EGR codes for failed circuit??? According to Haynes I need to check my harness and PCM next weekend. Hope this helps.

So you are having the same acceleration/hesitation problem and after disconnecting EGR the car runs well, right?
I would like to try the same test. I have no codes set, but I think that problem with EGR system half of times will not trigger any PCM codes.
Is it safe for engine to test run the car with unplagged EGR?

I am not aware of any problems with running the car short term with the EGR disconnected. The computer seems to make the required timming changes, so no knocking or pinging is noted. Long term it may affect the catalytic converter. Unplugging the EGR will set 4 codes and the service engine light will come on, but on my car results were instant. Autozone and some of the other auto parts stores will read and erase code for you if you need to turn the service engine light off after testing.

The other day I disconnected EGR and test drove the car for 15-20 min.
No change, car behaved like before. (This test set up SES light and threw a couple of codes that I all cleared with my OBDII laptop after reconnecting valve.)

Also, OBDII scan showed that EGR valve was opening properly under load. Commended EGR percentage was equal to actual (executed) which made me believe that my EGR valve was OK.

I wanted to check the air passage underneath of EGR valve for possible carbon blockage so I removed EGR and checked. No visible carbon deposits or blockage. EGR valve gasket has to be replaced if you remove valve.

Conclusion: EGR valve dose not seem to be cause of the problem.

Well, I have taken my Buick to another Buick dealer, again.
The car was well warmed up when Service Chancellor took it for drive with me on passenger side. As soon as we reached cruising speed around 35-40 mph, the RPM dropped down and the car exhibited famous “poor acceleration”.
He asked me if this is my problem and I confirmed. He said that was OK, the car behaved like it was supposed to. I was stunned.
He technically said “You need to keep in mind that Buick is a luxury car designed for smooth cruising, comfort and better fuel economy. Let’s say you want to cruise at 35 mph. As soon as it passes 35 MPH, first time you set up steady speed it will always switch to 4th gear and lock up torque converter, even if the current speed more suites 3rd gear. Being in 4th gear at 35-40mph will not give you any quick acceleration or passing power. What you need is to disengage “torque lock up” with any known technique like releasing and pressing pedal deeper, touching brake pedal or pressing harder to downshift. He said that PCM is not even so smart to disengage torque lock up when the car is going uphill and the car start bogging down. You need to press harder to downshift or even choose lower gear manually. WOW.

It seemed to me as a lot of leg shifting and science for an automatic trany. According to him the car is OK, it is design. My only problem is that I own a Buick Century.

My understanding was that other GM products like, let’s say Pontiac Grand Prix, will behave quite differently with the same engine and seemingly the same transmission due to sportier design targeted to younger people.

Comments are very welcome.

BAH! I think you got a bunch of double talk from someone who doesn't know what to advise.
I have a 2000 century and it doesn't do that. Maybe the lockup is occuring too early for you, but both Buicks ('86 & '00) I've had come out of lockup when you depress the accelerator slightly. Maybe you're going into O'drive too early. If you drive it in 3rd instead of OD does it work better? My transmission shop tech said the solenoud that drives the lockup will stick sometimes.

PS: My 2000 century has a 4T65E - Are you sure what you have there?

Sorry the EGR did not work out for you. By the way my 1998 also has the 4T60 and it does not behave as you describe (at least not anymore)

I said my 2000 century has a 4T65E, on my way home today I tried noticing when mine upshifts in each gear. It's so mmooth its hard to tell but It never went to 4th (OD) at a slower speed than 45 mph and the lockup occurred some time after that, but I'd need a tachometer to tell exactly when since its so subtle. If your lockup is happening at 35, I'd say thats too low a speed - no wonder you can't accelerate. Maybe some other century oeners can try light acceleration like I did and report the results. Any GM tech's out there who have access to official specs for minimum upshift & lockup speeds?
After consulting my Chilton's guide, it looks like Century's may come from a couple different GM plants and from the best I can tell the '99 model can have either transmission. There is only one engine oprion though 1995 - 2000, the 3.1L 160HP V6.

Sorry I was not clear. I understand that your 2000 has the 4T65E, however I just wanted to offer my experience with the 4T60, which is possibly what we are dealing with. The 4T60 can be identified by the plug location and the presence of a vacuum modulator. I just wish we could help get this car to function properly.

Just be glad you don't have an older A-body Century with the 2.5 engine and 3-speed automatic. 1-2 comes about 10-12mph, 3rd comes around 20-25mph, lockup engages between 30-35, depending on year and whether AC is on or not. Those cars cannot accelerate hardly at all in lockup until over 40mph.

My 1995 Century has the 2.2 Cavalier engine with that 3-speed automatic and is programmed slightly better. Engages lockup at 35mph under light acceleration with AC off, 40mph with AC on. I'm used to it, and sometimes I will turn on the AC if I'm driving a steady 35-39mph so it won't engage.

The 3100 is a torquey engine for its size and type, but low rpms will still cause this lag. You may consider driving in "D" (3rd gear max) when you know you won't exceed 40-45mph. I forget the AT shift pattern on the 97-up models. Should be P R N @ D 2 1, you can choose "D" until you get on freeways. If there is no "D", there may be an overdrive off button somewhere, or a "3" position which is the same as "D".

