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Discussion Starter · #1 ·
Hi everyone, I am trying to tackle an issue I have been experiencing for a while. I have always had a steering wheel vibration in my Firebird for years. I finally tackled the biggest issue, which was warped brake rotors. That fixed my vibration when braking and when driving the car normally.

Now I am experiencing a problem when the car gets to around 40-50 MPH and the torque converter locks up and drops my RPMs to around 1100-1200 RPM. It feels as if my engine is really bogging and the steering wheel shakes like crazy. Up until that point, car drives perfectly smooth. No issues.

Does anyone know what this might be? I am assuming that it's my Torque Converter? Is there any kind of diagnosis I can do to determine this? I would hate to pull the tranny, replace the Torque Converter, just for it to be something else. All help is much appreciated!
 

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Hi everyone, I am trying to tackle an issue I have been experiencing for a while. I have always had a steering wheel vibration in my Firebird for years. I finally tackled the biggest issue, which was warped brake rotors. That fixed my vibration when braking and when driving the car normally.

Now I am experiencing a problem when the car gets to around 40-50 MPH and the torque converter locks up and drops my RPMs to around 1100-1200 RPM. It feels as if my engine is really bogging and the steering wheel shakes like crazy. Up until that point, car drives perfectly smooth. No issues.

Does anyone know what this might be? I am assuming that it's my Torque Converter? Is there any kind of diagnosis I can do to determine this? I would hate to pull the tranny, replace the Torque Converter, just for it to be something else. All help is much appreciated!
Have you changed your transmission filter or had it flushed? A transmission shudder can be caused by contaminated fluid or low fluid level.
 

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Sounds like the torque converter is locking up at a lower mph then your engine can handle without lugging.

Most decent obd 2 scanners will show the solenoid activity in trans. Some scanners will even show the logic switch data.

You can download the 98 factory service manual at the following link Section & is the trans section. It will have troubleshooting for your trans. www.mediafire.com/?40mfgeoe4ctti
 

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Discussion Starter · #4 ·
Have you changed your transmission filter or had it flushed? A transmission shudder can be caused by contaminated fluid or low fluid level.
I have not changed the filter or flushed the fluid. I can do this, but I'm not entirely too sure how to do the flush. There will still be fluid in the transmission if I pull the pan, correct? Once thing I forgot to mention is that if I press on the brake (even for just a split second) the vibration in my steering wheel goes away immediately. Does this mean that the torque converter is unlocking for that split second?

Sounds like the torque converter is locking up at a lower mph then your engine can handle without lugging.

Most decent obd 2 scanners will show the solenoid activity in trans. Some scanners will even show the logic switch data.

You can download the 98 factory service manual at the following link Section & is the trans section. It will have troubleshooting for your trans. www.mediafire.com/?40mfgeoe4ctti
I have a scanner at my Parents' house that I can use, I am not 100% sure if it'll show the solenoid activity. It's an older one, so I'm not sure if it will show it, but that's a good idea. You described it exactly though, feels like my engine is lugging and causing my steering to shake.

Is there a way that I can change the torque converter from locking up at such low MPH? When is lock up supposed to engage? I kind of wish I could just disconnect the lock up converter altogether, cause it runs fine when it's not locked.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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The vibration might be worsened, possibly transmitted to the front suspension, if there are damaged engine and/or transmission mounts. Additionally, check for looseness in the steering and front suspension components.

When you touch the brake, watch the tach to see if the engine RPM increases, indicating the converter has unlocked.
 

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The flush is done by a shop that has the right equipment. Pulling the pan and changing the filter can be done by you if you have the equipment, If you find burnt fluid or particles in the pan then the transmission is in need of further maintenance. Good luck.
 

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Discussion Starter · #7 ·
The vibration might be worsened, possibly transmitted to the front suspension, if there are damaged engine and/or transmission mounts. Additionally, check for looseness in the steering and front suspension components.

When you touch the brake, watch the tach to see if the engine RPM increases, indicating the converter has unlocked.
Thanks Injuneer, I will check jack up the car tomorrow and take a look underneath. I drove it home tonight, when pressing the brakes the RPMs do not increase, so I'm assuming that it means the torque converter is not disconnecting?

The flush is done by a shop that has the right equipment. Pulling the pan and changing the filter can be done by you if you have the equipment, If you find burnt fluid or particles in the pan then the transmission is in need of further maintenance. Good luck.
I will check the pan, that's no problem whatsoever. Thanks!
 

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Whether the RPM increases when the converter unlocks depends on how much load the drivetrain is under. If it’s transmitting appreciable torque, the converter will “slip” when it unlocks. But if there's little or no engine load, there's little or no slip.

