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Car bucks/surges in 3rd gear under light load.

T

thegoose

New member
Hi all. This is my first post on this forum and I hope you can help. Bought an '07 Grand Prix for my son for school and have noticed a bucking/surging with RPM oscillating around a few hundred revs when under light throttle on a slight upgrade. At first I thought it may be shudder from Torque Converter but can also happen when selector is in 3rd gear. Accelerating seems to cure it. Any thoughts will be appreciated. Thanks
 


Sounds a bit like an ignition issue to me. Maybe coils, wires or plugs. Do you have anyway to look for misfires while it's doing it?
 
BillBoost37 said:
Sounds a bit like an ignition issue to me. Maybe coils, wires or plugs. Do you have anyway to look for misfires while it's doing it?
Click to expand...
I have the Bluedriver OBD2, yet still playing with it. No codes present. I realise that there may be no codes present and live data would determine misfires if present. I have heard about TP Sensor going bad. I will try my best diagnosing the problem,It's getting cold here in Canada now but I will keep you posted with any updates. Again,thanks to all those who have replied.
 


[FONT=Verdana, Tahoma, Arial, Calibri, Geneva, sans-serif]3rd locks at under 44% throttle. These are stock 07 tables.[/FONT]
 


I am finding the Bluedriver OBD2 beyond my technical abilities at this time.Hooked up a regular plugin OBD2 scanner and under enhanced GM DTC codes found a P0703 (Brake Switch B input). Checked that brake lights worked and functioned correctly and they appear to at this time. Cleared code and will update if the code returns or I notice any changes. Thanks again guys on the inputs,I really appreciate any and all suggestions fired at me. "Billboost37"-have yet to check ignition system yet as Bluedriver doesn't have the ability to select misfires for the GrandPrix (or am I missing something),"Fordman77"-If gear selector is manually in 3rd,Torque Converter lockup should not occur-correct?
 
Correct me if I'm wrong, but there are no different tcc apply/release tables in the PCM for manual shifting. That's why i posted the images to give you an idea of the tcc control.
 
Thank you for the reply. Do I then assume if gear selector is in 3rd and NOT drive, then this buck/surge issue I'm having points to a problem other than the transmission? Going down the possible ignition,TB(throttle body) route I go if that's the case. I did do a quick visual inspection of the ignition system checking for any loose,damaged leads,coils. I did notice the leads were made by Delphi (labelled) Are they OE?
 
I think the thing is that you would probably not see 3rd lock in manual without really trying. Try driving constant at say 30mph with as little throttle as necessary to lock the converter. Hold the speed steady and see if it surges.

Like Bill said, scanning for misfires would help. If you can't scan for that, can you scan sensor 1 O2? You might see it acting up, maybe averaging higher like around .7-.800 if it's misfiring? That's just a guess. But there should be a way for your scanner to see misfires.
 
What's the mileage on the car? Have you pulled any of the plugs and checked to see condition? The wires being labeled as Delphi could be originals or someone just replaced them with OEM ones. FWIW just get the cheapest set of wires and they'll work just fine no need to spend the extra $$ on OEM stuff.

I'm not one to throw parts at an issue but usually the first thing I do on a used car is replace the plugs/wires, remove and clean the TB, clean the MAF and install a new air filter. This ensures I have a good start point and maint. history on the car. And when you replace the wires get rid of the metal shields on the plug end if it has them. Not needed and can cause issues. Been running both my 3.8's like this for well over 100K miles and not once had an issue related to removing them.

IIRC, the TC should unlock when you hit the brake pedal so when it starts bucking don't let off the gas just use your left foot and lightly press the brake pedal and see if the bucking stops.
 


Re: Car bucks/surges in 3rd gear under light load. (SOLVED-maybe in my case?)

thegoose said:
Hi all. This is my first post on this forum and I hope you can help. Bought an '07 Grand Prix for my son for school and have noticed a bucking/surging with RPM oscillating around a few hundred revs when under light throttle on a slight upgrade. At first I thought it may be shudder from Torque Converter but can also happen when selector is in 3rd gear. Accelerating seems to cure it. Any thoughts will be appreciated. Thanks
Click to expand...

Over winter the boy's battery wouldn't start the car. (You wouldn't either in -40 C. ) Anyways, put the battery charger on and the battery was showing only 4.7 volts. Charged 'er up to fully charged and have noticed that revs don't occilate any more as they did before. Perhaps the TCM was reset?-IDK. But he has a car that I fell will last until he has finished University hopefully without a burnt out tranny. (Will be installing a Hayden tranny cooler this summer with the thermal bypass for our polar bear winters)

BTW, a big thanks to ALL members who post questions and those who try to help them. That's the name of the game ,right?
 
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