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I have an issue with my 2001 Grand Prix, between 2,000 and 2,500 RPM (50-60MPH)the car tachometer begins to surge, or bounce up and down. If the car is given more gas the surging disappears, which eliminates a slipping transmission. Other than when presented with the above condition the car runs fine. This is more of an annoyance than anything, but do not want it to escalate into a high cost repair. Note:There is no malfunction indicator lights on the instrument cluster. Any help would be greatly appreciated.
 

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Tach is reported to the instrument panel by the PCM. The ICM is what sends the info to the PCM. Is the engine actually surging or just reported as surging by the tach?
 

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By the way thanks for the response. To answer your question the engine actually surges it is not just the tach acting flacky.
 

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rlee07 said:
I have an issue with my 2001 Grand Prix, between 2,000 and 2,500 RPM (50-60MPH)the car tachometer begins to surge, or bounce up and down. If the car is given more gas the surging disappears, which eliminates a slipping transmission. Other than when presented with the above condition the car runs fine. This is more of an annoyance than anything, but do not want it to escalate into a high cost repair. Note:There is no malfunction indicator lights on the instrument cluster. Any help would be greatly appreciated.
you might be having issues with the TCC soleniod inside the transmission, or the tcc/cruise brake switch. your vehicle is going into TCC lockup and then thinking that you're stepping on the brake, the ECM tells the TCC soleniod to unlock and process repeats... this occurs only between those mph and not able it is most likely that switch.
 

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Hi guys. I am new here and I was wondering if there has been any resolution to this problem. I have a similar type problem with my 02 GT. Mine only surges when the engine is in the process of warming up and the car starts seeing a load. The RPM will bounce 100-300 RPM. usually that happens for 2-3 seconds and it quits. If I mash on the accelerator a bit it will also go away. It only does it though when the car is warming up. Once it is up to temperature everything works as it should. The transmission was just rebuilt and the car showed signes of this problem before the rebuilt was preformed. I have no codes and the sensor readings look normal when I plug in my Auto X-Ray. you guys have any additional thoughts?
 

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very common to have problems with GM's factory fuel pressure regulators. mostly cold start issues, pulling off the vacuum line at the top of the pressure regulator and tapping it lightly with screwdriver [or some other good non-correct tool :)] will cause the fuel to "spit" out of the top nipple of the regulator. or just when pulling off the vacuum line sometimes there will be evidence of fuel in the line [wet].

if you have an aftermarket pcm/ecm sometime fuel trim programming will be not quite set correctly for cold start settings.

also if some type of ignition timing component replacement [ie crank/cam sensor, pcm/ecm] and crank sync relearn has not been done you may have a time delay while it "learns" what normal multipliers are.

my suspect is with the fuel regulator... too many to count for replacements that i have done.
 

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FreemenGMTech said:
very common to have problems with GM's factory fuel pressure regulators. mostly cold start issues, pulling off the vacuum line at the top of the pressure regulator and tapping it lightly with screwdriver [or some other good non-correct tool :)] will cause the fuel to "spit" out of the top nipple of the regulator. or just when pulling off the vacuum line sometimes there will be evidence of fuel in the line [wet].

if you have an aftermarket pcm/ecm sometime fuel trim programming will be not quite set correctly for cold start settings.

also if some type of ignition timing component replacement [ie crank/cam sensor, pcm/ecm] and crank sync relearn has not been done you may have a time delay while it "learns" what normal multipliers are.

my suspect is with the fuel regulator... too many to count for replacements that i have done.

The regulator was the first thing I changed. That did seem to fix the cold starting issue. Didnt do much for the surging issue. I am worried that either the fuel pump is going out or the intake gasket is blown due to a clogged cat. I was hoping though it might be a sensor somewhere that would be easier to replace.:icon_sad:
 

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msm500 said:
The regulator was the first thing I changed. That did seem to fix the cold starting issue. Didnt do much for the surging issue. I am worried that either the fuel pump is going out or the intake gasket is blown due to a clogged cat. I was hoping though it might be a sensor somewhere that would be easier to replace.:icon_sad:
sorrys i didn't read your first post correctly...