Or, with practice and experience you will determine the right amount of throttle to keep your lockup converter from engaging.

Also, a light tap on the brake (with the left foot) will disengage the lockup converter long enough for you to squeeze in a little more throttle.

I like early shifts and early lockups, because I drive relatively slowly for the best possible mileage, and unless I'm going up a hill, my 247,000 mile 4-cylinder accelerates just fine in lockup from 40mph on up to 60-70. It is a very rare (a couple times a week, and I drive 1200-1500 miles weekly) occasion when I am forced take the car out of lockup with more throttle or a tap of the brake.

In other words, it's normal. So get used to it, or try one of the suggestions offered here (like keeping out of overdrive til you're going over 40mph). Test drive a new 2004 Century, or any other mid-size 3.1/3.4 with a 4T60 GM offering (Lumina/Impala/Intrigue/GP), I'll bet it will do the same thing.

I think you may be fighting something that is normal. The manufacturer's need to eek out as much fuel economy as possible and low rpm's help them to achieve that. If you drive in 3rd gear rather than OD, you should get a little mord spirited performance. Third gear driving usually lets the ECM/TCM provide a little more aggresive shift curve.

Several days ago I test drove friend’s 2001 Buick Century. I could feel when it go in overdrive around 40 mph (mine do that at 35mph instantly) but it would “unlock” and start accelerating as soon as I slightly pressed acceleration pedal.

On the holiday weekend I drove to NC and the problem was present all the time even at speeds 70-80 mph. It felt like lack of power and hesitation especially driving even slight uphill. There is definitely something wrong. I still switching between “engine problem or transmission problem” question, but it is definitely a problem.

Like big says, maybe it is going in a bit early. I have a regal 4t65E with rough shifting probs, one thing I've learned is that mine learns. Over time the car modifies the way it shifts based on clutch wear and driving habits. Maybe yours learned to be slow, you can have these learned points cleared, I think it may take a while to see what comes of it... i am not expert though, it is just another direction to go in.

I have the same problem as I have read from the very top of this discussion. I have a 2001 Buick Century. I am not a "car" person, but all I know is that recently my car has had some serious acceleration problems.

I live in Bisbee, AZ, which is high in elevation. I travel to work, 60 miles round trip, and consists of extreme hill climbing. As with the first post, if I push down on the "sweet" part of the pedal the car will hesitate to accelerate. RPM go up and down down, very quickly. Also, I have noticed a drastic loss in MPG. I usually get 29 mpg, but I'm down to 26 mpg. Also, the problem seems to be getting worse. Just taking off it is starting to not want to accelerate. Also, if I push the pedal way down, as in to pass, the car will only drop into 3rd gear.

Today, I could only go 70mph; not enough to pass. :( Needless to say, I started thinking about the fuel filter (I noticed this problem in my 65 vw bus), and maybe the sparkplugs.

However, after reading the online posts, I am wonder what I should do myself. I am seriously debating seeing a mechanic, but now I am wondering if I should save my money and see what comes of this conversation.

BTW: I replaced the fuel filter about 30k miles ago. (My car has 82k)
Thanks...
JB

Yeah, when my EGR went bad I could barely get to 65 mph. As I would go up over a bridge I could not maintain 65, it would slow down to 55 or so before I got to the top. Good Luck. You may need it, My Century is one problem after another.(see post in nonspecific section re: which Buick should I buy?)

Hey Roaddirt. My wife owns a 1996 pontiac bonneville which happens to have a 4t60e tranny and acts up like yours. I have done a bit of research online and have seen that the problem has been caused by the internal shift solenoids on many occasions. but try to catch it quick because, although there may be no relation, my wifes car lost 2nd 3rd and 4th, which if you look up is also caused by solenoids. apparently there is a common grounding problem with the 4t60e's. I hope that you find this helpful. replacing the torque converter while the tranny is being serviced would also be reccomended if you can budget it at the time.

Hey Roaddirt. My wife owns a 1996 pontiac bonneville which happens to have a 4t60e tranny and acts up like yours. I have done a bit of research online and have seen that the problem has been caused by the internal shift solenoids on many occasions. but try to catch it quick because, although there may be no relation, my wifes car lost 2nd 3rd and 4th, which if you look up is also caused by solenoids. apparently there is a common grounding problem with the 4t60e's. I hope that you find this helpful. replacing the torque converter while the tranny is being serviced would also be reccomended if you can budget it at the time.

Welcome to AF.

Sorry but our community rules prohibit raising old threads that are too old. This one dates back to over two years ago. It serves no purpose and there is no continuity in the discussion.

Thread closed.


POSTING IN CLOSED OR OUTDATED THREADS:
If a thread has been closed, there is probably a logical reason for it. If you feel that the reason(s) for closure of the original thread are unjustified or wish further clarification feel free to contact any member of the moderating team. However, do not start a new thread about another closed thread.

Please avoid posting or voting in outdated threads. It merely clutters up the message board and makes it more difficult for fellow members to sort through the vast amount of information contained on the boards. If you have new and important information to add regarding a past discussion, feel free to start a new thread and if need be, add a link to the original thread.