Mechanics

I JUST REBUILT MY 350 5.7L V-8 OUT OF MY K-2500. THE ENGINE HAD LOCKED UP SO I REBUILT FROM THE BOTTOM UP. WHE I START THE ENGINE THE IDLE IS ROUGH AND ONLY KEEPS RUNNING WITH ASSISTANCE. AFTER ABOUT THIRTY SECONDS THE ENGINE WILL DIE NO MA

1992 Chevrolet Silverado • 210,000 miles

1992 Chevrolet K-2500 5.7L T.B.I. V-8 newly rebuilt.
Engine is in initial start up and break in phase of rebuilding.
New pistion Rings, main bearings, rod bearings, TPS, oil pressure sending unit, cam bearings, new stock camshaft, lifters, valve seals, professionally cleaned all engine parts, qualified all non replaced engine components, new timing chain.
adjusted rocker arms, checked timing, verified vacuum hoses are in good order and correctly placed. Crankshaft was professionally ground and polished to 10/10.


Avatar
Cvg1mak
May 13, 2012.



Have you done cylinder test to determine misfiring cylinders? I loosen wires at cap, start and lift them off 1 at a time to find cylinder that is not firing properly.


Tiny
Fixitmr
May 13, 2012.
I have not checked, the engine when running is rough at idle, but does not sound like a misfiring cylinder, and that would not explain the loss of vacuum that does not recover, but I will check tomorrow to see if there are firing problems. Thank you and any other suggestions are appreciated.


Tiny
Cvg1mak
May 13, 2012.
So you did vacuum gauge test and there is a problem?


Tiny
Fixitmr
May 13, 2012.
Yes I put the vacuum guage on multiple sources when the engine stalled the first time and the reading is consistent. The engine has good vacuum for about the first twenty seconds or so, although it is fluctuating, and then begins to drop at a rapid rate to zero, where the engine dies. I have tried everything to keep it running but once the vacuum drops there is no saving it even at WOT. This caused me to check and re check the hoses and connections against the schematics, and everything checks out. I pulled the timing cover and re checked the timing which was dead on, and I re adjusted the valves/rocker arms too but the problem persists.


Tiny
Cvg1mak
May 13, 2012.
EGR problem?


Tiny
Fixitmr
May 13, 2012.
Pinch off brake vacuum?


Tiny
Fixitmr
May 13, 2012.
Unsure if there is an EGR problem, with the EGR valve disconnected there is no change and the valve when hand tested operates like a new one. The power brake hose is not pinched or obstructed if that is what you mean. I did try to depress the brake pedal to put the engine under some load when it was running and there was no change in operation or unusual change in vacuum. The engine needed the crank ground and also nad a worn cam lobe, so I replaced the cam with a stock cam, and replaced the lifters, just for more info.


Tiny
Cvg1mak
May 13, 2012.
I am a diesel mechanic and have been wrenching for 17 years. The machining work and cleaning was done at my diesel shop under my supervision so I am sure it is accurate and everything is clean and in good condition. There was a gap in the intake manifold after manifold was set in place although I used extra sealant on the front and rear of the mating surface. When I realized there was a gap I sealed it by pressing the sealant into the gap and added extra on the outside, but I am thinking if there was a problen here the engine would not produce normal vacuum initially.


Tiny
Cvg1mak
May 13, 2012.
I see what you mean. Try blocking off PCV to intake.


Tiny
Fixitmr
May 13, 2012.
When the PCV is blocked off the idle increases a little but the vacuum problem is still present. I blocked the PCV for a few attempts and got the same results, however when the PCV is disconnected the engine will start better and sometimes did not need the throttle opened to start, and on the first attempt idled on its own at around 300 RPM for almost a minute.


Tiny
Cvg1mak
May 13, 2012.
Page 1 of 2