RPM drops when shifting 3-4th gear

On one of my 2002 GT's (138K miles) I have been experiencing a hesitation (two or three times) as the transmission is shifting from 3 to 4th gear. When this happens, the RPM's drop about 500 RPM. The car has recently had the MAF replaced and new AC Delco 41-110 plugs and new plug wires (AC Delco 746BB). Also, I replaced the fuel filter and PCV. When it hesitates, if you let up on the gas pedal slightly (or if you give it more gas) the hesitation will stop. By the way, there is no SES light. It only seems to do this as the transmission is shifting from 3 to 4.

The transmission was shifting hard but I went through Bob Naylor's regiment of "sea foam" and two fluid changes (new filter, of course). Transmission is now shifting smooooooth. I don't think it is transmission related (a slip would cause RPM's to go up not down). Any suggestions where to look?

if you access to a back pressure gauge you should pull pre converter o2 sensor and put gauge in and see if you got more than 11/2 psi your converter could be beginning to plug up it wouldnt be the first grand prix with that problem they even extended the converter warranty to 100,000 miles if this your problem have the dealer check it for warranty coverage before u pay someone

Catalytic converter was replaced at 75K under warranty. Symptom was very different. In that case, reakky could not accelerate or get RPM above 2000.

hmm...if you drive the the shifter in the "3" position instead of the "D" position does it stop? I'm wondering if there is a problem with the torque converter not wanting to locking up. i would have the car scanned with a transmission capable scanner and see if any codes pop up

Good idea. I will give it a try. Do you expect the RPM's to drop when the torque converter does not lock?

when this happens, are you doing highway speeds? how fast are you going? and i guess give us a little more info on where the RPM's are. are they around 2000 and drop down to 1500, or...:confused:

Approximate speed is about 45 MPH. I am not sure about RPM's but I think they are about 2200 and fall to about 1700. Talking to others and researching this it seems to fit what others call "shudder" that occurs when the torque converter fails to lock. Does that sound right?


Oh, I almost forgot, i did not see the problem when I manually shifted. But that was only a couple of times and the "shudder" is very intermittent. Thanks for sticking with me on this one.

When was the last time a full tune up was done on this motor. Many "shudder" at lockup (45mph) conditions are caused by secondar ignition missfires.

Good to hear from you again Tim. In the past week I replaced all plugs (AC Delco Iridium's), new wires, new fuel filter, new PCV valve (I did it because I thought this was a possible cause of the shudder).

Mitch

Good to hear from you again Tim. In the past week I replaced all plugs (AC Delco Iridium's), new wires, new fuel filter, new PCV valve (I did it because I thought this was a possible cause of the shudder).

Mitch

Uh oh... :tongue:

When did this "shudder" start to happen? Right after the new plugs and wires were installed?

Couple years back, I had an 02 GP that I just finished replacing the LIM gaskets. Afterwards, it started, ran, and idled good. On the road, it ran good up untill the point when the torque converter locked up at 45mph in shuddered. It did not do this before the LIM gaskets, so I spent a couple days checking for vacuum leaks and things like that. Then I replaced the plugs and wires. Turns out the plug boot on #4 cylinder had a small cut in it. At highway speeds in lockup, the spark jumped through the side of the boot rather across the spark plug gap causing a missfire or "shudder".

It doesn't sound like shudder to me. You'll know when you get either launch shudder or shudder when the torque converter locks or during shifting. For example launch shudder is pretty violent. The front end will bounce up and down or feel shaky.

Shudder = convulsion effect.

I'd get the tranny scanned or checked out with a scan tool capable of turning the torque converter on or off.

BTW - Could be "chuggle" or "fishbite". :biggrin:

Actually the "shudder" began before the tune up. So I am not thinking that the tune up is causing the problem. I originally believed that was the issue when the problem began (and the plugs were really bad so I thought I had the problem fixed with the tune up but the problem was still there) By the way, you mention a slight cut in the boot on the wire. A GM mechanic showed me a quick way to check for that. He put about a pinch of salt in a spray bottle of water and sprayed the wires while the engine was running. The openings in the wire literally lit up with electrical arcs.

