Popping Sound Shifting Under Acceleration
 

Today, I went to OC Nissan Irvine to have my oil changed and everything went well. I leave to drive to Newport Hills to fill up with some race gas for a change and did a roll-on starting in 2nd gear onto the highway. When I shifted to third, there was a loud pop; almost like the soft pops that come from an FI exhaust on decel but much louder, and it sounded like it was from in the cabin. The clutch was fully depressed on each shift.

The clutch felt fine and nothing changed in the car, so I drove gently for a little while and got gas. On the way home, I did a quick 0-60 sprint and again, another pop from 1st to 2nd this time.

I checked the clutch fluid and it was normal, I didn't smell anything burning, there were no additional noises from the drivetrain, and the clutch felt normal. Do you all have any ideas what might be happening? On the way to work and to OC Nissan, I did the same type of shifting and it was perfectly fine.

I'm going to check the sway bars and look for anything under the car now that it's parked and will update.

TIA! :tiphat:

Could be not all the gas is burning and you have that creating the pop in your exhaust. Might be flames shooting out the back :)

That's what I was hoping it was haha, it was just much louder than the usual pops on decel or when revving. It happened before and after I filled with race gas and switched to my high octane map.

All sway bar bolts are torqued to spec, fluid levels are all perfect and the fluids themselves look good. Will see if it happens again on the way to work.

Sounds like a backfire to me.

You should talk to the tuner because you may mess up your 02 sensors in the future.

yup^ i've got a 4.6 mustang that i'm taking care of for the summer for a friend and it's got some hellacious exhaust on it. normally when downshifting it makes nice burbling noises as it engine brakes but when it's cold it will actually back fire substantially. i was pulling out of my neighborhood the other day, revved it up to about 3k in 1st and let off and BOOM!!! scared the crap out of me. after it was warmed up, it doesn't do it. the 370 is a completely different engine though, i'd check with your tuner. sounds like you might be running way rich

I'd like to think it's just back fire, but my clutch engagement has definitely changed. The engagement point hasn't changed, but it engages less abruptly/with less 'bite' and the car actually feels easier to drive haha. It did it again today shifting from 3rd to 4th on a WOT pull.

I want to take it to the dealer since it just started doing it after my oil change there yesterday, but the only time it happens is when I'm shifting quickly while accelerating and don't want them to just say it's not covered since I'm romping on it.

Anyways, keep it coming guys. Your help is much appreciated!

I hope your dealer is nice about mods. I know the dealers around my area would rush to point at all those engine mods and refuse to do anything.

oh ok, i missed that part somehow, sounds as tho one of the springs on your clutch has broken then perhaps

Everyone in the dealership knows me, I try to be friendly and nice as I think that makes them much more willing to work with you and help you out. They don't seem to mind the mods, but I haven't needed any work done haha.

HK: Great point, I will check the clutch pedal helper spring on my lunch break as I have a lighter non-oem spring in there ATM. Will let you know if I find anything. :tiphat:

Back fire, You said you filled up with race gas so 100 OCT right, WOT and shift you will get a pop for the unburned fuel.. I only get it once and while when a down shift to slow or if I'm riding first in traffic and go above 3k or so and get off to slow down again.. Normal

Yep, but this happened before I filled with race gas and switched maps too. But the exhaust definitely pops more on race gas, just not as loud and those pops don't sound like it's coming directly from the footwell in the cabin. Thanks for helping, how do you like your Stillen SC btw? I was tempted to get a used kit with the 951 impeller :)

I looked at the clutch pedal and assist assembly and my es14 spring looks a bit loose. I sat in the car with the engine off and did some quick shifts to replicate what happened on the road and it sounds very similar. All fluids are still perfect and nothing is leaking under the car, so I will put the stock clutch return spring back in and see if maybe the slack in the es14 spring was causing the sound.

Clutch feel is normal.

Yea will pop alot and you will feel it there it is actually travelling thought the exhaust, :) My buddies old GSX would shoot flames out the back when he shifted at WOT ,

The SC kit is good, Bad seal rigth now. we think car is at the dealer, But I just ordered a upgraded heat exchanger, and looking into swapping the pulleys, But overal I really like it ,412 WHP is pretty good for a AUTO. :). See my thread "Starting steps" Cliff has been helping me alot,

Did you mean the 928 Impeller? :)

I was actually following your thread, I bet the car will feel a lot better with your upgraded heat exchanger and a little boost! I meant the 928 impeller, a member was selling a Stillen SC kit and had the blower modified and was making great power.

I'm just wondering why that popping decided to happen all of a sudden, and it happens when shifting quickly between any gear. It also is very loud and sounds like it comes right from the driver's footwell, it's just one loud pop like a speaker popping. Shifting a little more slowly at WOT does not produce this sound.