Air intake backfiring/car stalling.
 

So a few days ago my 1991 S10 Blazer (4x4) started acting funny. I had the gas down and then the car just started to "stutter" for a few seconds with some popping sounds but then rode again just fine. It then stated to do it more frequently the next day.

Day 3:
I took the car to auto zone to hopefully find some help with my friend. we popped the hood to see at least where the popping sounds were coming from. when i pushed on the gas we saw the lid at the top of the air intake (where the circular air filter is) pop up. so we took the lid off and did it again and we could see air shooting outward in random pops. im no car expert but im pretty damn sure that the air should be going the opposite direction.

here are the symptoms:
this "popping" or "back firing" only occurs when the gas is pressed
when idling or costing it will not do it
it is now easily doing it when accelerator is pressed harder
air shooting or backfiring out of intake
when accelerating, if popping goes long enough the car will stall out and shut off

please help if you can

feel free to ask questions and i will answer as best as i can


what sux is i just dropped 1400 total for parts and labor to swap out for a new transmission and im nearly broke and i gotta drive 32 miles a day to and from work.

preciate any help at all.

I had something so similar happen to me on two vehicles that you might check.
84 S15 Jimmy - had a bad spark plug wire. When you loaded it up it broke down and would backfire through the carburetor. There's a test you can do on the wires that will let you know if one (or more) is bad. You also might pull your cap and check that for arcing. Wire test as follows. Chiltons says to pull off both ends of the wire, factory says just the plug end. I guess it's your choice. Don't know how you would get the probe on the distributor end without pulling off the wire. Some folks say this won't work but I say argue with the book. Use an ohmeter. Depends on wire length too.
0 - 15in. 3000 - 10,000 ohms
15 - 25 in. 4000 - 15,000 ohms
25 - 35 in. 6000 - 20,000 ohms
Wire over 35 in. 6000 - 25,000 ohms
It's preferred the value of any wire be below 25,000 ohms but 30,000 is the absolute limit.
70 GMC pickup truck - this is the bad news. Cam lobes were worn out and once they start to go it really accelerates the wear. The engine only had about 200,000 on it. Overhaul was definately the fix for this one. 400 big block Chevy.

I was going to say that the timing could be jumped or just too far out of adjustment.

I would be guessing at a timing issue too. If the tranny guys had the tranny out then they probably pulled the distributor to get at the 2 top bolts on the housing (I like to get them from the top with a wrench too)... In which case they could have not hooked the advance back up properly, or installed the shaft in the wrong position and it needs to be retarded back a notch. Not sure if these trucks have an electronic or vaccum advance but thats where I would start looking. If you have a timing light, hook it up to the battery, and the drivers front spark plug wire (I think thats #1) and point it down at the crank pulley and see where your timing sits at idle and then under load in drive (1500rpm) with someones foot on the brakes hard. It should change drastically under load, if it doesnt, then the distributor is not advancing properly. You can buy yourself a cheap timing light for about 20 bucks at places like autozone and walmart and princess auto. I only own a cheap one and it works good enough for me.

The backfiring is caused by the spark happening when the intake valve hasnt fully closed yet, thats how the name 'ignition timing' comes to be. That makes the fire travel up the intake instead of staying in the closed cylinder.

update
 

Well i havent had the time to check anything yet so whatever is wrong is still wrong with the car but now...

I tried to start it up to get it to auto zone and it wont start now. it will turn for days but wont catch.

any ideas with this as a new symptom.

any ideas that follow i would be asking another question. does whatever thought you have the problem is have the ability to cause the air intake to backfire?

fixed!
 

so glad it was nothing major. after car not starting i popped that hood, removed the air intake to get to the distributor cap and cable and noticed that the coil cable has completely corroded and disintegrated. explains why problem went from small to to big to not starting. runs great now with brand new cables. thanx for your help guys.

Glad to see you got your problem fixed. Guess you and your friend at Auto Zone missed it the first time around, huh?

Good deal! Thanks for the feed back on your problem and solution.