Help with upper and lower manifold & air intake valve

[Daisywheels]

Hi everyone - I believe I have finally found the cause of my vacuum leak which I am assuming is giving me the rough idle, and misfire codes. I checked the seating of the upper intake manifold to the lower intake with a VERY bright flashlight, and sure enough, I could see part of the gaskets. I assume that should not be with a properly mounted upper manifold?

1) I just tried to reseat the upper manifold to the lower, and it is not seating properly. I followed Haynes, and several guides here, and I just can't figure out why it won't seat properly. My best guess is the EGR tube is not allowing the upper manifold to seat right. Has anyone had issues with this?

2) Also using the flashlight, I discovered a possible hole in the air intake valve on cylinder. Can anyone point me to a thread on how to replace these air intake valves? Having trouble locating directions. The valve is only like 5 bucks at rock auto and look like this:
http://www.rockauto.com/catalog/moreinfo.php?pk=5579595&cc=1354542&jnid=564&jpid=0

3) I am going to pull an all nighter and see if I can get the lower manifold out and mate it up with the upper off the car just to make sure there is no warping. I'm doubting that - more leaning towards the EGR tube.

4) Any other ideas or suggestions would be greatly appreciated! Thanks! - DW

 

[JusTheUsual]

could be your egr catching up but highly unlikely. the plenum or what you call the upper intake manifold is made of plastic and there is some stories of them warping but hardly happens. It almost seems that's whats wrong. I doubt the egr is holding up the plenum from attaching correctly, highly unlikely but can happen, make sure you shove it in all the way. The valve you would have to pull the head off and how is their a hole in it?

p.s.
don't tell anyone I told you but you can tighten your plenum more than whats called for to help seal it. I was talking to a ford mechanic at a dealership years ago who had dealth with this problem many of times and he said "don't be scared to tighten it more, crank down on it" his exact words. I just wouldn't go over like 25ftlbs because then you might perm. warp it

 

[chrisb87]

Or break the plastic. Hand tighten it down to the lower manifold then in sequence start tightening the upper intake down with ur socket wrench leave a little leway for the torque wrench to finish up the job.
An easy way to find a vacuum leak in the system is go buy a cigar and then remove one of the vacuum hoses take another hose and attach it to the one u popped off with the engine running start blowing cigar smoke into the vacuum system. If you have a leak the smoke will point it out.

 

[Daisywheels]

could be your egr catching up but highly unlikely. the plenum or what you call the upper intake manifold is made of plastic and there is some stories of them warping but hardly happens. It almost seems that's whats wrong. I doubt the egr is holding up the plenum from attaching correctly, highly unlikely but can happen, make sure you shove it in all the way. The valve you would have to pull the head off and how is their a hole in it?

I'm guessing something - some piece of foreign matter got inside there and caused the damage. I live in the forest and pine needles are falling everywhere - they find their way in regardless of me covering up the ports.

p.s.
don't tell anyone I told you but you can tighten your plenum more than whats called for to help seal it. I was talking to a ford mechanic at a dealership years ago who had dealth with this problem many of times and he said "don't be scared to tighten it more, crank down on it" his exact words. I just wouldn't go over like 25ftlbs because then you might perm. warp it

The first time I tightened the upper plenum I torqued it too hard and broke a bolt. That's when I called my mechanic in He suggested it was warped and I bought another set of both the upper and lower manifolds so I have two to play with.

I have the lower manifold off right now, and immediately saw a huge puddle of coolant under the lower manifold. I know I have a coolant leak - I thought it was coming from the T-stat housing which I know has a crack at the very end of the hose connection. But I have read many threads here that seem to associate coolant loss with upper manifold and/or gasket problems. I can't remember if there is a connection. Is there?

Also, almost all the six intake valves have burn marks in the center of them, it's more brown like than black, so I don't know if they are burnt or not?