Another thing to consider - in 1995 GM changed lockup in the 4L60E (at least on the F-Body) from a hard switched (on or off) to a pulse width modulated lockup. In effect, there is almost always some slip, except under conditions that justify 100% lockup. And I've never driven a 4th Gen with a 4L60E, so I can’t really say with absolute accuracy what the lockup strategy is. Brake switch position is an input to the PCM, with regard to 4L60E operation.
 

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Discussion Starter · #9 ·
Whether the RPM increases when the converter unlocks depends on how much load the drivetrain is under. If it’s transmitting appreciable torque, the converter will “slip” when it unlocks. But if there's little or no engine load, there's little or no slip.

Another thing to consider - in 1995 GM changed lockup in the 4L60E (at least on the F-Body) from a hard switched (on or off) to a pulse width modulated lockup. In effect, there is almost always some slip, except under conditions that justify 100% lockup. And I've never driven a 4th Gen with a 4L60E, so I can’t really say with absolute accuracy what the lockup strategy is. Brake switch position is an input to the PCM, with regard to 4L60E operation.
Hmmm I don't quite follow, are you saying that if the RPM's are not high enough, the torque converter is not slipping, which could cause a vibration?

Ahhh and okay so that pulse width modulation lockup, that is what I keep seeing about when I search these forums, I see it as a PWM valve? This gives me a lot to consider. I have also searched other forums and members have said their wheels were out of balance, causing a similar vibration to 45-50 MPH range.

Ugh I hate trying to find vibrations on this car, I feel like I finally had it solved with my brakes (no more pulsation when braking)... this is hopefully the final one lol!
 

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Hmmm I don't quite follow, are you saying that if the RPM's are not high enough, the torque converter is not slipping, which could cause a vibration?
In post #8 I was not trying to relate the lockup/PWM to the steering vibration. I was simply trying to explain why the RPM may not have increased when you touched the brake, as you indicated in post #7.

Sorry for the confusion.
 

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Discussion Starter · #11 ·
In post #8 I was not trying to relate the lockup/PWM to the steering vibration. I was simply trying to explain why the RPM may not have increased when you touched the brake, as you indicated in post #7.

Sorry for the confusion.
No problem! I understand what you mean now, I appreciate the help. To update, my problem is solved. I decided to get my wheels balanced because I noticed some had wheel weights missing. Took it up to 50 MPH, no vibration whatsoever. Torque Converter locked up and steering wheel was solid as a rock. Just wanted to update in case others experience a similar issue, check the blatant things first!

BUT of course with this Firebird... there always has to be a problem. I am driving it home after getting my wheels balanced, about 10 minutes after ensuring the torque converter was locking up. Car is driving fine. I get to some stop lights, stop and go, no problem. I am on the road to get home and I am going about 50 MPH, and suddenly I lose all power. Engine starts sputtering like crazy and it feels like car has gone into limp mode.

My wife was following me and said she seen some puffs of smoke when I was able to go. Car was "lugging and lurching" along I was able to get it home thankfully. Car did not go over ~5 MPH, it stayed in first gear. UGH! WTF. Injuneer you actually helped me with a problem I had in this thread. I was experiencing a problem with my fuel pump. Just checked my fuel pressure and it's not even getting 10 lbs pressure. Can a pump die so suddenly as I'm driving? It was only 4 months old, brand was Carter (I ordered it from Rock Auto). I was able to idle when I got it home, but now I can't even start the car up after shutting it off.

Since owning this car for 8 years.... I have gone through FOUR fuel pumps. Am I doing something wrong?! I am replacing my fuel filter; I ensure I fill the car up before I get below a half-tank of gas. I am at a loss. This is driving me NUTS!
 

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Carter is a good pump from what I understand, and Rock Auto is pretty reputable so I wouldn't question the legitimacy of the pumps. The 3 main causes of pump failure are fuel contamination, clogged filters and/or strainers, and electrical problems like loose connectors, oxidization/corrosion in wires or connectors, etc. The electrical aspect may be a problem given the age of the vehicle and/or aftermarket amplifier installation. I had corroded tail lamp sockets and the wires in that harness were oxidized 1 foot behind the connectors. That oxidization and corrosion not only caused funky issues with my tail lights, it also caused my fuel gauge to stay pegged at full at all times because somehow it affected the sending unit. Replaced the connectors and bad wiring, got my fuel guage back.
 

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Not so sure about Rock Auto. Two guys on CamaroZ28.com reported buying AC Delco ICMs (LT1) from Rock Auto. They were in an AC Delco box, marked “Made in USA”. But the part was marked “China”. Two people reported having this problem:


A counterfeit fuel pump wouldn’t surprise me.
 

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Discussion Starter · #14 ·
I've never really had any problems with Rock Auto otherwise. They are usually my go to store if I don't need a part ASAP. When I last changed my fuel pump, I looked in the tank and it looked spotless. No signs of rust on the inside of the tank anywhere.

