Torque converter issue, maybe?

[pjrocco]

2005 Trailblazer LS I6 with 135,000 miles. Previous owner put a new transmission, fan clutch and water pump in around 100,000. That’s all I know for the history of this vehicle.


I’ve owned it for about 8 months now. Below is everything I’ve personally done since I picked her up.


All new fluids
New tires
New brakes
Wheel bearing
Alternator
Spark plugs
Ignition coil in #3
Camshaft position sensor
Variable timing actuator solenoid
New rear sway bar
Blow motor resistor


I first had an issue with lost power and rough idle. Ran it for a few hundred miles before she threw a P0300 and a P0014. I found the coil in #3 was shot and the VVT actuator was bad. Replaced both, and she was happy again. Shortly after that we hit some brutally cold temps here in Chicago and the rough idle came back. This time it was only when the engine was cold and only when in gear. Once you put it in “P” or “N” or the engine warmed up, the motor idles smooth as glass. I chalked it up to bad motor mounts and I’m going to replace those in the spring.


Now to my problem that has me puzzled. Right around the same time the motor mount issue popped up, I started getting a very slight vibration in OD while doing 45. It would go away when locking it into 3 or bringing the RPMs up past 1,600. (58mph) I was pretty certain that it was a torque convertor issue. Since my daily driving is all city driving, I’ve been locking it in 3 since I rarely go over 45mph. Here’s what has me puzzled. Just recently, when I’ve popped it into D by accident, the vibration has now become a buzzing. It used to only be in OD while the RPM range was between 1,300 and 1,600. Now it is doing it when it’s locked in 3 between 1,200 and 1,500 rpm, but not always. I’m even feeling it a little bit in 2nd when I’m doing 20 mph. To me, this is ruling out a torque convertor shudder. I first checked the fluid and it was in the normal range, but at the bottom. Added a hair and she’s perfectly topped off.


Could the motor mounts/trans mounts be an issue? U-joints? Any suggestions on where to start? I’m pretty mechanically inclined, but have never messed with transmission issues.

 

[gmcman]

Curious as to why it's locking up at 1200 rpm's, I know mine will vibrate slightly around 1300-1400 when the converter locks and really doesn't smooth out until above 1600.
I changed out my factory PWM control of the converter lock using a PWM TCC eliminator valve as other members here have as well.

Your trans could have this mod done, hard to say.

I think your issues are from the torque converter locking early, not sure about highway speeds though.....could be the converter clutch slipping.

You said the previous owner put a new trans in.....new, reman, from a salvage yard? Can you look under there and see if it looks new?

 

[Nexus1155]

When I had problems with vibration, shudder, and power loss it was related to a couple of items. First my cat was clogged attributing to the power loss and destroying the valve on my first cylinder head. Second, grab your clutch fan up front and give it a wiggle on the top blade to and fro. If it has play your waterpump needs to be replaced. Mine was bad, twice, causing a shudder of the fan and more issues that I could feel in the driveline and while accelerating. Stupid I know, but it was happening. I replaced the WP and tossed in an e-fan from a Corvette.

 

[pjrocco]

Curious as to why it's locking up at 1200 rpm's, I know mine will vibrate slightly around 1300-1400 when the converter locks and really doesn't smooth out until above 1600.
I changed out my factory PWM control of the converter lock using a PWM TCC eliminator valve as other members here have as well.

Your trans could have this mod done, hard to say.

I think your issues are from the torque converter locking early, not sure about highway speeds though.....could be the converter clutch slipping.

You said the previous owner put a new trans in.....new, reman, from a salvage yard? Can you look under there and see if it looks new?

Depending on throttle, the TC will lock up anywhere for 1200 -1500 RPM. When I’m easy on the throttle it locks much earlier and the vibration is much more pronounced. When I’m on the gas a bit more, the vibration is barely noticeable. Unfortunately, most my drive is right at 40-45mph with light throttle which keeps the RPMs around 1,300. When the transmission is cold, the shudder is much less. The shudder really comes to life when everything gets up to operating temp.


Previous owner said they put in a new trans at 100,000. It has 135,000, so it’s hard to tell just by looking at it. I can see some cooler lines were cut and new ones reran right below the factory ones. Not sure if that’s an indicator of anything.

 

[pjrocco]

When I had problems with vibration, shudder, and power loss it was related to a couple of items. First my cat was clogged attributing to the power loss and destroying the valve on my first cylinder head. Second, grab your clutch fan up front and give it a wiggle on the top blade to and fro. If it has play your waterpump needs to be replaced. Mine was bad, twice, causing a shudder of the fan and more issues that I could feel in the driveline and while accelerating. Stupid I know, but it was happening. I replaced the WP and tossed in an e-fan from a Corvette.