Thanks! -DW

 

[Daisywheels]

Or break the plastic. Hand tighten it down to the lower manifold then in sequence start tightening the upper intake down with ur socket wrench leave a little leway for the torque wrench to finish up the job.
An easy way to find a vacuum leak in the system is go buy a cigar and then remove one of the vacuum hoses take another hose and attach it to the one u popped off with the engine running start blowing cigar smoke into the vacuum system. If you have a leak the smoke will point it out.

I tried an E-cig because the vapor is supposed to last longer than regular smoke. I just used the break booster hose. But with the manifold not seated properly, that vapor or smoke would just shoot out before I can see it. Thanks for reminding me of that test though. It's definitely a good idea and I'll try it once I get the manifolds seated properly. Still need to take a better look at that valve before I try to put this back together. That reminds me - can't beleive Haynes says to take off the valve covers to remove the lower intake manifold. There is absolutely no need to do that. -DW

 

[Daisywheels]

Also, If I do have to take the head off if that valve does indeed have a hole in it, would anyone recommend just taking the head to a machine shop for a complete valve job? Any idea what that costs these days? Truck has 126K miles on it.

Last time I took a head in for a valve job, it was from a 4 cylinder motor from a boat. The motor actually came out of the Nova factory if anybody remembers the old chevy Nova's. Any ways about a year later (after warranty expired) a valve dropped and put a hole in my piston. So much for that motor! -DW

 

[2000StreetRod]

valve replacement

If you remove the head to replace an intake valve you have to retime the camshafts which requires the use of timing tool kit OTC 6488.

In order to compress the valve spring you need another special tool.

A compression test will indicate if your valves are leaking.

There is no coolant flow in either the upper or lower intake manifold on the SOHC V6. The coolant under the lower intake manifold in the valley between the heads is probably from a leaking thermostat housing.

I'm familiar with the 4 cylinder Nova engine built in Mexico and used on the Mercruiser inboard/outboard. I had one on my 1984 Sea Ray.

 

[Daisywheels]

If you remove the head to replace an intake valve you have to retime the camshafts which requires the use of timing tool kit OTC 6488.
View attachment 83726
In order to compress the valve spring you need another special tool.
View attachment 83727
A compression test will indicate if your valves are leaking.

Ok, thanks Streetrod, I'll start with a compression check and just hope. All those tools look expensive and complicated as hell.

There is no coolant flow in either the upper or lower intake manifold on the SOHC V6. The coolant under the lower intake manifold in the valley between the heads is probably from a leaking thermostat housing.

That's what I thought. It's a slow leak and an easy fix. I actually just took a soldering iron to the T-stat housing at the end where the hose fits on - it was a very small crack, but obviously I didn't fix it.

I'm familiar with the 4 cylinder Nova engine built in Mexico and used on the Mercruiser inboard/outboard. I had one on my 1984 Sea Ray.

Mine came in a 1973 Larson. The motor was built in 1964. 140 HP Mercruiser inboard/outboard, just like yours. Thanks again Streetrod -DW

 

[Daisywheels]

Hey Streetrod, you seem to know my vehicle very well. Can you tell me where my PCV valve main hose ends - from back to front? I can only trace it as far as what looks like some sort of control box approximately six inches away from the PCV valve itself. That box actually might be just in between where it T-s off the upper plenum. Everybody says there is a notorious elbow down under the t-stat housing or throttle body? not sure, but I can't trace it that far out. Does my model have a PCV line that actually has that elbow near the T-stat or Throttle body? - underneath em of course. Thanks again - DW

 

[2000StreetRod]

PCV valve location

The first photo in the following thread shows the location of the PCV valve:
SOHC PCV Valve Mod thru 2000

 

[Daisywheels]

The first photo in the following thread shows the location of the PCV valve:
SOHC PCV Valve Mod thru 2000

Right - I know where the PCV valve is located and how it has a t connector for two lines to the upper plenum. I guess what I'm asking is where does the main line/hose - that does not go to the plenum, where does that end? Does it go as far as to the front of the motor or does it basically end in that little control box right under the plenum? Thanks - DW

EDIT: I read a bit further and what I'm calling a "control box" is actually what you call the "crankcase breather." So it does not go very far at all, certainly not to the front of the motor.

