Vehicle Shudder After Engine Rebuild

[magoulet]

Help needed - please !

 

I just got the engine rebuilt on my Yukon XL (2005 5.3L) at 62000 km

 

Now I noticed the following problems right after the rebuild:

 

1- Vehicle shudder while driving at constant speed (at around 60km/h and between 74 and 79 km/h) on a slight incline, with the engine under load.

 

When it happens, if I tap the brake pedal the RPM goes up and the shudder stops instantly. Also, the shudder stops if I accelerate, getting the RPM up.

 

2- Harsh 1-2 upshift

 

The engine shop I dealth with told me the transmission was the problem and kindly offered to give me a quote to put a new one in...

So I took the truck to a transmission shop. The tranny fluid & filter were replaced as well as the TCC lockup solenoid and the TCC pressure switch. The fluid was in good condition and there was nothing to signal in the pan.

 

(I took this opportunity to get a pan that has a drain plug installed – thanks for the idea guys !)

 

I still have the same problems though…and no codes are showing-up.

The tranny shop guy says the shudder is probably due to a problem with the "truck's computer", and the harsh 1-2 upshift problem is due to a defective valve body...

 

So what should I do next ?

Is there something that needs to be re-programmed (TCM? PCM?)

 

Any other ideas ?

 

Any help will be greatly appreciated !

[Bucknut]

Oh Lord..What caused your engine to go at 62,000? Ugghh..

 

Sorry to hear about your shudder troubles , I have the same issue with my truck...But being a700R4 , there's not much computer involved...So it's ready for arebuild..

 

Hope it's something easy in your case..Can you reset the pcm\tcm?

[green 788]

If your transmission didn't have a problem before the engine rebuild, then I doubt it's the transmission. That is extremely unlikely that the tranny would go on you just after the engine was rebuilt.

 

It sounds like the transmission is shifting at a default level from 1st the 2nd, which explains the hard shift. It is going by the tachometer, rather than taking road speed into account. It feels like it's got a shift kit...

 

Since you can accelerate the engine and the shudder goes away... and I assume that the engine does not shudder when you're sitting still (in park) as you race the engine to full RPM... right?

 

So the shudder is being caused by an issue with a speed sensor I'm going to guess. It's possible that when they had the engine out of the truck for the rebuild, they pinched or pulled and unplugged one of your wiring runs going to one of the speed sensors on the transmission. If that sensor is working only part of the time (going in/out... in/out...) that could confuse your transmission and cause the torque converter to lock... unlock... lock... unlock... and that will definitely make one shudder.

 

Another possibility is that that computer may need to be re-flashed (re-programmed), and your dealer would have to do that.

 

I would have someone scan the engine computer for fault codes. Advance Auto and such stores will do a basic test for free. Just because there's no check engine light doesn't mean that there aren't stored fault codes.

 

I really doubt you have a tranny problem. I'd be looking for something related to the engine removal and re-installation... loose wire... ground strap not re-connected (or loosely connected)... or something such.

 

Dan

[magoulet]

If your transmission didn't have a problem before the engine rebuild, then I doubt it's the transmission. That is extremely unlikely that the tranny would go on you just after the engine was rebuilt.

 

It sounds like the transmission is shifting at a default level from 1st the 2nd, which explains the hard shift. It is going by the tachometer, rather than taking road speed into account. It feels like it's got a shift kit...

 

Since you can accelerate the engine and the shudder goes away... and I assume that the engine does not shudder when you're sitting still (in park) as you race the engine to full RPM... right?

 

So the shudder is being caused by an issue with a speed sensor I'm going to guess. It's possible that when they had the engine out of the truck for the rebuild, they pinched or pulled and unplugged one of your wiring runs going to one of the speed sensors on the transmission. If that sensor is working only part of the time (going in/out... in/out...) that could confuse your transmission and cause the torque converter to lock... unlock... lock... unlock... and that will definitely make one shudder.

 

Another possibility is that that computer may need to be re-flashed (re-programmed), and your dealer would have to do that.

 

I would have someone scan the engine computer for fault codes. Advance Auto and such stores will do a basic test for free. Just because there's no check engine light doesn't mean that there aren't stored fault codes.

 

I really doubt you have a tranny problem. I'd be looking for something related to the engine removal and re-installation... loose wire... ground strap not re-connected (or loosely connected)... or something such.

 

Dan

 

Thanks Dan

 

The transmission was fine before the rebuild. Noticed the shudder around 600 km after the rebuild.

When the vehicle was scanned at the tranny shop, there were no codes showing up (seemed to be a recent model Snap-on scan tool)

 

I too doubt the tranny is the problem, since the fluid was in good condition and the pan was free of debris.

 

The shudder only occurs when driving at around 60km/h and 74-79 km/h, never at idle

When the shudder occurs, any of the following actions will get the shudder to stop:

1-tap the brake pedal

2-put the tranny in "Tow-Haul" mode

3-step on the gas pedal

 

I'm taking the truck to the dealer tomorrow, hoping they get to the bottom if it quickly ($)

[magoulet]

Oh Lord..What caused your engine to go at 62,000? Ugghh..

 

Sorry to hear about your shudder troubles , I have the same issue with my truck...But being a700R4 , there's not much computer involved...So it's ready for arebuild..

 

Hope it's something easy in your case..Can you reset the pcm\tcm?

 

I would love to know !

Engine rebuilder said the main bearing was spun. Unknown cause though... that's about 2000 miles after purchase.

 

I bought this "GM Certified" truck from a GM dealer in Montana a few months ago in total confidence.

Did not feel I needed to purchase an extended warranty (I also own a 96 chevy suburban since 1997 that now has 314 000 km and never had any major problems with it, mostly normal wear repairs - so I was confident I did not need the extended warranty), I guess that confidence has worn down now... !

 

I hope the solution is $imple too. Dealer is telling me is usually takes a half hour to re-program (each) pcm-tcm.

 

Will keep you updated when I find out more....and good luck with your rebuild !

[Bucknut]

Well good luck with yours too , just learned somethin here myself..

 

Never did think about the Torque converter, that could be causin my issue..My TCC lockup solenoid may be stickin , so I'll be swappin that before anything else....