Acceleration problem above 35 mph...

[kilroypr]

Well as the a good friend (Ripn12s) there are many things that can cause knocking. In my case even a broken exahust manifold would cause knock. If the tranny fails and make the engine jerk the knock sensor may register false knocking because insted of being from premature ignition would be related to exagerated vibration. So in this case could not be real. But nevertheless. Did you check all the air/fuel intake system that is clean and working properly? Because if you did and is supposed to be ok then this knocking could be related to exagerated engine/tranny vibration and not necessarily due to premature ingition

[roaddirt]

I did replace air and fuel filters, according my tests fuel pump and regulator works and provide pressure within specs. Removed air intake duct and cleaned throttle body, no impurities found.

Yesterday I was using my OBDII software again. This time I was able to enable some kind of "enhanced" GM diagnostics that gave me some more readings.
The most interesting was that I had random misfiring on cylinder 4 and under higher load cylinders 1, 2 and 3 would have some low misfiring counts as well but cylinder 4 was worst. I guess misfiring count was not too serious for computer to be alarmed and treat it as malfunction.

Considering this (and occasional spark retard) I wonder if my problem is ignition system or maybe dirty injectors.

I will check my Haynes Manual and somehow try to check spark plugs, wires and coils (especially cylinder four). Also I thought I could spray intake cleaner around intake manifold gaskets while the car idling and see if there is some vacuum leaks around cylinders.
Injectors and their connectors are hidden under upper intake manifold and there is no much that I could do to test them, right?

[rafraf77]

I have EXACTLY the same problem, but my car is 2002 pontiac grand prix. Funny thing it has warranty remaining... but when I took it to the dealer they did a test drive and said: "everything is fine"!!... nobody knows what am I talking about. I did the injection/throttle cleaning, changed tranny fluid, fuel filter...the car stills starts act poor at 35-40 mph. When I press the pedal harder it downshifts & accelerates really good until cruise speed is reached, then again engine sound becomes low and the car "locks". It is really annoying when driving at 40/50 mph and traffic is dense. Car is on 4th gear and RPM is jumping between 1600-2200
Sorry, It is hard for me to describe it accurately in english. I am a foreigner and it is my "learnt in school" language.

R

[roaddirt]

Thank you for post rafraf77,
EXACTLY the same problem in details. After bringing the car to my mechanic and dealership for diagnostic and getting "the car is fine", I do not know what to do. I got back to my old "trusty" Volvo untill I figure it out.
After my all diagnostic tries, I think I will have somebody check my catalytic converter and exaust. If they are partly plugged it will cause power loss, change vacuum and vacum change will affect the way transmission works.
I still hope that the transmission itself is not culprit :-(

How many miles was on your GrandPrix when you noticed the acceleration problem? Is your trany fluid level OK? Was there any change to fluid color since the problem started? Any burning odors?

roaddirt

[kilroypr]

Guys, let me tell you. Before breaking the new engine the car has now(Thanks God the waranty already sent a new one and I am installing it) when the engine was under load it would get a heavy missfire on 4 and intermitently on 2,6,3. Then when it broke was related to the car running really lean under load and the pistons that cracked were 3,5.
After the first time I got a heavy missing on 4 it would get it under almost any normal driving conditions without a SES. I even replaced the spark plug cables with MSD 8.5mm and still got the misses(less missing but still got).
Misses could be related to a clogged injector, worn spark plug cable, worn spark plug, bad ignition coil or too lean mixture that would not cause the air to ignite properly.
In my case I think could be related to the coils and AF mixture since when we took the engine apart to check what the heck happened all the exahust valves and headers where clean(No black dust what soever). So now when the new engine arrives the first thing I would make sure is that the AF mix is richer and that the ignition coils are correct. When a car is running lean could break internal engine components(Specially pistons) since the upper side of the piston is running really dry on the cylinder.
Bottom line check that the AF mix is not too lean and that the coils/cables are ok.
Roaddirt, IF the catalytic converter is partially clogged the hesitation would be constant.
As I told you before on my Z34(1993) I got the same behaviuor. When I replaced the tranny because it spraks broke the problem went away.

[roaddirt]

In another thread related to this problem, "Public" posted that his 1998 Century has the same problem and after several weeks a mechanic could not narrow down the problem. Public suspected EGR system problem and test ran the car with unplagged EGR. According to him the acceleration/hesitation problem was gone. He will now go and narrow down the problem to EGR valve, wiring, blocked passages or PCM.

I want to run every possible tests/check ups before I suspect a major component as trany or engine.

I too would like to run the same test. I assume that test running the car with unplagged EGR will not cause any damage to the car, right?

[94gpse]

I have a 94' gp with the 3100 and it does the same thing, around 35 40 mph I have to almost put it to the floor to pass. "Roaddirt" I think my car has the same problem as yours with the spark advance. Where did you get your testing equiptment and how much was it??? I would like to get it. Thanks

[kilroypr]

NOt really, just worst milleage. Remember the EGR is to let pass not completly burned gases back to the intake. Again, I am not sure if your hesitation problem is related to the EGR. I had EGR problems on my Z-34 and never cuased hesitation. Then when the tranny was replaced it all went away. But you are correct it is a lot cheaper to check the EGR than replacing the tranny. Go ahead and let me know, there is always new stuff to learn

[roaddirt]

Yesterday 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.

[roaddirt]

Originally Posted by 94gpse

I have a 94' gp with the 3100 and it does the same thing, around 35 40 mph I have to almost put it to the floor to pass. "Roaddirt" I think my car has the same problem as yours with the spark advance. Where did you get your testing equiptment and how much was it??? I would like to get it. Thanks

This OBDII scanner is for OBDII equipped vehicles only, generally from 1996 and later.

I bought PC based kit "Car Code OBD-II On Board Diagnostics" for my laptop from Car Code. That is a piece of hardware attached between your PC and OBDII port in the car and software dowloaded from their site installed on laptop.
This is home page http://www.obd-2.com/

I ordered VPW and ISO interface combo
ISO - for European and Asian cars, Chrysler
VPW - for General Motors

Single interface is $122, combo only $142 plus a few bucks for shipping

[94gpse]

Do you know of any software or any diagnostic equiptment that I could use on my 94'????

[roaddirt]

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 starts 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.

[andyd00]

Mines some what similiar but really missfires when i floor it.

[Ripn12s]

the 40mph lag is something the GP's have dealt w/ also. Remedy - DHP/CYA/INTENSE pcms

DHP has a 3-1 and 4-2 "skip shifts"

Roaddirt,
I'm going to have to aggree w/ the technition that its just the TC locking up. I can feel when the tc locks up in my car.
btw, did u get the misfire problem solved??
Check plugs and wires first before spending big bucks on other stuff

Tim

[spotts]

I have the same problem with my 1997 Grand Prix. Genisys says Knock sensors are picking up a knock other than spark knock and retarding the timing. The knock sensors can pick up almost any knock so I'd listen and see if you can hear abnormal engine knocks.