5.7L Vortec Problems

[YukonGTmaster]

I was having a rough idle, and the Amber engine light would flash (Random misfire) when I started up in the morning. I would cycle the key off for ten seconds, the light would go out and I would drive to work. It was not latching any codes. I had a bad coolant leak as well. Then I started to hear a whistling sound, like a vacuum leak on the passenger side engine. I also had fouled/residue at plugs 4 & 6. I ordered parts: MPFI Spider from Motor Man, Felpro Gaskets P/N MS 98000 T, Felpro lower intake bolts P/N ES 72224, and Bravex Distributor. I disassembled...and was horrified what I saw. The coolant port at the lower intake manifold was extremely corroded and pitted at the gasket mating surface.

 

[YukonGTmaster]

I cleaned the Intake in a CUDA parts washer, media blasted the pitting, and built up the surface with Metal Set A4. I let cure 2 applications over 48 hours. I then wet sanded the surface with 1000 grit paper, wrapped around a metal flat bar.

During the disassembly process I destroyed my EGR hose. I twisted the hose badly damaging it, but at least it unthreaded from the intake. I ended up cutting the hose off near the exhaust. I sprayed penetrating fluid and left over night. I got a 1” impact socket, with a 6” extension, and the impact gun removed the remaining fitting no problem.

 

[YukonGTmaster]

The oil pressure gauge had been dancing around on me for a while, so as it was staring me in the face at this point, I ordered the Oil Pressure Switch /Transmitter, and the EGR tube off Rock Auto, and it was delivered in 3 Days.

 

[YukonGTmaster]

I got the new MPFI Spider installed, but had a heck of a time getting the upper intake manifold to seat down over the spider O-Ring. I pulled the manifold off and put Petroleum jelly on the O-ring and a lot on the inner bore of the upper intake. When I got it installed I noted a 1/8” gap between the spider and the manifold. I grabbed the sides of the spider with smooth jawed Knipex pliers wrapped in paper towel and pulled with all my might to get the O-ring to seat and close that gap. When doing the torquing of the upper intake, 44 inch lbs, then 88 inch lbs, I thought I was stripping threads because some studs torqued, and some kept spinning. What I noted was that there was a gap between the washer and the nut on some. I had to run them all down, and guesstimate the torque (I work on helicopters, so I work with 1/4” drive ratchets often.) The helicoil threads looked in good shape, but new studs/bolts would have been the way to go, and maybe threadchase the helicoil inserts?

 

[YukonGTmaster]

I replaced the Heater Hose coupler with a Dorman (wish it was AC Delco), Thermostat, and EGR valve gasket.

 

[YukonGTmaster]

I am going to clean all gasket surfaces with MEK, and install the intake tomorrow.

Will. 1997 Yukon GT. 1 owner, daily driver. 415,000 kms.

 

[drakon543]

going in hard and heavy there. hope everything works out when your done

 

[YukonGTmaster]

Thanks drakon543. I got the intake bolted down. I soaked the threaded inserts at the cylinder heads with ACF-50 for about a week. I blew them out and dried them with compressed air. I noted some coolant sitting onto of the valve in #1 cylinder so I got a 1/2” flexible tube and taped it to the nozzle of my shop vac. It cleaned out the ports and oil gallery well. The new Felpro lower intake bolts torqued down smooth and even. I am going to let everything set up overnight, and then start reconnecting.

 

[willxfs]

Good stuff. Keep us posted on how your rig runs after all the hard work.

 

[east302]

Looks good, just got done doing this as well.

Don’t forget the o-rings on the fuel lines at the firewall.. (I got that t-shirt)