Very low vacuum, decent idle.

[90FoxBdy]

I put my car back together after changing out headgaskets. Now car will start and idle but there is very little vacuum, 3-5. It revs fine and idles fairly smooth. Car is also very rich, eye watering rich. I tried the card cleaner trick and found my pvc hose on the lower was a little loose and the hose on the blow off valve was a little loose. Fixed both of them and nothing. One thing I am wondering, will the thermactor tube that goes from head to head not sealing cause a vacuum leak? I had some problems aligning that and think some of the silicone may have got pushed away from it. I checked all my lines and pulled all of them off and on with nothing. Thxs.

Also I left all the valves/rocker alone.

 

[jrichker]

The odds are that one or both of the intake manifold gaskets isn't sealing properly. New gaskets need to seat against bare metal and not the residue left from the old gaskets in order to seal leak free.
My favorite trick that saves time and effort is the stay in place gasket. Be sure that you scrape (don't use a wire brush) all the old gasket material off, then clean all the surfaces with acetone or MEK.

When the surfaces are clean, use weather strip adhesive on the head to manifold surface, and on the side of the gasket that mates to the head. Follow the instructions on the tube or can and when it gets tacky, press the gasket down on the head.

Clean the area where the rubber rails mount to the block in front and in the rear with more acetone or MEK and do the same trick with the weather strip adhesive that you did to the heads.

Coat the rubber seals and the gasket area around the water passages with Blue Silicone gasket sealer and put it together. Whoopee! no leaks, and no gaskets that shifted out of place.

 

[90FoxBdy]

Hopefully its the upper. The lower had better sealed. I always take my time with that 1, due to some bad expieriences in the past. I did have a nasty backfire through the intake when I put the dist. 180 out. We will see tomorrow morning.

Would that thermactor tube cause a vacuum leak?

 

[jrichker]

The thermactor tube provides air from the smog pump to help burn up any leftover HC in the exhaust of a cold engine. It does not connect in any form to the intake manifold, and cannot be the source of a vacuum leak.

 

[joel5.0]

Suggest to revisit the valve train and make sure you don't have an excessive lifters preload problem. LUK

 

[90FoxBdy]

Looked over everything and didnt notice anything obvious pulled the upper and nothing. Also I was able to get carb spray all the way around the lower and didnt notice anything. Wouldnt it be a kind of obvious, since the vacuum is so low. One thing I did noticed is that the car will make a loud "pop" sound and the vacuum will drop with that sound.

If I rev the motor the vacuum will increase and then when it pops the vacuum will drop off significantly. Used two different gauges and noticed that the vacuum fluctuates from around 2-5.

 

[90FoxBdy]

Pulled codes and got 41 and 91. Is it throwing those codes casue I have no vacuum?

 

[jrichker]

The 41/91 codes are evidence of a vacuum leak. But you already knew that...

 

[90FoxBdy]

Looks like its gonna be the upper to lower. Removed it again today and noticed that both gaskets were wet. Have a phenolic spacer thats why there are two gaskets. Put a straigt edge on the bottom of the upper and it is definetly warped. I just had this repaired as I clamped the throttle cable under it a couple weeks back. Hopefully this takes care of it. I should have it back tomorrow.

 

[90FoxBdy]

Put the intake back on and nothing changed. Still getting the same readings. Any other ideas?