Trans bucking

[MDOC111]

I recently had the 5.7 engine replaced in my 1996 Suburban K1500. I took it for a drive on the interstate today. I noticed when your are coasting, like going down a hill, and you let up on the gas and when you barely apply the gas pedal it starts to buck. It did not do this before the engine replacement. Any ideas what causes this? Thanks!

 

[skylark]

The cam retard isn't set properly. I have yet to tighten the distributor on our 99 after an engine swap and I accidentally left it too loose. It slightly turns every couple hundred miles and I have to turn it counterclockwise to stop the bucking. It isn't far enough out to throw a code. I guess that I should get off my lazy ass, set it and tighten down the dizzy!

 

[highspeed]

I recently had the 5.7 engine replaced in my 1996 Suburban K1500. I took it for a drive on the interstate today. I noticed when your are coasting, like going down a hill, and you let up on the gas and when you barely apply the gas pedal it starts to buck. It did not do this before the engine replacement. Any ideas what causes this? Thanks!

Could be timing or possible Torque converter. I assume your not getting any CEL?

 

[MDOC111]

Thanks for the replies! No check engine light is on. I believe that is how he set the timing. He would run the engine and when the light came on he would scan it and then adjust distributor. He kept doing this until the check engine light stopped coming on. It does feel like it has a miss at cruising speeds. I gave him a new distributor gear due to the old one having over 250,000 on it.

 

[skylark]

Mine has to be -25 or so to throw a code. It bucks around -15. Spec is 0 +or- 2.

 

[jrollings]

My 4l80e is doing this. I just set my base timing to 4* btdc lastnight with no change. Previously it was at 10*btdc? Maybe Im not quite understanding what you guys are saying by the timing will do this? My suburban will miss like crazy if I don't let it warm up but it always does the bucking around 65-70 if I try to maintain speed or on decel. I am also not getting a CEL

 

[someotherguy]

Timing on the Vortec is done totally different than your TBI, so don't get yourself all mixed up reading this thread.

Richard

 

[jrollings]

Thx Richard