2005 PCV Valve & Vacuum Issue

[roamineye]

Finally got my 05 stock Astro running much better - replaced the extremely worn distributor with a new one and made a world of difference! But it still occasionally runs a little rough, throws the P0420 code, AND seems to have a vacuum problem. With A/C set on the "normal" setting (not Max A/C) it stops blowing through the dash vents when I go up hills on the highway. I know the actuators under the dash are vacuum controlled, so I must have a vacuum leak or another problem somewhere. I inspected the vacuum lines on top of the engine and everything looks OK - previous owner said that he'd had them replaced. So, it leaves a couple of possibilities:

1) Catalytic converter is plugged, causing vacuum to go away under higher engine loads - I haven't done the tap test yet to see if anything inside the converter rattles. That's easy and I'll do it this morning. I'll also unplug the rear O2 sensor to see if it makes the engine roughness go away.

2) Also thinking it might have something to do with the PCV valve. I bought one to replace it with, but I can't find on on the engine anywhere. The locations on the valve covers where you'd normally expect to find them have lines running to them, but they're attached to what appears to be permanent fittings that don't seem to be replaceable. Any suggestions where to look would be appreciated. Or, maybe the later models don't have a PCV valve?

Thanks!

[photo_van]

One common problem (I had it) are the rubber vacuum lines at the solenoid tucked below and center of the heater motor in engine compartment.

[roamineye]

One common problem (I had it) are the rubber vacuum lines at the solenoid tucked below and center of the heater motor in engine compartment.

Thanks, photo_van, I'll check that out. Any idea where the PCV valve is, or whether it even has one?

[photo_van]

I seem to recall one on the '98 toward the rear of the drivers side valve cover.

[roamineye]

I seem to recall one on the '98 toward the rear of the drivers side valve cover.

Yeah there are fittings in the valve covers, both sides, that are similar to those that used to be used for the PCV, but they have connections in them that don't look like the classical PCV valve. They have tubing that runs to other parts of the engine. One (driver side) goes to what appears to be a valve with vacuum lines that run to the vacuum source lines for the under-dash vent controls. I've read on this forum that the crankcase is supposed to be under vacuum all the time, so if my catalytic converter is plugged, the backpressure would offset the crankcase vacuum and cause the vent actuators to move back to their default position. I think this is what I'm experiencing. I unplugged the rear O2 sensor (nearest the muffler) and drove it, and the engine didn't run rough as it had before. I've read here that this indicates that the cat converter is plugged. Any other thoughts on this will be appreciated, but right now I'm planning to get quotes on replacing the cat.

Thanks

[photo_van]

Sounds like you're tracking it down. I think I'm in need of a new cat too as I keep throwing a 420 code and the cat is rattling, seems to run fine tho.

[roamineye]

Sounds like you're tracking it down. I think I'm in need of a new cat two as I keep throwing a 420 code and the cat is rattling, seems to run fine tho.

They say if it's rattling it needs to be replaced. I tapped mine with a rubber hammer this morning and didn't get any rattles. Also, I drove it again with the O2 sensor unplugged and it's running rough again. So, I'm not sure yet what's going on. It's driveable, so I'm gonna drive it.

[Slicky]

I was having the same symptoms and it turned out the rubber fitting coming out of the firewall for the heater controls that has the two lines coming out of it was leaking between the two vacuum lines . It looked fine but on a whim I put some goop on there and it cured the problem. Good luck vacuum leaks are a pain to track down .

[roamineye]

I was having the same symptoms and it turned out the rubber fitting coming out of the firewall for the heater controls that has the two lines coming out of it was leaking between the two vacuum lines . It looked fine but on a whim I put some goop on there and it cured the problem. Good luck vacuum leaks are a pain to track down .

Thanks, Slicky. I'll have a look. I have a cheap vacuum tester, so maybe I can zero in on it with that. The thing is, it has to be a pretty major leak to cause everything under the dash to go awol. At lower rpm and lower throttle settings, everything's fine. So, it seems like it has to be something happening with the main vacuum source itself, such as too much exhaust back pressure, or maybe the throttle opening more than normal to get up a hill. I haven't replaced the fuel filter yet, so I'm doing that today. If it's starving for fuel at higher engine loads, then the throttle would have to open more than normal to meet the power demand. It could mean that the fuel filter is beginning to clog up.

Thanks!

[Slicky]

Yes that is exactly what my van was doing . What we have is a solitary vacuum line coming off the left valve cover that goes into a check valve then is split and goes into the firewall on that rubber fitting I mentioned above and another line that goes down to an actuator for the ac I believe . If the check valve has gone south then your engine will rob the hvac system of vacuum and set you onto the default defrost. Or... if you have a leak like I did the check valve did an okay job until I was loaded down on holidays and pushing it hard up hill the ac conked out and the blower went from the vents to the defrost , as soon as I crested the hill and let off the throttle the cold air came rushing back out the vents. It took some sleuthing but I swapped out the check valve and the problem didn't improve. Then I swapped a few lines around bypassing circuits until I zeroed in on the problem .

[roamineye]

Yes that is exactly what my van was doing . What we have is a solitary vacuum line coming off the left valve cover that goes into a check valve then is split and goes into the firewall on that rubber fitting I mentioned above and another line that goes down to an actuator for the ac I believe . If the check valve has gone south then your engine will rob the hvac system of vacuum and set you onto the default defrost. Or... if you have a leak like I did the check valve did an okay job until I was loaded down on holidays and pushing it hard up hill the ac conked out and the blower went from the vents to the defrost , as soon as I crested the hill and let off the throttle the cold air came rushing back out the vents. It took some sleuthing but I swapped out the check valve and the problem didn't improve. Then I swapped a few lines around bypassing circuits until I zeroed in on the problem .

Good info. Thanks!