 

[JusTheUsual]

I have the lower manifold off right now, and immediately saw a huge puddle of coolant under the lower manifold. I know I have a coolant leak - I thought it was coming from the T-stat housing which I know has a crack at the very end of the hose connection. But I have read many threads here that seem to associate coolant loss with upper manifold and/or gasket problems. I can't remember if there is a connection. Is there?
-DW

Yes, my intake, not the plenum or upper intake some people call them, but the intake manifold gasket blew out on mine in the front and antifreeze poured out like a rainbow up six inches and down onto the fan. There has been known problems with intake manifold gaskets leaking.

 

[Daisywheels]

Well, I took the intake manifold plenum and lower manifold off the truck and tried to mate them together on my bench. No luck. I did 10 passes of torquing
and I still have openings in the center on both sides ~1/8" or 1/16." Either way, its not seated properly.

Question: Which is more likely to be warped? The upper or lower intake manifold? Or should I just buy both? I hate throwing more money into this truck at this point. Thanks! -DW

 

[Daisywheels]

Also, can I do a compression check with the entire intake manifold off the truck?

 

[2000StreetRod]

use a straight edge

The lower intake manifold should be flat.

Try placing a straight edge across each bank of ports on the bottom of the manifold to determine if it is warped. My lower intake manifold bottom was keyed at the two center port mounting bolt holes but the heads were not keyed to match.

The top of the lower intake manifold has a guide pin(s) for alignment with the upper intake manifold.

Make sure the pin(s) fits into a matching hole(s) in the bottom of the upper intake manifold. Try rotating the lower manifold 180 degrees.

A compression test only requires the heads with camshafts and valves to be in place. Without the intake manifolds you don't have to find a way to hold the throttle plate wide open.

 

[Daisywheels]

Ok, good info StreetRod. Thanks for your help! -DW

 

[Daisywheels]

Hey StreetRod - What do you mean by "the heads were not keyed to match?"

Also, what do you mean by try rotating the lower manifold 180 degrees?

I know where the aligning pins are - one in the center as shown in your pic, and one on each end of the the lower manifold. These were lined up before I started torquing the two parts together off the truck. Just confused by car lingo I guess. Thanks again! -DW

 

[2000StreetRod]

bolt holes

If you look closely at the middle bolt holes in the bottom of the lower manifold you'll notice that one hole is smaller in diameter than the others and one is a slot. However, there was nothing on the heads that prevented mounting the front of the manifold at the rear and vice versa. I think the lower manifold is symmetrical but I seem to recall there was an L and R stamped on opposite sides.

 

[Daisywheels]

I would think the guide pins on the lower manifold would keep this from happening? Since there is only one pin in the middle, and one on each side of the front or back, the only way the upper manifold could go on correctly is if the lower is mounted correctly. The guide pins are actually on different sides at both ends on top of the lower manifold. Hope that made sense? Thanks - DW

EDIT: Never mind. I think what you are talking about can actually happen with the manifolds off the truck. It would be easy to still have the lower not properly rotated if not on the truck. IS that what you were thinking?

Stupid question, but I'm brain dead right now - I see the L and R markings, but what side is L? Is it the driver side (I hope) or is the L the left side (passenger side) when standing in front of the truck?

2nd EDIT: Nevermind X 2. I can tell L is the driver side just by looking at the orientation of the upper. I did mount it wrong while off the truck.

 

[Daisywheels]

If I look closely at the bottom of the upper plenum, there is a long recessed area that runs roughly 1/2 inch from each corner of the plenum, and on both sides. It appears this gap is supposed to be there. What I'm actually seeing are the very tips of the runners, not the gaskets. I just tried mating the upper to the lower with no gaskets and no bolts, and it's a nice even fit on the corners, but not along the sides. Can anyone confirm if that slight gap is supposed to be there?

The OP in the following link shows pics of his/her gap and concluded it is supposed to be there, but he didn't back up his conclusion.

http://www.explorerforum.com/forums/showthread.php?t=403128

Getting frustrated now - Thanks - DW