Upgrading to mpfi should i do the lower intake gasket?!

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Pinger

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I changed mine. I was losing coolant and oil and there were signs of antifreeze in the oil (analysis). My truck was on 45,000 miles so pretty certain they were the originals. They were and needed changing.

If you (or anyone else) decides to do this job and doesn't have a scan tool - this worked for me.

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delta_p

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I did the mpfi switch about 4 years ago. I wish i would have done the lower intake then too. This would be the third time since '96 when the truck was new. I got oil drip on the starter bolts and around the trans cover. I pulled the transmission last year and replace the oil seal and pan gasket. The oil sender and fitting looks dry. I can't think of any other place the oil could come from, so the lower will come off soon for a another gasket set and RTV, and new valve cover gaskets.
 

HotWheelsBurban

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I changed mine. I was losing coolant and oil and there were signs of antifreeze in the oil (analysis). My truck was on 45,000 miles so pretty certain they were the originals. They were and needed changing.

If you (or anyone else) decides to do this job and doesn't have a scan tool - this worked for me.

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You ought to make a pattern or scale drawing of this! I'm sure many of us contemplating this job could use it( I know it would help when I get around to it). Thanks!
 

Pinger

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You ought to make a pattern or scale drawing of this! I'm sure many of us contemplating this job could use it( I know it would help when I get around to it). Thanks!

It's going to be different for every truck though!
It wasn't difficult to make. Mark and drill the two holes for bolting it to the manifold, bolt it to the manifold then drop a sharp point down through the dizzy hole enough to mark the plate then drill a hole on the mark.
As back up - just in case it didn't work - I set a vernier caliper between the dizzy hole and one of the manifold holes. Caliper was an old really stiff to move one. I could have probably aligned the dizzy from it. I'd trust either of those methods more than scribed marks.
 

L31MaxExpress

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I would change the intake gaskets. In 2004 at 57K miles the OEM 350 in my 97 Express failed catastrophically on startup from hydraulic lock caused by leaking intake gaskets. Never even knew they were leaking until it snapped the #2 rod on startup.
 

HotWheelsBurban

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Yes I want to do all this stuff together, so I don't have to go into it more than once. Just trying to save up some $$$ to get parts.
 

L31MaxExpress

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Yes I want to do all this stuff together, so I don't have to go into it more than once. Just trying to save up some $$$ to get parts.
I cleaned the intake by soaking it in a mixture of simple green and water. Then kept it clean with GM Top Engine clean before every oil change. With EGR enabled and functioning it will get dirty very quickly.

This intake I ran on the 305 in the Tahoe had about 40K on it since I had cleaned it and had used top clean every 5K before oil changes. Still very clean compared to how the one in my Express van looked at 57K when the stock 350 exploded.

I would also do a little port work to the lower intake while it is apart. While I opened this one up to match a 210cc port head the factory manifold castings have terrible port shift and port alignment even on a factory vortec head. Probably 15-20 hp to be gained even with the factory cam porting the intake. Stock cam truck I swapped a ported lower intake on picked up about 20 gms/sec airflow through the maf at 5,100 rpm.

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L31MaxExpress

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It's going to be different for every truck though!
It wasn't difficult to make. Mark and drill the two holes for bolting it to the manifold, bolt it to the manifold then drop a sharp point down through the dizzy hole enough to mark the plate then drill a hole on the mark.
As back up - just in case it didn't work - I set a vernier caliper between the dizzy hole and one of the manifold holes. Caliper was an old really stiff to move one. I could have probably aligned the dizzy from it. I'd trust either of those methods more than scribed marks.

I used scribed marks when I did the first engine swap in the Express van. Ran it like that for years.
 

HotWheelsBurban

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I used scribed marks when I did the first engine swap in the Express van. Ran it like that for years.
At least in a van you have some access to the back of the engine once the doghouse is off. Had a company van years ago ( the older style unibody van though) and that's how it was. The express model is the same way?
 
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