1984 351W HO with Motorcraft/Holley 4180c in a 1978 E-150 van. Except for the engine & carb, everything is 1978 stock.
Key symptom: Stalls when put in gear. Manifold vacuum, engine at operating temperature, is 18” and behaves ok per the charts. But put in gear and work the throttle to maintain an idle it drops to 5-6.”
I’ve spent many hours trying to resolve what I thought was a carburetor problem. But recently found this forum and a review of previous postings suggest that a vacuum leak could cause my symptoms. AND I FOUND A VACUUM LEAK!
It appears to be above the #1 cylinder. When sprayed on the upper edge of the valve cover, which is also the location of the intake manifold edge, propane or carb cleaner will cause rpm to increase; water will cause a decrease in rpm.
Is this confirmation of an intake manifold leak? Or is there anything else in close proximity that could be the culprit? Will that cause the stalling? Also, would such a leak affect the mixture for all cylinders? Examination of the sparkplugs - #1 does not appear different from the others.
If I remove the intake manifold, is there any other inspection or maintenance that should be done while the manifold is off?
Finally (for this post ), mounted on the intake manifold to the left of the carb is a vacuum operated device. Is this the exhaust heat control valve? There is no vacuum line connected to it, and it doesn’t engage anything anyway. There is a rotating rod sticking into the manifold, but nothing connected to it. Do I just leave it as is or is there something I should get for it?
I might still have carb and other problems, but vacuum leak seems to be the first to fix before tackling. All comments appreciated. TIA.
Portland, Oregon USA
I just botched the intake manifold gasket replacement using “regular” gaskets. Even with two people it seems impossible to place the intake manifold squarely on the new gaskets with out displacing the end seals. (This is a van - installing from the inside.)
I now realize that there is a one piece Valley Baffle gasket for vans, instead of the two intake gaskets, which appears to mount on top of the end seals. My 1984 engine doesn’t have this (I don’t know what vehicle it came out of).
What is the purpose of the valley baffle on the 351W vans? Before trying again, I especially wonder if it will help with intake manifold placement? Any other tips, guidance, suggestions?
Portland, Oregon USA
Don't use the end seals,just put a good bead of hi temp silicone.It helps to put silicone around the water jackets for insurance and let the silicone set up for a few minutes so the gasket won't move when you set the intake.Just push on it a little, if it moves let it set up a little longer.Then put the silicone on the ends,you don't want this to set up long before you set the intake.I have seen people take some old intake bolts and cut the heads off or use allthread and put it at the 4 corners so you can set the intake.Then replace them with the proper bolts once it sets up.As for the valley gasket's,most later model motors that have the solid valley don't use a valley gasket.
Thanks, Billy. Using RTV instead of end seals will certainly make the process easier. Using guides in the corners is a “no-brainer” I should have thought of.
Can you help me visualize this valley terminology - what is meant by solid valley? With the intake manifold off, the “valley” I see is just a gaping area, lifter rods exposed and a few holes in the bottom, for oil drainage I assume. There is no “pan” except for the riveted plate under the carb mounting area. (I don’t know the original source of this 1984 engine - but that’s another story. The rest of the 1978 van is stock - I’m the original owner.)
The valley "pan" Is the solid area between the lifters and pushrods.Some older engines have a valley gasket that is part of the intake manifold.Most newer engines have the 2 piece intake gaskets without the valley cover.When you install the gaskets make sure you seal the corners where the intake gasket and the head meet with a bead of silicone.
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