Intake gasket leak?

[BRUTUS_T_HOG]

I may be thinking of the 4.0, not sure if 2.9's also have that gasket. You would know by looking at the fuel rail. If the fuel rail is just a piece of pipe then it doesn't have a gasket. The one I'm talking about if an aluminum fuel manifold. Also if you are having a vacuum leak at the back of the lower intake where the intake meets the "great wall" then something is really wrong cause the crankcase shouldn't have vacuum like that. Have you tried pinching off the PVC? Is there any vacuum hoses back there?

 

[Spitfire1975]

The 2.9 fuel rail is the "pipe" style. The PCV is in the middle of the left valve cover with the hose running straight to the throttle body. Pinching off the hose didn't make a difference.

I am starting to think think the lower manifold, which I believe is aluminum, is warped just enough to create the leak back on the "great wall" where the RTV silicone goes when changing the lower gasket. It runs great when the gasket is first changed, until it gets warmed up, then the leak returns.

 

[BRUTUS_T_HOG]

Ok. But there should be no vacuum at the great wall. That is part of the crankcase. If there is vacuum there the intake will need to come back off and closely inspected. Have you verified where the vacuum leak is by spraying starting fluid around the leak area to see if the engine reacts? Be careful doing that and have an ABC fire extinguisher handy.

 

[Spitfire1975]

I have not done that yet. I have only been going on the sound.

 

[Spitfire1975]

Ether sprayed along the back of the intake manifold and along the back of the right side valve cover lowers the rpm's.

Compression test on the right side shows:

Cyl. 4 = 130
Cyl. 5 = 132
Cyl. 6 = 130

All cold.

Other than a warped or cracked lower manifold, what else would cause an air leak back there? Pretty sure I am installing the gaskets correctly.

A possible thought here......I have not re-torqued the lower manifold bolts after the engine heated up.........could the heat expansion break the seal, and I am simply not "re-sealing" it properly?

 

[Spitfire1975]

Well, I re-torqued the bolts to no difference so I went to the junkyard a got a manifold.

Changed it out and as of so far, it all seems good to go. We'll see how it does. If it develops a leak back there again I am going to give up. 3 years is enough.

 

[Spitfire1975]

the saga continues. Manifold leak is fixed. Now, the valve cover gasket is leaking right next to the #2 cylinder fuel injector when I cup my hand over the throttle body. If I spray ether on it (while blocking off the throttle), the motor dies. If I unplug the IAC valve, the truck dies. I didn't think there was that much airflow thought the valve covers?

Something sound screwed up?

Help?

 

[BRUTUS_T_HOG]

Is there a strong vacuum in the crankcase if you put your hand over the oil filler hole? A piece of paper might be a better way to check for vacuum on the crankcase. I would be suspecting a vacuum leak on the intake or the fuel injector before the valve cover gasket sucking air.

 

[Spitfire1975]

It's a strong vacuum in the valve cover. At first I thought it was the #2 injector, but then I put some paper down there to see where it went and it was getting sucked into the valve cover, straight across from the #2 injector. If I pull the PCV valve, the vacuum is still there. through both the oil fill hole and the PCV valve hole.

 

[BRUTUS_T_HOG]

Better pull the intake again then. Or start looking at cylinder heads if you have that much vacuum in the crankcase

 

[Spitfire1975]

Great. This is going to be the 4th manifold pull. I don't understand why I am not able to get this thing sealed.

 

[BRUTUS_T_HOG]

Great. This is going to be the 4th manifold pull. I don't understand why I am not able to get this thing sealed.

When you do that take a look in each intake port of the heads and see which one has oil in it. Then take a really close look at what is going on

 

[Spitfire1975]

When you do that take a look in each intake port of the heads and see which one has oil in it. Then take a really close look at what is going on

Will do. I am going to be out of town now for a couple weeks, so I won't be able to get to it for a bit.

Hopefully it will be the last time I have to do this.

 

[Spitfire1975]

I give up on this thing. I reinstalled the manifold again and it took care of the valve cover vacuum. For about two heat cycles. Now it is back. Nothing looked out of the ordinary in the ports and head. Runs like shit and I need to take it to the Utards to be inspected. Crap.

3 wasted years and way too much money down the drain. I miss my '89.

By the way, compression on the left bank was great.

Anyone want to buy a Bronco II?

 

[MJ'sBlkBII]

I suspect the initial failure was made known after I replaced the very nasty air filter so the engine was getting to much air at that point. The first time I assembled it I don't think it was completely dry and I covered the TB "just to see". It was working fine just up to stall then found a weak point to get the air it was fighting for. The second time I belive I went VERY liberal with the RTV and overlapped every seam then just left it be. Didn't even start it till the next day.
It was running well after the first reassembly, but I wouldn't leave it alone, so it was my own fault for messing with it and having to do it a second time. Can't say which if any made the difference.