surging as in highway speed..... as in your TCC is coming on and off!... the 200-500 rpm bounce is the normal off loading of the TCC when it applies

well there are a few things there with highway cruising speed surge... first and quickest thing is to check and make sure that your _TCC_ brake switch is good... in some models they are intergrated within the regular brake switch, and in others they have a seperate one just above the regular brake switch... a faulty brake switch can tell the trans controller that you are stepping on the brake when in fact your foot has never been close to it... all the trans is looking for is loss of signal.
the controller doesn't see the correct signal [internal overheat/outside of resistance values even] and it will think that you're stopping, drops the TCC out to prepare for a stop. gets the signal back and locks the TCC back up...
rinse wash repeat!

a faulty TPS would do the exact same thing.. thinks you're going WOT and dumps TCC for a hard downshift, finds out that is not the case and comes back on line, and locks in the TCC again.

there is also a poor ground issue that is located on the upper unibody support that is the trans sensor ground [located next to the left upper strut tower] sometimes cleaning the surface of that and the ground eyelet then after retightening use an undercoating spray/ anti rust spray to cover the bolting point.

just things that i have seen... naturally you could have a bad TCC pwm or apply solenoid - those can be resistance checked for correct values.
 

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FreemenGMTech said:
sorrys i didn't read your first post correctly...

surging as in highway speed..... as in your TCC is coming on and off!... the 200-500 rpm bounce is the normal off loading of the TCC when it applies

well there are a few things there with highway cruising speed surge... first and quickest thing is to check and make sure that your _TCC_ brake switch is good... in some models they are intergrated within the regular brake switch, and in others they have a seperate one just above the regular brake switch... a faulty brake switch can tell the trans controller that you are stepping on the brake when in fact your foot has never been close to it... all the trans is looking for is loss of signal.
the controller doesn't see the correct signal [internal overheat/outside of resistance values even] and it will think that you're stopping, drops the TCC out to prepare for a stop. gets the signal back and locks the TCC back up...
rinse wash repeat!

a faulty TPS would do the exact same thing.. thinks you're going WOT and dumps TCC for a hard downshift, finds out that is not the case and comes back on line, and locks in the TCC again.

there is also a poor ground issue that is located on the upper unibody support that is the trans sensor ground [located next to the left upper strut tower] sometimes cleaning the surface of that and the ground eyelet then after retightening use an undercoating spray/ anti rust spray to cover the bolting point.

just things that i have seen... naturally you could have a bad TCC pwm or apply solenoid - those can be resistance checked for correct values.

I will definately check these items out. Yesterday on the way home when it surged (remember it only does this before the car reaches operating temp) the rpm bounce was less than 50 rpm. It was kind of like a hesitation in a carburetor. When i noticed it surging a bit I kept my foot on the gas and lightly pressed on the brake. After the brake pedal moved a bit I felt the TCC unlock and the rpm moved up about 500 rpm and the surge went away. On a related note I just had the transaxil rebuilt and this problem existed before the rebuilt. However I will definately check out the switch(s) on the brake pedal and I will look for that ground wire. The car came from up north so it would not surpprise me if I had a shaky ground or two.
 

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sounds like to me you have a brake switch overheat issue... the internals [from constantly passing voltage to engage the tcc] become overheated causing an overload or high resistance - dropping out the ground on the tcc [the controller commanding it off] the switch cools and starts working normally - rinse wash repeat. but on only a few secound increments.
 

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FreemenGMTech said:
sounds like to me you have a brake switch overheat issue... the internals [from constantly passing voltage to engage the tcc] become overheated causing an overload or high resistance - dropping out the ground on the tcc [the controller commanding it off] the switch cools and starts working normally - rinse wash repeat. but on only a few secound increments.
So the old switch checked out but I went ahead and installed a new one. Problem still exist but it is intermintent and sometimes worse than others. I am still thinking it is more of an enigne hesitation than the TCC.
 

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msm500 said:
So the old switch checked out but I went ahead and installed a new one. Problem still exist but it is intermintent and sometimes worse than others. I am still thinking it is more of an enigne hesitation than the TCC.
would suspect if you had a scanner and could read it that trans tcc slip speed [the ammount of torque loss in fluid coupling - comparing engine rpm to transmission input sensor rpms ] is matching your bobble in rpms... some is ok between 25-50rpm [non feelable] but wonder if you're having a 50-100 rpm slip speed change [would be noticable and also reflect on tac] they PWM it so it gives a cushy engagement of tcc so it doesn't hammer on [gramps and grans love not feeling anything in the trans shift points]

question dead spot on tps or the tcc pwm solenoid inside the trans... also wonder if your trans calibration is up to date if you still have an OEM pcm... not sure off top of head if there is an update to "desencitize" TCC PWM or allowing it to take greater varriance in PCM change before TCM would make adjustments.

