Guys I just keep wondering if the CAT is clogged. This is what it feels like. It will run for a about a minute then slowly die then I have to wait 10 minutes or so before it will start again. Does this ever happen to Zs? Also the previous problem I had was an immense amount of white smoke from running too rich. Could the extra gas have screwed up the cat?

Edited August 13, 201113 yr by garretthes

Moving AFM flap away from the sweet spot on a tuned and functioning Z will affect motor's operation almost instantly. It will slow then stumble and you may get back fire (rich) and intake popping (lean)

If you are over-fueling from some other cause then the AFM flap may not make as big a change.

If you think it is the exhaust then maybe disconnect at base of manifold and try it. Maybe wee critters nested inside and built a clog.

However I am not sure how a clog will cause plugs to foul from excess fuel?

Would a lot of back pressure cause the vacuum to suffer? Would this in turn cause the fuel pressure regulator to fail which would increase fuel pressure on the rail and then cause a rich mixture? I have learned so much about this car but I still feel like I'm swinging in the dark sometimes.

Before I tried to drive this car we had it running pretty good. At one point it sat for at least 30 minutes idling with no smoke and behaving normal. One of the short trips I made around the neighborhood it backfired pretty bad and sparks blew out of the exhaust. I'm thinking this was NOT good for the cat.

Did the yogurt leak test (except I used duct tape) and discovered that air is flowing freely into the throttle chamber through a tube. After blocking this off I found a pretty bad leak in the tube that runs to the valve cover. The manual calls this a 3 way but it only runs from the rocker cover to the throttle body on my 79.

I'm guessing this is s special order vacuum hose since it has a 45 degree angle?

That hose helps vent the motor at higher rpms. Ported vacuum at the throttle body sucks the blow by out of the crank case. There is also a spark-arrestor in that hose.

Usually you can get that hose at a junk yard.

For testing and trouble shooting, just plug both ends for the meantime and deal with it after you fix the problem. It is more of a long term house-keeping item so plugging it for the short term is ok.

Edited August 13, 201113 yr by Blue

Removed the CAT only to find it has been gutted. Ordered a fuel pressure gauge. I guess I have to wait a few days to check the pressure

Bummer. Seem like the home stretch however: Either the fuel pressure is too high our your ECU is doing something it should not.

That hose (from your labels on the picture) runs through the Air Regulator and just bypasses the throttle blade to keep the idle up until the Air Regulator valve closes.

Have you checked the PCV valve and hoses underneath the intake manifold? That would cause a vacuum leak. The crankcase should be totally sealed to everything except intake manifold vacuum. You should find a diagram in the Emissions Section. Might not fix your main problem but could get your manifold vacuum back up.

I sealed the system last night and it is holding pressure and not leaking so I'm pretty confident that's not my problem. My problem is CAUSING the low vacuum

Recently a member had an unusual problem. The manifold casting eroded under the EGR allowing exhaust to go directly into the intake plenum.

Here is a photo of a white wire threaded through the hole.

His symptom was low vacuum and fouling of #6:

That is bizzare!

CRAP! The Summit Fuel Gauge doesn't have ANY connectors. Have to go shopping tomorow