Engine Shudder And Shake

jhoch · July 22, 2007

Hi

I have a 99 Yukon w/ a 5.7l V8

At first i would go up small hills at highway speeds, going at about 70mph, and the RPM's would stick @ about 3k, and once it shifted finally it would shudder the truck until going downhill.

Most of the time it did not throw a code.

A couple times it threw "random misfire code"

So I replaced the plugs wires, and dist. cap and rotor.

It has not thrown a code since, but the shudder comes back, but not as frequent.

Since then I have changed the gasoline I put in it, and use FI cleaner or Techron every tank. And this works for a brief period of time. and then we go back to the beginning.

Has anyone had the same symptoms? I'm really getting tired of fixing things that don't need repaired only to find out it is not the problem.

If anyone can point me in the right direction I would be most grateful.

thanks!

omegafiler · July 22, 2007

Try running some seafoam (or amsoild equivalent) - that stuff did wonders for my '00 Tahoe (5.7l). I was having similar problems and pretty much replaced everything related to the ignition system before finally using the amsoil stuff.

Just keep in mind that you will need to change your oil after doing this. Also, in some cases, if your engine is dirty enough, it could foul out your plugs - so just be "aware" of that fact. I had about 3 or 4 that went bad and just decided to replace them all again.

Never had any issues after that and she ran good as new.

jhoch · July 23, 2007

Try running some seafoam (or amsoild equivalent) - that stuff did wonders for my '00 Tahoe (5.7l). I was having similar problems and pretty much replaced everything related to the ignition system before finally using the amsoil stuff.

Just keep in mind that you will need to change your oil after doing this. Also, in some cases, if your engine is dirty enough, it could foul out your plugs - so just be "aware" of that fact. I had about 3 or 4 that went bad and just decided to replace them all again.

Never had any issues after that and she ran good as new.

*bump*

No one else has any other ideas? guess I'll have to take it to the garage.

Draenor · July 23, 2007

Is the shuddering when your cruising or maintaining highway speeds? Or just downhill? It could be the torque converter. Did you do the sea foam treatment?

07Graystone · July 24, 2007

My '97 5.7l Silverado had a similar issue. Stumbling under acceleration and even dying while coasting. This was soon after a fuel pump replacement. I tried gas line water remover as well as driving in "3" thinking it was TC shudder. I also got a random misfire code. I was convinced the new fuel pump was defective but dealer could not duplicate problem in 2 attempts, telling me to drive it until it does it again. It turned out to be a corroded and partially melted connector on the fuel pump wires near the tank, or so the new owner told me. Service writer told him this was not unusual on "older" models. Check out the connector near the fuel tank if you think it could be th fuel pump spiratically cutting out.

jhoch · July 24, 2007

it usually shutters intermitantly at highway speeds, or most the time on the way up hills on highways.

I'm a little too new at mechanics to try the seafoam.

O_show · July 25, 2007

it usually shutters intermitantly at highway speeds, or most the time on the way up hills on highways.

I'm a little too new at mechanics to try the seafoam.

Hello, I am having the same problem with the same vehicle, 99 and all, all new ignition componants, am going to try fuel filter and top end cleaner this weekend. I get to about 65 mph, kick it down, let it get into 3rd and 4th and get a misfire condition, slowly let up and it comes out of it, sometimes the service light comes on and doesn't, P0300 misfire. I am a Ford tech more than a GM tech, I work at an independent shop and we have a Tech 2 scanner and when it happens I can see #5 and #6 misfire in the datastream, I will let you know If I come up with something or if anyone else can help us both.

Greg