2000 Chevy Astro 4.3L CSFI Vin W

Astro · Posted at Mon Mar 19, 2007 12:03 pm

po302, po507: Replaced all of the following: fuel pump, cat. conv., fuel injectors (no.2, no.6, no.5), fuel pressure regulator, pcv valve, IAC sensor, HEI coil, plugs, wires, cap, rotor, fuel filter, all three O2 sensors, VSS, Ignition control module check was good, EGR valve stem clean, new vacuum lines, no.2 spark plug replaced again just to rule out a factory defect., TPS check good, CPS check good. I've given her lots of love. All work has been completed within the last 8mo. I should have a lean machine at this point. Exhaust doesn't really seam to have any tell-tale signs of water (white smoke) Hope to avoid replacement of head gaskets. Could the intake manifold gasket be a cause of the misfire, and not the head gasket? Since there is a PO507 with a PO302 wouldn't this be more likely?

Service Writer · Posted at Mon Mar 19, 2007 2:45 pm

If you have been losing any coolant:

Let the truck set 12 hours, Have it jacked up enough to have access to the oil drain plug. Slowly back out the drain plug so there are drips coming out and catch them in a clear jar until you can confirm any coolant iis or is not present in the oil. IF not obvious, just fill the container a few inches high and allow it to set another 12 hours. Completely drain the oil. Then pressure test the cooling system with the drain plug out and catch the drainage into another clear container, letteing it set under pressure for 8 hours or so. The coolant will settle to the bottom of the container.

IF you have not been losing any coolant. compression test the #2 cylinder.

Astro · Posted at Tue Mar 20, 2007 3:47 pm

1st stroke=90
2nd=100
3rd=110
4th=about 120 and this is where it topped out.

Service Writer · Posted at Tue Mar 20, 2007 4:09 pm

Good results. I should have looked at the po507-high idle. Typically this is a vaccum leak source. There are couple ways to go about this. One is using an un lit propane torch and running it around the intake gasket areas, the # 2 cylinder and injector, or spraying a combustible liquid like carb cleaner. Listen for an idle change and then focus in that area.

My hunch is an intake manifold gasket problem.

coudriet · Posted at Mon Apr 02, 2007 1:49 pm

What was the end result or what fixed the problem?

Astro · Posted at Sat Apr 14, 2007 11:54 am

Replaced intake gasket. Engine performance improved. BUT. Went on a road trip (1100 miles round-trip. 30 miles from arriving home, started to misfire (constant). After compression test (#6 and #4 bad), decided to replace the head gaskets. And what fun it was. Had two bent valves, HEAVY carbon build up on valves. Cleaned and inspected heads for cracks. Installed two new valves, lapped all valves, replaced valve seals. Everythings back together, fired her up, tap...tap...tap (when you lightly touch the gas pedal there is also an intermittent knock. Sounds like something is hitting the bottom of the intake. What am I looking at hear, bent push rods? Did the bearings go on the balancer shaft? I feel pretty sure some valve adjusting will clear-up the tapping, but the Knock sounds bad.

Astro · Posted at Mon Apr 23, 2007 6:15 am

I removed the valve covers today to start checking for the obvious, and I found it. I have a bent push rod on the #2 exhaust, the rocker arm bolt is broken, and so is the end of the rocker arm support (rocker pedestal or rail) whatever the correct term is for the bar they rest on. I applied enough pressure to the valve to make sure it wasn't stuck, I was able to depress it with little effort, so I don't suspect a bent valve. I don't know a whole lot in this area, and need to know what my next step should be.
Could it be that I simply didn't have the push rod seated properly on the lifter. And I can get away with installing a new support/push rod/rocker arm & bolt. Or is it likely that there is more damage below the surface. Did something else cause these parts to break (a bad lifter? camshaft?) or vice-versa did the damage I found so far, most likely damage the lifter, cam, etc.