08-10-09, 03:10 PM
96 sts. cracked old manifold. got used one. engine backfired and now blowoff seal whistles. i can move flap slightly from left/right, maybe 1/8" or so and tweak whistle. i decided to get another used manifold but am not sure if i should even touch blow off flap to clean it with anything. of course intake is oily and somewhat grimy. should i just leave it alone and put it on as is?
08-10-09, 03:32 PM
It's spring loaded, and that play is normal. Just open it up and wipe it clean with a paper towel or dry rag. The whole reason it was whistling was probably from it not seating right because it was dirty. A simple cleaning is much easier than changing the whole manifold any day.
08-10-09, 04:55 PM
i got carried away and tried to use some solvent on a rag to wipe off the seal and the silicone lip dissolved and shredded on manf #2. dayum. yes, i agree. wiping the seal/area is much easier than getting another manifold. who knows. maybe a new manifold will get rid of my annoying occasional miss.
08-10-09, 05:42 PM
If it backfired as a part of your occasional miss, I would definitely start double checking the spark plug wire routing and check for any evidence of arcing between the spark plug wires. Maybe mist them with water in a spray-bottle when it gets dark out to see if you get a light show.
You should be able to buy a new gasket for that valve so you don't have to do a butt load of unnecessary work.
08-11-09, 06:07 PM
had a bad fpr last spring. engine would occasionally not start well. than it would backfire. got another manifold for $25. guy had motor with cracked block. water instead of antifreeze in the winter will do that. had the throttle body too for free. passed on that. they seem to be popular on grand prix websites. oh well. i checked with dealer and they did not have any listing for seal. car seems to run the same. smooth idle, blip, smooth, blip. wires are gm but 6 yrs old? pretty easy to swap out manifold. 3rd time so i am getting good.
Use the flap from the first manifold - or is a '96 different form a '97?
08-13-09, 02:33 AM
The spark has to be jumping somehow or a couple wires are crossed. There's no other way that I can think of for it to backfire like that. Somehow a spark plug is firing with the intake valve open.... Mist it with some water at night to see if you get a lightshow. If you do, it confirms my beliefs that the wires are bad. Separate the wires and see if there's white stuff on the insulation in between them. That's evidence of arcing.