Lately, I've been noticing something different when I drive my NA '82 280ZX. I could swear it's slightly louder, but more important is this noise I've been hearing. When I let off the throttle but am still in gear (coasting), I hear this burbling noise, almost like coffee percolating or popcorn popping. Any idea what this is or how much I should be worried? Is this some kind of misfiring or fuel issue? (my gas mileage still seems ok)

The engine was rebuilt by the previous owner and I have had no mechanical difficulties in the 6 months I've had the car. Supposedly it's had some internal work done and its got some bolt ons like, intake, exhaust, MSD ignition, and a high flow cat.

It's probably normal combustion processes. My bro's Spec V made backfiring noises out the exhaust once we added a header on it, and so does my friend's RSX-S. I think the decrease in backpressure is what causes it. My Z does the same thing under deceleration.

if your getting back fire then try tighting your header bolts i have to do this all the time lately for awhile they are all good but awhile after that there not .so tighten that **** up cold air sepping in with the hot air coming out of the head makes a nice little poping sound when i let off of it after its been reved up..its like it sucks up a little air right in between the head and header.... it seem to do this more when my timeing was off. it was BAD so maybe check your timeing .. try to turn your cap and see if it moves at all if it does then mabe your nut that locks it in place came lose.put it on the timeing light and addvance it pop pop pop means more power . hope this helps after some messing with mine my pop pop seemed to gone but i still hear it after i decelerate hard from 95 mpg to 65 mpg thats the only time i hear it any more

I don't know if it's just me ... but I like my Zed to sound like a high-strung rally car.
A straight through side-exit exhaust helps.

Man, I hate it when my gas mileage drops from 95 mpg to 65 mpg... wait a minute... my mileage really sucks compared to yours, I'm getting like 22-25 mpg! that sucks! How'd you get such awsome mileage?!


Rod.

yeah no **** man. I think I averaged about 17 before the swap started...

I've been getting 21-24 for a long time. That's pretty good for the L28. That's overall milage. I have taken some long road trips and average 27-28mpg for the trip wich means I'm probably getting close to 30mpg while on the highway.

Guys with the L24 with dual SU's are getting 16-19 mpg on well tuned engines. We have it easy.

I have a L24 with SU's, and it got somewhere around 23 mpg, and like 26~28 mpg freeway

Damn, I get 17 mpg averaging city and highway. Missing 5th gear though, that could contribute to my S@#$y highway mileage. I heard these things don't get great mpg anyways though. I try to keep it off of the highway for long trips.

On my recent trip to Los Angeles, mostly highway miles, with some stop-and-go rush hour traffic, I got 26mpg.

So anyways, the concensus here is that I should not be too concerned about the noise? I could swear the car does smell a little gassier when the window's down. ^^ No one thinks something's up with my fuel system?

maybe its time for a new cat?

If the BCCD (or something like that) valve is capped off, it will do that. Basically, what that valve does is make the car's idle evenly decelerate on a shift down. If the valve goes bad, you can cap it off to avoid "chatter" in the valve, and the car will "burble" while coming to a stop (shifting down). Normal....

Wheres the BCCD? Is that the thing underneath the Throttle Body?

Back pressure transducer valve... looks just like the EGR valve but is in line ahead of the EGR (Towards the front of the car).

Rod.

!!!!!!!
That was the case with my BCDD. Friggin thing drove me NUTS!!! just disconnected it and now the car "burbles" when coming to a stop. dosent bother me tho, just sounds like normal back fire when using the tranny to slow down. check out the post asking about it, i point it out
https://www.zdriver.com/forum/showthread.php?t=11654

Yeah, That's totally different from the bpt valave... sorry.


Rod.

What part of the BCCD do you cap off?

the vacume line or niple from the bcdd

Thanks for the help.

Regarding the "popping" my car's doing, I do notice that it's pretty consistent at only happening when it drops below 2000rpms. I wonder if it's just the MSD multi-sparking at low rpms. If so, I wonder why I never noticed it months ago.

Is it the car backfiring up your intake manifold? Mine will do that every once in a while.