It’s funny you mention that.


The cat is shot, but it’s not clogged. (so I think) The fan clutch is on its way out, but there is zero play/wiggle in the water pump. I only know it’s on the way out since when it is idling the clutch is fully engaged regardless of the engine temp. When driving she’ll run right around 195, but as soon as I come to a stop, she’ll plummet to 160 or less. The RPMs will kick up from 600 to 900 since it thinks the engine is cold.


I’ll be doing a cat, water pump, fan clutch and t-stat in the spring. Although you have me curious if I have something else going on.


Upstream O2

Downstream O2

 

[gmcman]

When did you take the screenshot of your upstream sensor? During warm up, driving steady, was the engine fully warmed?

When cold, the upstream may appear lazy like that, but when hot and driving the frequency is much faster.

The downstream will follow the upstream when the converter is cold.

 

[pjrocco]

When did you take the screenshot of your upstream sensor? During warm up, driving steady, was the engine fully warmed?

When cold, the upstream may appear lazy like that, but when hot and driving the frequency is much faster.

The downstream will follow the upstream when the converter is cold.

These reading were taken at operating temp while idling.

According to my brother, the upstream should be fluctuating up and down while the downstream should stay constant. If the downstream follows the upstream, the cat is toast. Is that correct?

Could this contribute to the shudder issue?

 

[Nexus1155]

The operating voltage for an o2 sensor is between 0-1v. They seem to be okay. The front alters air fuel ratio the rear is from long term short term fuel trims. I think the only way to check it is to remove the sensor and hook up a pressure sensor, but i just blew mine out for tha gainzzz. The temp going up and down is odd though. Someone mentioned unplugging the clutch fan connector for some different issue but it try and see if something changes for just a drive but no code and it sounds like your coolant temp sensor is goofy? I dont want to tell you to just throw parts at it

 

[pjrocco]

On the way to work this morning I popped a P0420 code. So, I'm guessing my cat is an issue.

Should I start fixing everything else before worrying about the shudder?

The operating voltage for an o2 sensor is between 0-1v. They seem to be okay. The front alters air fuel ratio the rear is from long term short term fuel trims. I think the only way to check it is to remove the sensor and hook up a pressure sensor, but i just blew mine out for tha gainzzz. The temp going up and down is odd though. Someone mentioned unplugging the clutch fan connector for some different issue but it try and see if something changes for just a drive but no code and it sounds like your coolant temp sensor is goofy? I dont want to tell you to just throw parts at it

Thanks for the reply. I was under the impression the downstream O2 sensor should stay pretty even at .05 volts. If it follows the upstream sensor that means the cat isn't cleaning. No?

 

[gmcman]

On the way to work this morning I popped a P0420 code. So, I'm guessing my cat is an issue.

Should I start fixing everything else before worrying about the shudder?


Thanks for the reply. I was under the impression the downstream O2 sensor should stay pretty even at .05 volts. If it follows the upstream sensor that means the cat isn't cleaning. No?

Did you check yet to see if you have a shudder in 3rd at highway speed? The converter will lock in 3rd but it's an easier load on the converter so may or may not shudder.

Are you sure the rear O2 sensor is good?

Here's what I would do.... since based on mileage the rear sensor is likely overdue, also if you do need a new cat, it's wise to use a fresh sensor anyway, go ahead and replace the rear sensor with an AC sensor and go from there.

If the readings are the same, then look at the cat being faulty. If the cat is indeed faulty, then you already have a fresh sensor.

 

[Nexus1155]

This would be easier with hptuners so we can command/alter some items.

Regardless of the rear o2 being good or bad, it would not have a major effect like that since it just alters stft and ltft and not a direct relation to on the fly engine issues like he is experiencing. I mean, possibly if altered for so long, but it would only be to a certain % range +-

If you replace the sensor with a bad cat you could potentially foul it again needing 2 sensors in the long run.

 

[Mooseman]

It wouldn't foul the O2 sensor. All it does is report to the PCM if the cat is working correctly. One way to check if the cat is working is to measure the inlet and out temperatures with an IR gun.

Unless you're getting codes for either of the O2 sensors, I wouldn't bother them. However, the possibility of a clogged cat exists. A backpressure test would confirm that.

 

[pjrocco]

Did you check yet to see if you have a shudder in 3rd at highway speed? The converter will lock in 3rd but it's an easier load on the converter so may or may not shudder.

Are you sure the rear O2 sensor is good?

Here's what I would do.... since based on mileage the rear sensor is likely overdue, also if you do need a new cat, it's wise to use a fresh sensor anyway, go ahead and replace the rear sensor with an AC sensor and go from there.

