My 1999 Silverado pick-up (5.3) had misfires on 2 cylinders that I tried for months to fix. New injectors, new plugs, new wires, new O2 sensors, new cats, and no difference.

I finally found that the intake manifold was leaking slightly causing a lean condition and misfires. A new set in intake manifold gaskets fixed the problem. I have heard that the 99, 2000, 2001, were prone to leaks at the intake manifold. Spray some carb cleaner around the manifold at the misfiring cylinders and see if it is sucked in.

 

with just a misfire it won't actually come on per say. It will just flash

 

thats what i mean, it never threw a code, but i have the truck back now and it doesnt do any of that stuff anymore so im thoroughly happy

 

You get your spark plugs figured out and running well? I couldnt really undrestand you on the phone the other day. You still buying the 5.3 heads?

 

I just threw one this week......P0300(multip and rand). The light came on and stayed on. Cleared it @ home and I guess I'll see what happens..

James

 

mine has been doing that lately as well, but i believe it is related to an o2 sensor...

 

yea turn out the threads were stripped so we couldnt get the plug to seat fully so its still got a couple turns left in it but it wont do it without stripping it all the way but it sparks well and runs great no more misfire. im buying the heads, they shoul dbe here early this week. i needed the new valve seals etc. i might have my old heads repaired and cnc'd and p&p to best suit my cam but who knows. truck got pretty much tuned by charlie last night and it runs strong