I guess I am not sure if it is truly shudder. There is only a slight couple of hesitations at about 45MPH as I am going from 3rd to 4th gear. The RPM's drop during that time. I will try to get a trans capable scan

Bob, I am not sure about "chuggle" and "fishbite". First time I ever heard these terms. Could you elaborate on these? :confused:

....By the way, you mention a slight cut in the boot on the wire. A GM mechanic showed me a quick way to check for that. He put about a pinch of salt in a spray bottle of water and sprayed the wires while the engine was running. The openings in the wire literally lit up with electrical arcs.....

Funny you mention that. Thats exactly how I found what was causing my missfire issue on the 02. :sunglasse

This one is going back a ways! 2006.... whoh! :lol2:

http://www.automotiveforums.com/vbulletin/showthread.php?t=656443

Bob, I am not sure about "chuggle" and "fishbite". First time I ever heard these terms. Could you elaborate on these? :confused:

Common terms and used by GM in their tech bulletins.

Based on your symptom it doesn't sound like these either. This is when the torque converter lock and unlocks abnormally causing what feels like a misfire condition or a bucking feel. Normally under a load like going up a hill and in 4th gear (OD) only.

A drop of 500 rpms going from 3rd to 4th gear could be normal and especially if the torque converter locks up during the shift or right after depending on your speed....45 mph or more.

I watched it a little closer today. RPM's dropped about 100 to 200 RPM's. And it follows more your description as to when it occurs. But it alsmost always happens 2 or 3 times. It is very intermittent and it does seem to happen more with slight hills. But it is more like a hesistation (but very similar to a miss fire in feel). I agree, I need to get a scan for codes from teh transmission (most people want to charge for the service, so I am still looking for some place to get the scan).

I guess it could be a form of chuggle/fishbite. :dunno: Just to clarify the rpm drop. Does it occur only during the 3-4 upshift or once in 4th (OD). The issue could be caused by a tranny problem related to the TCC - torque converter lock/unlock functions or pressure control (PCS), as mentioned a secondary ignition problem like spark plugs. ignition wires or even coil packs, and according to a GM tech bulletin possibly the Throttle Position Sensor (TPS).

The scan sounds like a good starting point.

Well I wish I could be "crisp and clear" on my answer to your questions but it is never that clear. I think I saw it once when shifting from 2-3. It seems to happen as it is shifting into 4 (but it is very intermittent). The reason I am not clear on this is due to my sense of the shift. 1-2 is very clear and distinct. 2-3 is clear and distinct. But there are times when I would sware that it shifted from 3-4 (noticable change in RPM's). But then a little later it "feels" like it shifted again. (no shudder in either of these instances BTW).

The TPS is an interesting idea because if I change the accelerator even the slightest amount (increase or decrease) the shudder stops. (BTW shudder may not be the correct term. This only a slight sensation. It is not a violent change).

I agree the scan is the KEY to diagnosis. I still have not found anyone that will scan for free. The last scanner I used was from O'Reiley's and it could not give the info on Chasis codes but it did read them. I just wonder if it will read the power train codes. It is at least worth a shot! I will let you know :biggrin:

Bob touched on everything i thought it may be. i was going to say either the TCC, or the TPS.

hope you get this figured out. keep us in touch...i will be following.

I will keep everyone posted. I will try to get a scan tomorrow on the tranny.

I still have not got any codes pulled from the transmission yet. I assume I need it to perform the hesitation and then have the codes pulled (in other words I believe the code will not be stored. Let me know if they will be stored after the car is shut off).

But I do have some news. Yesterday I decided to try the manual shifting again. I had the hesitation while in 2nd and in 3rd. So I am now thinking it is a more classic ignition "miss". Does that sound right?

Since I have changed plugs, plug wires, and fuel filter, should I check coil packs or what?

when you changed the plugs/wires what kind did you use? i would check and make sure all wires are tight. You could check the coil packs by having someone turn the car over while you hold the wire real close to the coil pack. you should see a nice blue spark jump from the pack to the wire. any orange/yellow spark would indicate a weak coil pack. (of course be very cautious while doing this)

and yes, the tranny DTC's should store even after the car is turned off, until removing the codes with a Tech II scanner, or unplugging the negative battery cable for 5 mins or so.

The OP stated he is using AC Delco 41-101 Iridium spark plugs ad AC Delco Premium Silicone 7mm ignition wires based on the Delco part number.


Since I have changed plugs, plug wires, and fuel filter, should I check coil packs or what?