If the readings are the same, then look at the cat being faulty. If the cat is indeed faulty, then you already have a fresh sensor.

Thanks for all the replies, gentlemen.

To answer your question, the fastest I’ve been in 3rd gear has been about 60 mph. All my driving is city, so I rarely get past 45 mph. Not sure if 60mph would be considered highway speeds. When doing 60mph in 3rd, it is smooth as glass. Although, if I pop her in OD the shudder isn’t that bad at that speed either. After 1,600 RPMs, she smooths out some. 42 – 52 is where I feel the shudder the most.


One of my coworkers is a backyard mechanic and he suggested to drop the trans pan, clean the magnet, top her off with fresh fluid and add a tube if Lubeguard Shudderfixx. Thoughts on that? Fluid is bright red with no burnt smell.


Although I’m not opposed to doing work, if a bad cat or failing fan clutch is the culprit, I don’t want to waste my time. Not sure if these items could cause the shudder I’m experiencing.


Thanks for all the info thus far!

 

[gmcman]

When you ease into the gas in 3rd, generally always above 50 mph when the trans is hot, it should be locked and the tach needle will not bounce up but stay steady with a rise in MPH.
If you lift your foot, it will unlock and with steady pressure on the gas it will lock again...will be pronounced.

I'm not sure why yours locks at 1200 RPM.

 

[gmcman]

Did you add a tune or something to your TB? I want to speculate the vibration you're feeling is the engine possibly lugging or other harmonics happening with the engine under load from 1200-1500 RPM.

I feel you need to address that issue first. Im fairly confident your converter should not be locking at 1200, or even below or at 1500 RPM.

 

[gmcman]

What did you do before it starting acting up? Disconnect battery? Clear PCM? Change tire size?

 

[pjrocco]

What did you do before it starting acting up? Disconnect battery? Clear PCM? Change tire size?

The only thing you mentioned is tires, which I just put on a brand new set of 235/75/16 General Altimax Artic about 2,500 miles ago. Bought off TireRack.com and installed by Discount Tire.


It actually started on Christmas day, that's when I first noticed it. The only thing that comes to mind is the weekend before the shudder started I changed the coil in cylinder 3 (P0300), put in a new VVT actuator (P0014), cam positon sensor and changed the oil. The only thing that I did different was clear the P0014 code while sitting at a stop light. After I replaced the parts I took her for a 30 mile ride to see if the code would clear on its own, which it didn't. I pulled up to a light, came to a stop and cleared the code. I don’t think that would cause an issue, but it is the first time I've ever done it like that. I noticed the shudder exactly 7 days later.


All maintenance is up to date. But like I mentioned previously, I need new of a fan clutch and cat. Fan clutch stays fully engaged only when idling and I do have a P0420 code. Both upstream and downstream 02 sensors are reading the same voltage.

 

[gmcman]

Ok, I was able to get mine to lock the converter at a low rpm in 4th...I tried a few times and it finally locked while I was at about 1500-1600 and dipped down to 1300.

I didn't experience anything that resembled a shudder, perhaps a light resonance with the low RPM but I was surprised it actually locked so it seems they will lock at a low rpm with a TCC PWM mod if given the right circumstances.

The rpm's didn't stay there long, it climbed up quickly to 1500 but I couldn't replicate a hard vibration that could feel like a shudder.

You could have a converter issue, could be in the valve body, could be low pressure to the TCC allowing slippage. I know when I did mine I drilled the plate in a certain spot, that could solve your problem.

If you go into the valve body I can find the location and drill bit size so you can raise the pressure on the TCC.

 

[pjrocco]

Ok, I was able to get mine to lock the converter at a low rpm in 4th...I tried a few times and it finally locked while I was at about 1500-1600 and dipped down to 1300.

I didn't experience anything that resembled a shudder, perhaps a light resonance with the low RPM but I was surprised it actually locked so it seems they will lock at a low rpm with a TCC PWM mod if given the right circumstances.

The rpm's didn't stay there long, it climbed up quickly to 1500 but I couldn't replicate a hard vibration that could feel like a shudder.

You could have a converter issue, could be in the valve body, could be low pressure to the TCC allowing slippage. I know when I did mine I drilled the plate in a certain spot, that could solve your problem.

If you go into the valve body I can find the location and drill bit size so you can raise the pressure on the TCC.

Thank you for testing that!

Would you happen to know why the shudder isn't there when the transmission is cold? The shudder only happens after the truck is up at operating temp.

The first 10 or so miles are silky smooth, then she warms up and shudder city... I would think there would be more internal pressure the hotter the fluid got.