if it was an engine thing you should be able to get the miss to happen within the same rpm band with a brake stand. [only do this for 15 sec maxs or clutch dmg may occur] i recommend using HI-Volt or some other thing to detect wire misses than to brake stand.
now that i say that... i have [on few cases] been able to get that to go away with one longer "wot" style brake stand [longer as being defined as under 1.5min] - my theory is that causing the TCC to stall for extended time may be freeing up some material that could be causing slip... kinda like a 3rd gear high rpm launch from dead stop to seat a new manual trans clutch - burns off the chatter marks.

LEGAL SPEAK ---> this is just a theory and is no way intended for a fix, repair, tsb, factory authorized modiciation, or proceedural update! this is just some idiot talking out his butt. :)
 

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FreemenGMTech said:
very common to have problems with GM's factory fuel pressure regulators. mostly cold start issues, pulling off the vacuum line at the top of the pressure regulator and tapping it lightly with screwdriver [or some other good non-correct tool :)] will cause the fuel to "spit" out of the top nipple of the regulator. or just when pulling off the vacuum line sometimes there will be evidence of fuel in the line [wet].

if you have an aftermarket pcm/ecm sometime fuel trim programming will be not quite set correctly for cold start settings.

also if some type of ignition timing component replacement [ie crank/cam sensor, pcm/ecm] and crank sync relearn has not been done you may have a time delay while it "learns" what normal multipliers are.

my suspect is with the fuel regulator... too many to count for replacements that i have done.
Scott, what do you do for a living? Like I dont know, but just wondered, you are up to date.
 

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donniearcher said:
Scott, what do you do for a living? Like I dont know, but just wondered, you are up to date.
Master ASE certified at this point in time to 09 and have been in dealers [2 - 1 for 5.5yrs chrysler, 1 for 6.5yrs jeep/gm auto trans mostly on gm] of last 12 years... till the previous year in may-ish [log story involving bad dealer location in the "hood" unions and lowest senority]

i do run my own shop on the side of a temp job [getting head straight and wondering if i want to go back to the rat race - you know - they are all the same bs different buildings and mgrs] still have many friends inside the dealers [imports and domestics for vast base of knowledge if i ain't got it] i also have dealer net access still that they haven't cut off up to this point... + backup routes into dealer databases for tsb etc.
 

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So the old switch checked out but I went ahead and installed a new one. Problem still exist but it is intermintent and sometimes worse than others. I am still thinking it is more of an enigne hesitation than the TCC.

Okay so now I am wondering If i changed the wrong switch. There are two switches on my car. One switch has a 2 pin connector plus a 4 pin connector. The other switch has a single two pin connector. Which one controls the TCC?
 

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Anybody have any idea what this second switch is? The parts department at my local pontiac dealer could not even tell me what it was.
 

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Anybody have any idea what this second switch is? The parts department at my local pontiac dealer could not even tell me what it was.
the one with the 4 pin will control the speed control and the brake lights

the 2 pin is the TCC dump switch... should be the one that is at the upper part of the brake pedal arm.

i cannot believe they could not tell you that? that parts monkey new?
 

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So i finally get a hold of one of the mechanics at my local pontiac dealer. He says that the upper switch is the cruise dump. And autozone lists a single switch for cruise dump. I am confused now.
 

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So i finally get a hold of one of the mechanics at my local pontiac dealer. He says that the upper switch is the cruise dump. And autozone lists a single switch for cruise dump. I am confused now.
i have not a wiring diagram to show you here... but i am 99% sure that the 2 wire is the tcc apply..

you see corperations are cheap... they build things to make less in engineering them... that same ONE switch with the 4 wires would be good for controlling brakes and cruise for vehicles with automatics and manual transmissions... the tcc apply is for vehicles only built with AT. now smart corperations would have a 6 way switch and make it all one switch... but [ahem] that is those that are not paying yet another engineer 6 figures to justify his job.
 

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On my car the TCC switch and brake switch are on in the same. Changing out the switch helped but the problem didnt go away untill i reset the PCM. I am on day three with no issues so far. Im keeping my fingers crossed. :D
 
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