I have an 86 Z28 with a 5 liter carburated motor. My problem is that just recently when i am driving and i kick it in to passing gear i get a sound from under the hood that sounds like a popcorn popper. It just started doing it and i can't seem to pin point anything.So any ideas that you have i would appreciate it. Thanks.

 

Check your ignition timing. Why it would suddenly start doing that, I don't know. Unless it has been too far advanced and the knock sensor has now given out.

Is your SES light coming on?

 

Yup, sounds like a little bit of recent history might help illuminate the cause....

And, what happens when you put high-octane gas in it?

 

Thans for the reply. I have no lights that are on or come on . As for the gas question i have owned the car for three years and always put regular in it with no problems. A guy at a garage i went to told me " the last time i heard a noise like that it was a bad cam shaft'' that scares the crap out of me. The car still runs fine i dont lose any power when it makes the noise. Hope this info helps some.

 

Is it spark knock, or is it spitting back through the carb?

 

This is a q-jet carb, right?

Kind of rare, but a secondary metering rod cam that has busted apart or otherwise disintegrated so it isn't pulling the rods up when the air valves open would cause a very lean condition, which would pop pretty good through the carb.

Guess we need to know if it's more of a rattling or popping noise.

 

I just took my car to a garage and found out that it is popping through the secondaries at full throttle. The mechanic has no idea what it is because he said it has been a long time since he has worked on a 4 barrel. Help please!

 

Is it a regular popping, like once each engine cycle; or is it irregular and random sounding?

 

The popping happens every engine cycle only at full throttle.

 

OK, I was afraid of that....

Do a compression test.

You will probably find one of 2 things: either 2 adjacent cylinders that are both low (probably #5 & #7), or one cyl that's WAY higher than the rest.

Don't forget to take out all 8 spark plugs, disconnect the pink wire to the distributor, block the throttle wide open, and MAKE SURE the battery spins the motor real good and consistently throughout the test (not, like, it's dead by the time you get to the 6th cyl).

 

Thank you for the help sofakingdom. I appreciate your time. I will get the compression tested as soon as possible and let you know what i find out just incase your interested. Once again thanks!