 

[Mooseman]

Could be because the fluid is cold and thicker, thus creating higher pressure and possibly higher holding pressure in the TC.

 

[gmcman]

Just a shot in the dark....but are you sure the 4WD selector is in 2HI and not A4WD?

 

[pjrocco]

Just a shot in the dark....but are you sure the 4WD selector is in 2HI and not A4WD?

Yep, it is in 2HI. I've only used 4HI once, never even tried A4WD or 4LO.

I dropped the pan this weekend, cleaned the magnet and added 3.5 quarts and a tube of shudder Fixx. Drove about 60 miles, no difference. Not sure what else to do except bring it to a transmission shop for an estimate, which I prefer not to do.

My buddy suggested adding Lucas Transmission Fix as it has the constancy of honey. He said the thickness should add pressure in the TC when locking. Thoughts?

 

[gmcman]

I would wait on the additives for now.

Since you have the Torque app, set up your screen like this.



It reads injector pulse width, misfire cyl# current, misfire cyl# history.

I have them arranged front to back, 1-6, also the shift times and TCC slip speed.

See if you can replicate the shudder while this screen is up and see if you get any misfires or torque converter slip.

The inj pulse width shouldn't be an issue but I have it displayed only for a quick reference.

 

[gmcman]

The converter won't lock until the trans is warmed up. I would monitor your torque app with the TCC slip displayed, once warmed up and locked, see if the slip speed rises substantially when you notice the shudder.

The only thing about having a trans worked on, is you never know what exactly goes back in and if they are the correct part.

If that were mine, I would try to find out exactly what was done to the trans, I would think you could contact the shop that did it.
After hopefully getting that info, if rebuilt to stock specs, I would go to the dealer and get a separator plate match to your VIN. Either way, a new dealer plate should work regardless and then I would drill the hole for the TCC clutch to a certain size (I can find that out).

Would be a much cheaper option albeit a few hours of labor and beer.

 

[pjrocco]

I would wait on the additives for now.

Since you have the Torque app, set up your screen like this.

View attachment 80132

It reads injector pulse width, misfire cyl# current, misfire cyl# history.

I have them arranged front to back, 1-6, also the shift times and TCC slip speed.

See if you can replicate the shudder while this screen is up and see if you get any misfires or torque converter slip.

The inj pulse width shouldn't be an issue but I have it displayed only for a quick reference.

I drove the truck for about 45 minutes to make sure she was nice and warmed up. Not sure it matters, but today it’s 41 degrees outside. Sorry it took me so long to get back to you, boss has me pulling 12 hour days.


Here is what I got from the torque setup you gave me. I had all 6 IPW up, but they are all constant with each other, so my OCD made me take 3-5 out. When idling the TCC slip stays in sync with the RPM. When I feel the shudder the TCC Slip drops down around 50 and hovers there till I pick up speed (above 65) or drops into 3rd. Not sure how to read it…

 

[gmcman]

The TCC slip should be very low when locked....50 rpm is alot. At idle it's not locked so it should mirror the idle speed.

When hot, at hwy speed, when the converter is locked, it should be 0 or very close to 0.

 

[pjrocco]

The TCC slip should be very low when locked....50 rpm is alot. At idle it's not locked so it should mirror the idle speed.

When hot, at hwy speed, when the converter is locked, it should be 0 or very close to 0.

As soon as the TC locks (45mph) the RPM on the TCC Slip stays around 50 or less. While my speed increases the RPMs decrease. While doing 65 the RPM slippage is around 20 or less. I've seen it dip down to 13.

Not sure if that tells you anything.

 

[gmcman]

I never checked mine when I had the factory PWM still enabled, could be that it's good, perhaps others can chime in on that.

 

[pjrocco]

Thank you for all the input and guidance! Very much appreciated.

It’s odd. Since the temperatures have been up in the 60’s and even hitting the 70’s, the shudder is barely noticeable now. Seems when it dips back down into the 30’s/40’s it comes back much more pronounced. In short, it seems temperature has an effect on the shudder.

I’m at a loss.

 

[Mooseman]

Just temperature or oil temperature? Once it's warm, how is it?

 

[pjrocco]

Just temperature or oil temperature? Once it's warm, how is it?

Engine/transmission temp has no change on the shudder. Exterior temp does though. The warmer it is outside the less noticeable it is. The colder it gets the more you feel the shudder.

 

[Mooseman]

Very strange as once it's warmed up internally, outside temps shouldn't affect it. Only thing I would recommend is either a shift kit or a PWM eliminator kit.
http://gmtnation.com/forums/threads/removed-pwm-control-from-tcc.7238/