With a digital multimeter the coils should read:

Ignition coil primary resistance = 0.5 to 0.9 Ohms
Ignition coil secondary resistance = 5K to 10K Ohms

Best to check them to rule them out. Also, clean the electrical contacts where the coil packs insert into the ignition control module(ICM). Also, clean the ICM module electrical connector. You can use electrical contact spray cleaner.

The above doesn't cost much except your time.

Bob was it the 41-101's that had quality issues where the porcelin was cracked and would cause a slight miss like s described? I can't remember now.

Oh I was so hoping someone had found the cure for this, and posted it!! I'm having the same issues with my 01 Impala 3.8

Going up a hill about 30-35 mph around 1500 rpm in 3RD gear the RPM's will bounce to 1700-1800 rpms. If I give it gas or let off the gas it stops surging.

* I have checked for Vacuum leaks
* Replaced the TPC
* EGR Valve and Gasket
* Cleaned the Throttle Body and replace rubber gasket.
* Replaced the MAP sensor
* Replaced the IAC (Idle Air Control Valve)

Looking to do the Plugs and wires this weekend. Last time I changed them I had 110,000 miles and Have 193,000 miles now.

To eliminate the TCC.. From what I have read on hear, correct me if I'm wrong. But the TCC will only act up in 4th/OD and normally at HWY Speeds.

It has been a while since I have posted on this issue but finally, I have gotten back to it. I have had several other items to address with this vehicle (new brakes/rotors; new control arms (due to damaged ball joint by S&S tire with new tires and alignment); new front struts), my son's 2002 Grand Prix had transmission issue: replaced EPS, TCS, PCS, 1-2 solenoid, 2-3 solenoid; all OK now), daughter's 1997 Buick Regal GS (had to replace all brake lines and fuel lines due to corrosion); wife's 2005 Ford Freestyle (had to replace internal valve on scroll compressor, recharge system: all OK now). That is enough whining by me,,,,,back to the problem on this post

I would say the fishbite/chuggle has gotten worse. It seems to occur in every shift pattern intermittently now (1-2, 2-3, and 3-4). I have even felt and seen RPM surging at highway speeds (but very slight). Here are the latest things attempted:

1) tried BNaylor's Seafoam for trans cleaning followed by fluid change ; definitely easier to do with drain plug added to the pan thanks to BNaylor's advice on this) It seems to have helped but not fixed by any means. Highway "fishbite" is better and I do not see surging at highway speed but still surging at shift points


2) had EGR codes show up about a month ago P1404 and P0404. Cleaned EGR valve (soaked bottom in contact cleaner for about 1 hour then washed out with spray, installed new EGR gasket (saw no evidence of the old gasket at all??), checked wiring. Removed battery negative cable for 1 hour (approximate) then reinstalled EGR. Seems to have corrected problem (jury still out in my mind on this one) Still watching for CES light

3) Installed new air filter (discovered one clip missing on air box. need to find another at salvage yard. temporary fix with duct tape)

4) Installed new PCV valve (never replaced for about 100K miles)

Because of the missing clip on air box (only slight gap) I am now concerned about MAF condition. I plan on checking/cleaning the MAF. I looked at the screws on the MAF, WHAT KIND OF TORX SCREWS ARE THESE????????

And I will check the coils (sorry Bob for not following your suggestion sooner)

I need to get codes from the transmission. No one around to get the data that I have found without paying $75. But I am really starting to believe that this is a secondary misfire.

Should I also check fuel rail pressure while driving? (for some unknown reason I am suspicious of this)

I plan on checking/cleaning the MAF. I looked at the screws on the MAF, WHAT KIND OF TORX SCREWS ARE THESE????????
it is a Tamper Proff Torx bit - Size - T20. This will also remove the TPS, and IAC sensors also on the Throttle body.

ALSO NOTE: Do not use Carb Cleaner on your MAF sensor. There is a spray made for MAF sensors.

UPDATE I disconnected my battery last night and hooked it back up this morning. (like stated in other posts)And this morning I could not get the car to fishbite at all. I'm not 100% convinced it is fixed. The weird thing is, now it feels like it shift through all gears a little different.

On the way home I will see how it drives.

Is that Torx bit commonly available? Thanks I am aware of the MAF cleaner fluid is unique. I have also noticed that when the battery is disconnected for a while the problem lessons. (For example, everything was dramatically improved yesterday. But today it seems to be back (I drive about 120 miles per day)).

