popping out my TB

[1 sExy BuiCk]

hey i just got my top end back together and it werked perfect for 2 days.. the it started making a popping saound out the TB.. not a back fire..

and just under load..

thing's i have checked are air and vacume leaks
valves, egr, plugs ,wires, ignition module

i was thinking maybe a intake leak at the lower intake or maybe the headgasket was faulty but i dont think it woiuld cause those symptoms

any idea's??

[tractorman]

What all did you have apart?

You may not want to hear this... but a burnt intake valve will cause a pop though the intake, especially under load. I'd do a leakdown test.

You're sure it's through the intake though? Does the car run ok otherwise? Any noticeable miss, especially at idle?

[1 sExy BuiCk]

i had the rear head off due to sombody helicoiling the plug hole and it getting blown out...there was 0 miss...ran perfect

i checked and seen that the valves were seating right by putting some gas in the head.... u know what i meen?

and im 100% sure its out the intake cause i put my hand near the TB and flet the air come out...i even ran the car on 5 cyls b pulluing each plug wire off so if it was a valve issue wouldnt it affect it if there was 0 spark?...

[tractorman]

What year is your car? What engine? Is the pop steady with engine RPM, or is it just random?

If you checked the valve seats by filling the ports with gas, then yeah- you can be reasonably sure that the ones on THAT head aren't leaking. I do the same thing myself to check valves, but I use diesel. Gas should work fine too.

Here's you a tip... depending on what engine you have and how easy the coils are to get to. Pulling plug wires to check for a miss is a BITCH. It's a pain to remove the boot, and if you're unlucky you'll get a nice jolt of several thousand volts. Also, you're cutting out TWO cylinders when you pull a plug wire on these engines, so this doesn't tell you much. Here's an easier way:

Remove the plug wire boot from each coil terminal one at a time, and install a paper clip, bent so that the wire goes against the outside of the metal connector, and the paper clip sticks up when you snap the boot back on. Now take a piece of wire maybe 3 feet long, ground it to the engine block on one end, and strip the insulation off the other end. Hold that wire with a thick glove, and touch it to the paper clip of the cylinder you want to short out. This method works great- you're cutting out only ONE cylinder at a time, and you won't get zapped.

Even if the engine runs good and smooth, and passes the cutout test... my guess is still an intake valve unless somebody here can come up with a better idea. A valve has to be burnt pretty bad to cause a miss... maybe one is just burnt a little? (on the front head)?

[1 sExy BuiCk]

ya definitly possable...once i get it running again today i'll see whats up and im thinking of having a leakdown test done... i'll let u know the results

btw its a 94 sunbird 3.1l 5speed and if u rev it slowly theres no pop runs 100% but under load in gear or a fast rev will cause the poping.. weird

[1 sExy BuiCk]

back together now... still doing the same.. gonna try another ignition module sorta feels like it has a miss...

[1 sExy BuiCk]

ok is there any way to know if ur valves are fine by not ripping off the heads??... is that a leakdon test or what?

[tractorman]

a compression test is probably good enough- a leakdown test is better still.

If it feels like a miss, there's several things to check including compression.

[Doubt_Incarnate]

what motor is this?

the gen1/2 motor you need to adjust the valve lash prorpely or the valves will end up slightly open when they shouldn't be, gen 2/3 its important that you get the push rods in the right place (int or exh). gen3 you just torque down the rocker pedestals.

it sounds like you have a valve open when it shouldnt be.

[1 sExy BuiCk]

i made sure that the longer of the 2 rods were in the exhaust... and what about a rocker nut too tight??...i torqued them to spec tho..

its a gen 2/3

[Doubt_Incarnate]

if its a 3100 (SFI, 96+, 95 is different i think), you just torque the bolt down holding the rocker

for the 3.1 (MPFI, 90-94) you need to go throught the valve lash adustment procedure found under maintainance

[1 sExy BuiCk]

hmmmi thought only the early one u had to do the valve lash.. oh well worth a shot i guess...

[bszopi]

Since its a 94 Sunbird, it will be a Gen2 MPFI 3.1L. So yeah, you'll have to do the valve lash adjustments.

[1 sExy BuiCk]

how long u think it'd last driving it daily how it is?

and would teh valve lash cause these problems?...

[Doubt_Incarnate]

btw its a 94 sunbird 3.1l 5speed and if u rev it slowly theres no pop runs 100% but under load in gear or a fast rev will cause the poping.. weird

haha yeah, i kinda got to the part where tractorman's book filled my screen, no offense, just when 1 post fills my screen i tend to skip to the end, lol