Drivetrain Shudder at 71mph

[Ozzzy66]

I am having trouble with an intermittent drivetrain shudder while accelerating on the interstate. It only appears while accelerating up to 70+mph. If I can accelerate through the shudder and let it come back down to speed it does not shudder. It will also intermittently through a P0300 misfire code also while doing the shudder. Myself and a trusted mechanic felt like it was a problem with the torque converter lockup. After pinning a valve in the transmission, installing a new torque converter, installing a new GM torque converter and transmission and then going through changing plugs, wires, distributer cap and rotor, new CV axles and another set of tires and rims from another vehicle the problem still remains.

I am now thinking the problem may be computer related. I do not know much about much in this area but the one common link with the ignition and transmission could be the throttle position sensor.

I know I have thrown way to much money and time at this problem and any thoughts and suggestions welcomed. Thanks for reading this string of run on sentences.

 

[PlayingWithTBI]

What year/model truck, what trans, and engine?

 

[Supercharged111]

You have a shudder and a misfire code, and your "mechanic" thinks it's the TCC? Misfires cause lockup issues, not the other way around. TIme for a new mechanic. Check fuel pressure, could be the spider, when's the last time it had a tuneup?

 

[Ozzzy66]

What year/model truck, what trans, and engine?

1998 GMC K1500 Suburban, 5.7/350, 4L60E

 

[Ozzzy66]

You have a shudder and a misfire code, and your "mechanic" thinks it's the TCC? Misfires cause lockup issues, not the other way around. TIme for a new mechanic. Check fuel pressure, could be the spider, when's the last time it had a tuneup?

Thanks for the reply. In the mechanic’s defense the misfire code had been cleared by me before I took it to him. Like most mechanics he assumed that the owner knows little about diagnostics.

 

[Hipster]

Thanks for the reply. In the mechanic’s defense the misfire code had been cleared by me before I took it to him. Like most mechanics he assumed that the owner knows little about diagnostics.

Was the mechanic aware of the misfire codes? If not, your diagnostic prowess helped him miss the issue and cost you a pocket full of money. Clearing the code doesn't fix the problem.

Nobody checked the coil or other ignition components? Ohms tests will not tell you if the these parts can keep up at rpm/vibration without dropping a cylinder here or there. What tune up parts were used? Some import stuff has issues out of the box.

Find another mechanic before he sells you another transmission.

 

[Ozzzy66]

Was the mechanic aware of the misfire codes? If not, your diagnostic prowess helped him miss the issue and cost you a pocket full of money. Clearing the code doesn't fix the problem.

Nobody checked the coil or other ignition components? Ohms tests will not tell you if the these parts can keep up at rpm/vibration without dropping a cylinder here or there. What tune up parts were used? Some import stuff has issues out of the box.

Find another mechanic before he sells you another transmission.

I had cleared the misfire code. Once the code reappeared after a test drive he started trouble shooting the ignition system. He checked and changed out what parts were bad.

 

[Hobie]

I had an issue on my 96' with the same thing, 5.7 vortec had a p0300 and would constantly set around 2000 RPM, but only in 3rd or 4th gear. Ended up being the EGR valve was so clogged up with soot. You should check that, just two 10mm bolts, and see how free the valve is, and also take a look into the intake to see if it is clogged. I ended up having to remove my intake and let it soak in carb cleaner due to the opening in the intake was the size of pencil lead

 

[Ozzzy66]

Was the mechanic aware of the misfire codes? If not, your diagnostic prowess helped him miss the issue and cost you a pocket full of money. Clearing the code doesn't fix the problem.

Nobody checked the coil or other ignition components? Ohms tests will not tell you if the these parts can keep up at rpm/vibration without dropping a cylinder here or there. What tune up parts were used? Some import stuff has issues out of the box.

Find another mechanic before he sells you another transmission.

I had an issue on my 96' with the same thing, 5.7 vortec had a p0300 and would constantly set around 2000 RPM, but only in 3rd or 4th gear. Ended up being the EGR valve was so clogged up with soot. You should check that, just two 10mm bolts, and see how free the valve is, and also take a look into the intake to see if it is clogged. I ended up having to remove my intake and let it soak in carb cleaner due to the opening in the intake was the size of pencil lead

Thanks, I will check that.

 

[Scott Martin]

I have the same problem and have been battling it for several years now... Whatever it is it will shudder for like 10 seconds or so and then suddenly clears up like a switch was turned off... This is a well known problem that many people have with these trucks and GM has been aware of it for years but refuses to do anything about it!