In addition my SES came on today. Sure to be P1404/P0404 but have not retrieved the code yet.

Removed the MAF today and cleaned it thoroughly (did not appear to be dirty). Removed and tested all three coil packs. Cleaned terminals on primary and grounds. Some possible corrosion on 1-4 coil pack terminal but not really bad probably more dirt than anything. Reinstalled coil packs. Of course battery was disconnected during repairs.

Misfire is still present. Mostly observable in 1st, 2nd, 3rd. The RPM change from 3 to OD (4) did not happen (but could be from battery being disconnected?) I would also say the miss lessens as the car gets hotter (very hard to say conclusively though)

Suggestions what to try next? Fuel pressure? Replace coil packs anyway??(never replaced, mileage at 175K). Vacuum leaks?:confused:

Common terms and used by GM in their tech bulletins.

Based on your symptom it doesn't sound like these either. This is when the torque converter lock and unlocks abnormally causing what feels like a misfire condition or a bucking feel. Normally under a load like going up a hill and in 4th gear (OD) only.

A drop of 500 rpms going from 3rd to 4th gear could be normal and especially if the torque converter locks up during the shift or right after depending on your speed....45 mph or more.

I am experiencing this same problem right now. I took it to the tranny shop and they said misfires but also that my TC is locking up too soon and that I should get the PCM reflashed to include my high mileage so that the TC lock-up is delayed a little. (I have a DHP 1.0 tune right now and don't want to screw that up. Can I take the car to a dealership and have them delay my TC lock-up without messing with any other settings on the PCM?)

I'm desperately hoping that my issue is just misfires. I had this a while back and new plug wires solved it (only the jerking/bucking wasn't as severe/hard as it is now). I did recently change the plugs and I'm hoping a wire is just jacked, but I have no clue.

My issue in 3-4 (OD) disappears when I remove the battery cable for 30 minutes. It will eventually return. However the "missing" is occurring in 1st, 2nd, and 3rd all the time.

I still have not been able to get code (if they exist from the transmission). I really need this piece of info. I am almost at the point of buying the reader for this.

My next plan is to unplug the MAF. Then I will look for vacuum leaks. Followed by possible High voltage breakdowns (cracked spark plug insulators etc.)


Since I have two 2002 Grand Prix's and one is having no issues at all I have the option of swapping components (like coils).

I would, what would it hurt. so you have put about 40k on the car since this issue start? Has it gotten worse or stayed pretty much the same?

I was thinking about doing plugs and wires this weekend, to see if I could get mine to stop. How did you test your coil packs?

Instructions on testing coils in this thread from BNaylor. My only concern is that this method will not check for high voltage breakdown. But on second thought, a high voltage breakdown in the coil pack will result in an arc path which eventually will change the DC resistance.
On Monday morning, I was ready to remove the connector from the MAF. But for some reason I felt I should drive it. I cannot explain it, but the miss in 1st, 2nd, 3rd is now gone :confused: But I am glad for the recent smooth driving!!! I am going to add the shift kit soon. Hope it all holds the way it is now!

I finally got the engine light to flash the other morning. So I replaced plugs and wires this weekend. 200 miles later Car runs so much better and it is not jumping around or doing the fishbite and more, but I'm still getting a misfire in cylinder 6, only noticed an issue sitting at a red light. I will replace the coil packs this weekend. I'm hoping this will take care of all my issues.

Well it is definitely better than it was. Very seldom do I see an issue issue in 1,2,3. I still feel a slight fishbite effect in OD on occasion. Now I have a window regulator to replace on the passenger front side as well. Waiting for the shift kit addition on the next oil change.

Well I finally found the secondary miss. The SES set with an EGR code (prittle out of position). I replaced the EGR and reset the PCM by removing the battery cable for 1 hour. BOOM! the miss is gone; no more issues in 1,2,3. Strnage that it took so long for the code to set but it is amazing how much the EGR was affecting things.

I still have a slight fishbite on occasion as OD is engaging (very seldom). But no RPM drop?? I have the shift kit ready to install but must wait for a few more weeks. I am in China to oversee the build of some electronics. :mad: When I get home it will be on to the shift kit.

After much whole lot of work and money I found a soution to this condition in my car..water ingression in to the electrical connector of the EGR Valve