Can't get intake to stay sealed. Advice?

[ponkotsu]

I'm about 99% sure my problem is the lower intake manifold gaskets. I suspected I had a leak so I replaced with Felpro. Seemed like it helped my rough idle but started getting worse again. I later realized that the intake was leaking again. So I pulled the intake and sealed it off with the same gaskets and blue RTV. Engine ran beautiful for an hour and starting getting worse. Pulled it apart again and very carefully sealed it off with big bead of grey RTV. Same thing, ran good for a very short time then got worse and worse.

Typical intake vacuum leaks symptoms. Rough idle. Slow to come down to idle speed. Rough when coming down. Stumbles a little on decel. Only about 14.5hg of vacuum. I've also tried disconnecting the IAC valve and pinched off all the vacuum lines. The engine will often still idle at over 600RPM so that is pretty conclusive it is an intake leak.

Looking at these gaskets, they appear to be a poor design for this intake. Looks like there isn't enough squeeze on the seal and its so soft it can get sucked in by vacuum.

Anyone have suggestions on how to get this thing to seal once and for all? I've not pulled the lower intake 4 times and it's getting really old. Thinking about just buying some OEM gaskets and see what happens but hate to spend the money for nothing.

 

[ExplorerFreakz]

First check your intake for cracks, the plastic over alot of years gets brittle and the intakes are prone to cracks... dorman makes intake manifolds for this, which should tell you something. Their intke will solve your issue BUT make sure you use their gasket.

http://www.stockwiseauto.com/product_info.php/products_id/245985/fit_id/8902/Year/1997/Make/Ford/Model/Explorer/source/googleps?gclid=COK5nev927sCFYg-MgodYiQA_Q

Hope this helps!

 

[ponkotsu]

First check your intake for cracks, the plastic over alot of years gets brittle and the intakes are prone to cracks... dorman makes intake manifolds for this, which should tell you something. Their intke will solve your issue BUT make sure you use their gasket.

http://www.stockwiseauto.com/product_info.php/products_id/245985/fit_id/8902/Year/1997/Make/Ford/Model/Explorer/source/googleps?gclid=COK5nev927sCFYg-MgodYiQA_Q

Hope this helps!

Aviator has a unique cast aluminum intake. Definitely not cracked or leaking.

 

[ponkotsu]

Happy New Year, I pulled the lower intake again this morning. Got it down to about 35 minutes. I think I could literally do this blindfolded now. The mega grey RTV sealing technique was a total fail. I can see some pretty clear leak paths. So I'm going to get the OEM gaskets. I think this should be installed with some high tack or Gasgacinch but I'd really like some pro advice on that. I measured both surfaces for flatness and they are within .001" across short distance. I don't have anything to measure the entire length of the surfaces but it really looks good so I don't think that was the issue. No evidence whatsoever of cracks anywhere. I think the issue was simply a bad design gasket.

As a side note, anyone trying to smoke test this intake can forget it. It has long runners that act like a trap. Not likely you will get smoke coming out of it, even with a massive leak. And the gasket sealing surface is so buried down in there that I couldn't reach it with carb cleaner to test either.