Hey guys whats up, got a problem with my engine maybe someone has had before. This started yesterday and i did a upper and lower intake gaskit switch on it about 4 months ago, but the engine idols rough, blows white smoke out of the exhaust, and builds alot of pressure in the oil fill cap and when the car is running if you take the cap off it sucks air and then dies, im thinking maybe PCV but not sure. Any ideas?

 

Is there Pressure or Vacuum at the oil Cap? If you are blowing WHITE smoke out your Exhaust and your Idle is rough that sounds like a Head Gasket. Have you checked your coolant for oil and/or your oil for coolant. Are you burning oil quicker than you would expect, or loosing coolant with no signs of a leak? These are the things I would check!

 

White smoke is a sign of anti-freeze getting into the cylinder. A common cause for that is a failure on the UIM, there is a "stove pipe" for the EGR that comes up between the coolant lines for the throttle body. Over time, the heat breaks down the nylon on the UIM and coolant comes up around the stove pipe.

The cheap answer, plug the coolant ports in the UIM and put an end to coolant passing into the throttle body ever again.

But that is the first place I'd look to explain the white smoke.

As for the vac leak, with the car running, mist starting fluid around the engine and vac lines. If you have a leak, it will suck in the fluid and change your idle. That will help you pin-point the issue.

 

Maniac, Can you post a pic of this stove pipe? or the coolant connections to the TB? When I cleaned my TB i did not have any coolant lines going to it. I thought that was strange but didn't give it a second thought till I reed your post!

 

There is vacuum at the oil cap, and i replaced the UIM and gasket and the Lim gasket, and the coolent and oil looks normal

 

Well then I have to second what maniac said. White smoke in your exhaust indicate coolant getting into your combustion chamber. The rough idle is Also indicative of that!

 

If there was white smoke when it first broke down and now there is no smoke when its running, Does that indicate head gasket or UIM?

 

I don't have enough knowledge to answer that. Maybe The Maniac or one of the other members can help point you in the right direction! Good Luck!

 

The coolant lines for the throttle body are cast in the nylon UIM. If you take the throttle body off, you will see a small pocket on the throttle body and two holes on the UIM that circulate coolant in and out of the throttle body.

Below is a picture of the LIM in my Monte (I port matched it and did a little extra work with plugging the throttle body coolant ports and expanding the coolant bypass).

The red arrows point to the coolant ports I plugged off (tapped and filled with JB Weld holding a couple of stainless plugs). The green arrow is the "stove pipe". I happen to have a narrow stove pipe. The Dorman UIM gasket kit I got had a narrow stove pipe so it's not resting right on the nylon UIM, helping to prevent/slow down breaking it down and causing a leak.

Yes, white smoke is commonly an indication of a bad head gasket (coolant travels from the water jacket to the cylinder, white smoke out the exhaust). But it's far more common on the 3800 to have the UIM fail around the stove pipe, causing coolant to leak in with your air intake. This causes the same effect, coolant dumping into your cylinders.
I've been fooled by a visual inspection and thought a UIM was good. Don't do just a visual, use an air compressor. Take the UIM off (I can take it off with the throttle body on), leave the throttle body on, place you finger over one hole and blow compressed air in the other. If you find coolant in the tubes or air is blowing out the port for the stove pipe, you found your problem.

Your fixes are:
- Plug the ports like I did (and if this is the ward off a failed UIM at the stove pipe, I would consider filling the tubes on the UIM with JB Weld for extra security).
- Replace the UIM. From what I've read from the Bonneville guys, this is the best replacement kit:
GM Intake Manifold Kit
- Upgrade to an L26 aluminum UIM.

And it is also possible for a failed throttle body gasket and UIM gasket to cause this problem. They both have common access to coolant and air intake.

If the UIM, UIM gasket and Throttle Body gaskets check out, then I would consider looking deeper at head gaskets.

 

thanx for all the help, I think I might have found the problem. when I replaced the upper plenum I must have forgotton to put the PCV valve in the new one(wish I could sound smart and say it went bad)but I put one in this morning and took an hour test drive and it seems to have fixed the problem hopefully permanently. ill keep you posted if it stays the way it should be. PS also seems to have fixed a really loud squilling sound the car had randomly developed. fingers crossed