I'm wondering if it could be my fuel lines? They are definitely rusty... could they possibly be contaminating my fuel and burning up my pumps? Could it be my injectors? It seems like there could be so many different options. My Carter pump was under warranty and Rock Auto is sending me a new one; but still really annoying that I have this reoccuring problem of a fuel pump going bad. Is there anything I could be missing that could be doing this? My filler neck is somewhat rusty as well... ugh, could it be my tank? I have no freaking clue.
 

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Make sure it’s getting a full 12 volts at the connector near the rear axle.

Have you changed the fuel filter?

When changing the pump, have you inspected the filter sock?

Are you still using the plastic bucket that encloses the pump - critical that you use it?

Do you run it with the fuel gauge at 1/4 tank? At that point you are lucky to have 2 gallons left, because of the shape of the tank. Pump can overheat.
 

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Discussion Starter · #16 ·
Make sure it’s getting a full 12 volts at the connector near the rear axle.

Have you changed the fuel filter?

When changing the pump, have you inspected the filter sock?

Are you still using the plastic bucket that encloses the pump - critical that you use it?

Do you run it with the fuel gauge at 1/4 tank? At that point you are lucky to have 2 gallons left, because of the shape of the tank. Pump can overheat.
Make sure it’s getting a full 12 volts at the connector near the rear axle.
Good call. I will check that with my multimeter. Pump should get full 12v at the connector near the rear (like right behind passenger seat) with car set to the ON position, correct?

Have you changed the fuel filter?
Yup, new fuel filter was installed with the new pump approximately 4 months ago.

When changing the pump, have you inspected the filter sock?
I have not done an inspection of the filter sock. I remember seeing it was dirty, but I didn't inspect it.

Are you still using the plastic bucket that encloses the pump - critical that you use it?
So I have actually researched this and I hope this is not what is doing it. Here is a photo of what my new carter pump looks like per Rock Auto:

Is the "bucket" you are referring to the white plastic enclosure? I believe that years ago, when I first had my fuel pump problem, it had an orange-ish colored "bucket" that the fuel pump sat in. I just recently replaced the fuel pump on my 1988 Dodge D100 and it looked exactly what I remembered my (what I consider to be original) Firebird fuel pump looking like, here is a photo of what I mean (I took this photo of my 88 Dodge, this is not the Firebird pump):
Wood Material property Gas Machine Roof


This "bucket" encloses the actual pump (looks like a large bullet, for lack of better description).

Do you run it with the fuel gauge at 1/4 tank? At that point you are lucky to have 2 gallons left, because of the shape of the tank. Pump can overheat.
In the past, yes. Since installing this particular pump ~4 months ago, it has NEVER dropped below a half a tank. So I don't see how the pump could overheat constantly being surrounded by fluid.

I hope this info helps. I really appreciate your input, Injuneer.

 

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The problem is the pump bucket is not always covered with fuel. When mounted in the tank, the pumps is at about a 45-deg angle, meaning that when the fuel level drops, the pump bucket starts to become exposed. It's also possible with very low fuel that the pump can pull in air under hard driving, emptying the bucket.

Here's a good description from Racetronix, a highly reputable supplier of F-Body fuel systems: Although it refers to the LT1 fuel system, the same setup was used in the 1998 cars, V6 and V8.

Why use a Racetronix F-LT1 Fuel Pump Assembly?

The LT1 F-body cars have a pump that is inside a plastic fill-bucket. The fill-bucket's inlet and check-valve system in combination with the fuel pump are designed to draw fuel from the bottom of the tank via suction. This keeps the bucket full at all times and the pump fully immersed in fuel regardless of the tank level so that when the tank is low on gas and you are doing some hard cornering or acceleration the pump does not run dry and start aerating (air bubbles) the fuel. This happens as the fuel sloshes from side to side in the tank leaving the center low on fuel. The F-LT1 cars have minimal to no baffling in them. This can cause detonation and possible engine damage. The bucket also allows the car to operate with lower fuel levels in the tank due to its scavenging effect. The bucket can also effect motor cranking time as the priming time is reduced under certain conditions. The return line from the fuel pressure regulator is diverted back into the bucket via a filter sock inside so that the unused fuel also helps keep the bucket full at all times. Keeping the pump constantly immersed in gas within the bucket can extend the pump's life by not allowing it to be exposed to open air. Open air within the tank contains moisture and in time will cause the pump to rust / seize up especially if left to sit for long periods of time without the tank topped-up (i.e. winter storage). The Racetronix pump assembly is modified so that it will seal in the bucket’s rubber check-valve so that its function is retained......
Based on helping people with 4th Gens for the past 20+ years, fuel pump failure after running out of fuel is fairly common, and running 1/4-tank repeatedly failures at a somewhat lower rate.

As far as the bucket, this is the complete original assembly (minus a hose of two, and the level sensor) from my 1994. The bucket is off-white plastic, althu9gh sitting stored in my garage for the past 20 years may have altered it.

HOLD FOR PHOTO
 
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