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Old 12-30-2016, 09:25 AM   #1
Mr Bear
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Join Date: Sep 2014
Location: All Over
Posts: 22
4.3L Vortec Manifold Gasket Replace/Spider Upgrade

So....its been leakin out the top side, slow but steady. Ordered the gaskets and the MPFI upgrade....they came in today and a frost plug let go too. So, can't delay any longer. Wish me luck, its a huge job.

its a 4.3L but the manifold gasket leakage and replacement is about the same on the 5.3 and 5.7. Mostly work with basic hand tools and a real pain. But, fortunately all the connectors for the electronics are different and its about impossible to confuse them and get them in the wrong spot.

So...to the job.

Here....the frost plug on the rear drivers side started weeping today.



And here on the passenger front of the motor, the intake manifold gasket has crumbled (they are plastic and 100% fail between about 100K and 150K miles....mine has 149K). Fortunatly, both leaks are to the outside and not into the oil pan. So, no washed out bearings. The intake gaskets fail to the inside about as often as not, usually destroying bearings before you find out ya got a leak.



First, I removed the air box system and then the throttle body. I'll be doing the throttle body mod (remove the blockage at about 10 oclock on the throttle plate that reduces low and midrange torque since GM surveys determined that folks didn't want lots of power off the line). Clean it up, cut off the offending blockage and reassemble for reinstall tomorrow.



Once the plastic plenum is removed, I note the original CSFI (Poppet Valve) central fuel injection. Been getting the occasional slow start. This will get replaced with the more reliable MPFI electronic fuel injection which is a standard GM upgrade since there were so many complaints about the unshrouded poppeds gunking up and sticking, etc. CSFI was last used on the Blazers in 2002. This one has 149K on it so, might as well replace it with the better/newer system now. Amazon to the rescue, $160 saved and arrived in 2 days.



To get the lower manifold off, remove everything on top. Pull the wiring up and out of the way, loosen the bolt holding the fuel pipes and pull the assembly up out of the way (no need to crack the short lines from the bracket...just blead it down before pulling out the pipes). Remove the coil. Remove the PCV, breather pipes, water neck, heater hoses, EGR, etc. I pulled the alternator for more room and also removed the ac compressor (just lay it out of the way, don't open the pipes), take off fan belt, water pump bypass hose, brake vacuum hose, distributor cap and wires.

Finally, remove about 3 bolts and 3 nuts from the AC/Steering Pump bracket and slide it forward 2" to uncover the one hidden intake manifold bolt on the DS front of the manifold.



Turn the engine by hand to TDC on the compression stroke. Rotor should point at the triangle on the dizzy base....marked in white. There is no timing adjustment, so the dizzy has to go back in exactly on these marks or it won't run right or at all. Once the dizy is out, do not rotate the engine or the oil pump drive shaft, so that later, you can back the rotor (counter clockwise) up to line up the marks on the lower shaft and drop it right back in the hole. When the marks line up like shown, you'll know its in right and will start and run.



Pull the eight bolts that secure the lower manifold to the heads. Yank the manifold and you get to see the crumbling and broken plastic GM gaskets. Even with the radiator/block drained, you'll get some coolant in the valley, that'll have to be mopped out and with all the work, an oil and filter change, immediately, is indicated.







Cleaned up and the new Fel Pro perminant gaskets sitting in place on the heads. Threaded holes were swarfed out with solvent and a good set of gunbrushes. You can tap them too but will need a long extension for the tap....brush is easier if they are not too cruddy. RTV is used on the front and rear in the valley. And a bit more sopping up coolant to do. Final assembly will be tomorrow. For now, cleaning all the threads on bolts so they can be sealed and properly torqued. While in there I replaced the valve cover gaskets. The plenum and fuel rails will get all new Fel Pro gaskets too, they are in the kit. $20 saved on Amazon for the Fel Pro best kit and again, here in 2 days. They all arrived as I was finishing cleaning up the manifolds!




Tomorrow is reassembly and I have to fix the frost plug. Then a 24 hour sit for the RTV to cure and with luck, Monday morning is Fire Up.
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