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Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 4x4 Cowboy, Feb 15, 2003.
all i can think of is that it is pluged or its shot
yup, your right!! /forums/images/graemlins/thumb.gif
The cat will glow red if the engine is running over-rich, that extra fuel, instead of being catalized is burnt in the cat...
A simple engine miss, like a dead plug, or bad wire..can cause this too...
Also, on a non-computer car, if the A.I.R. pump is not working, it too can cause the problem..the AIR pump supplies AIR at all times except decel, to burn a slighly rich mixture these engines are set up to run..It is supposed to pre-heat the exhaust to the cats..but if the pump is not working...extra gas goes out the exhaust, and the cat thinks its a rich mixture
(Computer car/truck AIR pumps and mixture are set up a little differently )
Unfortunately, the cat is not designed to do this..and it usualy fails after a little while
Need more information on engine carb or computer/carb or FI etc..to suggest what to check..
I am a California EA Smog Technician... /forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif
well i have a 360 bored out with flatthead. 4 barral card.(quadrajet) truck has no computers. and never will. were is the air pump.
That silver thingie, with a pulley, driven by a fan belt with the valve on top, and 5/8" hoses (heater hose size) going to the A.I.R. manifolds screwed into you exhaust manifolds or headers..
If you took the AIR pump and hardware off...forget the cats
If the AIR pump is there..the engine doesn't miss..and the carb is an emissions carb (not some 1968 or aftermarket one)..
there is a possiblity that the "check-valves" on the A.I.R. manifolds, on the exhaust went bad..they are diaphram looking things..screwed onto the manifolds and the hoses to the pump go onto them...they are about 1" or so wrench, and unscrew ccw...hold the manifold or you will twist it off..the usualy cost about $10 each..
there is a way to check them:
Take the hose off the check-valve..start the engine, and take a piece of paper and hold it across the port of the valve...it should vibrate, and pretty much stay in place..if it blows off, or exhaust is comming out..they are bad..for sure
If that is incoclusive...and it might be..sometimes getting someone to hold rag(s) over the exhaust, making back pressure, will show it better..If still not sure
you can take them off and poor oil or water into the threaded side..little if any should come out the other end...
Also the AIR pump may have gone bad..usualy always if the check valves go...exhaust goes into the pump..
Check the AIR pump by pulling both of the outlet hoses off the Diverter Valve (thats what the valve is called)..run the engine and hold you thumb over one of the outlets, and see if air comes out of the other...it usualy won't be too much without the check valves, but there should be a good flow..if not, the AIR pump went bad...not unuaual on off road vehicles..
The Diverter valve may be bad, but they usualy last pretty good..
Check that, by putting thumbs over both outlets, and see if any air comes out the silencer thingie (a metal pie piece shaped thing on the diverter valve)
If all these items check out it might be that:
You Q'jet is probably in need of a rebuild...and/or leaking
A common cause of rich idle in a Q'jet are a "sunk or sinking float"...
Or extremely common:
The "primary jet well plugs" or "the secondary jet well plugs" are leaking..
Is your truck hard to start after it sits all night..like it ran out of gas...
The carb is leaking down..
Pull the carb, take the base off..the silver part.two screws at the back, come from the top...there are two about 1/8" lead plugs, and 2 about 1/2" flat plugs sticking out on bosses on the main body..if they are leaking it is usualy obvious..
Even if you don't see any leakage, clean the area around the plugs with brake clean then acetone..lightly sand it with 180grit sand paper..and aply a hi-temp epoxy..preferably on that will take 400 deg...or as high as you can get (JB Weld is great)..let it sit overnite...
Put it back together and try it again
If it still runs rich..rebuild and float time...
These are things a tech will do to find you problem...Hope this helps..good luck
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